1 4The Callosal Syndromes

ERAN ZAIDEL, MARCO IACOBONI,nNo IOSEPH E. BOCEN

DAHLIA W. ZAIDEL.

l l r t

{ , I

l l r

l ;(l l

-f l r t ' tol lec't ions of nene f ibers that cl irecth

tur)ne(' t one <.ere'bral l i<'rnisphere u' i t l r t l re' t l rer. c 'al led t lre

"cert ' l l ral c 'orrrrrr issures." irr-t l rrde the corpus cir l losunr. the anterior c'orn-tt t issun'. and the I i ippr-rcarrrpal cnnrrnissrrres.()t t l rese. the co4rus cal losurn (CC) is bv f i i rt l r t ' largest. with at least 200 nri l l iol { ibers. TheI x lOb estirnate of Tornascl (195.1)rvas baseclon light nricroscopr. o1'a {'erv ciises. Accordingt ' l 'nocenti (perso'al cclurnru' ic.t io' , l99l )ttteasureurt'nt lx' electron rnicroscopy u.ill atleast tnple the previous estirriate (-see also(l l i t rke et al. . 19fJ9). Alxri t iz et al. ( l9t l2) ()rr-tltrt:tecl ii coliprehensive analysis of the lrurnan(,(, with l iqht rnicroscopv iurd a l i rnitecl anah-srs "rrth electron mic,roscopv ancl estirnaterl thetotnl 11,trn1,t ' . o{ ' l ibers irr the hurnan CC to berrr lr 2(X) rni l l iorr.

' l l re posterior arrt l the lr irbenular couirnis-

\ l l res i is vucl l i ls ot lu, 'r cclntrrr issrrres o1't lre sPinalt ort l artt l l l rr i insteur are not i lc lur: le<l arrrorrg tht,t t ' rebra l r r l t r r r r i ss r r r t s .

TERMINOTOGY

Srrrgitral secrt ior i o{ 'al l of the cerebrul corrrni is-sttres is cal let l "corunrissurotorrrr." rvhereas that" l t l t , ' , , r t l r t t s t ' , L l l , r s r r n r r l o t r , i s t , t l l . ' . 1

" t ' i t l l , , s o -

to t t t r " l t i s r ros c r r r rn r ro r r to r rs t ' t lLe ie r r r r

"sp l i t

brairr" to refer to c'ases of cal losotortn' as u'el l

as corrrpiete cottt l t issttrototttr ' . sir tc 'e botlrgroups of pi i t ients rnani lest t t ictst o1't l ie sartte

signs arrcl sunptonrs. Tl ie' Los Angeles spl i t-

brir in patients (Bogen and Vogel, 1962. 1975:

Bogen et al. , 1965, 1988) hacl corrtplete cere-

lrrrrl c'ornrtiissurotornv (including tire anterior(ronunissure. dorsal and ventral hippocanrpal

corrrmissures iind, in sorne cases, the tnassii itt-

terniedia). In the erperirtrental anirnai. split-

bririn prepartrtions often include sectiorr of all

of tlie cerebral c'orrnnissttres plus the optic chi-

asl i ; t l i is rrrakes i t possible to restdct visual in-

lrrrnrir t iort to one hernisphere rr ierelv bt 'cover-

irrg one t'r,e. In tlre hrrnrutr u,ith iui intact

chiasrn, restr ict ion o{ 'r ' isui i l inprrt to txte helr i i -

spl iere rerluires restr ict iort of the visrral st irntr l i

to one or the ot l ier visual l t t ' rrr i f ield.

[TlotocY

Srrrgic' ir l sectitxr of ull or paft ol-t lre crrtlus t 'al-Iosrrrn. uith t.rr u' it l tor-rt section of't lre othe'rt 'r.rr. lrral c'ornrtt issures, lras been rrseil {t lr treat-rrrerrt ol rrreclicallt intractairle, rrrrrlt i focalepilepsr. (Ret-l 'es. 19E.1: Spencer et rrl.. 1987).Sorne seizure <lisrirciers respond u't'11 to sc'cticinol clnlv tlre anterirlr l ialf or alterior hvo-tlr irclsof t lre <rallosurrr (t lu' "parti i i l split-br"ain"). Srrr-

348

geons rnav iilso qain access to cleep hernispherelesions b."' sectioning a portion of the corpuscallosuni. Exarnples ilre genu section for ante-rirlr <.ontrriunicating aneurysllt clippirrg, trlnksectiorrs lor access to the third ','entricle anclernirons, ancl splenial sectirln frrr ilpproachirrgthe pineal region.

Lesions of t lre c.rimus callosunr also occ.urr rat r r r iJh. ls t . l renr i t . s t i , rkes i r l ' fect i r rq t l re terr i -ton'of the iinterior c-,erebral iuten. can destrovI l re r r r r ler ior Lu5 t i l ' t l re ( ] ( l rFoi r and Hi l le-rnand. 1925; Critchlev. 1930; Etl ielberg, l95l),and posterior cerebral artery strokes can affectthe posterior 1/5 (splenium). Tumors (usuallvgliornils) can occur trnlwhere in the cerllosum.the best studied being tumors of tlre genu orof the splenium. Multiple sclerosis ""n "o,r."disconnection signs. Head traunra has alsobeen associated with callosal iniurv. Toncand./or infectious lesions of the caliosrim occa-sionnllv occur. From time to time an anteriorcerebral artery aneurysm rupture results in he-rnorrhirqic dissection of the CC or spasni withlnfarction of the CC. These naturally occurringlesions usuallv result in fractions of the conr-plete c'allosotomv swrdrome that improve overtirne. Farniliarih' rvith the cornplete s\,ndromenr i rkes ident i f i t , , i t ion. r f t l re par t ia l var iet ies eas-ier. Congenital absence of the CC (callosal age-nesis) has been intensiveir studiedl it is for thernost part rrot accompanied bv disconnectionsigns. a perplexih that rernains elusive to date

Callosnl lesions are often accornpanied bvdarnage to neighboring structures. As a result,neighbrlrhood signs rna_v o'n.ershadow signs ofcallosal disconnection. Although anl sign aftercortical damage (in a region grving rise to cal-losal fibers) could be suspected of being par-tiallv cailosal in origin, small lesions of the cal-losuni rarell'can be reliablv correlated witli anr,.behi l iora l def i t . i t .

HISTORICAT BACKGROUND

THE HUMORAL ANATOMISTS

Br'"hunroral :rnatornists" we lnean those rvrit-ers oi antiquitr, u.'hose concepts of brain func-tion enrphasizecl the contents of the Lrrain cav-

C L I N I C A L N E U R O P S Y C H O L O C Y

ities and the flou' of various flrritls such a.s air.phlegrn, cerebrospinal f luid (CSF). blood. etc.For them, the (lC seenrecl larllelr ir supportingstnrctrtre. Er-en that original Renaissirnce ge_nius, Vesalius. beiieved that tlie C(l sen,edmainlt' as a urecltrnical srrpport. rnaintainirrgtlre integrih' of the r..arious cilities.

THE TRAFFIC ANATOMISTS

The "traffic anatornists" took a rnajor step for-u'ard toward our unclerstanding of hrain func-tion. As indicated br.'Jornt (1974). it was at aboutthe time of \4/illis (1664) that anatornists besxnthinking more in terrns of a traffic or. "on,iu-nication betweerr the rnore solid parts of thebrain. This rierv becarne rlrrite erplicit in thestaternent of Viq d'Azrr, rvho wrote in 1784:',Itseems to me that the comtnissures are intendedto establish slrnpatlietic cornmunications be-tr.veen different parts of the brain, just a-s thenerves do between different organs and thebrain itself '(Clarke and O'Nlallev. 1968, p.592)

THE CLASSICAL NEUROLOCISTS

In the closing clecades of the nineteenth cen-tury (or more broadly construed. in the periodbetueerr the Anrerican Ciri l \4'ar ̂ nd the firstWorld War), there emergecl a group of neu-rologists whose discoveries and formulationsare still the core ofcurrent clinical knowledge;nranv issrres debated among tlremseh.es renrainlive issues todav. Arnong these investigatonwere severiJ. including \4'emir.ke. Liepmann,Dejerine, and Goldstein, who intelpreted var-ious neurological swnptoms as resulting fronrdisconnection. including interruption of infor-mation flou'through the CC.

The concept ol callosal :rpraxia r.vas devel-oped bv Liepmann and Maas (1907). rvho de-scribed a right-liander whose callosal lesioncaused a left limb aprixia as well as a left-handagraphia in the absence of aphasia. These dis-abilities have subsequentlv been obsenedmanl' times. Unilateral apraxia and unilatenilagraphia are not alr.vays present. and thev nravsubside as a stroke rictin'r progressive] .\' recov-ers. but thev rernain prominent signs of henri-sphere disconnection. Lieprnann's callosal con-

i,ii

.;

t 'I

a : . :

T H E C A L L O S A L S Y N D R O M E S

cept is now liardlr- cloubtetl. But this *'as nol

alrvar.s tlte r'ase.

T H E C R I T I C S

Even drrr ing the t ir l le r l f Lieprrrr inrr. t l tere u'ere

cntit's ancl clrtrrltters o{ his tlieories s'ho becatrte

proqressivelv tnore influetitiiil in tlre ensuing

ilecocles. Irt irn extensive rerieu'. Irtinside ancl

( luttrnacher t1929) conclut lecl: "Taking rnto ac-

count t l ie corrrpleteness of the cirse records' our

senes of turrtttt- cases rvould lead us tci believe

that apriuia is tlot a corlllllolt sunptotrt tif tu-

nror, uf the C(1. . . . The sl ' tr tptotns in ( lC tu-

nrors are largelr of the'rreighborhood'hpe and

,rnse from inrrlh'errietrt tlf. or pressure olt. trcl-

iilc'ent stntctrrres bv the grontlr" (p. '15'1)'

In aclclitiorr to tlie criticisll of herllisphere'

disconnection as i t ci luse <lf sunptonts. the sit-

rratiorr u'rts c'lorrclecl llv ceftain tlistractions tlriit

u'e shall c'onsicler ltrieflr' befcrrt' retrrrning to

the central t l tenre of cl isc'olutecti t l r l .

\ lental Srrnptorns

Tltese' distrac'tions ilrcise as tlre result of at-

ternpts to correltrte lesiolis. especitillv tutntlrs

o1't lre CC. wit lr niental sunptottts \ I t lst of t l i t r

sullptorns attributecl to tlie corPtls callosrttti

n'ere neighborhood signs" relating principalh'

to tlellcits that u'e no*' recogtrize as resultinq

liorn {rontal lo}re ciamage (Botez. 197'1: Barbi-

zet et al. . 1977: I) iurasio. i985t Stuss ancl Bert-

son. 1986: Fuster. 1989: Levin et al. . 1991). For

exarnple. :r rnerrtal callos:rl srlclrotre r'r'as ftrr-

rt trr latecl bv Rannoncl et al. ( l9L)6) antl t l reir

rier','s u'ere u'rcle'lr' accepteci litr rrt;inv l'ears.

Ther obsenec-i a cieftainloss tlf c'ortttecteclnesso1 irleas but no clcliriurn. a dilTic'tiitv with re-

cettt ruernon'. a ' ' l i izarrt 'ness" t t f nt i i r tner. antl

a labi i i tv of rrroocl., \ lpers t l t l l l6) redescdbecl the <ri l l l r lsal sut-

r lrortre. t .rrrpltasizing " inipeniortst less. ' or t l

certain irrdif fe'rerrc( ' to st innrl i as i f t l ie thresh-olt l uere ek'r 'aterl : r l i {} lcrr l t ies in crrnceritr i i t ion:arrr l i i lac,k ol 'elrrboratior of thought. After re'-vierr'rng tlie relevart litenrtrrre. iincl on the lta-sis t f 'personal ci isr.s. Bri l iarr ' ( in Rretrer et rr l . .l956t agreetl uit l r t l re obsenation o{ Le Bearr119' l l l ) that "f

t lherc rs a cerlain aPatlrr ' . that is

349

to siN-. a clorrci ing s' i t l iorrt s<it t i trolenc:e n'hiclr is

l ,urr i l , lv ve'n' specif ic." l \ \re are l lo\\ ' i rrcl irre'cl

io attr ibrrte t l l is srrrtpttnlt t lctt t t l inrrr lrert lent

o{ t l re genu t l f t l r t 'CC (u 'h i t ' l r . to be s t t r t ' . i s i r t -

volvecl) brrt rat l ier t t l involvetl terrt of t l re rrrt ' -

tlinl aspec'ts of tlte fl'ontal l<lbes inchrclinq the'

irnterir lr cingulate gri . I t is frerluentlv seett i t t

el ioblastornas o{ ' t l re atrterior coq)us ci l l lostrrtr '

c'ailecl "butterflr' qliortias" Lrecause ther. spreiicl

their u'ings into both iiontal lobes. This apatll

or irnpen-iousness rl)av be a nlilcler ftlrnr of irki-

rresia, often approaching il lnute irrirlrobilitr'.

see'n in patients uitli "tlie subfrontai slrlclrtlttte"

c'onsequent to bleeding lionl arr antet'ittr c'ere-

bral a*en. aneun'srll. or u'ith a thircl r.t'rrtriclc

turtror (also set ' Chapters l3 and 15).

Neigliborlioocl signs havc also lleen rtotetl

uitli posterirlr c'allosal lesitltrs. uitli iltrolvettterlt

r i f the l i ippocarnpi. IJscrrttrol le et al. (19751 re-

portecl that "Ia] c 'ertzr in t t t t t t iber ol t lur tut l t<lrs

o{' t l re spleniurrr Ihl ' jcre as col l l l t ]on i ls get) l l

gliorriasl \\'ere accolltparietl br- nleltlon' clvs-

{unction. whereas tlie antenor tutttors u'ertr

rrrore olien Irriinif'estecl bv iihnetic states rvith

rnutisnr, probablv because of bilateral iinterjot'

cingulate involvetlrent" (p. '16: trartslation orrrs)'

I)isconnectiol'r Signs \\'ere Not Often Secri

rrith Niiturallv Occurrilg l,esions

The r-'ciipse o{' Liepliirnn's trntlt'rstatttling of

the CC r,i',is onlv p:ir1lv attributable to il cltxrcl-

ing of the issue with neigliborlroocl signs:

nairrlv it u'as fronr trn unr.l'illingnless to accePt

as me-aningful such clisconnectioli signs as uni-

lateral irprtxiri. unilateral agraphiir. antl helri-

aleria. The objectitlns raised inclucled tht' fbl-

lor,r,ing three points:

L Callosal lesions are rareh'. il ever. istl-

latecl, so cleficits atiributed tcl such lesions

rrtav nel l result. at least in palt- frolrr as-

soc'iatecl clarrtage. This problerrr is rt'al

enotrgltr the r lnlv sohrt ion is to obti i i rr a

suf{lcient larietv rlf ctises srl thilt olle citll

reirsonabh' attr ibute to t l leir col l) l l lol l t t l l -

atontic aspects tltttse c'linical {'eatures that

thev rr lso I iave i I l c 'ol l l l l iol ] .

2. Signs ir t tr ibrrt i lblc ' to ct i l losal lesions r l f ierr

subside or disi ippear altoqether' Tl l is cr i t-

350

rcrsr n ls ({)rrect. €'speciiilh. fbr vounger pa_tierrts uith urrinianrral dt.spriuiit and uni_rnarrrral

-rhsgraphia. Brrt it cl<le.s not npplvio all cralbsal signs. n<ltablr the unilaieral; r r r o r r r i r r r r r r r I t l r e I r . r r r r i r l , , r i i r l i r l l r r r v r r r q r . i r l _losotorrn. Even if i t cl ir l. srrbsiclencre rkresrrot rrrean tlrat a sigrr u.i is njt lrout signil i_('an(,e. an\ rrrorr: t lran tlre f).equent subsi-tlenr.e ol aplrusia rrr(,rurs that i i is rurt a re_liable sisn {irr right-handers) of a leftherrrispltere. ( LH ) lesiorr. progressir.ecorr rpcrrs i r t ior r I i r l lor r i r rq l i r t . i r l darr rage is ac l r i r l iu ter is t i t . le i r t r r re o l t l re bra i r r .

3. In nunrerous cilses clf 'callosal &sease. rn_clrrding toxic clegeneration of the CC(\larchiaiava-Bignarni disease) as well asthe {iir nlore corllnon cilses of callosal tu_rllor or cailosal infirrc,tion. the ertectedtliscolnection sigris are rult "li"it"d. tnthe rrrassive revisecl edition of liis neurol_oln'text. Gou,ers (1903) reirsonablv con_r, l r rded, "u.e

do r rot ret k l rou.of anr .sr .nrp_tonts thirt are the result of the damage tothe call lsal f ibers" (p. rl l+) Horver.er, therlefinitive 1in Engiish) rieurologv text ofS. A. K. \\, i lson 1\\ ' i lsrtrr and Bnrce. 1940)not so rea.sonablv reaffirrnecl, on the ba_si-s ol turrror cimes. nruch the same corr_c'lusiol. \\'ilson rne,ntirlried apra,ria as arrinc.onstant srnptonr. .rnpl,asized certtunnrentnl strnptorn.s such as lack of spor,_taneitr.. iuid concludecl: .,In

f:rct. the clairrrrnight be arlr.anced that all callosal'svrnp_tor.ns ure of a neighboring or distrint Linil'.{p. l2l}5). \\ ' i lson s tl iscussion rel.ers tostrrclies bv Bristo,,l.e, Ransclrrr, Tooth.(luillain. Alp"., iincl flrant. f',r.i, arJA.l_son. Dr.ke ancl l)aricloff. iurcl the book br\I inqazzirri (1922). ir,s u,ell as the articleb.r Ironside and Guttniacher (1g2g)quoted rrbol.e in flie Critics. IIe cloes norref'er to Lieprnann.

.Sorne of these neqiitive findings can be at_tributerl to inarlerluate testing. One rnust per_torrrr specific tests to detect sigris of calils:rldiscrlnnection. and, in particular. one rrust pre-r - t ' r r t t . ross-r . r re i r rq. \ \ ' l ren prr t ients rv i th ina l_hrnction of the CC are appropriatelr. testecl.such signs rrs Lrnilateral or.,ir,r,ia iucl jvsprariaIrave been lirrrnrl {Gesclru.incl ancl Kaplur.,.

C L t N t C A L N E U R O P S Y C H O L O C v

1962r Lherrnitte et al.. lg77; Barbizet et ali978)

Callosal Sec.tion irr Anirnal Experirnents DoesNot Procluc,e Significant De{jcits

Thenegative experirnents ofZinn (in l7.lg). I la-gendie, \{'rato*,. Roussr., Franck. ,,r,,f p;;;;Ko.ran_1i. Dotto, iind Pusateri; L() Nlona(o: ;;ldBaltl i were all rerierved br. Ldr.r _\-rrje"ri , lsi i i ,r,r'hose own rnonker. tcrisma1,) arso negatii r.'ff;J:""ii: H:.ljl,"I:,r[ Laftrra and prados (1923). H"rt;"r;, .;;;;Trentlelenberg ( 192;). Seletzh ,,"a C:' i,, i .,r I928t , r rnd Kennard and \A 'at ts , iS3+r, .1]1, ;1. . jhr BrerneretaJ. . l956) . In ret rospert . th"r"nuo-ative resrrlts can he attributed to,r lack of reie'_vant testing. Besides. tlie more striking signs 1x1rlslrnptorns seen in human patients are a'[ribut-able to lrerlrispheric sper.i jzafion *hi.l, i ;;;:errdelrt in rats. <,ats. dogs. or e\.en rrrolrkers(Warren and Nonnerr-ran, lg76; Oewson. 1g77,Dotr,'and Overman, 1977; Hamilton. 1977, Har-nad et al.. I 977: Stanrm et al.. I g77: Denenbo_I 981: Harrr i l ton and Verrr re i re. lgS: . lg l ; ,Overmann and Doh'. lg82).

Surgical Section of tlie Colpus Callosunr irrHurnans Is Often Asr.rnptonratic

\Valter Dandv'r,1.'ent so far as to sar.the follo*,ing in 1936: "The

r.orpus callosu,,, is split hrr.grtudinalir'. . . [and] no sunptoms fojlow its dr.vi.sion. This sirnple experiment at once di.sgrsesot the extravagant clairns to the function, uf t1,,,corpus callosurn." (p. +O). Even more penua-sile rvas i lre negatir e testinq br Akel;urrrr l9{,t-,15 r of patients who had had callosal s,.t.ticln. These results were aclror.vledeed brTomascl r r lg54. 1957r, wl rose in terest rn thr .CC and anterior commissure led him to nra.liehis widelv known estimates of their fiber cun.tent. Of the Akelaitis results he wrote: ,Thn

showed very clearlv and in accordance *rthsome earlier authors like Dandv. Fo'enter.Meagher and Barre. r.r.hose material horr.ererwas not so extensive, that the comus callosurnis hardlr c'onnected rvit lr anv ps,clrokrgr, '.Jfrrnctions at all." Finalh, nfte, an erl"nsr\r rr.rierv of the literature. Etjrelbere (1951). cn.t ' l r rder l : " l t r r r rn be prernatr r re to considcr t l r

I

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l l ,

t i r

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i r t '

\ l l

i l l ;

i l l !

r ) f

' t r ) .l ) ; r, i r r r

i ) ' t ll "o t

t l l i

J ; , tt l r . r l

I X l t t '

r i l i l

I l . r r rI , r r , 1 r. , , r r Ir r i l r

' ' l l l t t t

i l r l r l it l r , , t . ,

; k r l ) r r

T H E C A L L O S A L S Y N D R O M E S

re(ent ciinical. surgical. ancl experiniental ob_s t ' n l r t i ons ru r oh i l uan o f L i epn ra r rn ' s r . on t . eD ts, ts t , r . t l re . ro le p lared

-h. t l , . , r , ,1ru. . , r l lnr , , , , , ' i , ,

t l r r r k re lop r r r t , n t o f ' t r ue 'ap ra r i a . B r r t t l r e r < .e r_

t i r i r rh suqgest t l re need . f , . , , , , * l res i lar ic .e i laccepting therri" (p. l l7).

About the sarne tirne, Fessard (1g54) surn_rnarizecl the r-ierv that u,as then generallt, ac._cepted:

fTJhere is a qreat < leal of data shouing { that ] sec_tron of inrportant associative u,hite tracts srrch as therrrrpus callosurn ckres not seedr to affect rnerrtal per_Irr rn iances. Othcr s i rn i lar obsen.at ions in man oia, ,_j rnals are rrot ,accurnrr l l ted in grcat nunrber and r .a_r ieh These resul ts are so disturbi r rg that one rnavlx ' t t , r r rptecl to adrni t the i r rat ional statenrerr t that aheterogeneous svsterr r i f act i r . i t ics in the nenorrssvstern could forrn a u,holt, in the absenct, o1. an,".identifiecl liaison (pp 20i_20$.

351

(iurrent vieu's orr callosal {urrc,tiorr i lre at-tributable in large parl to studies. unrler tli.aegis ol R. \\,. Spern,. of our piitients uitlr sur_gicai section of the cerebral coll i lnissures,Tlrese patients are incleecl u.itliorrt, in Danclr..srvords. "arir.

cleficits" in tlie ordinan. sociiil sit_t t i r t i o r r . o r eve l l as t l e te r r r r i r r ed l , r r r r , , s t , r f i r r oL r_t i r re neuroloqi<. r r l exarr r i r r i r t ior r ( Bogcn i r r r t l \ .o_ge l . IUT i : Bo lez : r r rd Bogen . I 976 , . l r r sne r . i a l hclevised testing situations. Iron.er.er, th.,' .lorrir"shou'n to liav.c a u.icle varieh, of deficits in in_terliernisplreric ctrrnrnunicration ( Gazzaniga. etal.. 1962, 1963. 1965. lg67; Spern ,,r,.1?;,,r-ztautiglr 1967; Spern., 196g, 1970. ig7{. l9S2:Spern'et al.. tg6g: (i i izzitniga, lg7(): Zaidel.197:1. 1963: Zaidel et al.. 19git, Bogen. l99g).

Nleanu'hile, we now realize that nrost of tliette-gative findings after srrrgical section of tlreCC resultecl fronr tw.o solrrc€s. As alreadl.rnen_tioned. r.r4ren surgical section of the ccinirrir.s_sures i.s incornplete. :r renrarkable capacitv f()rtnatntairiing cros.s-conlulunicatiotr ltet veen tl,ehenrispheres nrar. lte retained with cornrnis_surill retitnAnts. particularly when tlie paft re-ntaining is the spleniurn. Serond, legative 1ind_tngs otten result frorn the rrse of inappropriateor insens i t i \e tes l i r rq te r .hn i r lues . i i - l ,n i , , , ' r "ttttcts rleperrds on vr.hat one looks forr whereasDandr'(1g36) said that cal losal section pro_dtrc,e.s no ollsen.able cleficits. arnong Li, ;.;,patients u':is the one repofted hv Tresclrer irnclFor r l t , r l ra r r . l re r r r ia le i l .

THF TWO-BRAIN THEORISTSi l i the nint ' teentl l ( ,entun.. the consideratiorrthat t l re <rerebnnu r.r,as a

.. iorrble brain",r.n, "r_

pou.sed b-r ' \ \ ' igan (18.14), Jackson (1g7,1). arrcia-niultitrrcle. o1'others. as rlesc.rilleti in detail ltvI{arringtorr (tgg7). But sur,h ia"ur. nt"rrf r,,,i i i,Lieprnanrr's c,allosal concept, fell far ,rutirl.fa_t 'or hl the r:nd r i{ ' \ {brld \ \ 'ar I and rernainedSo lor rrrarrr.clec, ir<les. A dist inct rer.ersai o{ 'optnion occurrerl during the 1960s. followingp u l r l r < . a t i r r r r o I t l r e s p l i t - l r r u r r r e r p e r i r r r e r r t s . i r r r r lt h e t ' o r r . e p t o f r r " r l t r r r l r l e

l r r ; u n : i r t l i t i r r l i e t . i r r r r eP o p r r l r r r , l ) i r r r o r r t l . l g T f ' .

Arrinial Experirnents

The split-br;Lin hunans confinnecl in a partir,-ularly striking wal, the irripoftanc,e ,rf c.rlrr,,rrrr_su rai fibers for interherni.spLeric, corri rn rrnica-tiorr. But the essential fac,t irad alreaclv beenclescribecl in anirnal exp€,riltents clrrilrg the19,50s, init iatecl bv Ronakl Nlr.ers rnrl Spern,(1953, 1958; NI.vers, l956). lf ,na.s founcl' tho.eac'h liernisphere of il ciit or rnonker. coulclleam solutions to a problerrr cliff'ereirt froni(everr conflic.ting witlr ) the solutions leanrecl bvt l r t o t l r e r l r e r r r i sp l re re . T I r i s l r r i u l e i t t . l e i r r . l l r r r tellec.tir-e furrc.tioniug could oc<lrr inciepen_dentlv in tire two hernispheres. As Sperryr I 96 I ) p r r t i t :

(lallosurrr-sectionerl cats ancl rnonkevs are r.irtuallvr r r c l i s t i n q u i s l r a l r L . f r , r r r , I l r e i r . r r o r n r l l ' , . n g " , n r t , , r , , , , _r ler l rost tests ancl t ra in ing concl i t ions. IBut ] i l .onestrrd ies such a spl i t -brain nrorrkcv rnore carefrr l lv .r r r r < I ' r s p r c i ; r i l r a i r r i r r q l t r r r i l e s t i r r q t t r , r l i t i , , r , , , , 1 , , , r , ,thr. inflorv o{ serrson. irrfbrnriitior to the rliricleclIrt-rrisplreres .',,n lr" r,,po.atelr, res^tric,tecl arrcl c,on_tro lk ' t l . one f i r rds that eac. l r of ihr , t l i r ic lecl ht ,nr i_spheres nou'has i ts oun i r r r lepert l t ,nt lncnt : r l spherc()r ( { )qni t i \ .e svsterrr_t l rat is . i ts r t rur inr lepenrL.rr tpt ' rc ' i .pt r ra l . learning. r ) le lnor1. ar t l othenu,.utu j 1, . ,u( 'esse\ . . [ I l t is as i f ' the anirnals ha<i hrrr scp,r , .at , .l r ra ins 1p. 17.19).

It is inlpoftarrt to unclerstancl tlrat the clualitroi rrrirrds seen iifter Iremisphere clisconrrectiorrt s r ro l l r r r i n l e ren< r , so leh f r , r r r r t . e r t i t i n s t r i k i r r Il l i r r i < . r r l r . r r ses i t r r r I , , l , , , n t l i i , l o l s r r rq i r . i r l p i r t i e r r t r i

352

as soll letintes sai(1. Split_brain experinrentshal'e been carrierl orri u.ith rnanrj differentspecies b_r'hundreds ot irri estigators anlurtl thelvorlt l. Tliey are virtrrallr. rrruurinrorrs in corr_cluding that eac,h of the discor,n*",i t,",,,,_spheres crn act inclepentlentlr. of the other(Bogen . 1977 ) .

The split-brain experirrrents startecl r.r.ith theproblern of interocuiar transfer (Sperrv. ancl(ilark, 19.1g) Tirat is, if one leams wiih one "v"irorv to solr.'e a problern, tlien r.r,ith tliat eve cor,_ered and-using the other e\€. one readihl soivesthe problern without furtirer learning. This rscajled "interocular

transf-er o{' learnins... Ofcourse. the learning is not lri the eve ani thentranslbrred to the other eye. llrt that is the wavit is usuallv described. hi tliis case the questionis: horv can the leanring rvitli one "u"',,oo"n,with use of the other? Experirneni, ,l-'*",1that the transfer required the CC. Sperrv,sscheme rvas to split the optic chiasm so tliat tirenSf t gle goes to the right cerebral liernispliereancl tiie left eve to the LH ancl also to cut theCC' between the tu,o liemispheres. ifrrr-,, ""split-brain

cat." The cat can be trainecl witlithe right eve to choose it cross rather than -square, while the le{t eye is covered. The carchooses one of two cloors at the errd of a rur,_r1'a1'. the cross and square being attachecl to theclorlrs randorrrlr'. onlv the door witli cross lead_ing to a lbocl reward. After the cat has leamedthe problern (reqrrlarlv picks lvhichever doorll i ls the t.ross). ope c31 test the left er.e witlrthe riglit er.e cor.'erecl; the split_brain cat has ttrlearn all or..er again. that is. it starts at ETTI(cirtrnce). For each cat tlre learning curv-e fortlie left el'e (ancl LH) is ,,"n. ,iuiil". to theIeurrr i r rq , . , , , . e f . r r the r ig l r t " i . .S i " " . ; ; " l ; ;l r ra i r r r . i r t l ras to learn a l l or t r f rorr r t l re he 's in_ning with the seconcl eve. the cat can be trainedtri pick the square instead of the cross rvhenrrsing the second eve. The choice the cat rnakesthen depends on wlrich e\.e is open. Thus, eacliliernisphere has developed a cliiferent memon,ahorr t rv l rat is c .orrer . t : t i r i r t is to sar . eat .h l rerr r i_sp l re re l r ; r s i t s o rw r se r r ra r r l i r . s r . s te rn { i . e . . a s r s_tern.that gi\ies rlleaning to sr.rnbols). That iliehvo lieniispheres could be so disparate, gir.ingdif{'erent, even opposite rneanings to srrnbolst ' ross arrd square, r r rar l re srrqrr is inq s i r r r .e t l re

t rvo t l ra larr r i in r r t ' r r t r r rc qui te t ig l r t l r t .or rp led

C I I N I C A L N E I J R o P S Y C H o L o C Y

ruii,rtorrricallr-. Tlre irnatornical corrplirig of thal_arni in a rnonkel.is a-bit less. hence orie rniglrtexpect a sirnilar rlualih, of rnentation in split_brain rnonket's, rvliose risua.l svsten, i, u'ur..similar to th:it of hrrnrans than io that of c,ats.rvho learn rnuch faster, ancl u4ro hor," a ",rn-siderabkr capacih, frrr line finger r nanipulationIncleed. uiolkevs shorv even rnore than cats acluality.of nrentatiorr (Sperrv, tgO+). f*n ,rron_kev experirrients exemplifv the large literatr.,.eon this subject.

One of the rnost reliable signs of a bilateralprefrontal lobectomv in nionkevs is therrinabilitv to do delaved_altemation t.sk,(Jacobsen ancl Nissen. lg37; Sarvag""tri .naGoldman-Rakic, l99lr Fuster, lggi). It ;aslong supposed that this inabilitr,. niight be ex_plained as tlie result of the hlperacfii.iq an&rrdistractibilitv that is also characteristic'of ,u.it,monkevs. This supposition can be tested in .split-brain monkev. where each hemispherecan function -separatelv. If one hemispl ;i; ;*a prefrontal lobectonn.. it perfornrs poorlr. o,,l l re r le lared-al tenrat iorr tas i . T l r is p, ,o, n" i fnr_ntance bv the lobectoniized herriispliere is norirc.c.or npar ried br. I rrpe ractir.tv or diit ract ibilihApparentiv. the rernaining frontal lobe keeisthe nionkey quiet and attentive, even thoufhthe intact liernisphere is not participating in tirerecognition of various stimuli or the evJuationof their significance (Glickstein et al., lg63).

A tmlv dramatic exarnple occurs when onh,orre l rern isphere of a spi i t -bra in rnonker. l rasharl a temporal lobectomr.. A biterrrporal mon-kev rnanifests the Kltiver-Bucv srndrome.u'hich includes difficulties in the r.isual identi_fication of objects, oralih. (often mouthing in-appropriate

_objects). hrpersexualih.. Lip,r_motility, and tameness in the p."r.n..^ nfJrumans. When the intact hemisplre." can ree.the split-brain rhesrrs monkev behaves in theusual rlresus rnanner. nranifeit ing a fierc.e fearof humans. But if onlv the temporal lobec-tomized hernisphere receives the risual infor-rnation. the split-brain aninial acts like aKliiver-Buc_v monkey. particularlv as regards itsrelative tanteness. \['hen this was reportedrl)owner. 196 1. 1962) it was so amazing thatmanr of r rs dorrbted t l re resul ts . , r l t l ,oueh o.er'rere alreadv conrint.erl of the rluaiitr of mirrdi r r lhe spl i l -bra in rnorrker . . L i t t le roorn for

i l

(i i

rl\ .

I )5 (

r tu {

T H E C A L L O S A L S Y N D R O M E S

cloulrt rerr iairrs beciruse t i i is f inding lras. irr j ts

essentials. been rt 'pi lr ted bl a nurrrber o{ 'ot lrerinvestigators (Bossortr et al. . 1961: Bnrrett.1969: l )oh 'e t a l . . 1971. 1973: Hore l an t l Keat -ing . 1972: Doh 'a r r r l Over rnan. 1977) .

It rvas knou4eclge of the split-brain experr-rlents in l:rltorat<ln, arrinrals tliat alefterl( lesclnr. irrcl arrcl Kaplar (1962) to the possibi l-i tv ol r i l r t rnrsphere-cl isc,onnec,t ion srlclronie irrt l r , . I r r r n r i r r r . \ \ ' l r t . r r r r s r r i t r r l r l e p l r t i e r r i ; t p p c r r r * r It l rer searclrerl {br the cl isconnec,t ion elIec,ts.Frorrr rr c 'orrrplex. evolr ing cl inical picture. tht 'rteaserl r trrt the relevarrt pl ie.nclniena.

One r i{ thc. f l rst t l i inqs (}escl lrwirrd arrr l Kir-plan lilrncl rvas thiit altlirtuglr the patielt u'r<ttt.clearlv u. i th l i is nqlrt l rancl. he wrote "aphi isi-

t allr '

uith his le.li (an<l u'as astonished bv uilat1 , , ' l r ; r , l r l n t t e r r , . . \ n r ( , l l q o t l r r , r t l r i r r g s . t l r r . rlbrurd tliat an cibject placecl in his left hantl u,ashandled corrt'ctlv iurcl u,as correc.th' retde,r.erll r r t r . e l . l r r r t i t t . o r r l t l r r t r f 1 r e , , , , , ' , . , 1 , r r r , r t . , , r r l r li t be retr ielet l l l ' l 'eel r,r- i th lr is dght harrr l .(lesclnvirrcl anrl Kilplan repoftecl that "he

bt,-havecl as i{'his hvo c,ercbral hernisplieres r.r'erelurrc' t ionirrg nearlr arrtononrouslr ' . TItrrs. u,r.lourrr l that so Iorrg us ur- c'orrf inecl st irnulat ionantl resprinse u' i t l r in the sarne hentisphere. thr.

Patierl t shou'erl correct l ter lbrl tance." In corr-trast. the patient perlirrrnerl inc,orrectlr, u,hentlre. st irnrr lus u.as proriclerl to one hemisphereantl t l r t ' resp() l tse rerlrr ired l ior ir the other.Ther rrrnclrrik'rl that tire best explilnatiorr u,iisto sirppose that his lrelr ispheres u'ere cl isc<ln-ttectecl l tv a lesiorr of the ( l(1. ' f l reir

i rnatorrr icpreclit'titin rv:ts t.r.entueilh ccxifirntetl bv. au-t o P s r . \ r r t l t l r . i r c l r r t l u s i o n s u e r r , r , , , , , , , , , , , p 1 .trr l t f i rrrrerl l tr . srrrgical cases. cl isc'ussecl later irrt l re c. lra1ltr. t . ,

Li t 'prnunn's c,alkrsal c'orrc'erpt has been resrrr-ret ' tet l . There is ruru.u. idesprearl act,eptul l( ,e olatt i t l t ' rr lorrg iqrrort 'd. arr intt ' rest inq eiarrrple ol '$' l rat Kulrn ( l lJ62) hlrs c.rr l ie,d a Parircl ignr shi l i .( lesc' lr t i rr t l ( l g7-l t u'rote', "\ \ ' l r , i t

u,rrs astorr ish-r lrg \r 'as t lre l ix.t t l rat t l r is rvork lracl l teen sogrttsslv rregler,terl . . . . t Irat irrr l tr tr tant crrnf irr iu,r lic ierrt i i i r . obse,n' ir t ior is c,o,, l i l al ,r ,ost lx. ex-ptt l tge<l lrrrrrr t l re knori ' leclqe o1' conternporanx : ie t t t i s ts " tp l9 l . As l {a r r i r rg to r r (19 ,57) pLr t i i .rr 'avs of t l r i rrkirrg about t l re brir irr { i .e.. l r i t t ,ral-I t r l t t t t l r l r ra l i t i r r i l r i c l r s t ' r , r r r r l r t r r ru l e l lou f l l rt t0 r t ' i t i u i " r lu r i s l re t l

l r -o r r r t l r t , r r r r rk i r rg r i r r r : l t l

353

r ieu"' {br neiirlr '50 \iears, (l l lapter g of her bookis devoterl to tlre cause's uf thi, lrall-centune('l ipse. u'hich irrr. lucle "neurologr"s

re(l iscovenol the 'u' lrole"' led br Ntarie (1906). I{eri. l(1926). ( lo ldste i r r (1939). r rnc l . in the labora-ton. Lasl r ler (1929. 1951). Shc is par t icr r lar lvc'rit ical of Henrl I learl. u' lrose higli lr.selecti i i ,reference to .fac.kson

' l ior<lers on intellec,tual

dislionestr'." (loncurrent u't is a "trerrd torvarrl

psl'chologisrrr irr psvchiatn'." incluclirrg tlreu'ork of Blerrlel arrrl. espec,i ir l]r. Fr.errd.

(]esclnri lrcl i196'1) has suggestecl in corre-.spontlelcc tlrat. uit lr the nse of psvchoanitlr.-sis. t lrere u'as ir u' idespread re\ulsior aqairrstattelnpts to link brain to beliavior. IJe also liacla socicllogical explantrtion:

I l rnn l le,ar l ha<l l reer shrenr l t 'norrgh to poir r t out

that unrc l r of the gr t :at ( lenrarr grosth o{ l reurol-

oqr 'har l bet ' r t re later l to their r ic ton' in thc l i rarrcrr-

I'nrssiarr \\'i lr. lIe \\'irs not shleu'd r:rr<>rrgh to trpplr

t l r i s r a l r r a l r l t , h i s t o f i t . a l l e sso r r t o h i s ou r r t i r r r c and t , ,

r ta l iz t , t l rat pt . r laps the r le.c l i r rc of tht , r igor arrr l i r i

f l r renct , o l ( ierrnarr neurologl 'u 'as stronglv re late<i

to the r l t ' f i 'a t o1 ( lennanr. i r r \ \ 'or ld \ \ 'ar I and tht .

shi f i of t l re cert t r o{ qrar i t r - o l i r r te l lcctual l i l i , to tht .

lJnglish-speaking ri'orkl. rather than nect,ssarih t,

anl < l t ' fects in tht , ic leas oi ( i t . r r r ran scl ro lars tp. 6t3) .

But there u'ere other {actors. C)ne t}ringrrrissirrg u'as a vriclespread coltviction thrrt thet sserrtial facts coultl be obsen'ecl repeatedlv inhuninns urrcler c'ontrolled, prospectir.'e circ,urri-stiinces. SLrch obsen'ations (clescrilted ltekxr')are possible r,r'itlr persorrs u'lur liave had a ccl-n-plete ceretlral c,onintissrrrotolnv or. sliorl oft l r r t . i t t o r r rp le le t . i r l l oso lo r r r r .

\ le i t r r r , r l r i l . . i t is r rsef i r l to r r rerr t i , r r r l rn , . [ ' l tso t r t e o l r j t . t ' t i ons t r r t l r e l r t i r - l r l a i n r i r u l l r r r t l n r reIrt.t 'rr resrrrrecterl in t lre pirst feu't.ears.

TH I , REVIS IONISTS'flre

hr,o-brain 'u'icu'. rr-r-,ognizing a significiurtrlegree of c,erelrral l iernisphere inclepenclenc,elirrc'htdinq irr c,ats alr(l r i ionkevs) and conspicrr-orrs herri isplreric, spec'ializatiorr (in rnost lrrr-r i r i ins) caugl) t the pr ib l ic ,eve in the 1970s. Thcrrrerl i:r pushe'rl t lu. poprrlarih ol ' t lre 'r iglrt

I rrrri r r/ le{t lrnii r r "

ston' to f arl proportiorrs rcitc,l r -i r rg iur i r l r r rost 1r t 'nz icr l p t ,aL- l r r 19,5() . T l i is le t l

354

not (xlh' to sirnplistic t legrarlirt ion. ytrobabll. in-evitable u'ith poprilariziition. hut also tri r:x-pkritatir ln. Conrrrrerciallv rnotir-ated entrepre_neurs prorn:isecl to erhrc,irtc people's riglitlrenrisplieres (RIJs) in slrort orrier, isornetirrreseven o','ernight. ignorinq the lenqtlrr,. arcluoustrrrirring ne(,essan fitr arn. tnutrrrt, crtrnpetence.This u'as {bllou'errl lrr. a reac,tiorr or backlasir.n4iic.h itst ' l f ' sen.e'cl io t,onlirse nonspecialistslroping to clistinguish repliciible lilct fionr spec_rrlati<xr. N{Lrch of'the reric,tiorr inr.rilved tire'cle_bunking ofextravagant cliiirns. Sonre of it. hor.v_(.\'er. w:ls nrore rer.isionist. Br. this r.ve rneanrrork hr rvr i lers r r l ro t . l ra l lenger l l l re l r i rs i r . , rh_sen'ations bv etnphasizing lintitations on irenri_spliedc independence ancl b,v poirrting out therelative nature of hernispheric, speciaiiiation. asu'ell as enrphasizine the obr.iorr.s poirrt that forintact inciiriduals. nrost ac,tivities involve herli_spheric interaction. A notable erarriple is theextre.rrie d^enigration of herriispheric specializa_tion bv Efron (lgg0).

t _ L t N t ( A l N F t J R O P S Y ( H O L O c Y

one hancl rur <lb.jec,t palpaterl r,,ith t|e<lther.

3. IIenilsphefir' sTtt:ciali:atiorr tffect.s. Jly,heniispireric specialization trpical of hrr-rrran srrbjects results in pherionrena notseen. in split_brain animals. A hpic.al ex_anrple is the inabil ih, of right_hanclers t9narlie or clesr,ribe an object in the letthanrl. er.'en rvlien it is bei;e ^pp.np,-,.t"1'r r r i rn ipr r l i r ter L

1. Conpensatortl phenonrcrta. Split-brairrsubjects pro{ressir.'elv iicrlrrire a i.arieh ols t r r r t eq ies f o r r . i l r . r r r r r i e r r t i r r q t l r e i r i r r t c l -her nisplierir: trans{'er de{ici ts. A .u,r, n,,u,erxarnple is for the patient to speak outloud the name of aii t,hlet.t pol'pnt",l ,,,the rieht hancl: because the fifl ".n r..,.ognize rnanr. indiv-idual rvorrls, the obtectcan then be identified witli tlie left hanrl

In this section, after discussing tire ac,ute ef_fects o{' cornmissurotomv, the }ruman split_brain sl,ndronie will be analr,zed in its rajousdomains. \\iitliin each domain. the patient.sbehar.ior can reflect lack of interhernispherir:transfer, hernisphere specialization. or com-pensatorv phenornena, as discussecl abo,,.e. Inthis and subsequent sections frequent refer-ence is nrade to specific split_brain patientsTl're case histories of the rnost conirnonlv stud_ie<l pal ients i r re srrnrrnar ized in T i rh le l f l

\\'lien patients .,vho har.'e hacl a cornplete cal-los.ton^,'a'e recror.ere. fr 'ni t l ie ac.irte oner_ ACUTE EFFECTS OF COMMISSUROTON,IYati'e effects ancl rc'aclt , tiijrlr stitble state. the' In the immediate p.stoperiiti'e periocl and rli.rnanifest a r.rietr of phen'rrnt'rtrt tltat carr be rninishing fo,. r"""i, after, beha,"ioral cleficitsgrt^rped trnder lbLrr lre.tlirrgs: nral' be ."rnt"d to inj.n to the RII from re-

I sLtciot orrtirvtrinest one c,f the rnost re- :T:iT:,ri::TJi:f;l; ,:*"::,i:Hfirnarkable results is thtrt in clrdinan'social .sl,s. the dvsfunction o{ unclanragecl brain n,-situations the patients rire

_intl istingrrislr- gions relateJ ;;,h" loss of contact u,ith otherable {lor' nonrial incliricluals. Special iegions resulting from the suclden clestnrctiontesting rletltods, usuallv inrrllrinq the lnt- of -millions

of clmmissurai {ibers; and to drs-eralization.of inpr.rt. are neeclecl tir expose connection effects that will e'entuall' be c.rrr-t l l e l r ( t e l l c l l s ^ - - . r - - r r , I

2 Lack.f irtterherni,spherictran,sfer Auide tlTli:i:::Tl"::llT.."j#,St:T:l,l:Ii::?^j,l -:l:11.t:'.

(clescribed below) During the first ferv ctiil.s after conrplett,Irave beerr contrived to shorv that the hrr_ cerebral comrnissurotornl in right_hanclers op-rriarr subjects are in this respect tlie sarne eratecl on from the right .side]'patients crrr,,.as split-brain c:rts and rnonkevs. Atrpical nionlv respond reasonably well with their nqhterample is the iriabilitl to iclentifi-' ll'ith lirnbs to .in,pl" cornrnands. But the' are eirl-

THE DISCONNECTION SYNDROMEFOLTOWING COMPTETE

CEREBRAT COMMISSU ROTOMY

SYNOPSIS OF THE HUMANSPLIT-BRAIN SYNDROME

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356 ( L l N l ( , A l N t t j R ( ) p S y ( i J ( ) l ( ) ( , y

ih c',rrl irsecl lrr thretl-. or- c'\1' l i t* '.-piit1 c'. 'r- s'rrrpt.rrrs r{ 'hcrrrisplrere <lisr,rrrrne.tioll r.r)(r totttartrls. t 'rxrl i part rlf * 'hit ' lr is.lt i iorri lr rrrder- lre cl,rn,pe,rr,rtr '<l to ,r r.t,rrrrrrkrrlrk,-,1,1qr"". t,,s t rx l t l T l rest 'p i i t ients, l ieu l i t ' r l r r i t ' t l r u . t l r r r i l r p"r r , ,n" i ih- . i r s . r , i i r l s i t r r . t i ' r rs . i l ' ( l i r t , rost ( ) lseerlr rrri l t l lr ' " irkirreti<'." rrlt lr,rrqli t l te'r. ' croPer- . rrrri 're nerrrrl,qic .,,,,, 11,;, ' ;;;;r",,, ,u1r",,r,ate *4tett stirr.rl i i tetl Tltt 'rt ' is sotttetirttes arr rrrrrclr irs l lefi lrt ' . l l .*,ert,r,. *.rt lr i i l lnr.nri,r,,i tttpenirtttsttess reserriblinq that olteu seerr tests rrsirrg Llteralizerl i,,p,,t tt,,, ' ,t ir i. l ;;,,1.:i l : i

* ' i t l i 'a t r r r . l l ' . . r ' t t r t i t tg ger i r t l t 's i r t rs . The pa- I rerr r isp l ier t 's c . rur be ,1, , i r . , , t , , , f , . rn t " , , , , t . -t ients itre' o{ien rnrrte. e'ett *' l te't l *i l l i 's t ' perr<lt. ' t lr tr ir l irrqe ertt 'rrt. Ear,lr i i f t lr. lrerrri-*'r ' i te slt,rt (rrsrr:i lh rlrtt '-*rrrt l) i i lrs\\ 'ers (B'qt'n. iph,'.", , ipp,,".. t. lra'e its ,*. ' leur' irrq pro-1976)' Fri ihrre of It ' f i-sit le .esPonses t. r ' t ' I ial ,*rr., nrr,i iar,,ru' sr'1lirr.te rrrr.rrr,ries. rr;rrlr.,rt 'r l trtrnilrtt l is trsuallr severe attt l c'an be trt isti lkerr u'hic' lr trrr, largell i irac,c,essilr le to the otlrerfi ir lrt.rrriplegia. \\, i th irrrpr.r.rri. ' t.,o,"l l i ,;;;,;L,i;.""." '-t t x r r r l i r r r r l e r I l r r r l r r , l l c t i t i r r . r r . ; r r . l r i r r g . g rop ing .anrl qra.spinq rvith the leii Irrtrrt l sorrretirn.-.s re_sernbles a grasp reflexr grirsp rellexc,s mavtuallv be p."r",", biiaterallr. lbr a clar,.n. hr", :;-

THE cHRoNlc, srABlLlzED sYNDROMEter srrrscr., ' . \\ ' iren {irrt,e<l' grasping canrrrt 6e ::ffy,^StHERE

DISCONNECTION.elicited (lrv inserting hro firrgelrs i l to t l ie 'a-

DISSOCIATIVE PHENOMENAtie.t 's pii lrrr a'cl clrarvi 'g t ltt 'r ' <lut n..,,., t l ," Phe.or'e' it that suggr.st r.olit i 'ni i l aurbi'n-rveb betq'eeIr tire thurrrll altrl index finger). it le'ce, uriu be elicite<l b_r'histor' .r. k,ss c.nr-is ne'ertl ieless possil l le itt t l tttst cases to derrr- uro'lr. ,rtrr"r."a in the cli ' icr. There r'ar.he aonstrate a proxirtt:rl tractirln, resPorlse: that is. clisparitr hetween 1acial expression anrl ',.;.r,.rlthe patie't is rr'able,to relilx ihe ha'cl grip izati.n.lr betw,ee' rvhat tlie leli liiirrcl is 6oi,gu.'llert tlte,t'xarrrinerprrlls so as to exert traciiorr lncl y4rat t|e p:itielt is sa.,i1il. Or tlrere nraro' the elb.*' :rrlcl sliorrlcle'r flt'x.rs (Twitciell. be ii clissociatiicrn bet,"vee' qent,ral lrrrlijr. ,u,-l95l). A.s the patient irnproves. there rna,r.be U,r,rs,f risiug. *., it rnn, t,tc.) anrl ,,, lrnt ir ' i ,. in,lcotlrpetitive lllo'ernerlts het*.eerr the left ri'rl done bv eitire'r hancl 'r *.hat is l,"i,,g ,"ift. S,,.1,rigirt hands Tliese patients corttmonlv liave bi- air-.l",ir,x' L"u" ,,"".,rrerl s'llicientl'. olte'lateral Babjrrski sigirs .s rvr'll as lriiaterallr rtb- n,rr^tlttg- .,.ili,,rut ,""tron in .'irrirls (.rre-se't superficial abdtl 'r irr. l relleres 'Arthen. t9o5) irnd i ' l .rrnars tl iat the' slu'rkl.

Le'lt arnr l^potolri:i, It'lt arrrr p.sitir''e trnc- arolrse suspicio' ,,f 1,",r;;J,;r" ,r.r..,,,,,,",*,",tirilt re'sptlrtse. llilatc'rirl Bubinski resporrses. a'cl I'cleecl. tliere rnav be sorrre ,,rt,,rtnrr"" t,,"ti,,, 1ltt i ttt istt i rvere reqttlarlv 'bserretl irt our c:rses: notion that s,ch conati 'e,r r. l i t iorral ar'bi 'a- ;brrt there *'as c'onsiclt 'rall le ' i tr i i tt ion lrorrr one lelce. u,hen it occrrrs in rrrlrrnal ,,rfri"",r.,.,unfi ipatierit to irnotlter' both irr ' ttr st 'r ies iurcl in be attrib'table. at lea.st on som(, .ccasiorrs. to :,t l iers' (\\ ' i ls,n et al.- l!175. l!177: Iftr ltzrlan e't alterecl inforrnilt ion tr.risfer bv o,rnto,ni""l lr l in_ tal.. 1981: \Ic.Ke..er et al. l98l; Fergus.n et t :rc.t crir 'nrissrr,, . idJ,,. ' rrr i ," i i , l" ,r i . i rr, :al.. 1985: Ree'es. l99l: sass et ar.. t,qg|. ,{t In crrntra.st ,-ii, .,rlriu.,r,;l

^,,;;i;,r;".. iorle e\trerl ie' 'ur l irst patit ' ' t . \\ 'J lrarl pre- errrotionil l rrr,bir.alerrce (such ii.s ,fr" ,=p,,n r',., ,operati'e riglit-lrrlntal rltr,plrr. *.s ,ldest at the patient of posses.sing t*,o co'llicting l'tt,r- ,t l ie t irrre o{' lrrai ' i ' irrn.(agt, '; l( i) and at the tinie 'al feeli 'gs si 'rrrlta'e'rrsh.) has not been a ,Of operation (45). and srrl ise.rlrrerrth.sliorvecl t lte s\.rnpt.,rrr o1. colrrl issurotorn' ' 'r .f rnost re. :

rl)ost severe apraxic and relatetl srrnptorns. At ported niitrrrnl .,nr"r. i,r,t."li. t,r.rrrt,r,,Jl ',r,1,,the't lrt 'r i ' 'd of t l ie spec'trttrtr. L.8.. ; l3-re:ir- cerebr.l .orrrrnissurrtonr' are l"r, npt tt,,,n iiilcl b'r'(see Bogen et al . 1988. for NIRi sta- 'ormrJ inclivjduais t. cli.scuss their I'eelings. itus)' Iiad relatirelv little hrain.darriage bef.rc' conflictirig or othenvise (Hoppe a'cl Bogen.t:iF"ry.' had brai* injun at birth. rt,,ri.,,.,,rg"ra lg77). Tiris conclition. callo,sal alexithynia iat the tirnc' of operatiorr. antl sullset|rentlv had (TenHouten et al.. tgg6), nra' be explained br . ll.l:,:l:f','jl::t

prist'peratir',' ",,,,.r,j ancl i'i'i- a clef'ect in neht-to-left c,allosal conrluction lItrri l left-l lrrltcl aPriNia. ,_ (Speerlie c.t ri l ., lggrl: Klorrcla et al.. lggg). or :\\iithin a f-e*' rtrontlis afier oPt'rirticln. tire in RII func,tion. (\li' 1r1r. ge'erirlize c,allosa1

IIl l

t l

Il rl r

l ) rl r r

I t '

l i t

II X

l.iI !.)

t ' i r l

( ' { ) l

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I 1 . , ;

I r r . !

I 1.,r\'l-rtr

r1 9 9

1 9 9t .

. r f t , , 'tcqr,( { ) l I l

srs t I' l ' r ' r

T H E C A L L O S A L S Y N D R O M E S

alexithuriia to tlie nortnal brifn ancl predict

that inclir-icluals with iiiglier scores oll an alex-

ithvnria scale will shou'a greater RH cleficit ancl

ro,eaker callosnl transfer in titt etnotionahtr'jrrdqnrent task. Hou'ever. Tribibnia et al. 120011]lbund that this u'as not tlie case.)

Interruanual Conflict

The dissociiitive plienonien<ttt tttost clearir'identiflable r.r'itli lielriisphere disconnection is

internranuiil conflict. in u'hich the liands act at

cr()ss pur?oses. Almost all rlf the complete

cottrttrssurotonn' patients in the Los Angeles

series. nranil'estecl sortte deqree tlf itttermatrtral

corrllict in the t'nrlv postoperative periocl' For

exarnple. a feu'rveeks after one patient (R.Y.)

undem,ent surgen'. liis pln'siotherapist sai(l."Yorr

sltoukl lurrrr seett R.\'. I'esterda\''---{I1eItarttl u'us buttoning up his shirt antl tlie otherliartrl u'as courirtg trlclng right behincl it uncicr-ing the brrttons!" (Bogr:n. 1979). Another Pa-tient tA.\ 'L) exhibitecl sinii lar t 'onfl icts cluringBoqeu's follou'up exaltrinatiott il Febmiin'l97il: "u.'hen atterrrpting a Jenclrassik rein-filrc'eruent. tlie patient re'ached u'ith liis dglrthand to liold his left but the lelt hand actuallvpushed liis right hand au'ar.. \\rliile testingfinger-to-nose test (with tlie patient sitting). hisleft liand sudderrlv starteil slapping his cliestlike Tirrzan."

Sirrrilar phenomena a{ter callosrttotnv havt'beert obsen'ed bv others (\\'ilson et ril.. 1977:F'erguson et nl.. 1985: Reeves. 1991: Sass et al..I99i) as rvell as bv Akelait is (1944--15), rvlxrcallt'cl it "diiigonisiic rlvspraxiir." Interntanttaiconllict lias been describetl in rnanv inclir''itlrtalt'ase reports o{ callosal inlarcts or trttttorsiFrsher'. 196i1: Sclialienbrand. 1964r Jorlt.1977: Barbizt't et al.. 1978: Berrkeirrrtrrl et al .195(): \\ 'atsorr an<'l Heihnarr. l9,Sll: Sine at al..l9E'| l)egos et al.. 19E7: f,e'r ' irr c't al.. 1987:' fanaka

et a l . . 1990: De' l la Sal r r et r r l . . 1991.199'l: S<rll l 'artz et al.. I99 l: l laures et rrl .199 ; l

I ltterrtrarnral crl i{ l i t ' t rrsrrallr stt ltsit les so<llt, t l t * t t i r l l o s o l o t t , r . 1 t t ' , ' l , , t l , l r l r - t a t t s e r r t l t t ' r i l t -

teglrt t ive rrrecharrisnrs suppletrtett t or replat 'e

<rt l t t t t t issrrral { irnc't ion. Irr r i i r t 'cr i tses i t l l iav per-sist l i rr rr.ars. lbr reasons st i l l pr l t l rh t tr tclerstorl t liF t ' rq r rson e t a l . . l9 i i5 : Reevt ' s . l99 l ) .

357

Tlie Anarc'hic (Al ien) Hantl

Related t<l i tr tertr iat iual cotr l l ict is i t c ' i rcttr t t-

stance i t i u4tich one of ' the patient 's hi int ls. rrsrt-

alh' the left hand in t l ie r ight-harrded patient.

be-ltaves in a u'ar- that tlle patient iincls '{or-

eign." "al ien. ' ' t tr at least unt 'ooperatire Delia

Sala et al. (1991) point orrt t l iat such patients

rareh' clenv that the trotrblesorlle harrcl belclngs

to t l ienr: hence. ther. prefer t l te tenn "art i l rcl i ic"

to "al ien." Tl ie anarchic htut l (AH) ofterr leads

to interrnantral conflict. and has been seetr con-

sequent to cal losi i l lesions r l t least si l ice t l te re-

port of Goldstein (1908). Flvi 'n t l rr r .oringest

patient (L.B.). u4ro l t i rd t lo louq-tenl) eiPPre-

i'iable apra-riii to verbal crlttlItIartcl. rrrartifestecl

this phenolrretrt l t t 3 u'eeks alter surgen': ulr i le

cloing the block clersign test utritltittltrallv witlr

liis riglit hatxl. his left hallcl canle uP tl-orrr be-

neath the table and u'as reacltitrg lilr the blocks

rvhen he slappecl it with his right ltancl iitlcl siricl-"That will keep it quiet {br rr u'hile

" Anrong

orrr patients i t l ias l leen rrtost persistetrt i t i t i

subject (N.\\''.) u'ith a ratlie'r flarnbovarrt per-

sonalih' u,hich u'e believe contribr.rtecl to her

fi'erlrent cornplaints abotrt "tnv

little sister" irl

rel'erring to u4rrltttever or u4tatever it r'vas that

rnade her left hancl behave peculiarh'. Eri-

clerrce lias been steacliir- accurnulatitrg tlrat the

AH. to be persistent. clepends upon rttesial

fi'ontal cortical dvsfunction (Goldberg et al..

1981; lvtcNabb et al. . 1988; Banks et al. . 1989:

Leiguarda et al. . 1989; Starkstein et al. . 1990:

anrl Tanaka et r i l . . 1990). Della Sala et al. (1991)

suggest that, in lts persistent forrrr. AFI resrrits

fr,,,nr a krss of inliibition originating in Irresi:rl

frontal cortex (presumablv of actions orgiinized

or "progriirnrtred" eiservliere). This carr help trs

rrnclerstancl iurarchic belrari t l r o{ ' ei ther hiurcl.

or even brtth ]rancls (\{ark et al. . l9! l l ) .

,{r rtocriticis I tt

Irr a relatet l pl ienttt t tett t l tr . t lescribecl lx Briorl

rurr l Jeclr. ' rr irk r1975). anrl u4rich ther cal let l" l 'arrtocri t i tpre rrt terr l i6rrt isplr i ' r i t l t rc ' ." t l re 1la-t ient erpresses fair lv freqtrent astot i ishtttent i i t

the c'apacitl of tlrt' left ltiurri to llelrave indt'-

penclentlr'. \\'iren the lefi liand tltilkes sotrle

i ' lur ic 'e anlorg olr. iects, the patient l t t i tv sav that"rrrv

harrt l dial that." ratherr t l iatr takir lg t lr t ' re-

3 5 8 C L | N | C . A L N E T J R ( ) P S Y C H O I O C y

spo'sibil ih '\ patie't * 'as tlt 'sc'ri l letl b's*'eet l l 'cti..). eve' if ' i 'sull lc,ient t. cirrrsc. lorc,ell(M45) r r ss i * i t r q . "N rn r ' \ o r r \ \ ' i l l i t l l r e top r r t r n t , g rasp inq . r l ay re lease s r r i e r$ r .e i } . ec t s . A re -le'l i irr<lt 'x l i .qc'r on rt 'rrose." Sle therr put that t r". i tr l i i"r., ,"r..r" rleficit is arr inaSil itr.. t.I i 'ger i ' t ' lre'r r 'outh ancl saii l . "Tliat's

l ir 'rnr keep the tl irrr 'b exte'clerl *, lr i lr. er' l t '* ' ' t t ' t i t q' u1t t. ntr-*.se?' ,r, nO, ..,

' , fbr<..t i,t grip (\\,,artt, 'br.rg. 195;1) ̂ :;:1ff, i:Split- ltrain Prrtir: 'nt.s soon accept ihc,iclerr that t i.e.. relit ibli e.l icitecl l^.t l ie er.rnirrerr ar,tronstlt.r ' l ta'e c'riPac'it i t ' 's .1' rvhicli the' are rrrt slrrult l i ,. l ,t,rt i,,s,, irt,,,, i 1).,r,,, .,r.. l i irrr., l iunt., lIt* 'are" 'strc' lt . 's lefi Larlrl 'r ' tr it 'r 'al .f cihjr, 'c'ts rr,t lrelr.r ' i .r t irat is arrt.rro'rors. that is. 'e'ar.i 'rr lartreable ' l ' l le'

Itta' qrric'kh ratitttralize sur' lr t lrut u".,,r., ,r. ithorrt ob'i.us ,,ra".r",i stini, lrrsircts. sotrretitnes irr_rr tran.spar.entlr.erroneolls {i.e.. is sltontaneous). Tlie clistinctirlnr..*' '1'((J:tzzatriga iurtl Lt' l).rt 'r ' 197\r' 3,r1 "." ' rous \ '.s. enrloqenorrs" turcl .. inthrc,",r 'r."t: i l ;.r)1n,l\ ' \ 'ea's altc'r sttrgen. these pirt iertts rri l l oc'- ck ntal" t,"r. j ,. iru b.",, ,rff".. l . l . ' ' . ir"r,". arr^,c'asi,nalh'be s'rprisetl t ' t . ' ' ' , ' , , irr itated u4rerr i, ,t"r"utp"j nr,cl ."petit ir.e carr br: rl istin-sorlle *'ell-crrorrl inatecl or rt ltr i 'rtsl '" uell- g"tri,"a'i 'rt-n ,r,ell-clir"cterl rrr,r.errenf ss-irt l 'rrnr:d.c't l ia's lust bt'e. c'rrrriecl .rri brl1t1e i l"; J"pi"a^a" tJre surro.'tr ings of.apar-lell l lanrl ' This is partic'tr la.lr ' ",,urn,,ur , ir.,I". t icula.noniint. Ariv of t l iese beirarirlrs nra'. ' t,c',rtclititl's t'f "u't.i',',n,,ttt t,,i.'.,,t1r".i

't,,p-r, acc.rnpaniecl (o'ot) br. r.erbal rle'ial. sirnpl.(Zaidel' 1977' lgTlJar Zaicle-l arrrl Peters. 19El)- .,'"ug,ritiu,r. "iobu."t" ratio'aliz,ti.r. or ew.rlPr.ise'tl b' the exarriner frilr'wing successfirl "pp,ifo"rrrr,..-''

perlirrrnanc't, br L.B.'s disconnfctetl ,rght r 1

hernisphere (DRII) on clif l icult t"rrnrng" tn.rt,l ie *,, ' lcl srnretirrrers excl.i 'r: ,.I{,; ;,,, f i ;. TlieAlierr Harrrl: Ternrirrolclgr.t r r r r e t ' t r v l t e t t I r L r r r ' l k r r r x r n l r i r t l . j r r s t ( l i ( 1 . " B r l i t l t t l P i r t l t oqe r res i sit otrc'urs evt.n irr sot,ial sitrratirrrrs. In tl ie.,,rr,_ Tlie tr:rrn ..alien

hancl..\\r i i .s erroleonsly rntro_Ittertlf l9tJ9. L.B (then24r,earspostoperratire) d,,c"<l {B,,g"u'lg;g, u., t 'e res'lt,r l i ,,g,,n,,*'iis h.r'ittg lrrrtc'lt behvee^n.testing sessi'ons *.itlr ,'isreadi'j 'f Bri,n ancl Jeclr.'ak (1975). \\.env. t r t 'c 's t iq i t t r l rs or i r :o f therr taskedabouth is , l i . , ,pprn, in f l th" , , r " . f th is te ' r .Arecerr t re_

attit'cle t'*':rrtl his left lrantl lle replierl. "I *"q;;g 'rok"r'"1"n. that Brion ancl Jec6nakItarrl l-r 'e'er rrs(' i t " ' fhe

other t 'xarrrir 'r". tn,,- ur".l th" ternr "la nrirrn 6trangdre,,to descnbeqen) ti ien p'i lrtetl orrt that lte rvas. at that r 'o- a rnisiclentif icatio' rt,sulting fronr l ir i lure of in-trrelrt' li'ltlirrq up a cirP,f.irric'e in his ieft hantl t".il;;i.pl*n",r:.,,,r,rr-r, tr:r'.si'er. rv'ere.s the'a'rl hacl jrrst takt' ' " t l l l :L ": ' ]] the c',p. ' lsure

usecl th; terr' ' ,1'a'tocrit ique interh6nri-t ' r t . r rg l r " 'he.sai r l . kr .k inq i r t i t . " r g 'Lss i t is sprr6r ique. ' t 'descr ibe seerningl 'p ' rposel i r rgoocl lirr sorrrething." action,s ciis:rr.or.r,ecl bv the patients.

The erriphasis br. Brion ancl Jedr:rak (i975rSigns '1'Releirse fror' Fr'rrt ir l Corrtr. l a'cl,bv Bclgen (_197g) ' ' collorai clisc.nnection\\i' r'a- rristi,,s'isrr bet*,ee' beirari.rs ,r i.- ;:iiT:Tiilirfi:fi: :'JiHfi,,"l: fil.c'reitsilrg conrplexitr antv.r appr'priatenes.s in

1,1"i"a p"at"rra.'*0,r, a right AH srrbsequent krthe tilrecte'cl (btrt ',np,.reli: lllltil*t.'l

,,pp"," left,ne.siai f-niuir,rrn."tion. The role of rnesiallirrrb Relati'c'l' si,rple is. ftrrc.tl g.o.rplire. frontal danrage is clifficult to ev.lrrate sinceIlor'''e'er' titere' rrta' als, he gttpi"; ,ri;,.] such lesions fl.picalr'.also in'ol'e the cc., Thetttc'nts' c'allerl "ir'puisi"e graspiirg't if ih.t "." 'ecessih,' for calkrsar discorr'ectio' (particu,{irllo*'c'cilx graspingup"cont.c,t. \'isu.rlguiri- j;;Lr

";;;

;H;:* cii.ses) trrus resurting i'itllce ll)a! ql'e aII appearall('e of purposeful- h",nirph"i" -iu,i"p"no"n""

would be rlis-Iress' ils ttl "tlrag'etic' apr:lria" (l)ennt-Bro*ryt. p.uu"i if AH enreryecr irr heniispherectomizerli!l5E) .r' rvhelt tlirlre- cotrtplex. ",itilirati,r'

Lclividuals suffering subsequent {rontal clarn-beharjor" (Lherrrritte. l98il: i , irt 'rrntu" "i ,, i .. age.Thisclebateisunres.lr..ed. It ir.sbeensug_l9E6: LaPla'e et ar" lggg; sliatir '" "a oi.. sestecl (Fc'i 'berg et al.. r9g2) trrat t 'ere arel9E9) l"rt lrrtal i ' I i irc't i ,n lr lr tra'sie't cl 's- hv. lbrnrs of AH. ,ne c,allosal antl t 'e .t 'er

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T H E C A L L O S A L S Y N D R O M E S

mesiofrontal. To tlie extent that a calkrsal le-sion is essential (Geschwind et al.. 1995) theAH supports the idea of an "otlier

nincl" (Bo-qen. 2000). Alteniativeh'. it rnav be that the be-hariora] dissociation (betrveen hand action andverbaiization) is the result of interhernisnhericdisconnection of visuallr guided motoiplarr-ning frorn verbal awareness (Milner ancl(kxxlale, 1995: Bogen, 1997).

\'larclietti ancl Della Sala (in press) arguethat the "anarchic ]rand'' is not associated withan ranterior) callosal lesion but is attributablekr clarnage to tlie contralateral Supplenentiin.Itotor Area i l the rnesial lrontal lobe. In thisrrerr'. the SI\{A converts intentions to self-ini-tiak'd acticlns. ancl damage t<l it leads to failureto rnoclulate and inhibit externallv-triggerecl ac-tiott gelieratecl bv the Prernotor Area on thesarne side.

The literature refers to a r.arietr. of ohe-Ironlella with the terrn "irlien harrd.'; All siiarethe occurrence of involurrtan' nlovernents. butt l re hp65 o l r r ioverr rent d i f fer . l r r t l re t .a l los i r lforrn. tliere are purposeful cornplex rnove-rtrents of the nondontinant liancl. In the frontalfirnn. there is grasping arrd utilization behav-lor of the dorninant h:rnd. Forced grasping oc,-curs about equallv often with either tiie riglrtrrr t lre left hand: it is rrsuallr a stereoh,necl re-slxrrrse follor.l'ing stiniulationl ancl it is trpicallva sign of contraiateral frontal lobe dr.sfunctiori.r t ' t l r t r r i r rq r ro t l i re t , l t . l l losal invol r .e l i rent in t l r t ,lesion. The alien hand associated with cofti-cal-hasai degeneration is cliaracterizetl bv u4rat; tPPear\ to l re sporr taneorrs e levat io l rs o l ruramt. antl a better term for tliis plienornenonrrr rq l r t l re " \ \ 'a \ \ \ . i l r ( l

or " rvarr r lennq" l rarr t l . l t is

rnisleixling to desc,ribe anv forrn ni'AH a, oli",,I x ' ( : t l l \ ( ' . l s po i r r t e t l o r r t l r r De l l i r S i r l a e t i r l . .199 ' t ' t l r t , pa t i en t s r l o r ro t us r . r i h t , t l r e l r a r r r l t , rsollleolle else brrt recognizt, it as tlieir ou.rr. al_tltortqh orrt o{' control- \\ 'hi le all thret l i innsr , . . . l l - . r .' ( i ' t r r ( )sa l . I ro t r t i t l . I r : rs r r l -q i r r rg l i r r r r i t . , i r r r r rh c L rs ,ttt ntottlr coltrol, onlv tlr. r,allosal {orrri invrilvr:stt t 'nial of puqroselul nrovelnent ancl the occur-rettt'r' of internianrral con{lic,t rvlriclr cal bc,t t ' r t r r t ' r l r r l i e r r "

\ \ ' r , l l r c r e l i r r e p r ( ) l x ) \ e t l r r r t t l r e( l l l l e r tsn t l i rn r rs repres t , r r t r l i s t i r r r l t s r r rc l r , r r r r t . s

attt l slrould lr t , so narrred. l-or t i re tr,Trt l ol 'nrort,-t t terrt t l rat is u,el l-cgorcl inated. seernurqlr. prrr-

359

poseiirl. aricl corrrrnonlr. e{lectir-e. rve prefcr tcruse "autonornous

hand."

THE CHRONIC, STABIL IZED SYNDROMEOF HEMISPHERE D ISCONNECTION:SYMPTOMS, S ICNS, AND METHODSOF TESTING IN SPECIF IC DOMAINS

The testing of split-brain patients irr tlrt psl-clroloqr lallorirton ltrs lrer'or r re pr,,qre.sii ,. irrnore sophisticatetl. ancl is o{teri urr{iuriiliar er.errto <ltlienr.ise experiencttl nerrropst'c,lrologists(Zaidel. et al.. 1990). Tirus. u'e u.i l l { lrst errr-phasize sintple lr)aneulers that can bt, rrserl rnthe clinic vr,'lien iienisphere <lisc.onnection rssrrspected. The general logic frrr studring lienu-spl rer i t . speciaJ iz i r t ion i r r sp l i t -hrr r i r r p i r t ier r t r isto restrict senson'input anci motor resporrse toone hemisphere ilt a tinre. lnd (.ontpal.e latenc,ror ilccurac\; in the hl'o conclitions. In the c,trseof visual and somesthetic input. predorrriniurtir.contraiateral innen'atiorr guarantees that lefi ri-su:rl field (LVF) aricl left-hancl infonnatron. re-spectir.elr-. u'ili reach the RH. w4ieretrs right ri-sual field (RVF) ancl right-hancl input r,".ill reac,irtlie LH. In the case of auclitorr. stirriuli. con-tralater:il input can be as.surned oulr siren hrrracousticallv sirniliir, but rurt idtntic.al, stirrrrrhreach both ears sirnultanerluslr' (dichotic listen-ing). For motor responses. it is assurned tl iateach hernisphere lias better c'orrtrol ol the con-tralateral hancl. especiiillr- at distal rnorrernents,but in the chronic, rlisconnection srrtrlrorne_both hernisplreres develop ipsilater.al rrrotorcontrol sufficient for siniple actions. suclr as bi-nan' choices. Consequerrth . experirrrerrts .houlorelv on cornplete or ptrrtial lateralization at tlreinprrt side. Cliven the cnrergen(,e ol speecli insorrre cliscorrnectecl right hemisplieres. it slioultlnot be iissurned u.itiiorrt fitrtlicr testirrq tlrat r,t.r-bal output reflec.ts lr 'spr)ris('s lx thc tl isrrrrr-rrected lelt i iernisphere ( DI.II).

Tlie descriptiorrs proi'icletl here apph torigltt-hiinders. Irr leli-hanrlt 'rs t lre sitrtrt iorr israrelv a sirnple rer. 'ersal. Usuallr. it is rluitt, corn-plex. as can be seen in the. c,asr: lr istories cle-scribed irr t l ie' l i terature (L,ieprnrrnn. lg(X): I16-( i r ( ' r f ar r r l A. j r r r i i rqrr t ' r r i r Ig f i { : }Jo| ' t ,Lr r t l( l f iqhel . l ! l7 l ; Tzavaras et i r l . . lg71: I le ihnanet i l l . . lg7 l l : Sc l rot t e ' t a l . . 197-1: Aptr r rurr t ' t i r l . .

360

tll77: l l ircsc e't al.. l !177: poncet e,t ri l .. l97S:I l t ' r rorr . l t jEO; H6i .acn et a l . . lgg l : Grrr et a l . .19,5-1: Ioseph. it],36; Barnes t:t ir l.. l ! l9g:Sperrc, t ' r e t r i l . . lg88) .

Olfixrt iorr: I i rr i late,ra] \ i , rbrr i , . \rrosrr r ia

Llrr l ike nrost other sensol l pirt lnr.avs. t l re ol_l i i t . ton 1>at l r r r , :n ,s " . " , , l , ru , r t e rc , lus i r t , l v r r r r_c,rosserl. IJerlu<rc,hi ari t l Agl iot i r lggg) r leic,nbethe patln'"rtr .s as l i t lkrrvs: . . Inl i trnatir tn

{ronr pr. i_lnAn selrsol l ' nelrrons irr the ol lacton.epithe_l irnrr of erlcl i nostr i l is tr irnsrrr i t te,r l t , , i l , . t , l iac_tr in l l r l l r of t l re sanre sicle. Tl ie a-xons of t l i t :prt i ;e'ct ion l teux)ns o1't lre <l l{ i t . ton, l tulb f irrrrrt l r t , l : r t r - r i r l o l l ru . ton t r ru . l t l r i r t , " , , , . i , " , t l re ips r_lateral olfucton. cr_rrtex consisting of paleocur_ticrrl (prepiritirrnr anil 1r",.rn,r,ifrlnl,,'i.l "r"nr,alid mesot.oft icul c.or rtponents (eutorhinalarea)" (p. 656). The anterir ir ol lrrctorY nucjeus.u l r i t . l r re t .e i r .es i r rpu t f r .o l r r t l re second_orderl ) l t l h a r t r ( ' r t r ( ) n s . r r r i t r l l r e r r s e r r t l i r t f o r r r r r r t i r r r tilcross the atrterior cotnn.tissur(.. and cortical ol_firc'ton' art us. suc,h as tlre pirifrrrrn cortex. nra\; r l s r r p r r r j e t . l , r t . r o s s t l r t . . p l , , n i , r r r r , , f t l r e r . , , r n t r . scal lr isurrr. lJerlrrc'c,hi iurcl . \ql iot i { l99g) bel i :vethat "t l rc

irr terhernispherici transntissiorr of ol_facton' irrlirnration cloes not inr..olr.e the (iCand rel ies rrpol i t l ie iu)ten{)r anrl l r ippocanioalc o r r r r r r i s s r r r t . s ' r p 6 , 5 6 r .

F<lllrlu.inq ()llrplete c,erebrirl c,ornrnissuro_tornr ' . the'patieri t is unable to ni lrne odors Dre_sentecl to tlie riglit rrostril, even u,hen ther.'1a1be. narnerl r lui te. re.acl ih.u. irerr presentecl to theIt,li nostri]. 'fhis

is not a Lrnil'iitt.ral dei.cct riI.snrel l . sirrtr tLc l tat i t ,nt c,an selec,t. bv fe,el inor r i t l r l l r t , l " l i l , i r r r , l . r r r r o l r j e 1 . 1 t t , , , f , , , , r . . p , , , , , i ito the oclor ltresented to tiie right nostril. srrcnas selectinq a plast ic bi lnana or ir plast ic f ish a1_tc.r lrarirrq srl lel ic( l t l ie relaterl ot lor (Gorclonr rn r l Sg . rn . lg6g) .

TIre oriqir ial sturlr" of conlrnissurotornv sub_.ft .c ' ts louncl that t idor icL,rrt i f ic.at iorr {ui ing arronl ingrr ist icr task antl respol lse rnocle) rvas .su-peririr rrsirrq tlit' le.lt nostril as c,orriparecl to us_inq t l i r . r iglrt {Grirckrn anrl Spe,rn.. I^SOSt. A srrb_seqrrelt strrr l .r of cal losotorrr_r. patierrts founcllel i l rernisplreric special izat ion lor oclrr rnern_rrrr ' . al thrlrrqir not 1br odor iclenti l icat ion (Es_kerrazi et al. . l9E8). Other populat ions srrggesttLe oppositc pattenr o{'lateiafitr. Su,r,e ,tii i i".

L L I N t C , { I N E U R ( ) p S y ( _ H O l 1 . r s , y

slrorv rrrore. irnpirirrnent in olfac,ton abilrt larl lorru patietrts u.ith riglrt- rirther than lelt-sided_brain darnage or terrrporul lnb",tn,,, i 'te,.9.. \ l 'est anrl I)oh.. l9Sl5). althorrgh otlreisliavr' frnrntl no clifl'erenc,es (Zuiorre u,r,t t,,,,".-Cloturrur, I991). Tasks designt,rl tci rrreasurr,t lr,,olfac'ton' abil itr of r.acli lrernispi,".e i,t uu.,,,alsuLrjects har'.,, i lr,, srrqgestecl nif rp"",nt,r,, iu,,,{e.9. . I {urnrnel et a l . . lggE). but Lra in act i r .a_tion studies iire c.orr{licting (Zal<l ,urcl pa.d,,.1997: l )ade et a l . . l t jgg: Sol re l e t a l . , 1999r_ Rt'garclless o{' tlxr reliltive abilities ol tlrtlremispirerc's. tirere are trr.o Iirres of ..,i,t",,;:,,rvhich strggest that the henisph".", nn.ru,,tt,ivork toqet l rer j r r o l l i r r . t ior , . f l , " t i . r r i * t i " , ii l l l onq r r , r r r n , t l i r r d i r . i r l r r i t l s . , , r i , , q l r , , t l , , , , , r t r j . ,(birhinal presentation) inc,reases tt," p"r,,"i.,:.Ainterrsih' of oclors rt,,lative to using orlr-. nu. ,,nr-tril (unirliinal presentation) (C.rin, 1g77, G;;.cia Nleclina and (_lair. l9g2) ancl {a"ilitnt", uri,,,nternory (Brornlel.ancl Dotv. 1995). but it cloesnot affect detection threshokl lDotv et al ,1992). Secr_rnd, patients rvlio lac,k iute.lr",r,,_spheric fibers sufl-er olliicton, ,l"fi"itr. i,, ,,study bv Eskenazi et ai. (lglSt. t"u "nllr:rr,,_toniv patient.s lrrrcl ser.ere inipairnrents in rxlorcliscrimination ancl iclenti{ication IIr"r",r,,-tients rvere also epileptic, rvliich appears tocause a qeneralizeci clecrease in olfacion lirrrr,-t i o r r / \ \ ' es t an t l Doh . l gg i ' . l r r r t i t l t l r o r rq l r p t r_frlrmance *'as incleecl srrbnorrrral i' tir" l,;;,pr r l ient testcd presrr rq i r . i r l l r . i t r ras f r rd l r r r r r . -t l r r t ' ed l b l h ru ing t . r r l l oso lo r r r r .

Is it possible lirr olfircton. infirrrrration krl ra l rs ler hetween t l re l r , , r r r isp l ' reres at ; r l l in t l r r, r hscn t t o f t l r e ( . ( I i r r r r l i r r r t e r i o r l r r r r r r r r i s s l r r t , iPrerious experirnents Ir:n,e aclclressecl this urres-t ior r hr t t ,s t i r rq t l r t r r l r i l ih of sp l i t_ l r r iur r p l t i r , r r t ,to rerbr:illv narne unirhinirllv presenteci ,xlursCorr lorr , r r r r l Spern r lgFig ' l , r r r r r t l t l ra t furr r o lf ive. complete cornnrissurotorrrr. ltatients trrrrlr ln i r rne odors preserr ted to t l re le f t r r r rs tnJ, brr t r ro ltiiose presentecl to the riglit. Tliis suqgest.s thatlrtorrnation r.vas generalh,rrnable to cro.ss Inrrrrt l re r ig l r t r r l lac.krn t r rder to ext . lusn.e l r le l i .s i r le t l s l lecr . l r r . t r r ters. Horver .er . t l re f j f i i r sr r l ,ject irr this studl' (patie.nt N.G.) was able tonarne riglit nostril iterns tibor.e ciriince in olre ol'four well-controlled blrxrks, wirich suggests thatsonie transfer lliav still occur. Of the hvo in.te' rheniisphe ric c,onne<:tiorrs in tlt, olllc,ton. sx.

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T H E C A L L O S A L 5 Y N D R O M E S

tern. the anterior cornurissure appears to berrrore irrportant. The three callosotorrrv patientssturl ied bv Risse et al. (197E) and the two na-tients of Eskenazi et al. (1988) rvere ull abl" t,,nane odors presentecl to tlie riglit nostril. lnsharp contrast to the cornntissurotornv patientsstudied bv Gordon and Spern'(1969). sonte ofthese patients with intact anterior cornrnissuressho',ved no difference behveen nostrils or evenbetter nanting of stimuli presentecl to the rightrrostnl than the left.

In a recent stuclr'. Aliison and Zaiclel (2000)exanrined three corrtrnissurotonir, patieltsirorn the Los Angeles series (L.B.. N.^G., anrl.\.A. t. rlne agenesis patient u.ith an intact an-tenor coniniissure. and an epileptic control.Thei usecl a stanclardized set of olfacton' stinr-r r l i sr ' ra t<. l r ant l s l r i f l " s t r ips i l ro t r r t l re L 'nr-versih' of Pennsvlvania Surell Iclentific.atirlnTest iUPSIT: Dotr-et al.. l9E4). The first 1ind-rrtq of this stuclr. was tliat tliere is tr consistentrrrrpairrtrent of odor identificatiorr arnong indi_r i t l r ra ls lar .hrrq t l re CC. as in prer iorrs s tudiesttl patients r'".ith callosotornr' (Eskenazi et al..l9 \ \ anr l t .a l los i r l , ,g . , , " r i . , Kessler et i t l . .l99l t Second. the results do not pror,.itle sup-port lor the lnpotliesis that tliere is henri-splteric specialization fcrr ol{action. Third. pa-t terr t r i r r u l rorn t l re CC la i led to l i r r rn drr r i r rgdevelopnrent shorved no disadvarrtog" *4r"iithe ,rdors to he dist.rirrri lrated were rl 'resent*dto separate liemispheres. In corrtrasi. both of'the c<inimissurotomr.patients u.4ro ccluld do tLetask at a i l t , " r " s iqr i i f ic .ant l r . rvorse t l r r r i r rq t l r isnt 'h ieen-henl isp l rere r .ondi t ior r t l rarr rv l rerr t l reodors nere presented tn tire sirrne hernispiiere.Patient A.A.. hou,ever, rvas still able to conr-pare odors between hentispheres alxrvecltatrc't . \\'hen tested br' Gorclon ancl Spern,i1969). patient N.G. u'a^s also sornetinres'abletr) I larne odors presented to the RI{. This sug-Ilests that sonre subcallosal routes niav be alriet ' t ( t t l r t e \ i r r l i r r r r r i r t i o r r , r bo r r t o t l t r r s . S r i h t . a l l os , r lr{)utes l)tril exist firr other senson. rn<tdalities ast re l l ; r t x l t l r cs r r r r r t es i r pp ( , i u . t { ) \ i r n i u . ross i r r -rt ividual patierrts tClarke antl Zaidel. tgSg).

Tastl

T l . - |I r r { ' la te ra l o rqr t r r i z i t t ro r r o I t l re q r rs t ; r lon . pa t l t_$ a t t t r l r r r r r l t n s i s i r r t . o r n p l t , t l l r , r , , r . 1 " ' r s t , , r r , l .

36.1

\Iost strrtlies suppoft iln rincrosse(l projectionlrorn each side cl{'the tongue to the cortex. butreports o{' a crossed rtrgiinizatiorr continue toappear. The afferent gustaton fibers fronr eachlialf of the tongue ;ire knou.n to tral.el ria the\rllth and lXtli cranial rrerl'es to the insilateralnucleus o1'tl ie solitan'trac't (NST). Tlris prc4-ects to the panricellular part of the ventropos-teromediai nucleus of t]re thalarrrrrs rVPNIpc;.rvh ic l r in t r r rn pro jer ts ips i la tera lh lo t l re pr i -rnan' gustaton' cortex in the {rontal operculuriri ind anterior insula (Kobrrr.akawa et ri l .. tggOt.Tlie unsolr.ecl question is u.hether the, pro-jection frorn NST to VPNlpc is c.rr,sseci orruncrossed. Follo$.ing unilateral brairr lesions.gustaton' inipairnients suclt tts ageu.siiis. ltr-pogeusiils. or dvsgeusias can be loc:ilizerl to orrr_.sirle of tlie tongue. But both subcortical andcoftical lesions give conflicting results (re-rierved in Aglioti et al.. 2001).

Agiiod et al. (2000) studied the lateriil orga-rtizaticin of the qustaton'patliwav in norrtriil con-trols. a rnan with a cornplete callosal agenesis.arrd :r rnan w{th a crornplete sectirur of tlie (jC.a rieht anterior frontai lesion. and lalguiige inthe LH. Sapid solutions \vere applied to one orthe other side oi'tlie tongue arrcl subiects re-ported the taste of the stirnuhrs either i.erballvor l , r r r r r rnrra lh point ing to t l re narr re o l t l r t , tast t . .There were no differences in accuracr-ancl re-r r< ' t ior r t i rne iRTr hehveerr t l re r is l r t ar rd le f thernitongues of the controls ancl ihe acallosalsubject. Bv contrast, the callosotontr. subiectshou,ed a constarit rnarkt'rl aclvarrtage of tire'lefthernitongue over the riglrt for both accurao'andspeed of response, tliough peribnlrance u-ithright stirnuli u'as clearlv ilbove chance. Assum-ing LH control of speech in the callosotomy pa-tient. tiie results reject an exclusivelv crossecl or-giurizatiun of t lre gnrstaton patlnvar l iolr t()nguetr r 1 '61s*. arr r l laror a b i la tera l l t d is t r ihr r ted r r r -qarr izat iorr of t l r is pat l rsar . r r i t I r a r r r r rker l prc-t lor r r inan<.e of thc r r r r r ' r t rssct l or l r . l l , . r . r , , is t , t lcorliponent. These results, liou'ever. c.annot nrleout arr exclusiveh' uncrossed organizirtion.

Be r . l r r r . t . l r i , l r e r so r r i t l r . ' r r r r r r r ' r i r . i r t i . r r . f 0 ( x ) rlras sirrce cclnilrnre'cl t l iese results irr hvo rrorecallosotomv patients u'ithout coftical lesions.Still rreeclecl is ir clernonstratiotr that tiie rrn-c'rossecl gustaton' crintponent is stroriger thanthe crossecl <lne irr the. clisconnectecl riglit henii-

362

spliere irs u,t . l l . . fhr:re rrrar. i r lso he irrcl ivir irral

i l i f lererr<,es in t lr t relat ive rrr i lgnitrrr le ol. t i re un_c,rossetl ruir l r ,ro.sserl gl lstat()n, (,()rtrytorrerrts. i rrrr lt l iese r l i l1i ' r t ,rrc,es rnigirt expl:r irr t l : r i , ,rr ,r i l , tr , , :rthe' nerrrol<igic.al l i ter i i trrrt , .

\jisior r

] I e t Ju tr l ,s. l 'o restr ic.t ser lso11. r isi ral r nl irn r rrt t iorrto one lrenrislrherr,. lat, :r i i i izerl r isrral st inrrr l iare presentetl l i rr < l5O rrrsec.. Tlr is prer.ents t lr t .corrfoutrding el lects of ir tvr i l rurtun .n.",n.I i . ," , "I t tove t t ten ts . w ' l r i c l r l r r r r r , , r ia te r r r , r l , r f ah , r r t I !0

l l l. l i. l- T:, ar rritI Possible c,o,rIil,nils clue to pre_(t()lnllt iutc.t, ol c,trrsst_cl over ulc,rossecl f ibeis at

the cli iasni. binoculiu.rrsron is rrsecl. Altltorrghlrurnans rrre belie'ecl to show. ".1qfrgrbl.,T,he rnisplieric' irnatornic o'erlirp "rn,,ia-J," r.'r_tici i l rnericli iul (on the nrrl". ,,f rnirrutes .; ia;)it is prudent to present stirnrrl i u.ith their out_enrro.st edge at least l,_2,,arvav frorn fi_ration.Altirough elec.tr.rincephalogiaphic iili;,rec,orcli 'g is o{telr ,,s.cl io ,r,u,rit,r. "r., ' ,;;r;_t t t e n t s ' J o r r l l r r r e l r r l . . l g t ) \ r . i u | . r l r r ; r t r . l i r r r t i , r rcarr usrrti i lr.be asc.ertajnerl b_r rir leotapirrg or rl i_rec,t inspec'tiorr. Crrrrenth. Irernifielcl taclris_

l.l.,op.l is rrsualiv irrrplerrrentt,rl orr personal

c'orrrprrters.To. stri<lr ' 1tr<lc,essrng o{ crlrrt irrrrorrs risrral

stinruli restricterl to rirre hc.rrrisphe.e. E. Zaiclel(1973) tlelelolterl a conttrc.t leris svstern tltat ist 'ffectir e brrt rerlrrires inrl ir it lrral l i tt i ,;. ; l ; i ;".itnestiqrttorr rrsetl paft_oltaque t,ontact lensesrf.rrrrrorrrl et 1.1.. l!175) or goggles (F_ranc.k.s c,tal.. 1985). ulriclt are irrrprec,isr.. Instearl of vok_ilg tl ie herrri l iekl .,r",,1,,.1". t l ire,ctlr. ," 'ai:r" "r.,via rr c.orrti ict lerrs. it is possilrle h, track ererrlovenlents rrorrinr.asir.eh. irncl rrse ihe l ir ir izoir_tirl

.c,ornponent ol tht, e_\.e uto\.ernents to c,orr_trol irernil lekl oc,clrr.siori. r: ither optici, l lr-;;"c'hanicallr ' (Zaidel ancl Frazier. t97;;; .;,; ' .,vicleo rnonitor (\\ jtt l irrg. l9g0). f l," "ri i i"*lt t t ,ed-s i t f t , to s t ,n : i l . : r f rr._.. .- . ' e\.€, l l lo\_ernent.s f i .r tnrl lci t( l l l lovetnertts. oLltairr un tt( .( .rrr.ate nleasrlreol eve ntor.errrents {u, i th an errortrt a,fO ,rr i lutes o1 arc) w'itlrin a relati,,.el_r.wicle visrral sciur-t t jnq area (aborrt 10. of , , . . i ) . arrcl , ,r ,r , , ." ,r . i_c'lusion in real tirne. No {irllr operatic,r,"i ;r;tr i rcker- lr irserl sr.sterrr { ir . i i , rr , , lat i ; i ;" ;r"r r r ro l rs i i r r . r r r rc r r l l r c r i s ts ,

C L I N I C A L N E U R O P S Y C H O L O ( ; Y

f-oilura tf' Intcrlrt,trtispht,ric .fntn.s.fi,r: Dortltlc

IIt:,rrt iarutpia Stirrrrrl i conl}rerl to out, r. isrralhali-{ielt l u,i l l reac,h rlrrlr. t lre ",r,,tr,, l ,,t"rolhernispherc. Callosal sec,tiorr "ltt p,..,r,:,, i tt,"l rerr r is l - r l rere ips i l ; r tera l to t l rc s t i r 'uu l r ,s f r , r ,nItit\- l lr{ i l(.(.r.\\ to tlr is stit i trrlrrs. Tlrerefirre,. orrh.one lre'rrrisphere (,iul reliabJr ,.,.pn,t tI,., pr,. i_errcr. of the stirrrrrhrs .\ lt lrorrqh iaclri.stoscloprc.prt,st 'ntatiorr is it leal fbr corrl ininq tire stirrrrrlrrsto one lrernispherr_,. t lre rl istrinne.c.tiorr c,iursonietirles ltt. r lerrorrstratt,cl wrtlr sirnple corr-lronti it ion tc.stirrg o1'tl ie rjsrral l ielrls. if lu,

,....-tient is allou,erl to lrrr,,.t. lrotlr err.s ,r1_r"r, lr,,t ,l,tr.,,not sperrk. iirrrl is allou,e.l tu ,ir.. onlv one lranrlt<l respontl (sitt ing on the other hanrl. lbr er-arnple). Using the lree, I iarirl. the srrbjec,t inrl i_cates the onset rif a stirnrrlrrs. ,,,r.1, or't lr" ,r i1,_glilg of the exarniner's 1inqers. ff,itl, .,,.i,testing there rtrar.altpear to Lr" nr, l,ar,rr,rnr.,,,,ru,lieunanopia c.ontraltrtertrl to the irrrli<,atirrs

]rurrl (the patient reliablv poirrts to .1,; ;;i;

half'-field stinrulus rr...itli tlie rielrt hancl ir;';;;to a left half-f leld stirnulus). \ i-herr the pnti"utis tr.sted ndtli the othc,r hirncl there seerrx to bean.Iiornonvrrrorrs lrerniarropia in the utl,", Irull._fielcl. One can also tr.st foi this rlefic,it frr:f ,"i ii r r g , r r p ( )ne o r r r r , r r r , f i r r qe rs i r r 6 r r . l , , , i f , l i _ i , i, r r r , l ask i r rq t l r c p r r t i t r r l t o s l r ou . f l , * , , , , , r " , , , , u ,_t )e r ( ) l l l l l qHrs .us i r t q l l r t . I r i r r r t l i ps i l ; r l e r i r l ( ) r ( . o l l _t r i r l i t l e r i r l t o l l r e s t i r r r r r l r r s . r r r l , r r r sk i r rg t i r r , y r , , .t ierrt to derrrorrstritte a hand postrrre i j,,,r,r,tr,,onl_\' one henrispliere.

() t t r "t,t

p t: t t,.s a t t t n1 S t rat t, gi e.s. Nl ost patients err. rr -trrall_r'ac'hieve a crinclit ion in n.l i icih no l ielrl r le_tect carr lte denicinstratecl b.r.the c,onfrontatiorrt e r , l r n i r ; r r e T l r i s r l epe r rds r r r i r i r r h , , p , , , , t 1 , , . " t ' , i 1 .itr oI eac.h Lenrispirere to clirei,t t ire hearl ;urtler.'es towarcl the r.,isrral target: this can signllt l ie l iernisphere ipsilateral'to the sti,nului turespo r r t l . I f l r r r r r i r r q o f i l r e l r ea r l i s p r c re r r t r . r l .r t l r r tera l q larr r .e r r i l l sr r l f i t .e to t . r re t i re pat i t . r r tSorne patients learn to ..cl ieat:"

l irr exanrpl,,i l . \ .s{ )on t rs i t is r tppi r rerr t that t l rere is r ro s i r j t -r r l r l e s t i r r r u l r r s i r r t l r t , r i q l r t r i su i r l l r i r l l - f i ph l t l i , ,l iq l r t l rarr t l r r rar poin i to t l re le f t r isual l r i r l f -f i e l r l . T I r i s , , 1 , * , , i i , r 11 r . : r r r so r r re t i r r r es I r . , 1 , , .tected bv pror.icl ing rro stir iruhrs :it all orr sonrr,triills.

Each hernispliere. especiajlr.thc leli. c,rn t,r.ert a rrrorlicrrrn rif ipsilaterai control. especrrrllr

I

l ,l rI

\ l

f (

t l

;ri' r l

s i t

l)t I

l r r ;\ f i l

t ic '

, i l t (

r r r t l' l ' l r ;

l r r r tr r i r r( i u

198toki,

str i t t, r l r . .i r r t lt{) r(( i l l I

r iglr l

for qross arrn ltioverrlents. As a resuit. stirnuli

in the riglit hal{-f ield (seen onl', 'bv the LH)

mav lie pointed to rvhen the patient is using

onlr, the left hand. and similarly for the left

l ,n l i - l^ i *k l s t imrr l i rv l ren ot th t l re r ig l r t I rand is

available. But such pointing is less reliable and

accurate. as cortipared with the dependnble re-

sponse and precise lociilizatirlrr possible when

the pirtient is using tlie hand contralateral to

the stirnulatecl hernispirere.

T H E C A L L O S A L S Y N D R O M E S

\ti,wal De'ficit.s Related toI I er r risl t l tt ' rt ' 5 lttr ial i:n t i l ,t t

Yerbal repctn of lcft d,vnl .fiekl .\tinuili: le.frlvni-rtrutntia. Sinc'e verbal output is controllediilmost exclusir,elv br the LH. there rntrv be noi'erbal repofi io stirnuli con{inecl to tlte lelihtrlf-field. u4rich access onlv the RFI. If stimuiiare presented sirnultarreouslv in botli visualhaif-fields, onh'the stirtulus in the right lialf-field is described bv the patient. that is. br theLH. There is usuallv no verbal response to tliestinruhrs in tlie left visturl half-field until the LIIrealizes that the patient's left harrd is also in ac-tion. pointing to the left iialf-field stirnuius.

Split-brain patients ruav be unable to narneiiloud objects presentecl in the left half-field.This problern is usualh'not evident in patientswith left hemi-alexia frorn acquirecl splenial ie-sions (usuiillv with right hentianopia frorn a le{tpostenor t '"rehral arten terri lon irtf i trt ' t iorr).i r r t t re t Poer.k , l9S-1r . rv l rose pat ient u i t l r a lex i iLri'as also unabie tci rrame objects. i.e.. hacl op-tic'anornia as u'ell tis herriialexia.

I'<'ft heni-alt'-tic. In tirr: :rbserrce of Lemi-irnoprr. subiects witli lelt henialexiir carurot reaclindi\i(hrd u'ords flashed to the leli h.ilf-field.This is tme not orrlr' {br cornplete' caliosotornvl r r l t ; t l ' o l r r r pa t i e r r t s i i i t l r se t ' t i , , r r , , l o r r l r t l r c sp l . -nttrrtt (Trescrher anrl Ford. 1937r lvlaspes. 19'18,( , iv .zr t t t ig l r i r r r r I Fr t , , ,< l r r r i i r r . I 97; ] : I ) l r r r r r rs i , r , t l l . .1980: Srrqisli i ta et al.. 19E6r Strgisli i ta anrl Yosh-tttka. l9E7). It is srlrrretirrres possible to demorr-st r l t t . L ' l i l rer r r i l t levrr hr t l r . ' l r r ie f presetr tat io t rst t l r ' , t r r ls . s l rorr i r r { pnrr tet l lc l ters or l s l t , r t l u , r r t ls .ttt tlte le{t liall'-field. Patients are' o{ten unablettl read a cirrcl presentecl this u,ar'. rrlthougli ther'catt readilr, r'ead it u4ic-n it is nreserited in thenq l r t l r a l f - f i t , l t l . A l t l , , , r r { l r ( . \ ( . r r r ) \ e r r ( , l r t \ i r r { '

363

rrsuallr. too actir.e ftrr sucli sirtrple testing rneth-,x ls . l rern ia lexr i t was. i t ) l i r t ' t . , rbsenet l r rs ing srr t l r

nethocls, long before its derrirxrstratitln bv

tachistoscopic presentation (Trescher and Ford,

1937). Henrialexia lias been irttensil'elv studieclu.ith both tachistoscopic anrl ctltnputerizecltechniques bv Suggshita et al. (1986. 1987: see

also Griisser and Landis. l99l).

Conrpensation. There is sotrte apparerrt re-

co\ren' over the vears. pafi tlf u4rich is attrib-

rrtable to setnantic' transl'er: tliat is. the rvorcl in

thc, LVF is recognizerl bv tlte RH ancl this se-

rtiantic in{brlnaticin someltorv triursfers to tlre

speakrnt l LH. rv l r i t l r t 'ar t t l te t t apl l r r rx i r l ra le t l r r '

stirnuh,s rvord. Indeecl. if the stirnuli are kttourr

ancl not too nrtrllerttus. the diilirse selnantic itt-

fbrrriation rnat' be used ttt identifv the lr'orci(\ lvers ancl Spern'. 1985: Sidtis et al.. l9Eli i:

C'ronin-Golotrlb. iggOb, Susisli i t: i et al.. 19E6r

Zaidel et ai.. 1990).

Auclitiorr

Lqft Henrisphere Suppressiot of lpsilote:ralYerbal lriprtit. Auditon'liforrnation to each ear

crosses at the ievel of the superior olive anclthe rnidbrain (inferior collicuius)r hou'e'er'there are also ipsilateral projections. so thateven in tlie split-brain patient. eacfi hen'ri-sphere receir''es input from botli ears. Nlonau-ral stirnuiatiort tlierefore proiects to both lierni-

spheres. Dichotic stit'uulation. in u4rich distinct

but acoustically sinilar stirnuii are presetttedsimultaneouslv to each ear. suppresses the ip-

silaterirl projections and rc'r'eals an aclvatttage

{rlr tlie cotrtralatertrl ear-henrispliere projec-

tions irr norrnal subjects. \\rhich of tlte cxlur-

petinq trvo stirnuli is iilentified ck'pencls rrporr

thc' degree to rvhic'h the ipsilatertrl stirllrrlus is

suppressecl bv tlie strorrger c'rltttrlrlirterril itrrcli-

ton projectiorts. itt i t l aiso trp<ltt hellr isplre're

spet'iaiizatirxr {or processing the spet'ific' tr'pe

of aucliton' input. Thus u.' l teri r. 'erl lal stittrrrl i are

r r s , ' t l . t l u ' r e i s r t r i g l r t e a r l t t l r a t t t i t q e t t t t t ' r r l t t r t l

srrirjects. bec,ause tlie LII preferelrtiallv ana-

h zes the verbal stirnuli. atrd crlrrtralateral ( riglrt

t ' ; t r ' l l r t - r . ic t ' t i r t t ts to t l te LH dor r r i r r l r te rv , 'akt ' r ' ip-

sililteral ( lefi ear) attcl cross-calltlsrtl projt'<'tions'

In split-briiin subjects, this riglrt eal' iitlvirrttriqe

364

bec,or les r r r r rch r r r r i rc pronorrncr . r l lNI i l r rcr_ eral . l !168: Sparks irntl ( ' l t,sc,lnr-i,,,1. t 'gOi, C;,,r_jlul; ,19-711

Springer. rurrl Gazzauig,i. tS;;,Zaic le ' I . 1976. lg f , r } Zai r lc l e t , , i . lg i t t i , , ,s-gestirre that irrterrrrption ol <.irl losal trrurslbrprt 'r 'ents the LtI l iorn ac.cessing aurliton. rn_firrnation fiorrr thi, leli *ar. , i,, t i ,. f l f f

-U*t,

ipsilateral srrppressirin antl lrerri isplr,,,.r., .r,n,_petence r,rur be asses_serl in t lre spiit_brain pa_tient_br- rrsirrq lateralizecl r. isual probes to lx_rnatclrecl with the sen.rnrl in either eiir fZaictet,1983) Althouilli leii ear rvorcls are poorl_r" re_ported verball,r,. the,ir perception b_r,.i1," fin i,occasionali.i ericlenced br.,pp.up.inte actionsol the left l ianrl lGordou, ff j i ;1.'

Lefi eirr extinction liiis aiso been forincl rrrpatients u-ith lesions of t lte LH. i i .the lesionsare ltrirlr deep. u4tere the.r.are apt to internlptconinris.srrri i l f ibers. Sinc,e LII lesions a.re l lsrr_:rllv associatecl lrith suppression of the riglrt ear.the ,suppressiorr of tirelefi errr b.,. ,, f_fil,.rr.,,,lras bt.en r iillecl "piiraclorir.rtl

ipsi lat,,r"l ".rtl,r"t ion" (.Sparks et al., I g70). Frrrtlrer obsen.ationssLrpport t le c,onclLrsion tl iat lesion.s close to tlrernitl l ir ie irr eit lrt.r l ierrrispliere ",,,,." .r.,Onr.r_s io r r o [ ' l e l i e i r r . s t i r r r r i l i i r r i r r t r , r n rp t i ng i i r t , , r _l r e r r r i sp l re r i r ' pa { l r i r r n . s , l \ l i r . l r e l , , , , , ' l l 16 rn , , , , " t .1975: l) iLrnasio antl Darrrtrsi1t, l97g; Carribieret a l . . lg8- l : Rrrberrs et t r i . . lgg5; Rao et a l . ..1989: Pujol et al.. Iggl ). Bec,arrse pn.n"nllor"llesions c,an iilsu resrrlt irr riglit ear,,rii,,"aiun tir.rronverbal rrrriteri ir l such a.s cornplex pitctr dis_cnrninatiorr. it has been .suggested th:rt the so-called pararLrxicii l krss ivorrl i l bette,r t " t".,rr",t"callosal

ertinction" (siclt is e,t al.. lgfJg).

Rigltt Heyrtis1tharc Stq4trt:s.sion tl NonoerlnlIp,silateral Auditonl In1tttt. \\'t, have testecl na_tient L.B, <ln a r.erlrtil identilic,ation ,.ersiorr'of.Lc'r- and B n tlen's clichotic u,ortls/el rotions test(1982). This test consists ol ' fr lrrr rhvrrinqconsonarlt-r'ot'el_(rlrr.sonirrrt ( fl\'C ) u..rircls spo_ken in forrr different ernotiorrtrl prnrn.li".. iir"u'orcl identification task rielded a rnassir.e riglrte'ilr adr.autage u4rereas the ernotionrr] iclent?fi_ctition test rieltlerl ir ura.ssir.e le{i ear atlviintage.c'onsisterit r i i th crrlrnplerrrentan. he.nrisplieic,spec.ialization l i lr u,orcls a,rcl e,noti<ins obs^en,edin nornral subjr,c't.s. The .sirnplesi irccclunt of thisp ; t t l en r , , f r . es r r l t s i s t l r i r t 1 l t 1 , , . r , . i s qo r rd i ps i_lirte,ral srrppressiorr firr botli tasks i,, f,.tf, fr"lrli-spiieres: r9.i t lre LFI spt,c,ializt,s l irr i ind rlorni_

C L I N I C A L N E L . ] R O P S Y C H O L O C Y

rrittes the irleritiflcation o1. tite u,rlrcls. exhiltit-ing iur experterl nrassive rigirt ear ",l"nutng.,

] , l l : RFI spr.t. irLlizes lbr rinrl dorninates the

roelrtrl l(,atr()11 oI errrotirinal prosotlr,. uelrl irrg anrassive ieft ear adr.autage: ,u,.i ,1, ,,,.[,o] kl"u-tification of the ernotions reflect.s either Rllspeech or else LII r.erbalization oi't l ie ",,r,rt,uuor tr crlde irlentifting it u..iric,lt is transferrerlsrrbcnllosalh' frorn't l ie RH to the LII.

Sidtis (ldEg) clernoristratecl arr apparent lt l-vantage irr the l)RH f,rr. t.,,r,tplt,r- pitclr rl is-crir-nination. Trariro ,rncl Banrt.lr,r r lt.)gI t lorrnrlan aclvantage for tlrc J)RH lirr l,or,,r,r,,,.l prn_q ress io r r a t r t l usso t , i t r t i i , , i r r r t l i t on l i r n t . t i o r r .

Sornestl iesis

Sornatosensory projecti<irrs to the lrenrispherrsare rnore lateralized tliarr arrcliton pro1..tiu,,".but not as cornpletely. r.ontraltrter'af ", ,i.,,"fprojections. The niedi:rl lenrntscus ststerrr.rvhich is rnainly involved in the transrrrirri,",'"ftactile

, ancl prciprioc,eptir..e inllrrt. anrl everr

rnore the spinotiralanric, sr..sterri. u.,hich rnairrl,transrnits thc,rrnai anrl pirirr sen.sations. prolet,tr r t { o r rh t . o r r t r r r l r r t e r r r l l i l r r r t r r l * , r i p r l t , , i " o i l ,\,\rhile the ipsilateral corrnectiorrs i.r,,,r ,lirtnjbodl pafts irre alrnost absent. atr,r." frnu,'"ri.tr rnd pror i r r r t l h .dr prr r ls ; r re r ler rs t , . l \ t , , r , ,n ; ; ; .sorr rest l re l i t . i r l lererr ts f rorr r t l re la t . t , qo to hot l ripsi- ancl c.oltralaterirl c,ortical areas iberlucclrraricl Aglioti. 1999).

Faihtre 1l'

Interherni.splrcric Trntr.s:fi,r. The lackol inte.rliernispheric transfer follourng brairr bi_section can be delronstratecl with iespect tosornesthesis (iriclucling toucfi. pressu.". u,,,1propnoception) iri ir r.arietr,.of rvavs.

Cros,s-retriexal of ,snmll te,st obiect,s. The na"tient is given an object to feel with one hanrl,ancl then asked to retrieve tlie sarne obiect fronri l l l lonq r r r r r r rn l rer of o l r jer . ts . Srr<, l r ; r r io l ler , t i r , r rrs rnost

-cunvenientll placecl in a ptrper plateabout 15 c'nr iu diarneter. arounJ,i lcl i th.,.subiect can slmffle the obiects u,.jth one hanrirvhile exploring for the terst objec,t. \I'hat tljs. itingrrishes the split-brain patients frour nonnrJs :is thiit their exr,ellent sarne-liancl retneval iultheither hand) is not acconipaniecl bv abilitr to iretrie'u'e u.ith one lianrl oir.jects fr.lt sitjr th,. iotiier.

ff

I

I

(

I -l t

l rI t('(

I

i tL

l r .

t l t ,\ i l i

titI

fi*t

I l t

. ' tnr ler, r.s lrt ( ) Il r l rs ,; r l r l r( ) , Io t t t t

l t r int i t re

Pr( { ) l } l

. l r ' ( ' tr lv rr;t l r l te lr lesc'r

n i t l ) t (I t , ( f

r('qiul

l ran<1.I 98S)| l l q a r i

I c l so l r

I nt e rnnnual point localizallori. After corrr_piete cerebral commissurotornv there is a Dar-tiirl los.s of tlie abilitr.to name exact points siirrr-tulatecl on the left side of tlie boclr . This clefec,rl \ Ie i rs t i rpparerr t . i f a i a l l . { )n t l re far .e anr l i t isrnost apparerrt on the clistal extrenrities, espe_ciallr tire- fingertips. This defic.it is not clepen_(lent otr language a.s it can be done in a trorr_lerbal fasltion and in both clirections (rielit toleft and rice versa).

Young children also liave difficultr..in cross_lrx'alizing or cross-rnatc.hing (Galin et al . 1g77.1979r but cl Pipe. l99l ). possiblr. lrecause theircunrrnissures iire not vet fulh functioningr)-akovlev iinrl Lec,ours. igOZ, trut cf. Brodv etal.. I987: Baierl et al., lgEg). Lrrrnatuntr. ol.trarrsc'allosal inhibition has beerr suggested ,,sthe sourc,e. of unnecessan dupllcation clurirrgsirnple reachirrg (Leiinrrin" 1g7g).

Ilenispheric Specializatiort: LeJi Tar:tileAnonrlo. One of the most conr.incing u,ays todenion.strate liemisphere disconnecticln is t<riisk the patient to feel with one liancl and thento nanre lariorls small. common objects. in theabsence of vision. Uniiater:ri anomia is a reli-

1!., and pe rsist er r t si gn lcrl loui r rq,.ol ln.ui, -r .( ) f t l re r r r i r r r r l raneu\-ers der .e lorred in t l re lab_

r)raton to test sp l i t -bra i r r pal ients. t l r is is t l repnt t<tpal o l re to l re adopter l as par l o l r r rou-hne nerrrological exarninatton.

Patients urth exterrsive callosal lesions arr.crrttt l ttorth' unable tci narne or clescribe an ob-lect helcl irr tlrr: left harrd, althouglr ther, reitl_ti.t tlattte ob.jects held in the rigirt iranci. Sorne-

i i l l " . , :

. r ( , ( .u \ ( ,nng prr t ier r t t .ar r q i r . i r \ i r r {u.

oes( 'npt iorr o l l l re o l r ie t . t l r r r t s t i l l I re urrahle tottattte it. AIier a Jlatient u.itir a callosal lesion'e.8, a <'allosallv clissecting herrurrrhage) hasre{arrer l t l re a l r i l i t r to 11;s11, , , o l r . ie t . ls i r r t l re le l t

i1 i ' j : ,1" : abi l ih r r rar ext i r rgrr is l r , \ lar l r e t a l . .rY55 i r r i t l r d i r , l r ap t i r . s t i r r r r r l a t i o r r . i . , . . l x p l r u ._lnga l r oh je t t i l r *a t . l , I r a r rd s i r r r r r l t r t , , . , , u r i , , , \ \ . i -telson. 1g7,1)

r H T C A L L O S A L S Y N D R O M E S

C r o ss - repl i c a t i tt n of h o nr! p ost u r e,t. Spec,ificpostures impressed on one (unseen) l iand bvthe erarnirrers c'arrnot be minrit.ked hr the pir-tient's opposite hancl. But if more proxiinalstirnuli are used, it rnay be difficult to demon-strate anv failure of interhemispheric cornrlln-nicatrorr. prohablr because of ipsilateral lrenri-sphenc projections of sensory stirnuii.

365

To establisli hen'risphere disconnec,tion. it isnecessarl' to exc,lucle otlier causes of rrrrilate.ralanornia. particularlr.' astereognosis (or everr irgross senson'deficit). as nla\.occur uit l i a riqlrtparietal lesiotr. Tlie best rr-iir to erc.lutle rster-eognosis or tacti le agnosia tCaseli i. lggl r is tosliow_ that the object has in firct beerrr recog-nized even tirough it cannot be r.erballr..iclen-tified or describecl. hl' retrier.ing it c.or.rectlvfrorn a collection o1' sirr-rilar objects. as dt,scribed abor.e.

Cornpen.sotory JIt:chani.:nts. hi te.sting lbranomia. one must be au,are. in <rertain clevc.rpatients. ol strategies for c'irc.urrtr.entirrg tlie de._iec,t. For exarnple. t l ie patie.nt rnar.rirop arr ol;_.ject or rnav rtranipulate it in sorrre oti ier rvar(sucli as mnning a {irrgeniail clorvn the. teetir ofa comb) to produce a cliaracteristic rroise bvrvhicli the object c,an be identifiecl. In the sanrrvein, a subject nra_r- i<lentifv a pipe or. sonleotl ier object bv a characteristic'snreli arrrl thuscircurnvent tlie inabilitv o{ the LH to iclentili.l r pa lpa t i o r r a l o r re . a r r o l r j e t . l i r r t l r r , l e l i l r i r r r r l .

\\''ith tirne, it niar.be increirsingll difllcrrlt tode rnonstrate :rnv irer nispl,",-r", i i i ..u,-,nectiorr.e'ven using distal stirnuli. E. Zaidel i lgggb)lbuncl that pe.rsisting deficits in tests o{ stt,re-ognosis rellected extracallosal danriige rnorethan faiiure of interlierrrispheric transfe r.

Neuroinutging. Fabd et al. (lg9g) iuragerl nor-rna] controls ancl callosotornv patients frorrr tlreAncona series rvith lunc'tionrrl rriagnetic. reso_nance irnagirrg (fN{RI) t luring rrrri laterirl so_rnatosensora' stirrrulation. Norrnni sultjectsshorved contralaterai actir-atiol in Sl. posteriorp:irietai cortex. ancl parietal operculai (()rtex.as well as ipsililter:rl activatirin irr honiologousposterior parietal rrnci parietal opercuiar crrrter.In patients u.ith anterior-callosal sectiorr rrp toarid iricltrcling the posterior bodr'. ipsilateriri ac:-tivation n'as rrrissirrg. irtrplic,ating the, postt.riortir ird o{'the hoch' o1'the CC irr thc trrirrsit.r.

l\Iotor Functirtns

Itfonrmtion T'rans-ft,r \\'e hai.t. lter{ornierl ser.eral stuclies on lrou,niotor irrl irnrrati<tn is tr.arrs_lt,rred ti irorrglr t ire (l( l irr risrrornotol irrtt,gr.ir_tiorr tasks. Tlie task is a sirnple r.eiictiori t irrre

t366

(S RT ) to lateralizerl 1laslres l lroflc,rrberqt,r.l! l12). \\ ' lrcrr srrbjer.ts rt,spourl u,ith the lrturclipsilatt 'ral to the r.isual .stirrnrlrrs. the sanr.hc'rnisphert, proccss(,s tlre r. isrrir l stirnuhrs anrlirrit i i i tes t[te rnotor resporls€,.,rrrcl t l ierelirrt:t lrere' is ro neecl I irr trarrsl 'errirrg irrl irnnatiorrt l r rorrq l r t l re ( l (1 , I r r corr t r r is t . rv l ren t l re s t i rnu_lrrs is trntralterirl to the lcsporrcling lrancl. t lrevisrral stirrrrrlrrs i.s rer.eivetl lrr the irernrspliereoplxrsite to tlre orie tontrclling tlie rc.spoirtiinehanrl. irrrcl thrrs ir trrursl 'er of lnii irrnatlor,throrrqli c'allosal libers is ne.t,cle,cl. The rliffer-errc,e in reitc'tiotr tinres betlvec,n crosscd re-sponses i in(l l ir icrossc,rl resporrses is an estirnateol t lre c,oncluc,tion tirne tjrroueh callosal f ibers.Trpic'allr. irr rurrrnil l subje<,ts tl i is rl i l l i ,rent,e.c'allecl tlre "c,rosse(l-un(,rossecl

clifferc,ncr:.,(tjLIl)). is i),-l 11156.,,. u,hert.rts in split ltrain ptr_trerrts it is l l()-60 niset, ancl in cii lkrsai agenesispatients it is 15*20 rnsec (Cllarke ancl Zaidel.1!189: Nl l rz i e i a l . . lgg i . .

\\ 'hat kinrl ol inlirrrrraticin is transferrerlthrorrqh c;i lkrsal l lbers-rnotrlr. r, isurri. or cos_rrit ir.e? Our series ol'strrclies srrpport t l," "cri]_c'lrrsiorr t lrat it is rrrotor. Onlr ri irral rireits relr_resenting tlre r.ertic.l l rrrr.ntl ian har e tl irecrcaliosal c'otrnec,tions. so that eccentric .stirnLrlithirt,r 'erlrrire adrlit iorrrrl s\-naptic corrnectionsslrrlrrlr l prothi<'e a lorrger CUD. T]nrs ., isrraltnursl-er slrorrlcl be sensitir.e to stirnulus eccen_tric,ih., \ lore qener.:t lh,. onh, r. isual trans{ersiulrld be serisit ive to risrral jrartrrneters. srrclias ltr iglrtrress. tsr the sirrrre tokerr. rrrotor tr: irr.s_fi 'r slrorrlcl lre sensitivt, to rrrotor pararrreters oftlre SRT prirarl igrrr. suc.l l as ,lra,rgirrg respollselirrqer or rrlterrratinq l irrger responses. \\.e stucl_icrl ir patient belirre anrl aliei paftial c,allosrr-torrn sparirrq_tl ie splenirrrn oi t l ie CC. Tlie sple_niurrr shcnrkl srrppoft risual ancl not rriotortransfer. (l iranging risrral paranreters of thestirnrrlrrs prerdrrced no change in the CtjD bt _iort' partial callosotomr'. rvhich suggests thiit,rrornra]h' in t l i is task cailosii i transfer is notvisrral but rrrotor. After srrrgen,. rvlrt n tire trans-1i r of infbrrnution u,ils likelr. onlr risual. thert:nrts :t c' ltange in tlte (ltrD rrit ir cirlnqirrg risrral])ararlleters (lacrrboli et rrl.. lg9.l).

ln ir later stuclr. u,'e nranipulatecl ntotor anclvisrral pararneters irr botlr norrnil l subjects anclsplit-brairr patients. I1'the trans{i,r t l i i i t cleter_rrrines tlre behar.ioral (lUl) occrrrs i i t rnotorlevel. the urotor nrrrnipulation sliouici affect the

C L I N I C A L N E U R O P S Y ( - H O L O C Y

(lUD in nonrt l l str l t jec,ts. n. l iereas t lr t , r . isualnri inipulat iorr sl ioult l not. I i rrrtherrrrorr, . i1. t l ieef l 'ect o{ ' t l re ruotor nlanipulrrt iol l is tr trh. nre-t l i , r t e r l l r r i r r l r . r l r t . r r r i s p l r t , r i t , , , , r r . t i c o t , , r r l i t . r l t . , , r r -rrect ions. t l i is r '1I i ,ct .shorrlr l rrot lre r. isi l t le inspl i t-brain patie nts. Again. t l ie {.r} lpir i( ,al r(,sultssrrpportecl lrot lr precl ict ions ( l i rc,oboni irrrr lZa ide l . 199,5)

As rrrentiont't l above. trrr<liton. pirt lnviLrsfiorn the brainstern access ltotlr h,,,ri isph"res.u,hert as visual pro.jec.tions are alrnost exclu-si.,r. lr- kt the lrernisphere oltposite tlre r. isuaihall-f ielcl stinrrrlatetl. t1' arrrl i ton stirnuli arerusecl insteacl of risuii l stiniuli in t l ic SRT task.one rvclrld preclic,t rro e{Iec,t o1'c,ro.sse<l stirnu_lation/response bec:ruse. both lrernispheres r.e-ceive the sensorf inlornration sirrrrl i i ineouslr.so that all ulrcli i ions are i ic,tuirlh. .,,,n".n*.i., i

To test-tliis li_rpothesis. u,e perlitrnrerl a sturlr

11n :i_1g]{-br,rin patient in u,hich ,,,., ,r,,,,1rn..,i

the (--UD obtained rvitir SRTs to late.alizeJflashes ancl the CL]'D obtainecl n,ith Snf, iuiateralizecl aucliton. stirrmli. As precli<,ted. aren l o r r t l C [ ]D r r i r s r r l l t i r i ne r l , , 1 , . r , t l r , , r , t l , i e r , tresponclerl to risrrtil stirnuli. brrt arlrriost uo clil._ference at all u'as obsenecl u4ren conrparinqcrossecl anrl uncrossed responses to a,iclitonis t i r r r u l i ' l i r r r r l r n r r i : r r r r l Z r r i r l e l . l ggg ) .

I

:t

I; i

I

( '

II ;

r ir lL '

. t l

l t (

l l l {

' l r

Binwntnl ]Iotor Control. I{ ' the Lil c,orrtroistlie right hiincl ancl the RH corrtrols the lefthancl. ho."v theri cloes birnanual rrrotor cnntrolhapperr ancl rvhirt is the role o{-the CC in or-ganizing it? Classic' iud rec,ent strrdies <tn cal_losal involvernent in birnanrral rnotor <ontrolboth suggest that rtverleamecl binrtrnual nokrrsequences. including either parallel or alter_nating sequenc.es. clo not rerluire irrtar,t c,allosalfibers. u'liereas noverl birrianrral rnotor se-quences, such as tliose rerluiritlg interdepen-clent birnirnual control. canrrct be iearnecl iical_losal libers are' tnlrisec,tecl. u,lietlier irr thepresenc.e of rision rtr irr the altsence ol'r..isrralgr,ridance (Zaidel anrl Spern,, 1977; Franz et nl,,2000).

Witli regarcl to terrrporal and spatial cfiarac-te r is t i t ' s o f I r i r t ra r r r ra l r r ro r .e r r re r r ts . i t seerns tha tthe CC is in-rportiint in coorclinating tiie spati;Jr t s p e t ' t s o l ' l r i r n r r r r u a l r r r o r e r r r r , l r t s , r r r t l i l r i c r , r , -t ' l t r o n i z i r r o l r i r r r i r r r u l r l r r r r r r . e r r e r r t s r e q r r i n n q at o r r rp lex te r r rpora l p i r t tenr . l . r r r r rz e t a l . , lgg6har.e shou.rr that norural subiec.is nrociuce trir.

t ' . \ ,

r l l ;

r t t l

t l r r

i l t ; l

J ) f (I l { ' (

II l l \ (

l t l ; t r

t l r r ., t s i r

l ( ' ( ' l

l r o t

I '( . ( l

II

I

t

T H E C A L L O S A L S Y N D R O M E S

jecrtorr.errcirs u'lren the spatiai clemands of the,task clifl'er behveen the trvo hands. Renrark-ablr. callosal patients were not irnpaired in tliistask. Terrtporal sr,-nchron\.. hcxvc.r'er. u,as sirni-lar ir i norrnal subjects ancl irr spl i t-hrairr pa-tients. rvhich suggests that spatial control iincltertrporal srlchronization are dissociable. In anearl ier stut lr ' . Trr l ler and Kelso (1g89) clenrorr-stratetl tliat pliase-lockecl birnanual nrovernentsare ven' stable irr split-bmin patients. u.4rere:rsirtelrrrediate states betrveen in-phase and anti-pliast' coordinated patterns iire severelr. af-ler ' tr , ,r l . Tlr is sl tggests thi i t corrrplex ternporalpattenls behr.een tlie tu'o hancls rerluire the de-srlc'lrrorrizing func,tion of callosal fibers.

\ lore rec.entlr ' . Ivn' ancl Hazelt ine ( lg9g)looked at tlre svnc,hronizlition o{' rnanunl re-sponses to ar.orrst ic, t i rni lg signals in a crai loso-tonn partient. Tlie task rc,rluirerl the patie.nt tosrr iclrronize l l inr irrmal or trnirnarrual responsesto arul i ton-tones, Botir nornial srr l-r jects and thepatient testerl rleltcinstratecl less ternporiil r.ari-ahi l ih irr t l re birrranual c.oncl i t ion. srrggestingtl tat rrrotor c,orrrrniurls lre not integraied brcal losal l ibers in t lr is task.

Dtlicits [)rrc to Ilcntis1theric Spccializa.tictrt.F'ollouinq callosal section, riglit-handerl pa-ttents irre oftcrr unaltle to crlrrectl.," executet l r r ) \ { , | | r ( ) \ F r r t . r r t s o r r v e r h a l r ' o r r r r r r r r n i l r v i t l r t l r clelt hancl tliat ther. crin readih.and accuratelr.ext,c'ute with tlxr right lianrl. Ilistoricallr,. tlil.swas tlre lirst c,allclsal svrnptorn clescribed. ln theahserrcr. ol arr elerrrental rnotr lr de{ici t . a pro-ttorrn<.ecl inabi l i t l - to perforrn certain rnrlve_tttents in the lef i l i t ind to verbi i l <rrrnrnanri isstronq evicit'ric.e {irr ii callosirl lesion, There art-hi 'o ot lr t .r 'expi iurat iolrs frrr t l i is t lef ici t . nclt tr iu-trralh erc,hrsirr ' . First. r t c,ari ref lect RH cl is-t ' t rr tnectiou l l l rrr LII language r.ornprehension:t lrc RIJ i lel l Irrrrrcl) carrnot 'perl irrnr t l ie cour-tt tartclr.r l rrroverrrent because i t l ias trot cttnr-l l relrr,rrt ler l t l re c.orrrrralcl . Se.<rrrrr l . i t r i rat. rr,-l I ' r t l . l I r k , r r r i r r i r r r r . r , l i r r . r r r o t o r . t r r r r t r , r l : l l r t .disrronut,r. te<l l l t l rnrn' rrnclerst i i r i t l t l re c,onr-rrt iurr l . l rrrt rrrar rurt hai.e t lre abi l i tv to t-xeclrt t .t l r r ' r r r r r r r r r r r r r r I c o r r r , r . t j r . \ , , r r r i , r l , r r l t r t s k s s r r t . l ri is i t tr i t i r trorr or t l re, use , l , l ' th.ee-cl irrr. ,nsional olt-jects rrr,n lr lp separate verbrr l r ,orrrprelrerisioril rol l l r r1ol() l ' proqrauurring dt: l i r , i ts.

T l r t s t r r r l r 'o l ' r r ro to r c ,o r r t ro l i r r abser r i , r , o { t l re( l ( ) i s i r r rpor lu r r t to be t te r . un t le rs ta r r< l thc ,o re t -

,67

ical aspects of lnotor behilrior iui(l to rlesiqrrbetter irrten'enti<tns irr clinical ptiprrlations.Tlie first sr.stenratic strrcit' of rnotor i,ontrol rnthe split brairi rvas reportecl ll D. Zaiclel arrclSpern (1977) lbr patients in the Los Arrgelesse r i es . T l r t . i ns ig l r t o l r t i r i r r e r l I r o r r r s t r rd r i r r t lsplit-brain patients rtr patients borrr uitlout tlie(lC is olien surprisingh.clifferent liorrr thirt ob-tained front studring piitierrts u.ith unilateralbrrrin cliirriage. For initance. beliirrioral rreu-rologr-studies suggest thnt the LII is rlorri inanttor prads (see. {br irrst: ince Chapter l l ). Tii isbelief lurs been challengecl br. obsen'ations irrsplit-brain patients. Tachistoscupic presenta-tions of clrau,ings of hatrd postures to the hvorisual herrrif ields of split-brairr ptrt ielts har.esirou.r that tlrev can ar,tuallv irnitate hancl pos-trrres u.ith botli hancls. o, loi,g as the hancl usedfrrr iniitation is ipsilateral to the risual lierni-f ield of presentalion (Spern, 197,1), Eariierstudies fourrd no substurtial cliff'erenc,e iu inr-tatirr. perlirrrllilnce betr.veen tlre riglrt arrrl theleli l iaricl (Spc.rn. 1974; \ ' ir ipe. lg82). Hor.r-ever, more recentlr '. Lausberg et al. (irr press){irund seier.tive leli hand np.*iiu in pant<xriirrreto r.isrrallr,presentr:d obieits in split brain pa-trents.

C r t r r tp e n,s at o n1 tr[ e cha n is n n. Inr rne<liatelv aftersrr rqen l r l l o f orr r pat ierr ts r ler , ' ur rable lo per-forrri actions tcl r.erba] cornrnands such as "\\'ig-

gle vour left toes," or "Make a fist *'ith vourI t ' f t l rarrd

" T l re t legree o l le f t l r r r r rd i r rn( [ le f t

lbot) deficit is subject to indivichral differences.The left lirnb dvspr:uiia is attributable to the si-rnult:rneous presence of tr,vo cleficits: poor corn-prcirelsion br-the RH 1u'hidr has good controlof the left hancl). and poor ipsil:rteral crrntrollx t l ie. LII (rvhich rrnclerstands vc.n well). Sub-sirlence of t lre clvspriLria t.rur t lrt ' ielort, resrrltlrorrr tu'ci c.orrtlteusaton' tnechiinisns: increasetlI ifJ t 'ornprclrension of u'orrls. anrl increaseclLII c:ontrol ol the le{i hand, Tlrt ' rrinac,itr.ol 't ' i l l r c r I r e rn i sp l re r , , . i r r r r I p i r r t i r . r r l r r r h t l r , . L t i . t , ,rrlrtrol the ipsilatt 'ral Irand r.irries frorrr one pa-tient to iuiotht:r botlr in the irrrrnediirte post,r rp t ' t ' l t l i i e p t ' r i o r l l r r r l r r r r u r r r r , : r r s l r r t r , r ' . T1 , , . * r -terrt o{ ipsilateral rrrotor contrri l can be testeilbt' flashing to tlie rislrt or le{i r.'isrriil hal{-fieldsket<'hes o1'thrrrnb antl f ir igers irr di{l-erent pos-t r r r r ' s . l i r r l l r t ' s u l r j c c t t o r r r i r n i t u i l l r o r r e o r i t l r r .otl lel Ir iurcl. Resporrses arc p(x)r uit lr t lu' lrarrrl

!

I

lI'?!

!

I

368

cln the' sitle opposite the visrtil input. witlt sinr-ple postrrres srrch irs ir r, loserl f i i t or an openhand being attainable alier lirrther recor.en.. Asrccoven' proceecls. qoorl ipsilaterrrl c.orrtrol istirst attainecl litr resporrses r.itrrie<l out ltv therrirlrr. l trrtrirnal rirrrst.rrlrrtrrrr-. .\1ier. st,r.eralri lontlrs. rrrost 0f t l iese patic,nts cail forl l l ir r 'a_rjeh- o{' lrancl ancl f ingt,r postrrres rrit l eitherliancl to r.r.rltal irrstmctions such as ..lv{iike

lr cir_clc with rour tinrrnb anrl little llrigc,r." and theI1KC.

Subsiclenc,c' of tire irpriuiiir crrntinrres buteven nlallv vears later. left-siderl apr:Lxia to ver_bal cornrrrancl c,an sti l l be denionstiate(l (Zaideli inrl Spern'. 1977: Trope et ir l.. lgg7). sorrie_tirnes unrler piiracloxical cirrrurnstances. Thus.spiit-brain patients are sornetirnes unable tofollou' r'erbal cnrnrnanrls with the left liandeven tlrcuglr titer. carr de,monstrate separateh.,recognition of the printed verb arrd ofthe pic_tured i iction (c1.. Zaidel. 2001).

Languaee

Tlie split-lrr:iir person proricles ii rrnirltre per-spective orr the indepenrlent contribution ofeach cerebrirl irernisphere to language pro_cc.ssing ancl on ihe role of interlienrisplieric ln_teraction in nonrral lanquage firnction. Hou.t'r.er. irltlrorrgh the iibsenr..e of the CC reducesiriterhernispheric firci l i tation. iniribit iorr. andcrrcpt nit ion. it does rrot elinrirrate tlrerir cror-rr_pietelr \\'e will crtnsicit,r descriptive clinicalobsen'ations o1' lanquirge in tlre acute anclchrolicalh. split-brain patient. follorvecl br. ananaivsis ol RH c:rpacities in lalquirge cornpre_hension arrrl productior-r.

(, ' i inicai I rrrpressiorr

. Postcallo,sotytnul nnftisnt It u,iis first thouglrt

that nrutisr r r follor.r,ing c,allosotor tr.v ruas siniplva neighborhood sign. a partial forni of okirr"ii"rrnrtisnr (u.ithout the akinesia) that resultecltrcirn retraction around the illrterior end of tliethircl r.'entricle cludnq section of the anteriorcommissure {Clainis, 1952: Ross ancl Ster.vart.1981: Lebnrn. I9g0). or retr:rctiori ol ' rnedialf ronta l lobe (Fuiks et a l . . l99 l : I ieer .es. lgg l ) .

But there is erjcle,nce t<l srrgqest tliat rnore.persrsterrt rnutisrn rnav in l irc,t result {ronilreruispheric' cl isc,tir inectiorr rather tl ian frornrrredial frontal extrrrciiilrisal rlarrraqe. Bogen

C L I N I C A L N E U R O P S Y C H O L O C Y

{1998) has lratl a nurrrber ri l patir:nts rvlio diclnot liave niutisrn. despite exten.sive retractlono{ eitlier antr:rior thircl r.c,ntricle ur rresial rishrfrontal cortex or both. In tlr"rl. p"il"nt., ,,,i,,-rnissural sr:ctiorr sparetl t lre splerri irrr,. Rarlt 'net a l . ( l9El} : person:r l cr r rnrr r r r r r i r . r r t i r t r r to J l [ .I logetr frorrr S. Fc.rguson in i9!J1)obse.r",l r, ithree o.f eight cases u.ith stagerl callosot,l,nr arnarked decrerrse it i spontarreorrs speetl witlr-rlrt paraphasia or cornprehensiorr t je{icit or irr-altilitv to sirrg. This cleficit occrrrrecl onlr afierthe seconcl stage of srrrgen-. \ota[le ,,]u, t l,"absence o{'irn."' rnutisnt trfter the first staqe (rrrs-tmrn. genrr, arrd nrost of the tn,rnk)r t l ie rlutisrrrappeared on11.-alier the seconcl stage (splenirrrnand rernirinder of the trunk). Jt hacl been prr-posed that hernispheric disconnectiorr inavlead to rnutism because of an rrnusual intercle-pendence of the hemispheres in language func_ticln secondarv tcl earlv brail irr.jun:. Tiii, ,r,01'lead to unu,n,,lnu, (incluclinq biint"rnll ,p"".i,represerttation (Bogen and \roqel. 1g7,5, Bo_gen. 1976: Strssman et al.. iggil: Sass et al .1990). rind particrrlarlv to cliscorclant rnanualancl speech clorninarrce (Fergrrson et al.. 19g,5:Spencer et al.. 1988), rvli icl i c,reates rrnrrsrralclepenclence on interheriiisplreric, interactiorrfor spee<. l r proqrr r r r r r r r i r rq. - \ l u t isr r r r r r iu t l r r rs r r , -sr r l t f ror r r i r r te l l rerr r isp l rer i r . t ,or r { ' l r t { r possib l r a tir irrainstern leve'l) or froni a bilateral rliaschi-sis that rtl-fects speeclr much ntore thiin rvritinq(Bogen. 1976; Ferguson et ai.. 1985).

Quattrini et irl. (lgg7) re\,ie\r,ed nost_callosotornv rriutisrn in 136 patients of the ,ln-cona series. Twt out of E patierrts with crtrn_ple le hro-stage sec. t ior rs an<l g , , r r l o f 17 r r r t |tinterior c:rllosotonties hacl transient rnutisnrlasting lrom ,1 to 25 dal.s. One patient w,rth asplerr ia l sec. t ion l rad no rnrr l isnr . T l re hvo pa-tients u.itli complete callosotontv had rnutiinrr r l ier bot l r t l re i r r i t ia l arr ler ior a i rc l t l re subse-rluent posterior callos:il sections. Nlutisrn rvasaccrlrnpanied bl. good cornprehensicin. follorr.ing of verbal commancls, iind r.vriting. Recor.-, 'n f rorr r r r rut isr r t rvas a lwar.s r r r r r rDle le. - \ lu t isr r rrvns n<lt associated witli ieft-liancleclness. butit lva.s associated with more cornplex surgicalmanipulatioD.

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llikl pragnvttic deJicit. Thoueh seerninqlrt rorr r r l r l or r <. l i r r i< . r t l r rp l ras io logic .u l tests. r r roresr rb l le oI rsen r r t i r r r r rer e i r ls per i is t err t la t 'unae in

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I H E C A L L O S A L S Y N D R O M E S

tlrl language repertoires of patierrts u.ith cere-

brir l c 'orrtni issurotonrr ' , These lacrui irr : inc,hrr lc

r, lrronic' inrpoverishrncnt of verl tal r lescript ion

,r i 1x'rsonal eurotional experit nc'e (alexithr.nria.

t 1 l lnHouten et al. . 1986). luihrre to srrst i i i rrlrlt'rlrrate crlrnprelrension u'hen leariing para-qraphs or extended text (Zaidel. 1982). arrcltlt lic'its in conversational interaction. The la-cunae involle pragnrntics, rather tlian phorrol-ogv and srltar. arrcl are highlr. r'ariable acrossprrtients. Thev include social inappropriatetressbr failing to fcrllou. leacls, usinq inappropriaterrrles o1'politeness. antl a tendencv to rational-rze nrisiakes anrl confabuliite l'easolrs lorstrange behavior.

F'orlral testirrg o{' t}re pragliatic. abilitv of, t i rr ' LFI of l conrnrissurotorrn' patients L.B..\ ( ' A A . . a r rd R,Y. u ' i th t l re RI I ( io rnn iu r r i -

catron I latten (( larclner antl Broruiel l . lgt6)slul l t .r l cronsistentlv severe del lci ts trcross al lpatients in t lrree teits: appreciat ion ofprosorlr. .the rrnrlerstandirrg <l{ pictonal rnetaplrors. anrlt l re retel l ing of stories. rel lect ing intpairt 'c lrerrlqnition of entotiori. nonliteral l:rlguage.iurrl irrtegrrttir'€, processes (discorrrse). r{.spec.-trrerlr . Tl i is sl lgqests selective uonrral RIl cttn-tn l r r r t io r r to t l rose s r r l t tes ts (Sper rc ' t 'e t i l . . 1990) .fo runinl l cl t 'qrees. lrou'ever. al l f ixrr patieltssltr tu'erl i i crrrrsistent and {rerluent use o1'hrr-t t tor irr conrt 'rsi i t iorr. Ther, ' also rrsecl cornrrrorrt c l i , , t r r s , u r , l l l r r r r e r l r s i r p l r r o p n a t r , l r r r r r r l l r * -r lrrenth. antl t l i t i r qestures ancl intorrat ionseenrr.ci nonnal.

(; l inical artd Lyterintentrt l Assc:s,stncrft of Lott-qutgc itt tltc l)iscorrtrt:cted Riglt Henrisphert,.Arrt l i ton' c 'ornprehension of rrouns lx. ' the DRHt i r r r q q e s t e t l l n t l r c s r r h j r . t . t ' s r r l r i l i t r l o r e t r i e r lnit l r t l r t ' k:{ i hancl various obj i .c.ts nanretl alorrr llx t l r t ' exarniner. \ ' isr ial c,orrrprehension o1printerl u'ori ls l tr t l re DRH is of ien present. t 's-

l letr ial lv short. t .onc,rete. higlr- lreqr,r lrrc,r ' r t , , .clr .l 'or t ' rarrrplt ' . al ier a prirrted rrourr is l lasl i t r l tot lrc lel i r isual hal l- I i t ,k1. the srrbjec,ts are t,pi-t al lv rr lr ]e lo letr i t ' r 'e uit l r the lelt l tantl t l rr ' <ies-igrratt ' t l i te 'rrr 1l 'oni iur lol lg An i irr ir \ . o{ objec'tshidt l t ' rr f l rrrrr l ieu'. Ipsi l i l teral , . , ,r i trol l l r l t l re,l ) l , H i r r t l r c s e t , . s t s i s t r t . l r r r L ' r l l r , . < . r u r s t . i r r t . o r - -rec't verl tal descript ions giren lrv t l re srrbjecti t tutrt 'diatclv al ier a c.orrec't response lrv t l re le{ iharul sl ir l ' , t l rat orr lv the t lHIl knr.w t lr tiilis\\('r.

369

Tiiere {irllou/s it llore cietirilerl ('onsi(l(.riltio}lol obsen'ations in h\'o series ofcirlk)sotonrv pa-tients: ther Los Angeles series (Zairlel 's lab) arr<lthe Daftrnorrth-Tolecio series (Gazzarriqa's lab ).Tlre tu'o laboratories use s<lnervhat dillerentrrretl ioclologies arrd orre slrould exercise c'autionin rnaking cornparisons betrveen thern.

The Lo,s Angele,s Sor'e,s. Experirnental studiesof RFI language in patierrts u'itli coltplete ({)nl-rnissurotornv have locrrsed on detailecl ca.sestudies of L.B. :rncl N.C. using a c,ontac.t lensslsteril for presenting extended clisplavs anclperrnitt ine lree ocular sc': irrrrir ig br cine irerrri-spliere at a ti lre (Zaidel. 1975), But or.t ' i tsi<lir l lstrrdies reported srlnie l itrr{uagc corrrltetr.rrce intlre .l)RIIs of <it lrer patients a.s u'ell. Th<lse re-ports inc'lude aucliton <:orrrprehension ln A.A.t \ebes. l97 l : Nebes ancl Spenr ' . l97 l ) , RI It 'rec'rrt ion of verbii l c'ori lnuncls br- R.\ '. (Clrlr-dol. 1980). piionologic.al encoclirrg irr the RHol (lC (Ler.l 'ancl Trevafthen. 1977). arrrl arrcli-ton corriprehension br, the RH in N.\\ ' . andl i .NI . (Bogen. 1979).

P I t o t t t: t ir:.s / pl t o r t ol o gt1,,v / nt o r. I t:ri t: a l .\ e nt an -tir'.s, ancl pragnmtics. Tlie DRHs have poor tiu-rl i ton disc'rinination (Zaiclei. l97Sb) i irrrl poorplxrnetic' iderrti l ication (Zaidel. lg6;l) (r '.e.. di-c'lrotic listening to tronsense stop collsonaltt-rou'el fC\' l srl labies). Thev also have a poorshorl-ternr verbal rnt.rrrory (Token f'estr Ziiiclel.1977) with a c:rpacitv of 3 -+ I items. siniiliir toiinterior aphasics. The DRtI canrrot rrrirtcliurrnls for rlrr.rning. i.e.. it has no graphelre-pironerne colrr:lrsiorr nrles (Zaidel ancl Peters.l98l). trnd rrrust reacl worcls through a lexicalnrrrte (Zaidel. 1998a).

Tlrt ' ])RH li:rs access to sorne nrdirrrntansr,'ntactic structures. suclr as passives or llega-tivr:s. it firrcls gnitntriirtir,al categories easiertlrarr srntactic stnrc,tures. and it fincls lexical-izt,cl rnoryrlrological constnrc,tions casier thiurirrf lec'ted orcs. \\ 'hen proc,r'ssinq srrit ix. itst 't 'r rrs parti<'rrlarlv crrnstrri irretl bv r r re'rrrorl krarlZ ; t i t l e l . l t ) o l '

' l ' lrc l)RII lras a ric,h autl rl iverse i lrrrl i torl

I t ' r t r r r r r , r r , , l i l r e r r rg r r i z r ' s i r r i r r i e t r , r f se r r r i r r r t i t .r t ' l i t { i o t t r . l t l r as l i r r g r r i s t i l i u . t i t , s s l o l r o l l repisoclic nncl serrrantic inftirrnatirln. antl its se-rrrarrticr netu'<irk is organizecl utnnotiitir.r,lr'. Ther i s r r . r l l t ' x i r r r r r i s s r r ra l l e l a r r r l o rga r r i ze< l , l i l l i ' r - -

370

r.ntlr ' , Tlre l)RH lrrrs altstritt,t letter itk:rrt it ies(l lviatirr antl Zaii lel. lgtl, l). It can perlirrrn lex_ic'al t lec'isiorr. and it erhibits sensitir. ih.trl u,ortll i 'e11ue'nc ' r ' lZr i i r le l . l (X) l ) r t r r t l r r rnt . ret t , r ress(Eriatar et al.. ig90) lnrt rrot to qrrrpherrre_plionerrre regularitr. iZrriclel arrrl peter.s. Iglj lrZairlel. 2001). It is sensitive to forntat rl istor_tiorr (zigzaq. rertic.al ). espt,c,i ir l lr for u,orrlsiZai t le l . 2001).

Dcu:loytntertol prtlfilc. The DRH does rrotexhibit a rrnilirnn ntentirl aqe profiie irr ri sarn-ple til arrditon. ltrngrrirge lirnctions (Zaidel.l97fibt Its cornpetenc,e terr<ls to bc, in therilnge ol rrornrirl 3- to 6-r'ear-olcls, but it has lit_tle ur rro spee.c,h. oncl it, arrcliton. r.or.ahrrlan.r ' i r r r r , , ; u . l r r r r r a r l r r l t l e r t ' l rZ i r i t l e l . i g76 r

Tl r e Do rtn u nih-Tolc cl o S tt rie.;

Pln t r etic.s/ pltonolo gr1. .t tl nt ar. and leical se-nmtttits. Patient \/.p. shorvecl RH abil it\.to dis_cr inr inate CV sv l lab les (Si ( l t is et a l , . l98 lbr .arrcl_patient J.\\'. shorverl plionetic cornpetenceil the DRH br,being able to cornbile i isualirrrcl aurliton' cues to prricirrc,e tlie McClurk Il-hrsion (Bilrnes et al.. lgg.l). All f ir.e patients{P.S.. \ ' .P.. J.\\.., D.R. ancl \.. j .) shor.ve<l soodcornprehensiorr of single spokerr rvrlrcls iri tlieDRH. Tliose testecl (P.S., \ ' .p., J.\V.) showeclsonle urArl)rl latical colrpetence. V.p. ancl J.\\,.could

_ perforrn grarri rnaticalih. .juclgrnerits irnclclisilrnbiqrate sl-ntactir,allv arirbiguous sen_tenc'es but not identi{i. llrssive sentences. Tlurs.tireir DRI{s huve .,rni*, qrarrrlratici l conlpe-tenc.e brrt poor griutunatical perlbrrnance. sirn-iliir to tht. (,'ali{bmia patient.s.

All flre patielts corrlcl read sinqle u,orcls.sonie (J.\\-.. D.R.) as nlanv as ther., could conr_prehend aurallr ' . P.S. anrl \ ' .p. but rrot J \\ ' hadqraplrerrre*phoneme conversion in tl ie DRH.Ail Iir''e patients clispiaved considerable lexiciilseniantic f lexibil i tv in the DRII.

Writing. The ilcute rlisconnection srnclromer rs r r r l l r i r r t . l r r t l es l e f t l r i r nd i r q r i r p l r i i r . ( ) r r l r p .S .iincl \'.P. could u,rite witli the lefi hand. V.J.'srriost ser.ere postriperatir.e language deficit rvasbilateralagrapha (Ba.r.rres et al.. 1g9,3). \'.J. r.vasli'li-hanclecl and LH clorrrinrrnt lirr speecli. SheItad hv<t-strrge ciJlosotrtnn at aqe. +l with loss

C L I N I C - A L N E U R O P S Y C H O L O C Y

o1 urit ing in either hiutcl (Barrres ei al.. lggE)Altlrrlrrqh \ '.J. n'as LH tLrrrrinalrt l irr speec.lr.slre hrid rechrcerl speech rlrtprrt i i fter c,alloso-tornr'. Agrtrphia lras been rerpofted lrs a c.<lnse-(pellce of callosotonn' irt otlrer patients r[is_corcliurt {br speeclr arrrl rnirrrual t lorninance(Spencer et al., lgu8). lrut rrot unirr,,rsii l lr ((lrrre t r r l . . I g5 { \ J r LH t . r r r l t I sp " , t k n r r t l , r r , -derstancl. read arrcl spell aloucl. Tlms ii coulclcontrol both spoken ancl u.ritten larigrrage.\/.J. 's I iII could rrot speak brrt it coulcl rrncler-starrcl spoken and r,r'ritten lunguage itnd rtrrrkelexicrrl decision. i.e.. it is sirnilar to the DRII ofL.B. It cxtrrlcl copv but rrot u,rite spclntaneousllto tl ictation or the nitrrre of lr picture, ir i theLVF, Thus. the lr'riting deficit of the LH ap_pears peripheral. at the ler.el of "alloeraphi.',

\ ' .J. 's RIi, in tuni. hacl no "orrtprrt graplieniic,buffer" ( Nlargolin, lg84).

Right Heni.sphere Speer:h. One of the rnost im-portant recent developrnents in the studl' ofI i r r tgrr rge in t l re DRH is r t rqrrabh t l re er i rer-gence of RH speech. The rlata on RH speechIiom the Califbrnia ancl Dartmorrt]r-Toleclo se-ries carr be sulrrnzirizecl as lirllorvs (TableI1-2):

L RH speecli is l iost l ikelr to occur soonir f ter sr r rqen anr l to s l r , r rv t l re qr .e; t testrange in patients rvith early clanrage tolanguage corlex in the LI{.

2. Ericlence for apparerrt RII speecli isrnorr: likelv to oc'r'ur in patients u.'ho sliouericlence for linguistic tmnsfer behveenthe liernispheres.

3. Right heniisphere speech rrrav develop orernergc. gradrrallv over the long terrn andthen it rnav asslrlne or lose control peri-odicallv.

-1. In rnost patients RH speecli llevererilerges or clevelops iit all.

Le.Jt Agraphia. Right-handers can rvrite leqiblv.if not fluentlv, with the left hand. This abilitlis cornrnonly lost u.itli callosal lesions. espe-cialh'(but not alwavs) those that cause unilat-eral aprilxi ir (Gersli and Darnasio, 1g81). In-abilitr-to rvrite to clictation is courmon \\.'ith LHlesions (also see Chapter 7). brrt tlie cleficit rsalrnost alu.avs present in both lirinds. In con-

t

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:/2

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sl

372

trast. ltatierrts ri. i t lr t,allosii l r l is<,rlr inectirirr art:alrlt.. to ctrpl. sirnple or (,\.ell c,onplex qeornet_lic, f igrrres u.it lr their leli hantl clespite herlgrrlabk, to rvrite uitlr tlu. le{i harid ,,r""r..",r ,,u1rr:u'ritnig previouslv rrraile rritir tlieir rlu.n riglitharrrl (Boqen and Girzzirrriqa. 1g65; Bogen.196!Jt r : Kunrar , 1977: Zai r le l arr r l Spern. 1d77,Dell ir Sala et al.. lgtl l) Cop)ing of biock iet_ters nlav lre preserrt ri ' lrerr t lre c,oprirrg o{'urr_sive ri r it inq is rrot: this rrrrt l rrot represent print-ing n'it lr the lefi hanrl brrt ratheiori ir.,copli leof gerinretric figrrres tliat itapperr ,ilso to-iavelingrristic conteni.

Srrtrtln,r,nl . \\'hereirs rnore lteharioral clatairre neerlerl to cliarac.terize RII speec,h arirlrnore phvsiologic,al data are ,,eeded to delin-r-'ate. the conclitions rrnrk:r u4ric.li it is expressecl.the ovenvhehriinq neuropsr c,lxrlogical ericiencesuqgests tliat tlie Dllll has a unique linguisticprofile. althou gh rliffe rent experir nental'popu-lations rielcl sonervhat clilfeient profilei. anclthere are c,onsiderable inrliridual cliff'erences.\\'herr tlie RH is clisc'onnected frorn the LH.tlie eurerging RI{ larrquage profile is charac_terizecl bv the fbliouing: 11J rrruch better larr_glraqe c()rllprehensiorr tlian speech: i2) betteraucliton' cornpreherrsion thari reading: i3,r vi_strirl u,oxl recognitiorr u'liich proceedi r.ia (ab-strac't). i<leograph_r' or througii orthographicn rles. brrt u.{thout grapherrie*phone me tr^ans_lation, so that lexical representations are ,,acl_

dressed" r:rther than "assernblecl',r (j) a ricltlexicirl sernantic svstenr but poor plionolog,.ancl an irnpoverisliecl s\lttLr: ",ra fil pa.oliiiquistic otrnpetence in appreciating the colt_rnrrrricirtive siqnificance of prosodv ancl facialexpresstolls.

Table 1.1-;l s|oq's lgrrr ptrtterls of lexicall,urquaqe in the. DRH. All patients har.e a sub_

C L I N I C A L N t t ] R O P S Y C H O L O C ; Y

stantial aurliton lexiclorr anrl rrt least ir rrtotler,irte reacling ,"rrt,abrriarr.. The, dill'erence irr pat-terrrs across irr<lir-idual patrt 'nts is in terrns rifspeech anrl u'rit ing. First. sonre patierrts, suc,l ias P.S. and \..1r.. har.e earlv evitlence for richRH spe.t'cl i and u,rit inq. Secoucl. s()rle pa-t ients. sr rch as L. I l . and J. \ \ ' . . deve, lop sornerrrterurittt l tt RII c'oritrol of speec,h. Thircl,r r r r is t p i i t ients. sr rc . l t i rs N.( i . . R.y. . A.A. . andI).11,. never rk:r 'elop RH speec,ir. Finallr. le{i-Landed ptit ients w'ith LH language clonii-rl i ince. .sucli as \ '.J.. rnar. srrl-f 'er sorne loss oifluencv aurcl mav be agraphic. in lrotl i hanrls,The f: ict thiit ail DRHs irnrlerstancl at leastsonre spoken langr.rage is imltortant to tht,clin_ician: testing o1'the DRH can be facll i tatedwith verbal instructions. Hou,ever. er.en. ef-fort should be rriade to i l lustrate tlre task'norr_i'erballv so as not to bias tlie r-esults in far.orof the DLH.

Visosp:rti:rl. Visuoperceptual. anclVisuoconstmctive Frrnctions

Steregp.si.s. Onlv rnidline stereopsis requiresinterhernispheric integration. Thus. ofi theniid.sagittal plane in front of or behind the fix_ation point, callosal section does not affectstereopsis_ (flazzaniga et al.. lg65). Split_brainpatients sliorv significant rniclline delicits r.vithrandom dot stereogranrs witli clisparities rang_ing frorn 15 to lEO minute arc witliin l" to i' off the ',.ertical rneridian (Hamilton and Ver_rneire, l9E6). In contrast, Lassonde ( lgg6) de-scribed a deficit in tachistoscopic deptli per_ceptron in comniissurotornv patients over theentire fielcl, iittributable to loss of nonspecificcliifuse callosal contributions (but see Rivest eta l . . 199i1) .

Table 14-3' Lt'xical Langragt' in the' r)isc.nnectccl Right I:r.misphertI

I

Pat ien tsArrditon

CJornprehension Re'ading Speech \\'riting

Ear lv RI I speech: P.S. . \ ' .p.Late. occasional RI I speech: t , .8. . I \ \ '\o RI I spet . r 'h: ) ; Cl . . R.y. . A.A. . I l .R.Lt l t -hancler l . L l l r lorn inant i r r speech: \ ' . j

-

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t l

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l l r

{ifi{!

ti.r*,t,

8'

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fct

fi'

RII . r is l r t herr ispherer +. preserr t ; - . abst ,nt

T H E C A L L O S A L S Y N D R O M E S

Spncr,. The DRH u'as l irrrrrrl to he superior tcrthc DLtl irr parVrvhole arrd gestalt cornpletiontasks ( Neltes. 1974 ). orr rnoclif iecl frrrrns of stan-clardizecl spatial relations tests. such as the Dif-ierential Aptitude Test (Lerr'. lg74: Kurnar.1977). on the user of perspective crres to assistin itccurate lterc,eption (Cronin-Golornb.1986a). ancl orr tests o1'geontetric invariarrceiEucliclean. Afline. projec,tive. arrcl topologicirl )tFranco iurd Spern'. 1977). The DLH rviislilrnd to be superior in figrrre-grouncl diserrr-beclrl ing (Zaiclel. 1978a).

\lore recentlr '. Frrnnell et al. (tggg) founclthat t ire DRII oi 'c'allosotorin-patient J.\\-. {ronrtl ie Dartrnouth-Toledo series u,as superirlr tothe DLII in rrratcli ing o{ rnirror-rcr..eried stjrrr_rrli. Frorn tlic.ir firidings ther- c,oncluclecl thatboth cliscrrnnecteci hen-rispheres (DHs) c,ilnperlbrm pattern recognition. but that the DRHis specializecl {or proc,essing spatial inlbrm:r-tion. (lorbrrl l is ett ir l. ( l9g9) strrdied i l luson, con-l o r t 11 '1 , ' , 1 ; t r r r , r r l ; t l < .o r r rp l r . t i o r r i r r t so . . , i 11 , , r , , -krrtn patierrts {irtrn the l)artrnoutli-Tolecloseries (J.\\-. arrrl \ ' .I,. ) rind l i iund equal bilateralperc'eptiort o{' i l lrrson'contorrrs irr t l ie I)Hs butbetter arnoclal conrpletion in tlie DRH Thc:r.t . , r r t l r r r l e r l t l r a t i l l uson t . o r r t o r r r s r r r i q l r l h t , r t i -trilluted to lon level risr,al proc'esses comrnorrto both herrrispheres. r.r4rereils anioclal crlniple-tiorr leflects a lriqher-levei, lateralizecl p.,r..sr,

Becarrsr- ol' lalgt' incliviclual tlifference,s. re-srrlts olrtarnecl froni a f'eu, patients sliould beirrterpretecl u..ith cittrtiorr rrrrtil tlrev are con-l i r t r r . t l i r r l r r l g t . r s r r r r rpL ' s o f t . i r l l os r r r r i - sec t i o r r t , r lpatierrts. <tr l ietter. irr l: i teralizetl paracliqtrrsrrith norrrral srrl lec,ts.

Vistlal lrrvtgnrT. I)iffc'rent ctxrrponents o{' r i-sttai inragen' itrc rli{i'ere.ntiiiilr. lateralizecl.\ l l r r t ; t l l ' o [ ; 1 { i 1111 s l ro r r s s r rPc r i r r r i t r i r r t l r e l ) l i l l, l- i t luh et rrl. 1g 5: (jr lr-ball is ancl Serqent.

,1,!)\5-r. Irnrr{t ' gcrreration sirou,s superi,,rit in

tlrt ' l) l- l I {F-arah et al.. i9fi5: ( lorbail is "rr, l !"l.q t ' r r t I9 ,3,S) .

I , l t r ' r i t r , l t i , l ) r ' r r ' t . 1 ) l i t t t t . l t l r l r s l r e r r r s r r q q t s t r , r lI l r i r t t l r l L l I i r s ; l t , r . i r t l i z t . r l l i r r . h r r . i t l l l r r r t . e s s i r r qtt l t ' tai ls) or t l re ruialt 's is ol ' l tatterrrs u. i t l r rcla_tirr ' l r higlr spatial Ir-c11u",,c,r. ,r . l ,er", is t l re RIIts spet, ial izt 'cl { i rr gkrl iai proc,essrrrq 1u.4xrles) ort l t t ' rurrrh sis ol l t i r t t t .rrrs u, i t l r r , l l r t ivt, l r . l rxv syta-

373

tiai lrerperrcl (Hell ige. l9g3). Left herrrisphereperception then proceerls bottorn-up. RH per-c:eption proceecls top-doul, ancl the tr.r,crstreanls are integrated ria the ClCl. This con_<reptualization is often operationalized il thcNar.on paracligrn (Navori. lg77). \\'lie.n larseH's or S's rnarle up of little H's or S's are pre_sentecl pc'ripheralh to norrnal subjects *lrcin."required to iclentifr,. the iarge (globril) or sni:rll( local) letter (H or S). Suhlects erhibit three ef-lects: iJ) it is easier to iclerrti{r ' t l ie large letterstliarr the snrall jetters ("global Drec,erleuce" or" t l r e

l e re l e f f e r . f " r : , j , r . o r r s i s l e r r t s t r r r r r r l i r r ru'hicli the large and small eienrents are tliesarne (e.g.. a large H rnade up of'srnall I1's) areeasier to identify t lran inconsistent stirrruli irrrvhich the large irrrrl srurill elerrrents iire clifl'er-ent (e.g.. a largc S rnircle rrp of snrall I1's) ("theconsistencv effect" ) : iincl i,3.t tl re r.<insistencr. el--{'ec't is stronger for loc.al irlerrtific.atiorr ( 'giobal

interference'") t l ian for glrrhal it lerrtif ic.ation("local inter{brerrce"). \i'e refer to the latter asthc' "asrnlretric

crtnsistetrcr.. e{Iect." irrrrl it rsreflected in a significant Lri iel v (jonsisterrcviriteraction. In norrrral sutrjects. sonre lincl RVFspec,ialization frrr iclenti{ring local targets ancl.less frequentl_v LVF spec.ialization fbr giobaltargets 1r'an Kleek, l9[Jg). On tlie basis of find_ings in patients rvith unilateral temporoparietallesions. Robeftson and colleiigu", itgtls) rio""-ulatecl tliat tlie corrsistencv effect. and paftiicrr-larly tire asvrnrtretric <,onsistencv effect. is rne-rliate.d bl'tlie fl(l. This prcdicts that the effecrshould be absent il patients rvith r.ornnletecerebrii l <,onrmissrrroirrrrr. (Rolrertson anrlL i r r r r b , 1 9 9 I / .

Rotrertson et al. (lggil) prescnted hierarchic.p r r t t e r r r s i n t l r e LVF o r R \ F . o r l l r c s i r r r r t , p i r t -t en r s i n r r r l t r r r r eo r r sh i r r L ro t l r \ Fs r t s \ ' F ro f t . o r t r -rrussurotorrn'patierits L.8.. N.Cl., i ind A.A., ancl\\ i:ekes et al. (lgg7) rrondrrc,terl a follou,rrns tu th r r i f l r hvo o l t l r t , s i r r r r e t u r r r rn i ss r t r , , l , , r r t ' rp t r l i e l t t s . t t s i l l q 1 1 . 1 1 s i r r r i l a ; s t i r r r r r l r l t r r t l r r r r t r l i -t ions. 'fogether.

the hvo strrrl i t s obsen.ed irr-strur,es of rrrrilatcral corrsistenc.u eff'er,ts anrl; t s r r r r r r r r l r i t e l l c r . t s . T l r re , ' t , on r . l i r s i t , r r s r . l r i I r cdrar.rrr frorn tliese resuits. First. the absence, aI-e'r'el x VF inte'racti<irr is riot a rrecessani (.oll-\ r ' ( l u ( ' r r ( ' e o l d i s t . o r r r re t . t i o r r . Se t r r r r r l . t i o r r s i s -tcrrcv elltcts ciin occllr. in t l ie' abserrce of t l ie(l( l. Tlrirrl. t lre irsr.ntrrretri<, c.onsistt.rrc.r e{1'ec.t

374

('iul (x,(,ur irr t lrt ' split lrrain. I lotlr disc,oriner,terllrerrrisplreres crrrrlcl pro<,t ss lroth locirl irnclglohiri stirnrrl i anrl erx,lr rrrrrlr l therefirrr,, exhibit( { , l r \ i s t ( ' n ( . \ , ' l ' l i . t . t s .

Rig l t l Oort .s tntc t ional , \pnr . t ia . Br . t , t instnrc. -

tional prinis' \\ '(, lruri lr l t lre ir lr i l ih to put to-qetlrer lr ureiinirrglir l t,orrl igrrr.rrl ior,. ,,,., i , ,,, unobje<.t tthret' r l init,nsiorr.s) or rr <,ompler c.lrau-irrg {trvtr t l i t l t 'nsiorrs ). ()ott.stntctiortol dt1.t_\trafia is tlre irrabilih. to orgarrize severirl pilrtsinto a crrnfigrrratiorr rlc.spite ir normiil abil i tr.,tolrarrcllc. or rlr, lrr. ' t l ic. irrdivir[rraJ parts 1B"nion,1962; Brntorr irrrrl Frigel, lg6i: \! 'arrington,1969; De Renzi . 1982). ( jonstruct ional 'chs_prirria c.an oc'cur lrorn lesions in eitlier heriri_sphere. Lefi lesions rrrin. resrrlt in an nltsericeof sorue_of the parts lrrci irr sirrrpli i iecl versionsoi a rnorlel. antl RII lt:sions tencl to result in rrr_appropriate relationsliips arllong the pirrts, in_cluding a loss of perspective iii clrawirres in_tenderl to represerrt three cli,rrerxiu,,,(l"a:ls-1l1, :inrl Zarrgrr.ill. lg4,1r \\arrington etirl.. 1966: l lenton. lg67: H6c,ae,i , inri.Assal,1970: Gainot t i e t a l , . 1977).

(jorrstrrrc'tional itprirria c.iui Lre. rluite prrlrni_ne.nt in tlrt. riglit hand tif rigirt_handers withc'allosal lesirins, Henrisphere tl isconnectiorr (irra right-hiurcler) is strongiv srrggestercl if the pa-tient carr c'opv rlesigns itetter with tlie left liandthal ri.-ith tlie riglrt (Boge.n. lg6gbi yaniaclonet t l l .. lg6;l). Of course. i l 'a c,allosal lesion is ac_c'orrrpanierl lx' llH irrr.oh.,ernerrt. the leii halclnrar-lte paretic,or irtitxic so that the patient cloesrro better nith the left hartrl than witir the riglrt.

Sputial Acalnilio. Beciltrse o1' spirtial clisabilih.u4iel using the right h,inrl. tlre patient u.ithhenrisphere clisc,onnection nlilv lrnve clifficrrl_l i es . r r s i r r q l l r , r r t . i l , r r r r l pap t , r t o i ohe r r r i t l r r r r e t i < .p r r r l l l e r r r s r D i r l r r r r , , n e t r r l . . l gb2 t ( ) r r r p r r t i e r r t sr'".ith cornplete cerebral cornrni.ssu^rotomvliacl sonie diffic,rrltr. u..ith u,ritten aritlunetici.a_.cleficit that progrc.ssirr:lv rececle,l (Sug"n.1969a. p. 92). \\,e u'ere .surprisecl to note tl iatsorrretirnes a patient f i l l lor!, iuq cornplete com_ruusrrrotornv u'orrlrl har..e rliffic,rrlh. irr doingarithr r retic.on pitpe.r rvhere.a, cu,,rparable prolilenis crruld be tkrne bv rnr.ntal crilculation.

C L I N I C A L N E L I R O P S Y c H O L O C Y

Attention irr the split brajn cal be vie.,vetl nroregenerallr- as ir rnorlel sr.stt rri l irr the problern o{irrterrnodular c.onrrrrunicatirtri. IItxi, (,arl anii_tornicallt ancl lunctionii l lr. separrrte ..ntodrrles,,

r r r i r i r r l l i l r r t l r e i r i r r r L ,pe r r r l e r r< r , t o p r r r r r i l p r r r . ; r l _lei pr()C'esstJlq ;rt orre fi11ie. l l l t c6rti1rl1iC.lrte atcitlit,'r titnes?

.S/r:e;-r. Sleep is controlleci llv tlie riiencephalonancl brainstern witli nr""u.ii,rg hrainste.nr svs.terns thirt prqect difluseh. to both ireriri-splieres. ancl it is therefore not surprising thatsplit-brain piitients are said to liar.e ,r,,.,unlsleep-rvake cycles :urcl slrrclrronrius EEG in-clices o{'sieep onset and arousal in the hvohernispheres ( Sperry', lg74).

\tigilarrce. There is sorne controversr.. aboutu4iether the split-brain s\rtclrome includes ab-normal gaps in vigilance and aborrt rvhether theDRH is more vlgilant than the DLH (Dirnoncl.I979) or not (Ellenberq and Spern, lgTg).

Foatserl Attention in Dichotic Li,stening. \fehave adniinistered to cornniissurotorn_r.paiients:r clichotic listenins test u,ith C\.svilaLLs (Drz,clea. gee, pee, tee, kce) rrsing iateralizecl r.isualprobes and attention instructions (left ear. rightear. clivided) (Zficlel.l9g3). \\re founcl t1t ex-clrrsive LFI specializ:rtion for tlie task and i2ripsilateral suppression of'the left ear sigual inthe LIL \\'e thus inl'errecl (3) thrrt in tlie nor-rnal brain. the left ear signal is relaved ironr theRII to t l re LH r i r r l t l re CC pr ior to processi r rg.\ \ 'e lbr r r r r l no e l fer . t o f l tx .usset l i r l tent iorr to e i_ther errr on tiie riglrt ear advantage in lorrnalsubjects but a substantial effect iri a split_brrunp i r t i en l , L .B . r . l r r t l r e l ) L l l . a t t t , n t i o r r t o t heright ear hacl no effect but attention to the leftear increased the leli eAr score and decreasedthe right ear score. Sinrilarlr,. in the DRH, at-tention to the left c'ar had no efi'ect but atten-tion to the right ear reducecl the left ear scoreand increasecl the right ear score. Taken to-qetlrer. t lre drrta suggest that fot.rrsserl attenhoni l r t l re spl i t hra i r r ru. f i r . ; r tes at tent ion_sDeci f icsubcalkrsal interhernispheric audito4, chan-nels. In the normai brain. these suLcailosal

t

l (

, 1 ,

) l

t -

i -

r l

l l

T H E C A L L O S A L S Y N D R O M E S

c,hannels rlre preslnnrlblr strperc'ecled lx c'irl-

Iosal channels that are less settsitive to spatiiil

attentiotr.

Dic'hotic ' l istening tests van'uiclelv in the i le-

qree of tenrpor:rl antl acoustic overlap behveen

left and right ear signals. The gre-irter the over-

lap. the greater the ipsi lateral srrppression antl

the less srrsceptible is the ear aclr-tuitage to

rnodulatiol br.' fcrc'usserl attentiort.

Cotert Orienting of Spatial Attert icur. I{ 'each

cerebral l ierr i ispl iere is an inrlepenrlent c'r .rgrr i-

t ivt ' svstern. t l ien ei l<'h l ias arr irrr lclrertt lent cror-

trol svstern. i .e.. arr irrr lept 'nderit i r t tentiortalrrrec'hanisrrr that regulates the resources arxi

operatiorrs of t i re l iernispl iere. But spi i t-brain

patients largelr, beliave as u.ell-integratecl ancltrxrrdin:itecl organisrns. and tliis suggests tiratthele is an overai l . sharecl attentional svstetrrtltat c'oorclilates the interac,tiori of the hvcrr l ist 'onnectecl lrernispheres. This c'reates ir puz-zk': is attentiorr irr thc' spl i t l l rairr diviclerl r l rsharecl? Forrr irr terrelt i ter l solut ions lrave' beerrproll<lsecl.

l Stage o.'l prorvssing. The tr.vo discorurer,teclI t t ' rnispl ieres c:an selec't st irnul i . encocle t lrern.tlecock ancl selec,t responses indeperrclentl"'.l tut thev share response executiorr rneclranislnsto avoicl behar.ior:rl conflict. Thus, earlr,' stagesol processirrE show attentional clisconnection.ult t ' reas late stages of processing are attel)-t i r inal lr unif iet l (Reuter-Loretrz. in press).

2 , \ tr totnatic r; . t . controlk:cl a.t t tr t t iort. One dis-tinguishes iirst arrtorriatic orienting due to pe-r iplreral t ' rres thirt are not infr lrrnative Irornslou strateqic. orientirrg clte to central c.uestir t ' rr ' , l i l ic l crres preclortr inate (c,1. Briancl arrt lKlein. lgf iT). Arrtornatir . or icnt irrg o1' spatialI t t te r t t ion is l te l i cv t ' r l to l r t ' cor r tn r l l t ' r l l r r - t l r cpanetal-1rrrt :rrrrt ' rr srrpt 'r i r tr t .ol l ic 'rr lus corrrplt ' ri l rr tsrter anrI l)r ' l r i r t 'nt ' . 199.1). Rr corrtnrst. corr-t t r r l l l r l o r i e r r t i n q o l s l l r r { i r r l , r l t . r r l i t , r r l r r l \ , r i s , ,e l lga{e t lu ' { i ' o r r t i t l l o [x ' i r r u r r cxccr r t i ve ro l t '\ l t ' s r r la r r r . 1990 r . l i e r r te r - l ,o lenz ( i l p ress) r r r -

qrrt 's t l rat u' lren sPatial atterrt ir tn is ori t ntcrl arr-torrt i t tx 'al lv via a periplu:rul crt, . ther-e is t :r . i ,ctt ' t t t 'e l i rr rrrt leperrr lent ant[ paral lel i r t terrt ioualsvstenls irr the tu,o r l isconnec't t .r l hcrr i ispl ieres.

375

u'liereas g'ht,'rr irtteutiorr is oriented strategi-cirilr ria ri cerltral c'ue. tlrc'rt' is er.irlerrce lirr asliared attentional svstt'r rt.

,3. Locatbn- t,,s. ollect-bo,sad attetttion. (lor-

l lall is t1995) argues that location-base'cl atterr-tron. as in cor.ert orierrtiltg in spirce. is unifietl.rvirererrs objec't-based attention is rliricied. tleirrglres that location-baserl atterrtiorr is rtterl i-atecl strbcofticall_r br tirc supcrior c'olliculus:rncl the seconcl risrrai svstern just rttentitnrerl.also beliel 'ecl to rnecliate ruic'onscious "blinrl

siglit" ancl projecting ria tlie prrlrirar to t'xtriistriate cortex. In tlie split brain. tliis svstern irp-plies to spatial irrliirrriati<ln in tlie periplien asn'ell as close to lixation. ancl it cloes rrot requiresrrstairiecl inpr,rt. Object-based atterrtiorr. lrrcontrast. is corticalh'nierl iatetl r ia the genicu-lostriate svstem ancl is rtet:essrrn'frrr consciousi r l e r r t i f i c i r i i o r r o f l b r r r r i r r l b r r ru r t i t , r r .

C o ft i c o I lq os.,v i l t c o rt ir, all q n v rt i at e d att an t i r t t t.Tlre subcortic'al svst€rlr is unifiecl via the inter-<'oll icrriar cornrnissrrre or perhaps via the dien-c'ephalon. rnidbrain. or c'erebelluni (Tre-viirthen. 1991), u4rereas tlle c'ortical s\.stcnr isdividecl. Tlie coftical subcufticai tliitirrctiotapplies both to atterrtiorr an(l to perception((lorball is, 1995). Thus, it is i lot the <'ase' sinr-plv that attention is integratecl in the split brairrwhile perception is dir..ided. as originalh'clairriecl bt'()azzaniga (f987). None of the lburviervs conrpletel'r'accounts lbr all avtrilable tlata.Sorne ket'er?erinlents iire reviewed belorv.

STtatial Cueing

Sirnplc reaction tinrc (SRT). Li Posrrer's cueparacligrn (1980). t-"r'o or rriore positions iic'rosstlre vertical rnt-'rirlian are predesignatecl as po-tentral target locatiols. One o{'these' locationsis cuecl c'entralh' (s,,rnbolic':,rllr', e.g.. a letter 1,or R) or peripherallr ' (at t lre locatiorr o1'the tar-get. e.g.. a box arourrrl t l ie stirnulus locatiorr)lrt ' frrrc tlr unset o1 the target. Tlie task is irnSltT u,ith rrnirnanual brrtton presses. l lc-sponses to crreci targets are usuirlh' {irster thanrespons€rs to unc'ued targets. Orred targets rrsrr-alh'r ' ielt l a srnall { lci l i tation (benefit) relatirtto a nerrtral cue (e.g.. cl leirrg all t lre targets).

. I

, l

376

{ l r r r ' r r t ' t l t r t r .gets r rsr ra lh cr l r i l r i t r r i lur .ger) i r r l r i -l r i t ior r i r .ost ) re lat ive to t l re nerr t ra l c i , ,e . TI rer'ost arrrl lrt 'rrefit ure otien (,orlceptlralizerl as l le_irrg rlrrc to shil is o1' ;rttt,rrt iol i ir sprt,e. Re,cirl lt l r i r t or re r l is t rugi r is l r t .s last i< l l5 i ) r r rsec. l re_hreerr r,r. le rrrrcl target) iurtonratic, prirninq drretu rrrrirrlor.nrative (nrostlr iur.alidj pr:ripherrrlcrres fiorrr t.orrtrolleil slou.. l lr irninn irf;0ri rst.t ' ) r l r rt ' to r.errtral inlirrrnirl ir ie 1 rrrostlr. r,alir l )c'ues. \\ 'hat uoul<l rve prerlit,t l lrr,rrt r.alicl r.s in_valit l c'rreirrq ac,ross tlre rertrcal rnerirl i lur in tl iesplit l lrairrP If t l ie trvo lrcrrrispheres l iave inde_penclerrt attention:i l sr.sterns. then the rno.ststraiglrt lonr.rrrcl prerl ic.t ion i.s t l iat there shorrlcllre rur l lerrelit or c.ost to srrr:ir c,ues. Arr,,. r. i i l icl_rh - i r r r i r l i r l i t r e f lFr . t rLt . r .oss t l re rer l i t , i r l r r rer ic lian in the split bniin is presrrniabir. rnediateclix' a u nilied atte'ntional *. ste r r r tliat representsbotli VFs. a svsteur tliat lras ac,c,ess to' ipsilat_eral visrral c,ue irr{irrrnation or to cltlier subcai_losal interl ierrrispherii, cue i l lr lrriration. Brrtu'ould srr c'h r.'iiliclitMnvi,rliditr . benefits/costs begreater rir snrirller in the split brain than irr therrclrrniil brain? Tlie sinrplest precliction is thattiier. shouid ber srniiiler. ()theirvise. srrbcallosalc'liiinneis nnr st_have spatial orie nting firnctiotrst l t r t t r r r e . r ro r r r ra l l r s r r l t l r r " sse r l l r r t l r t , ( l ( . l r r r t r t , _l e i r se r l l o l l o r r i r r q t . i t l l o s i r l se t . t i t _ rn .

Reuter-I-orenz antl Fenrlric,h (tgg0) usecl aPosrrer Pararligni witlr irrlbrutrtive pcriplieralc,ues urtlr

_ long stirrrrrlrrs orrset nr_.lr.nrrY(SOAs) ancl obsernecl unifietl attention in oti_tients u.itlr cortrplett callosritomie.. B" "rr,,_tnr.st. Arguin et al. 11000)rrsecl inlbrrnati i.e c.err_tral crres rurrl intennediate SOAs ancl forrrrrlthat sonre ltut not all callosoto,,,, p"ti.rrt,shorved attentional clisconnection nrril rur,," ,,r,-terior cirllosotclrnr- patients also shorvc,cl atterr_tional discorrnection. Thus. conll ict i l the l it_erature exists ancl tliere is a neecl frlr a conrrrrorrnrethodoloqr,'. Nonethejess. h.ro conclrrsionsenlerge. First, attention can be split in t l ie dis_t r l r r r r e r . t r o r t s r t r t I r o l r , , Se t .o r t t l . . o rne s r rh t . n . l _losal charureli can ,necliate attentional lrrt".*"_tions in the split brain

Passarotti et al. (unpublishecl clata; Zl:urlel.199,1) iidnrini.stered to crornlrissurotonrv Dit-t ients L.B. alid N.G. different ,,ersions of thePosner experiment u.ith both peripheral anclserrri-centrirl irrfcrrrriirtive cu"s arr.l dOAr rrug_ing frorn 150 to 250 nr.sec,, Target, app""r",I i,

( ' L | l . \ l ( , \ l N i : L J R ( ) p S \ ( H ( ) L ( ) t ; \ ,

orre' ol i irrrr lro.rt,s irr thc r.onrt,rs oi ir s(luarec,errtererl at I i_ratron. Irr this ri.ar.r. i,t t.o,,kl <,o,,r-prtre nerrtral rurrl r.alicl tr. ialr to irrr.t[ icl tr. jalscrrissing tht' horizorrti i l rnerirl irur. irn,alit l tr ialscrossinq the rr:rt ical rrrerirl ian. arrd irrvalicl tn_ais c,rossing botl i. Tlu, resrrlts rrit lr Irrrth para-rl igrns sliou'crl ctltrpler lttt:rrt iorral irrteractionsbetu'eeri tlie hvo VFs. lloth liic.ilitatorr arrtl in-hibiktrr. c,onsistent rrit lr rrrri i ierl atterrtion.Tlrese rl irta i ire r.onsisterrt ri i ih a rrrorlc,l u.hic,lrirssulles thiit i 1 I tlie ltFt has as attentioriai rlapthat includes both VFs. u,herc,:rs tlir: LII has arri ittentionii l nti ip that ir-rc,hrdes rlnlv the R\/F: i2tthe LH controls attentiori to R\iF targets anrlthe RH c'ontrols iittention to LVF targets: i.3ttire hvo liernisplieres slxxr. rlillerent pattemso{'costs ancl benefits. witli tlie ntt nrore likelvthan tlie LI{ to sliow costs clue to i,rvaiitl c,,ei,t1) tlte hvo attentiorial systerns can rnaintain in-deperrclence in the normal ltrain; t5) the at-tentional systern in tjre RH liris both callosaland subcallosal access to RVF inlbrnrationr t6lboth the callosal :rnd subcallornl irrt".lr",ru-spheric attentioniil effects inc,lude tu"ilit.tn,.as well as inhibiton.components: ancl iZr thereare large indiricltial .lifie.",r"", u".nr, ,plu-llrain patients in the nature uf,,rb"nllorali oi_terr t ior r e l lects preserr t . I r r l l r r r l i t . r r lar . t l re c l i r tal rorr r L.B. krqether rv i t l r t l re datr r f ior r r r rorr r ra lsubjects suggest tlrnt there is an asvnrrnetnqcallosalh' rnecliated rnirror lrnage iacilitationfrom tlie RVF to the LVF. o. lr.,ll ,.., n ,ul,.ni_losailv niediated rnirror irnage irrhibition in tli.sarne direction. Irr tlre normal brain. czrllosal {a-cilit:itiori clontinates. whereas the split brrrinr rn r r rasks sub r . i t l l os : r l i r r l r i b i t i on . ( ) r r r i a t r r s r rq_qest t l ra l . ( .o l l t ran to Reuter-Lor" , ,z 's l r ,pnt l ,_esis . autorrur t i< . r r t t t , r r t ior r t . i r r r l re r r r r i l ie t i [ r . . -hveen tlie tu'o disconnected hernispheres.

f!,j

i

dtft

Spatial cucing in choice rear:tiorr tirne. Sint-ilar discrepancies are reportecl frrr spatial cue-ing in choice RT tasks. Thus, Holtzman 09El)found evidence for shared attention. rvhereasNlangrrn et al. ( lg94) found eviclence fcir inde-pendent attentional sr,stems in the discnn-rectecl hemispheres. In botli experiments. sub_.jects rnacle binarv clioices of &ed lateralizerltargets. I{oltzrnan usecl central cues and large(1500 msec) SOAs, wlierea.s Mangun et al. usetiper ip l rer i r l t .ues i rnr l s l r r r r ter SOAs r l50_6{n

L

r l

T H E C A L L O S A L S Y N D R O M E S

nisec). Thlrs. clifferent attentiortiil svsteurs Ittar

have beeu engaged in t l te hvo tasks. I t is irn-

portant to note that er.'e'rr thougir invalicl cues

c'rossinq tiie verticiil rtiericliari liacl irn effect.

derrronstrat ing sorl ie unif ic 'at iorr o{ ' atterrt ior i

behr,een the hvo discrinnectetl herrrispheres. it

is nonetheless the case that irn'ai id c'u€rs cross-

ing tlie rniclline af{'ectecl tarqet cletc'ction irt the

otlre r he'rnisphere rather cli{lerentlr.- (rttort' er-

trerneh ) tlian invirlicl c'ues u'ithitr tlie sartie

lrernispl iere as the talqet. Thrrs. rrni l icat i t ln is

ftir {l"oni rrontial. The (l(l appears to be nec'es-

san for r locirr lat ing scirte rt{ ' the extrertre c' l -

fects o{ orientirrg to peripherrl l st irrrul i in the

spl i t br i i i rr .

\ ; istnl Searcl i . Searcl i o|r ' isrral targets arrrorlg

cl istract<irs el lgages corrtrol lecl atteri t iort tuul i ts

speed is rrc'gatir.elv correlatetI u.ith tire nurttberol distractors rvlien it rerluiri's li:titure c'on-

. jurtct iorr. i .e.. u4ren the target is cottpose'r l o{ 'a t tr i junction o{ ' features t lrat are also presentirr the t l istrac'tors (Treismrin arrt l ( lclade. l !180).Is visual setrrc'h in one r isual lrr :nri{ ielcl sensi-tire to distractors in the other visual liemiiielcl?Lrrc'k et al. (1989) showecl that. unl ike norrrralsubjects. one cal losotornv patient (J.W.) anclorte comrnissurotonrv patierrt (L.8.) exJribitet lsear<'h tirru's frrr targets in one VF u4rich u't'reinrlepenclent of the nrrnrbt,r ol clistractors irlihe oiht 'r . This then is an exauiple o{ 'dir ir led.qrntrol le.d attentional sl-sterrrs. arqrr ing agair isttlte autornatic,-controlled. clivirlecl-rrni{iecl Irr -

pt l thesis o{ Reutt 'r-Lorenz. Tlre resrr l ts i l re ( 'on-

sisterrt u. i t l r the locaticln- r 's. objet ' t-baserl arrclsrrlrcoftictrl-corlit'al hrpotlteses of Oorl;lallisi 1995i. since t l ie r isual sei lrc 'h t irsk o{ I-rrt 'ktt al. is nrost likelr oir.jer't bast'd arrrl t:oftic'allrr r re r l ia te r l .

Alr opposite' resrr i t u'as olrt i r ini 'd l t l ' l 'ol l rrr i tr trrlrul Zaidel (1998). u4ro strrr l i t .cl the elI-ects o1'ipsi iateral anrl <:orrtr i i lateral r l istractors ort lat-t ' ral izecl visulr l set irclr i rr tu.tr c '<lrrtrnisstrrotortn'

I ) i t t t r t r l s \ . ( L r r r r t l L . F l . ' l i r r q c t s r r r r r l t [ i s l r l u t o r stant '<l i rr relat ivc sal ience. Irr gerx'r:r l . cl istruc-krts slrlu'e<l clou.rr the st,arc'lr lirl crlntralateraltar{ets. sluru. ing t l tat. r 'orrtran to l-rrc:k et al, .t l l t st 'arcl l wus not irrclept 'rr<lt ' l r t in t l re turrlrcrr i isplrert,s ' f l r is

t , f l i ,<.t u'us erlr ir l lv tnre. { irrl() \ l - \ i t l i ( ' r( ' ( ' t i rr{t ' ts u'rt l r l r i gl r -sl i l i t ' rrc ' t ' r l rst l iu -t t i r s r u r l { i r l l r i { [ r - s . r l i c r r t c t ; r l g r ' t s u i t l r l o u

377

salience distra('tors. arguing agilinst tlie auto-

nratici tv l trpothesis ol Reuter-Lorettz. I lou'-

ever. the response itrrattgettlertt u'as tlnir|te:

patients \\'ere asked tc.r prc'ss u llrttrltr u'itlr their

left finger if a target u'rts preseut irl the LVF

and to press alrother buttort u'itli the dglit harrcJ

i{ 'a t trrget u'as present in t l ie RVF. Tl ius. l lot ir

liernispheric respollse svstettts \\iere Poise(l to

respond. ancl tliis ilta\' liar''e ac'tivatccl inter-

herrrispireri<' interac'tion to prel'ent conllict. Br

contrast. Luck et al. usecl birrranual r{ 'sPonses.

il4rich rnav rtot invoke :r strategic' resPonse colll-

peti t ion (Reuter-Lorenz. in press ).

Polhnrinn ( l !196) I iad clet i iclnstratecl earl ier

iur ext inct iorr- l ike i isrrt t tnetn' in the searcl i task

rrsing lou.-sai iertce targets ancl lr iglr-sal ieuce

ilistracrtors in tiie nonrral brain: R\-F clistriic-

tors interfered rvith LVF targets but not r'i<'r'

versa. This t-.fl'ect il'as reversecl irt coutrttissuro-

tornv patient L.B.. u4io is not able to trans{'er

i'isual {brnr inforrnatioti }retn'een tlre lienri-

spherr:s. but rtot in N.(1.. u4io is able to trans-

Ier such infornratiotr. Tliis is attotlicr exarnple

of iitterrtional interdepentlertce'. albeit abnor-

rnirl. between the disconnectecl helrrispheres.

Pollnrari and E. Zaidel. rlloreover. proposed a

nioclel fcrr the interclepettclertce. Tliev consid-

erecl tr'"'o competing rnodels {br tlte contralat-

eral distractor asunntetn' itr nortttrrl sulrje<rts:

i l ) Kinsbounre and Bnrce's (1987) proposal

that the LII orienting svstem is tloltiniutt. irttcl

, '2) Heihnan et al. 's (19u7) and \Iesrr larn's

( l9t i l )proposal that the RII has a rnore bi lat-

elrl coverage in space. together with i3) the

proposal that tlie RH is dorninant frrr sptrtial

orienting (Heilnrarr arul Vi in Den Abell . 19fJ0).

Tlie search rlrtii in splits support elettu'nts frorrl

l rot lr o1't i ie earl ier proposals. Thc'r ' art ' cot isis-

tent u' i t l r a nrorlel of arr attcnticlnal grarl iertt l i rr

the rvlrolc' l lelcl in eaclr lrerrr isl l l i r . ' r t ' . btt t r i t t tr

lhat is stereper irr ther LIL Tl i is explairrs t lre re-

i .ersed rclrtralateral cl istracrtor as\r) lrnetn' in

L.B. br absenct ' o{ ' ipsi lateral r jsual inlontra-

tiorr rirther than Lrr.'srrb<':rllosill inhibition. The

rrrorlel assrutres that there are in<lepentlent at-

tentional sr-stenrs irr t l re turr <l iscrxrnectet l

l r t ' ruispheres. brrt i t t ioes rurt i rssuln( ' t l rat ther

intr.rr ict r l i recth. Tlre rrrodel srrgqests that t l r t '( l ( l has a l i rrr i tr :cl role in spirt ial ori t 'nt ing drrr '-

inq scru.r: lr . i rrrt l t l r is rrral l re\r t 'xpl ir i rr t l r t ' rr lr-

s t ' r r u ' o l n c g l t ' r ' t p l r e r r o r r r t ' r r o r r i r r t l r c r l i s c o r l -

378

nected he.r'nispheres (pkrurtle irnd SDern.198.1). (Ser.eral split_brain .stuclies have ererr .._pofted righhvard attentirxral biases in lisualtiisksl see Proverlticl et al,. I 9g.{: Rerrter_Lrlrenzet al.. 1995: Berluccli i et al.. lggT)

Llenti,spherir:,sTteciali:ntittn. pollrriann anrlE. Ziride,l 's (lgglr) c,ontrollecl visuai searcli ex_perinrents (i.r'ith tirrgets. llontarqets, ancl clis_tractors) revealeci a LII irch.altage iu L.B. forboth lorv- and high-effot searching. witli anclu.itliout ipsilateral distractors. N.G. showed ncli rernisplie rir, cliffe rence. Br. c,ontrast. polhnanniincl E. Zaiclel 's (lggg) c.oritrolletl r isual searclrexperiments (rrith targets antl nontargets onlr,)suggested an RII aclvantage in L.B. and an LHadvantage frir N.G. {irr iroth loiv_ ancl higir_effort searclring. Kurgstone et al. i1g95) asked\ \ ' l te t l rer t l rere is a consistent henr isp l rer i<, sr re_cializatiori for guidetl risual search.\uh"." Lf_lortful, crtrrtrolled) conjunction search is cori_strained to a subset ofiterns that share a targetfeature. thus rendering tlie search ,n,r." "?fi_c ient . Thev usecl ' 'c :ongnrerr t responcl ing. .lpress a riglrt-harrd ke_r,rvhen a targei is pres_r.nt in the RVF. ertc.) ari<l iong prererrtuiiorrsri'liile ntonitrlring e,,,e fixation. The task was acl_nrirristerecl to call<tsotorn.v patient.s J.W.. V.p..arrcl D.R. All patients ,""urr"d bilateral arrar,.stwice as fast as unilateral arrar.s with the samer r r r rn l re r o f s t i r r r u l i . t l r us r , on l j r i r r i r r q Luck e t a l . . sevidence of diricled attention. J.\\ ' . and D.R.exlibited a RVF ad,,,irntage foi the stanclarclc'onjunction senrch ancl a seiective RVF bene-lit frcirn gui<led search. \'p exliibitecl a LVF ad_vantage for standard search and no rid\.antagelrorn the euided search. Kingstone et al. coi_clucled that grricled search is ipecializecl in theLl l ar rd at t r ihr r te Vp's t l is r . repant . r to ind i r id_ual clifl'erences. Taken together. tlie data fronrboth series of patients suggest drarnatic indi-vidual clifferences in hernispheric specializa_tion lbr attentional tasks and inclir.idual shiftsacross tasks. Generaiization frorn a lirnitederoup of patients und tasks is therefore unwise.

In surn, tliere is abundant evidence for in_terhenrispheric attentional effects in the splitbrain. It appears that sorne levels of nro""'rr_i r rq i r r r torr rat i r . r r l l r t . r rqage inter l rerr r ispher ic in_teqrat iorr br i r r lerat . t ior rs behveen the hvo at_teltional svstelns. even in the split brriin. Otlier

C L t N t C A L N E U R O P S Y C H O L O C y

levels of processing pernrit hernispheric incie-pendence-iti cognition br. also segregating 116attentional ̂ sl.stenrs of the h"o .lisr.onneited(and norrnal) hernispheres

Ihal Task,s. Trvo earll. erperirnents shorveclthat henrispheric disconn"itinn "",, p.ulu."superior performance of tlvo cclncurreiit ta.sls,()azzaniga and Sperry (1966) required subiectsto perform two different risrral cliscrirninationssimultaneousl_v in the hvo VF.s. Unlike nn.rn.lsubject.s. commissurritonry patients perfu.m"dthe tasks equally well c.oncurr"utl, "n,l ",l,,n"Ellenbe^rg and Spern. (1979) ,"po*"a ,i,r,ilo.results from a tactile sorting task performed ei-ther unirnanually or blmanualh.i"itl ort roru.tguidance, even when opposite iorting *1", op-plied for the two VF_reiponse tr"na"o*binl_tions. Franz et al. (1996) showed an analogouseffect in a drar,ving task.

o"-

(fther studies of dual tasks show dorninancebv the hemisphere that is specialir".l fo. p.o-cessing the stirnuli or bv thl henrisphe.e ihatcontrols the response mode (Ler.r,eial., 1g72j.This is consistent r.r,itli the stage_of_processinqhlpothesis of Reuter-Lorenz.

1 -'-r

Experiments on the psvchological refracton.periocl (PRP) suggest that the ittentional srs-tems of the two disconnected hemisph".", ̂ r.unified. In the hpical pRp paradigm, subjectsare required to perforrn two diffeient tasks ina fixed order. Tlpicalh,. the RT for task 2 in-creases as the SOA between stimuli in the hvotasks decreases. It is believecl that the pRp ef_fect reflects a bottleneck in resprinse selectionor rnovernent produt.t ion for task 2 (Reuter_

!95n2, in press). Contran,to expectation. the

PRP in callosotorny patient J.W. was robust andsirniiar to tliat in normal subiects (pashler etd.. 1995). even when the tasks were felicitousfor each hemisphere (Ir,ry.et al., lggg). Unlikenormal subjects. howeuei. the pRp in J.\\.. wasnot aflected by the t,onsistency- of stimulus_response (S-R) mappipg in the two |Fs rlr.rret rrl.. 1998). Taken together. this irnplies thateach disconnected hernisphere can

^m*int.in

distinct rules lor S-R mapping and can selectthe app ropriate response withiut interferencrlroni the other hemisphere, but the two hemi-spheres cannot initiate independent responses(Reuter-Lorenz. in press). This pattern would

l t

I t ,

,1 ,

T H E C A L L O S A L S Y N D R O M E S

be consistent with the stage-of-proc,essing 1i.,.grtlresis of Reuter-Lorenz.

Redundant Target Effects. Detection or iden-tilication of targets is faciiitatecl u.hen redun-dant copies of the target appear. This phe-nonlenon is called the "redundant

targete lTe<t" {RTE'and i t re f le< ' ts para l le l pro( .ess-ing rvitli unlinritecl resources. There are at leasrhvo possible mechanisms for the RTE: (l) airorse race betu'een hvo independent equalprocesses that operate at the stage of resp,rnseqeneration (probabiiltv surnrnation): and 12 rneural interaction/co-actir,ation behl,een thestintulus copies, leading to hrper-priming thatsllrpasses a liorse race and operates at an earlvprocessing staqe. presurnirhh at a ser.ondansenson' areA (neural surnrnation) (NIil ler.19132). One niav expect a sin-rilar RTE u.ithin aVF in a nornral and a split brain. but a rechrceclRTE behveen the twi VFs in split-brain pa-tierrts conrpared to norual subjects. Insteicl.u'hen the redundant targets occur in both VFs.t l r t , re is i r s tanr lar t l RTE ,wlr ic l r dot ,s nt r I e . r_t'eecl a horse race) in the norrnal brain but thererna'r'be a paradoxicallr. large hrper-RTE (n4iiclisltori 's neural sumrnation) ir i the split brain.T l r rs rvas s l r r rwrr hot l r lor SRT rRerr ter-Lorerrzet al.. 1995) and for controlled r.isual searchtPollmann and E, Zaidel. iggg). Iacoboni anclE. Zaidel (in press) fountl that the hyper-RTErn tlre split brain rvas greater * lren hiiajeral tar-qets rvere biocked than u4ren ther. altematedr , t r tdor ' r lv rv i t l r r t r r i la tera l tarqets or wi t l r re-<irtnclant targets in the sarne VF. This nreanstltat t l ie neural surnrrtation cal ellrerge rn a srn-

379

gle trial but that it can be enhancecl bv repeti-tion in tirrie.

The lryper-redundant torget e.j?rf. lacoboni etal. (2000) exanrined tlie RTE in SRT in hvo pa-tients witli complete comrnissurotorrn tL.B. iirrdN.G.), hvo patierlts u'ith cornplete c:rllosotorrn.(D.T. and G.C. ). three patients with anterior cai-losal section (B.NI.. J.P.. and D.\\ ' . ). arrcl hrrr pir-t ients with agenesis of the CC {M.NI. ancl f . i .).The occurrence of ir hr.per-RTE (riolation of tlr.IIrorse rac.e inetlualih ), sign.iling neural suurrna_tion. rlas not usociated with a specific callosalpathologi: hvo patients u.,ith corrrplete cornlllis-srrrotonn'. one patient with couiplete calloso_toniy. and one patient .,vith agenesis of the CICexhibited a lnper-RTE. Instead. the hrper-RTEu'as assoc.iatetl sit lr long Ct'Ds. ext."er[irrg l5nrsec (Fig. 14-l ) Tliis nrust be the tinre u{nclou'that pennits neural co-actir.atior-r.

The selective susceptibilitv of tlie split brainIo redurrdrr r r t targets appeir rs to he a r rs" f r r l t . l i r r -ical tool for establisliing structural rlisconnec,-tion because it is unconscious. Unfoftuniitelvi t pror i t les a srr f f i< . ier r t l ru l nol , r r ret . . rs i rn.s ig, , .T l re RTE is <.er ta in l r r r r rsefr r l test for i r r rp l i r . i tpercept iorr and has been user l i r r b l inr ls ig i r r . i r rl remianrrps ia r lue lo I rerr r isp l r r . rer . torr r rrTon ra i r ro lo e t a l . . l 9g7 r . i r r r r eg lec t ,N ta rz i r i ti r l . . 1996r. arrd i r r <.or1 i t ,a l b l indness , Iarr r l rorr iet al., 1996b). The hr,per-RTE appears to in-clude an attentionai release phenonrenon dueto rernola l o l t . , r l losal f r r r r t . t ion and i t r r rat le i rdto spe<. i i r l sk i l ls i r r largel deler . t ior r l r r r t , r [so i r , -creased distractibilin' in strclr cognitive actiri-ties as reilcling.

50

4Q

o 3 olO 2 0

1 0

0

G C N G L B J

Figure l4 -1 , T l r r ' t , rosscr l - r r r i c . rossd c l i f le r t , r rc l i l s i l i pJ r .reac t i { ) r r t i l r c rSRT) to ia tc ra l i z t ,c l l l as } res as a r r reasure o l 't l tt lrht'rnispherrr, tralrsfi,r t i lrt, in pati(,rits with callosaltnrr;l lenrent. Biack bars. patierrts slro shrxv a ln1x.r_redundant target i,{}er.t in SRT: s4ritc hars. patients rr4ro( io no t \h ( )u a l r rp t , r rc th rnd l r r t R l '1 ,1 . C . ( l a r r r ' l D .T l r rx l

DW MM DT JP BM

trrr r rp l t ' te cal losotorrn. \ . (1. anr l L. ts . l rar l r . ,orrp leteronr l i issrrr ( ) t ( ) rmr. D \1 ' . . B. \ ,1. . arc l J .p. har l l r r i tnter ior<al losal sect jon. J.1, . arrd \LM. har l ager ics js o{ t l r t , t rqrrrsta lkrsulr . Iacoboni t ' t a l . i20(X)) . Repr inted rr . i t l r pennissiorrlronr Orlirrrl (iniversitv Prrsr.

( t I N t c A t N E t , R O P s Y C H o I ( ) ( ; \

r\rr f\ lRl e'xperirrre't \\. i t l l a' rrge'esis pir_ i2.r crrrrgr.e't l i . lr l_lra't l resyt. 'st:s. *,lrr,;1,t ient (J . t - . )s l to* 'ed t l t : r t t ter t r i t l sr r r r 'a t i . r r .was srrb jects resp.n<l t , r , r ' r . t , l r { " i r , r i i r , t r , , , r " r iasstlciaterl *'itli activatirilt i' rrreclittl and lateral hn,irl n,r,l t. Ht.'tt trlrqt,ts, rr.rti t1,., ,.ilt,t liarrrlrriglrt extrastri i l te reqions ([ac,obrtni et rrl.. 2000) anil t,] l sirrrrrltarresrrs lr irrl i lr lr l , irpnn.,,,\\ 'e interpr.tecl this as sensoll t ' ,rt i<'al rir.chr- T]rese tl i l l i ,renlatiorr o1'ci.lli.'l.r a.ti'itr. rt is r..'sisie't *-itl qaee rlif{.ere,,.' li:iti::J'litli.,l.lir,# iil;:t lre rie*'t lr itt r icrrri l l stttttttt:tt ir lrt occ'rirs at rr se,rr- ir"r,risph"rrc i ' teracti,n ancl the experr.erlterson'ler.l lrrt let'd' ( l.r lrri l l is ( lt lgu) obsen'r'r l ir slrr,,rlt i choose ar.org tlr.r,, r,arellr l lr,. (-,,re,.ailrrper-RTti ir i sPlit-brti irr l l i i t i t 'rtts *']tert t lte tar- expet't r. 'ngnrent r.r,sp.rrdirrg t, irrcr...se 'errri-gets arrtl irac'kgr'rrrtt l r i ' t 're tl i f l-erent i ' hrrr11 spireric i ' ,Lp"'. lenc= nn,l ir i,,,,,nunl ,."r1r,,,,,1*nattce. l l ttt t lr is recltrc'etl t, rt "stiutrla.rl"

RTtl irg to i 'creiise' i ' terl ierrrispheric, interac,rrrn.r.r-it lr equilunrirrant targt,ts rtrrrl bar.kgrorrncl. Irr.ste.aci. Luck e.t al. (lggg) ft lrntl ericlenc,e l irrTIl is irrrpht'ates tlre sttperirtr t ' . l l ic'rrlrs irr t l ie cli i iclecl attentio, ihrri.g .,rrunl ,.,*,:h ,,. inqlrrper-RTE bec'.use thilt strrrc'ture is belie'ed lt,r],,"y.,] ."rfu,rr"r. rvhereas poll'ranrr .nrito rrrodulate lrrrninance lrrrt not c,ri lclr in{irrrnii- E. Zaiclel f tggg) {ound eridence firrrrnif ierl at-t ion' BI c.Ittra'st ' f\ ' IRI of t lre stir 'dard RTF terrtio' rlurinq risual

_se:rrch usirrg co'gnrentin the rtrtrt-rtal brain was assorriatecl rvitli bilat- responses. Tliiis. task dernancls <,u' o'erricle re-eral prerttotor acti'atio' (Iac,lt.'i antl r. ,pun." rrrode in e'gaging inclepencle't att..-Zaidel' ulipublished clata)' consistent with the tirnal svsterris i ' the two clisconnected herrri-iie*' that probabilit' sutttrtrati.. occlrrs itt ir spheres. ;;;";'".. ore ,.lA\. expect blocke<llate stage ,f response llnrgrirrnrning. uiiirrianual responses to inc.rease interlerrri-Pollnr.nrr irnd E. zaidel (1999) '.b.senecl

" rpir"t i..*"; i;.r, antl t l iat is u4rirt rve lorrnrl.lrrper-RTEduringaco'trolleclrisu:rlse'.rchi' Pirl irnann ancl E. Zaiclei (1gg9) {bund an rn-patient L B ancl in N G The lrrper-RTE o.c- terhernispheric hlper-RTE in L.B. 'sing'isrralcurrecl itt a trt,re'effrrrt i ir l ,. 'ur.ir \vith high- search ith rJgrr attentionii l clerr.nds *,1ensalieltc't ' t l istractors antl. l t,rt '-s.l ierrce_ targets errrplo-r.irrg unirrraural responses brt n.t r. l4renbtrt rtot itt i t less e{Iorttul search u'lth high- "u,,itor.irr!"n"frr""aresporses(pollr.annarrrlsaliertc'r' targets ilntl lo',r'salie,,". ,lirtro.'t,]is. li.

-zatclel.,u'prrblishecl '.f","1.

r"nrg itr" i,,-Patients resporrtlecl unirnanrrall.,.witl i response terhemisplieri i hrper_RTE as an inclex oi.uni-ha'cl iilecl *'ithin trial bftrc'ks 'ilt". ltrp".-n]]n fiecl attention, this 'rea's tlirit u'irnanual re-,.currefl fcrr the' slorver herrtispherl (hancl- sponses increase interhe.r'isph"ri" 1,rt".n",,.,n'is.al her'ifleicl) of botli patie'ti. This argues ,.ilotir'" to crongnre't responses. we concl,tleag:rinst the trllic-inhibition-of-resp,r,tr" rr,,r,l"l that the three iespo'.re ,r^ru6", engage unifietlof the RTE proposed-bV Rerrter-i,orertz et:rl. attentiori clecretisinglr.. in the follorving.rcler,i1995), *'hich is inrl iffe,re't trr respo.se ha'cl. rrninran'ri] > c,rrgnr"ut ) tri 'ra'ual.

Corball is (1998) lotecl t lrat er.ei u.4ri le erlri_ - '--i

Ittrrt itt i trrce recluc'eil the RTE, it t l icl not rrrri- Brain Inagingctf Respon.se selectiort.A differ-'r'rsall' affec't tlie c.ul)' argrring for an i'de- ent perspectir-e. .' r'ot'r c'ntrol issues i, tlrepe'nde'ce of the ttu? it.,^,|TE' _allegedlv

,pli ib.,. in is clerived {i.m neuroirrrasing strrrl-cottnter t. Iac't l l l t irt i et al. (2000). t lowe'ei, ies. Fore.xarnple,.l"uo,glr,"n." rr,,, 'pfrr, i,r,r,,,Iucrlboni arrcl E Zaidel's.argurtte't that the h-r- rnacaque brain has sho*..n that re:rches tow,arrlper-RTE o('c'lrrs lbr 'callosallr' challengecl" pa- r.isual targets in sfht-braln rrronke\.s are largelrtients rvitli (lL.iDs lrirger trian l- r 5 ,,rr"i,oppli", cc,'t.oneii t u trr" ..r"iJ;i;;J ;";;ryIr.." ,,,ato rliidbriii'-rltediatecl treural ,,,r'rrr*tiur.. inrohl,] " r";g" ""*ork of risual. rnotor, anrl*'hich is llrec'luclecl in Corbaili.s's seconcl ex- rntegrative areas (see review i. siivaki arrdperitrtertt' Dalezios, 1999). with regard to the role plaretl

I]::.,,!,{:,:..-uf R:,,}),,lt'(. trode Latc.ralizect il;iJl:"it*::":?TT#it$;Xrull:l"ut"'l

t|sti15_of snJit brain patients irr sirn- shown that the prinran'niotor activation in o'efl:^.:;..-Tl":, 11

,ir\ usrrallv takes one of henrisphere is 'assoc.i.rted

,,rtl, prt,,,on: ,,,,,tu,t l t ree iortt ts: 1r blocked unitt tanttal responsesi inhibit ion in t l ie oppclsite herni iphere (Nlevt,r

I H E C A L L O S A L S Y N D R O M E S

tt al.. i998: All ison et al.. 2000. ancl reference.tlrerein). Hou'ever. transhernispheric motor in-hibition niav be in principle rnecliatecl bv cor-trco-subcortico-coftical pathu'i*s rather thanlrr crllosal pathwavs. To test this hypothesis.ut, rec'enth' perforrned an INIRI studl on achronic cornrnissurotonv patient and on nor-rrral controls. Subjects were required to per-{irrrn unirnanual movements with the righthand in response to risual stimuli. Normal sub-jerts clen.ronstrated the expected patterrr of ac-tivation of tlie contralateral motor coftex andinhibition of the insilateral rnotor c'ortex. In thesplit-brain patienis. horver.'er. ."1'e obsen ecl onh,t c.ontralateral priman, rnotor activation duringtrnirnanual rielit-hand rnovements (Iacoboni etal.. rrnpublishecl obsen'ation). This suggeststhat the triinshenrisnheric rnotor inlfbition ob-st'ned during unirianual rnovements in nor-rrral subjects is callosallv mediated.

\ ler r ron

Slnft- anrl Long-tenn LIerrutry in Con4tletearttl Paftiol Connisstrototrry Patientr. Sec,-tioning the C'Cl alone or in coniunction u'itlrr r t l rer r reocor t i t i r l r r r rnrr r issures lear ls to i r r ro i t i r -I t t t ' t t t \ i l r r e ( . en { I ne lnon l r e r i e r ved i l r r l ) .Z.ude l l990hr . bu t in t l re ahsence o f ex te r rs i reertracrillosnl damage, no amnesia-like sr,rnp-totns are obsen'ed. The forebrain commissureslre rnost likelv itnportant in the encoding ratherthan in the retr-ievirl stages. Sernantic hrou,l-t ' t l qe , p . Za i t le l . l9g , l : Cron in - ( ,o lo r r rh . lgg5)<tr episodic events occurring before surgery arererlenibered (spern, et al. . lg7gr D. Zaidel.1994l' Explicit ancl iinpiicit nrernon., r'erb:rl orrrsttrrl processes are firnctionii.l after surgeS' H r r p p e r l . l g E l : ( l r , r r r i r r - ( l o l o r r r h e t a l . . 1 9 g 6 , .its is procedrrral rnernon' fbr rnotor skillsI ) Z r t ide l a r rd Spcrn . 1977, . i r l l re i t r r l l : r t a le re l

lrtrvt'r tharr norrrial. Uniliiteral lrelnon'. evenrvherr hernisplieri<r specializatio' lirr tlie rriate_nal is clornin:rnt. is irnttaired (N1ilner iincl Tiir'-lor. 1972: lvl ihier et al. . tggttr. The f irst sr ls-tetrtatic lrerron studr lbllowing surgic.alsectirxr of the iC;. and to date still witli tliegr( 'atest nunrber of cases (N : 10). u'as of eightp i t t ie t l t s u i t l r s i r rg le -s t r rge . r r r r r rp le te t .o rnr r r i r -strrt l tonn (( l(1. anterior ' . and hippoc.arnptr l coni-

3Bl

niisstrres) ilnd hvo u'ith paftiril conrrnissrrrotolrrof the CC' (splenium lefi intact and anteriorcomrriissrire sectioned) in the Boeerr-\'ogel(Caltech) series (D. Zaidel and Spern'. 1974:D. Zaidel. 1990b). Preriouslr.. a rlilcl thoughpersistent recent urerrion' irnpairment follou-ing the surgery hacl been noted b-v fanrilv nreui-bers. Severe :irnnesia lias never been obsen'ed.Nlemon' lbr person:rl clr liistorical events oc.-curring prior to surgen' continued to be intactafter surgen' (Spern' et al., 1979: D. Zaiclel,1993). N{enron'deficit on a specific test in tl iesame patients rn'as also confirmecl bv lvlilner anclTa-vlor (1972). These patients tere given sixstandardized tests of rec:ent lllenlon' postoper-ativeh', including the \\'echsler NIen'ron' Scal.r \ \ 'N l5 r T l r is bat ten teste<l ure l l l ( )n f r r r p i< -

t r r red obie<, ' ts . r r , r r r r erhal r isual r les igns. se-quential and ternporal-spatial order. l'erbalpaired-associates. diEt span. and other relatecirneaslrres (fbr a detailecl rer.ieu,. see D. Zaidel.1990b). The findings revealed tliat the mostsubstantial decrernerrt in recent lnerllon: wilsseen i r t pat ients wi t l r cornplete t 'or r r rn issulo-torrtr', but even u'hen the disconnection s\n-drome is absent. As was the casc' r.vith the hvopartial cornurissurotorriy' patients, rnernon'scores \vere belou'nonnai. There \\'ere no svs-ternat i t ' tests of lne l r lon preoper i r t i ie l r in t i r isgrollp. But because patients suffer frorn a highrate ofepileptjc seizures and receive high dclsesof anticonrulsant nredication preoperatively.:rncl surgen'often reduces both the need for an-ticonr.rilsant nreclication and tlie freouencr.' o{seizures. it is unlikeh' that corrrparis.,r, .-,f pre-vs. postoperatir.'e testing can r.alidlv assess tliecontribution of comissurotomy to mernon' loss.

N{ild to rnoderate nlelron, imoairnrentsl r rv t , a ls t , l ,ee l r r lo t ' r r r r rente( l in nat ients rv lurlurre r r r t r lergorr t ' t ' iL l losotorr r r iCt ; set ' t ior ralorre) to control intriictable e'pilepsr' (LeDourt't al.. 1977: I ierguson et al., 19E5: Phelps etal.. l99l). In tl ie \\ri lsorr-l)artrtroutl i serie.s. a(:irsc. repoft u,as published o{ il 15-.'-eiir-rilcl hor,uith RtI atropin-anrl substiintial right ternpo-ral lobe dirrnage incurrecl at age l0 uith re-potedlr,. no niernon' inrpainnent (Lel)oux etal.. 1977). Close scnrtinv o{'this reDorl. hou.r ' \ er re\ eals bel , , r r ' - r , r , rn r , r l per f r l r r r tar r t . t , o t r I I reston'piissages of t l ie \\ ' iVIS. t lre scores beingcloselv sirnilar to those obtainerl bv tlie hvo par-

382

i i r l cnrr r rn issrr rotonrv pat ie l r ts i r r the, Bogerr_Vogel series rk:scribed above.

Srrbsetlrrentlv. stantlardize,rl rrrerricin, testslvere achrrinistered to it feri. ;rrlr l i t iona] tratientsirr t lre. \\ ' i lsorr-l) i irtrrroutlr se,ries, sorr^re u.ithpartial and sorne u.ith c.orrrplete callosotonr."-(Phe\rs et a l . . Igg l ) . ' fhe pat i tn ts r ,v i th corr r_plete c<ll losotoril anrl t lrrrse uitlr Jxrsterior cal-krsal sec:tions \\,ere lourrtl to lrrrrle consistentnir.rnon' clefic,its, ltut not t lrose u,it l t antenorc'lr lktsotrtrrrr.. Irr contrast to tlrese fincling.i. aprrbiislierl ieport desc,ribccl se.,.en pnti"r,* iviti,anterior c,allosotornr- clue to ,ur",rn-sr,rs r,f thecorrjrrctival ancl peric.allosirl afteries w,ho clevel_oped menron' disturbances following surgery(Sirnernitskaia ancl Rurua, lgEg)

Role of the Fontit itt X.[erutn1. In none of tlief 0 cases of'the Bogen-V<lgel .series is there bi_lateral fornix clarnage, as judgetl bv surgical es_tirnates; in several cases thert, is no clainage atall, and in sorne there is only partial uniljeralinterruptr'on. It is hardlv pla,riible to attrihuretlie results of' the rnenion, tests acLninisteredto these patients to the stirtus oi tlre fi,rlix. asothers hitve ernrneouselv srrggestecl (LeDou.ret al.. 1977r Clark antl Gef1'en, l9g9: Berlucchiarrc l Agl io t i . 1999).

Rtle rlf thr Llippocarnpol ()ontnrisutre irt iletrron7. TIre Irippoc:unpiil crirrrnrissure connects theleft ancl rieht hippomnrpi. It is just beneath theposterirtr portion o1'the CC. Irr hulians it is rel_ativeh' rnucjr srnaller tlian in rnonkeys, ciits. orrats (Anrar:rl et al.. tg8,l) ,urtl i ts l irnctionalih.rnl r r r r r r i r r rs l ras h"en r iuest iorret l r \ \ ' i lsorr et i -J . .l!187). It u,as sec'tirxred in the eiglrt crlrnpletrcornrnissurotornv ptrtients lirrt rrot irr parti.rlcor nrnissurotol n\- cit.ses or in parti;rl c.,rllosotol lu.pa t i e r r t s i r r r v l r , r r n t l r e sp le r r i r r r r r r v i t s l e f t i r r t r u , t .Ancl vet rllerllon rleficit.s were filunrl in trvo pa_t i t r r t s r r i l l r pad r i t l t , o r r r r r r i ss r r ro t r r r r r r . . T I r r r s , r r t _t r i l r r r t inq iur terot l rar le rnern()n prohlerr rs i r r t . r iJ_losurri-secti<tned patients to the status of thehippocampal cornnrissure (Clarke et .r1.. lggg:Phelps et al.. I 991; Berlucclri et al., l gg5rBavresrr r td Cirzzaniq i r . l { )0Or r r r :n r rot be. just i f ie t l .

Rob 6f the Anterior Comnis.sttre in l lenutnt.The role of the anterior corrrrnissu.e alorre i,the rnemon'scores is diff iorlt to i issess in the

( L t N t c A t N E U R O P S Y ( H ( ) l o c Y

Ilogen-\irgel c'ases since it rvas sectionerl in 1lic,asc.s, iin<l tlrere irre f'eu, rep<lrts ol'sec,t.ions re-str ic ' tet l to this <rlrnrnissrtre. I lou,ever. 1,, , lgu,r,l i r r r r t l r e s p l i t - h r r t i r r u i r r k u i l l r , , , , , , , k , , r i ' i , , 'l ) o h ; L r r r l r . r , l l e r r q r r t , s r I 9 g 4 r . t l , i . r . . , , , , , , , , , r r , 1 r , .i r lone r loes not st t ' rrr to pl i lv a c., i t ic,al , ,r l , j i , rhurnart r lrenror", ' ,

Otttu'ht,siort.s altottt !ht, Rolc rf ()rtrltrt.s Orillo-tt trn ir t l lctnonl \ \ ' l rerr posterior regiorrs oi. t l iccal losrrrrr-are clarnagecl. nrelnon. l i r i r i r , lul , , ,u_t e n i r l s u f l e r s . r " q r r r . r l l * s s , , l r v i r e t l r * r t 1 , . . " . , -t r c r r l s l r i n e l r i u l r r r r r r p l e t e t , r r l l o s i r l r . , t i , , , ,(D. Z,aidel and Spern., lg7.l ; D Zaiclel. 1990*)r r r onh se t . t i r r r r r r l t l re pos ter io r t . i r l l os i r l re , , i , , " .r P h e l p s e t i r l . . I g g l , h r r d g e n , , , 1 t t , , . , . , u ] i , , , , '199 I ) . N lu l t ip le ra r iah les r r ra r r r l fe t , t , , r , r " , , , , ,niemon. tests. El.en so. three obsen,ations arer.vorth pointing orrt:

l. Sorne nlenron. clecrenrent. r.aninq lronrmild to substuntial in sevedtr.l, l; "f,;;;pre._s9nt lbllowing section of the CC alone.or ftillowing only a small lesion in the CC,

2. Single, as opposecl to serial. section iloesnot appear to iiflect occurrence of rnern-o4'unpairnrent.

3. The r.r'ord assoc,iaticln antl ston. passagessrrbtests of the WN{S appear t,t be ,",rri_tive to partial rtr cornplete forebrain corn_niissurotornv. These tasks nrost likelvclepend on lntact interhernisplr"rc i , , t"_gratirln. The nie.cliiinisrn for tlie integra_tion is ii rnatter frtr speculirtion at thispoint.

In hurni ins. uni lateral henrisphere lesionsr r r in l re assot , i r r te t l i r i t l r r r re r r ron . L rss , rv l re re iusi r r i r r r ima ls h i l r r le r r r l les io r rs i r re re r lu i red . \ \ .er r r a v s p e c u l a t e t l r a t i r r l r r r r r r i r r r s . a s r . r r r r n e t n . i r rt l r e r r r e r r r o n f u n t . t i r r r r s r r f t l r e h , r i r l , e r r r i s n l r e r e s(see D. Z t r ide l . lgg0 l . lgg , l : Be , r r , l swor t l r l r r r lD. Zaidel. lg94), increases the neecl for nrech-anisms of integration between tlie hernispheres.\1'hereas eriderr<,e suggests a proqressive phr.Ioqer re t i c redur , t io r r i r r h ippor .a rn l la l cor r r r r r i s -sural connections frorrt rats to cati to ntonkevsant l t , r l tu rnar rs (Amara l e t a l . , l9g , l r pandva anc lRosene. lg85: Rosene i rnd V i rn Hoesen. IgET;Wilson et al., lg90), we suggest that the CCrr ra r

^ func t io r r to in tegr i r te t l te spet . i i r l i zed rnenr -on. functions of the hvo hemiipheres.

T H E C A L L O S A L S Y N D R O M E S

INTERHEMISPHERIC TRANSFER

In spite of conrplete disconnection. residual

tlansfer of in{bnnation. ranging frotn senson'

to abstract. lias been repeatedlv reportecl Tlre

classic test of transfer is verbalization of stitn-

uli presented to the nonverbal (right) heni-

sphere. Tliere are manr- possible explanatiorislbr this. including ll / ipsilateral projection of

sensorf inforniatiot'r fronr the L\tF to the LII

t4rere verbiiliz:rtion occurs: i2) irnpr<lper lat-

eralization of stirnuli: (3) transfer of cognitive

inlbnration sufficient to identifv tlie stimulus

to the LII l ir l lowing recrognition l lr the RH: iJ I

cross-cueing frorr the RH to tl ie LH. usingshaled perc'eptual spilce (t ' .g.. the RH rrrar' f ir-rte on ir related itenr in tlte roortr, thus identi-fiing it to the LH. or it uiav trac't- the shape oi'the object in questiori u.ith the heacl so thetriovenrent c' iui be "reacl off ' bv tlre LII) (Bo-

een. l99E)t or f 5l if : i l l other aiternatives itrenrled out. RH speech (see above).

SENSORY INFORMATION

. \ r r r l r i e r r t ' P t , r i p l r e ra l r V i s i o r t

Trevarthen and Spern' (1973) described resicl-ual transfer followirig cornplete cerebral corn-rttissurotornv of gross peripheral changes in i,l ,tniovernent. 19,, orientation. t3J position, i4)size. tind i5 ) bdghtness. Thev attributed it to iisrrbcorticallv rnediated.

"se'contl." extriigenic'rt-krstriate rinil prirnit ive ambient visual st'sterrt.This svsterir. u4iicli rs cleclicated to spricearotrrrcl the bodr'. involves projections frour tlre'strperior ctrl l icrrlus to the prrlrittar nttcl r-isttalassoc'i:ttiorr areas of tlic. cortex. ancl alltlr"'s lirrtrarrsfi.r lletu'een sicles ria brainstern c:ottttttis-srrres ibllou'ir ig cerebral colrrtrissurototttr ' . Trt '-rartl ierr corrtrristerl t lrc subcrtrt ical. periplreral.sprit 'e-lrasecl arrrbient svstettt u' it l i the <'ortitral.ttxr'iri. object-based fcrc:irl gerrictrlosttiatc' svs-terrr u'hic' lr rrrr, ' t l iates shapt' perceptiort iur<i isdistrrnnec,terl lx t lre surgen'. L.ise o{ t l ie c'orr-ta<'t lerrs ftrr l iernisphefi( ' s<rtttttt irtg (Zaidel1975t prorirles optinial conrlit iorts tt i test {i irinterlrernisplierir. tr i ins{'el antl cl it l cl isclost'slrap*' t larisier' (r 't rbalizuti<lrr o{ LVF stirrnrl i ) o1i i r r rp le l r i r ran ' s i ,nsora l t 'a tures. s t tc l t i ts t r t t t rc t lr s . s t r l t i q l r t . l ong o l s l r o l t . s i r t q l t ' o r t u r r p r t r t s .

383

Focal (Parafuveal) \'ision

\Iore recent experirnents suggest that lbveal

visuospatiill infontration can :rlstl triins{c'r in the

split brain. Holtzlran (l!lE4) shori'ecl tlirrt ciil-

losotonrizecl patients coulci direct their eves ttl

a loc:ation'in one \/F on the basis o{' ii location

cue in the other VF. Ilog'ever. thev c'rtulcl not

clirect their eves to tr slnpc itt one VF on tlie

basis of a shape cue in t l ie i l ther \ /F. Sergetl t

(1987) shorvecl transfer of orientat ion. al ign-

nrent ( location * orientat ion). i tnt l al lgle. arld(iorbal i is (198-1 ) ref inecl these f indings. Ra-

niachanrlran et al, (19E6) f<luricl t i iat cclrt tr t t is-

surotornizetl subjects experieltced apparent

nrotion n'hen hvo stinruli in different locations

u'ere presentecl in rapid succession. evert u4ret't

the stinruli rve,re distributed acriiss the uridline.

This findinq u'as clisputecl br.' Ciazzaniga (l9ti7)

but confirrned bv Naikar ancl Corbal l is 11996).

\aikar (1999) showecl th:rt the direction but

not the color of bilater:rl apparent nrotion stirtt-

rrli can be perceived in tlrt' split br:iin. argrring

{or a superior-coliicular rnediation o{ apparelt

nrotion across tlte vertical rnericlitili. Apparelt

rnotion is presurrr:iblv inferrecl froll srtbcorti-

cnlly based shilis of attention (Naikar and Cor-

bal l is, tgg6).

Sergent (1991) also sl iorved transfer ofareit

size (large/sliall). and spntial direction

(lefyright. above/belorv). brrt the task irrcludecl

onh three levels in each st irrtulus t l i t t tensiott

nr'r,i the resrrlts can be explained bv subcrlrtictrl

transfer or cross-cueing o{ 'ole bit of infornla-

t ion. For exarrrple. the cue rnat ' l le a sul i t le rais-

ing or lorvering oi ' t i re tot igrre insit le the t lroutl t

(Corba l l i s . 1995)

TRANSFER OF ABSTRACT CONCEPTS

Tlrere are rr:rnv exarrtples o1- sulrcttrt i t ' i t l trarts-

f i ' r of abstract settrat i t ic ' fe'atures of t l r t ' st ir l r tr-

lr rs. general lv uit l rori t t t taking cor r rplt ' t t ' i t lerrt i -

f ic 'at ion possiblt ' . ' l 'hose { i ' i r trrres ir ic 'hrt le

al l 'ect ive l i tr<l connoti t t i le inlonttat i<irr (e.g..

Irappr. satl t ( lL Zaiclel. 1976; Spern et al, .

1979). associat ive f 'eattrres. l lot lr pr:rceptual

i in<l serttanti t : ( \ ' Ivers antl Spern. l9E5). cr i te-

gorical ir t frrrrt t i r t ion (e.g.. "anirtrals t lrat qo irr the

vn'ater." r"4tcre olte l l ic ' turt ' is sl l t lurt to eitcl t \ ' l '

s i r r r r r l t iu reor rs l r ) . l i r r rc t io r r l r l f i ' i r t t r res ( t , .9 .

384

"s l roe-so<.k" ) luu l u l rs t r rL<, t serr l i r t rc , re lat iorrs(( ' .9 . c 'ornrr r r rn i ( ' l l t ior r : t , r rv t . lo1t t ,_ t t , l t , l ) l ro l r ( , /( ( i ronin-( i rkrnrb. I gE6bt

Sergent argrrerl that solrtt rronrrrrissurltorrrvpatierrrts crlrrlcl tr:rnsfer t lre crrnc,ept of'a ..rrrrvel..(Sergent . l ! l8 l l ) . o l ' "gr( ,er1 ' rSt l rgent . lg t j6) ."oc lc l .or

cven" (Ser .qerr t . 1g,57) . or . ,ac l t l r rp t<r

less th i rn I0" (Sergeut . 19, !7 j . Brr t these c,an a l lbe explairrecl lt,r, ir sirrrplt,, grressirrg strategr.l l i rsec l orr t l r t . iu l i r r r r rat rorr i r r ont , \ .F. or br . t l retrarrsler of lt inan. irr{irrrrratiorr f(jrtrball is.1995). S(,r-gerrt ttd67) al.so l irrrrcl t l ,,,t ,f l i tbrain pr,rt ierrts c<lulrl detenuine l, lretlrer f irrr_letter strings strarldling tltt, rtrir l l irre u,er.e r,,.orclsor rrot. althougir thr:_r,c.oul<l rrot idt.nti{i.t lrer:l lou.evc'r. (lorball is iuirl .fnrclel

rlggli) r,orrklnot replic'ate tlr is ri. i t lr u l irrgcr set of stir irulithat- precrlrrt lerl cross-c,uerng. Sergent (199[rrfurt-l ier reltrlrtecl t ltat cor r rr rrissitrotorri_r- patientscould conrpare rliqits across the ,,crticiai nrericl-ian rrnder certain instmctiou.s rpr.ess orre kev i1either digit is lt igher tl i irn tlrt, ,,t l i"r. uncl pressanother kev if ther are equai) brrt not witLothe r instrr r ctio n s isame*dif{'eren t .1,ratr,r"rrt i.Agairr, appropnate strategies and l,irr,rrv t.arrr-fer can explain sorlle snc.(.ess. but Corball istt995t f iUieri to replicrite the finrl ings u,ith thesarne patients arrcl Se_r.rnorrr et ri l . ( Ibg4) laileirto replicate thern u.ith ertlrt,rs. Ort,rri l l , tht.n.Sergent's rlata pror-icle l itt le srrPport lbr thetransfer of high-ler.el infirrrnilt ion about shape,o r q r r l t r r t i h . o r l i r r sop l r i s t i r , r r t e t l t r r r r r s l _ r i t t r r r ri r r r p l i t i t r i L t l r c r t l r i r r r i r r r e rp l r t . i t I " r , . l .

For orie of the patients teste<l bv Sergent,N.(1.. w,e rrou'have er. idenc.e that. ,r l thougii shecarrr iot nirrnt ' LVF st irntr l i . \ ,G. can integratesrrqrnsirqh c.orrrplex Ibrnr inl irrniat ion alrosst l r t , r r r i t l l i r r e . S l r t , r r i r s i r l r l e t , r ( , o n t p i r r e l n e i r t r _rngle.ss Varrrleqrlirs sliapes .jrrst a.s ,r=ll lr"hr,"",,as uit i r in tht ' hernispireres (Zair lel . lgg,l) , in_tlepenclerrt ol t l ie visuit l crtrnplexitr. ol ' t l ie st ini_rr l i l ( l larke. 1990). Sire ", , , , ,k1 .,o, i , l rore letterstrc,ross t l ie lr idl ine l l shape tr l_r\ or o_a) brftnot bv naure (. .1-rz) (Flviatru.arrr l Zaiclel. 1994).5 l r e r . o r r l t l ( ( , r u J ) i r r e p r i r r r i r n r r r i o r s o r s l r i r d e s o l .colors I rehleer r I l re hvo I rer r r i l ieids I rui orr lv rrJ rerrI t t t t r r t r a r r t , , e u i r . r r r o t e r ' l r r i r l r \ \ e e r n s , , r , r l 2 a i d * 1 .t t r r p r r l r i i s l r e r l t l ; r t i r , . F i r r i r l l r . s l r e t . , r r r l r l r r l r l t . l rac'ross the tn'o \rFs trvo f,rc:es r,,.ith iclenticalvie'u's but not uitL rotated r.ieu,s (\\'eerns and

Intriligator et aj. (19g5) reportecl a pattenr.sinii lar to L.ts.'s in A.C.. a paiient ."r.ho ha,l ,,Ies ior r o f t I re poster ior t l r ; rd oI ' h js C( L He t .orrh lnarne unilateral or bilateral stinruli in both Vl-sranging irr cornplexitl'front sine w,a,,.e gratingstr r l ru 'es r rnr l objects. He <.orr ld r r9t . l rgrver t , r ,cornp:rre (sarne-diflerent) tlie sanre stirnrrliacross the vefticill meridian, although lie cou.klcompare theni within either VF. Tliis inrpliestliat interhernispheric transfer for visual cr:nr-parisons ancl for naniinq is carried out bv rljf.

)I

r i

/l r

Zr i i< le i . r rn l t r r l r l is l rer l < l i t ta) . Thrrs. she secrr r t , r l

l,r]"b]: to transler person identitr ,,,ul,.r. \\r,j,,un

take N.(1.'s transfer to be autonrrrtic arrrl rrnc<r,r-scic_rus ( correct saure-<lifi.erent .jr rrlgr nent but rroirlerrtification) ancl thus identifil tlre infur,,,,ni,,,,-proces.sirre locrrs ol uttentior/consc.iorrsnt,ss. ItrN.(1. t lrat l<tcrrs is rlr ite late or t leep.

DOUBLE D ISSOCIAT ION BETWEENLEFT HEMI -ANOMIA ANDCROSS-HEMISPHERE COMPARISONS

The hvo classic,al snrptonrs of the cliscurrner,-tio' sr'dr.rr'". un,i,"li.. LVF .rrrrria ,;,Jlli_uli' of <,ross-integration across tlre ,nl,lliu". fr,,,sliriw <louble clissociation in the chroni" ,.,r,A,-tion. On the orre l iancl, L.B. "au nour" ,,r,,,,,I,\'F pictures. letters, or words without beuioable to rnake sarne-clifferent i,,da,nent, olrrrlthe same stiniuli acrclss the r'e,tl..al ,rr".i,ti,,,,(see RII speech). On the other harrd, N.Q. clrrt t t i tk , ' r r ( t . r r rate s i t r r re-d i f fer t , r r i ; , , . . tg , , r , : , , i . ,abou l r i sua l s l i r r r r r l i i r r t l r e h r o , i " , n l - 1 , ; , , , , ; -f ields, without being able to un,,r" t lr" ,n,,,"stimuli in the LVF.

It is inrpoftant to notice that neither rrris-narning of LVF stinruli alone nor lailrrre atc.ross-rnatching alone is sufficient to establislic,onrplete disconnection. For ""urrrpl".,.r,,rr_rnatching nar. fail in the abserr"" nf ,lir.r,,,-r ret ' t ion I ret . i r r rse of a tet r r ler r r . r to l req]" , . , , , , , , .l r e r r r i f i e l d u i t l r I r i l a te ra l p r " r "n t , , t i u , , , , , , : , ,u'hile accurate verbalizing of lVf stirnrrli i.presen'ed. (ionr.'erselr,,,,,erbaiizing of L\.1-stirnuli nray fidl in the absen"" uf ilir.n,,u",l-tion. rvlit re crross-nratching is presc,nt. bec.atrsethe tralsferrecl cocle rn"u L" sl clegrac.lerl rr-s krbe sufficient onlr. {br visual pattern lratc,hinqbrrt not for stirnulus iclentification

T H E C A L L O S A L S Y N D R O M E S

l'erent callosal channels. the forrner rnore pos-terior than the latter.

IMPL IC IT TRANSFER

\\'e define interhemispheric transfer in thesplit brain as being hnplicit if both verhaliza-tion of LVF stimuli and cross-matching on de_rnand lail ( i.e., disconnection is present). butthere is nonetheless some automitic influenceof the unattencled stimulus in one VF (the dis-tractor) on a conscious decision ofan attencledstirnulus in the otl ier (the target). Given L.B.'sand J.\\r. 's abil itr-to narne some LVF picturesor rvords (see RH speec,h) and N.G.'s obiLt t.,c{)nlpare s}rapes across the vertical nreridial,tlte preconditions for irnplicit trans{'er rnar. r}otbe satisfied and nav nercl to be assessed foreach task and patient on a case-brrcase basis.The canonical case for irnplicit prinring irr tliesplit brain r.vould require (-/l eridence for i'ail-ure of explicit transfer, lZ) infornration aboutpriniing within eacli disconnected hemispliere,anrl 3 evidence fcrr signific.ant prirrrir ig he-tu'een the disconnected hemispheres. \\'e rnar-even require converging er.idence from thenonnal brain. Several examples of allegecl irn-plicit priming follou,.

Lambert (f993) sliowed presurned negatiuel,triming of rt RVF target br a L\-F prirrre in irlexical categorization iask in both normal sub-jects and L.B. Hou'ever. this result arvaits con_lirnration because the targets that shovvetl in-lrrbit i<,rn u'ere different frorrr t lrose tlrat did not.anrl various control conditions \vere notreported.

Iacoboni ancl E. Zaidel (lgg6) used a later_alizecl lexical decision task with simultaneousbilateral stiniulrrs strings and witli unilateraltargets cued pefiplierallr,. Norrrral subjects ex-Itibit three clistinct distractor effects oi a letterstnng in the unattencled iield orr the decisionrtl the target in the attended fielcl. First. therets a _lexicalitq prinring t,7ft:ct. sucli that uniit-tettde<l vvrlrd distractors enliancc. decisiorr ofrrclrcl targets reliltir,e to urrattended norlr.vortlt l is t rat tors. espt , t . i : r l l r i r r t l re LVF i l r r<.ohorr i i rnr lZai t le l l996 ' . - f l r is

t , l fer . t pers is ts in t l re spl i tt r r l t i t r , L .8 . r i t l t l r , r r r g l r i t i s r r r t . d i a l ed l l d i f i e r -ent su l r t 'a l losal r . l r :ur r , " ls rZai r le l . l9g- l r . Set , -

385

ond. there is a bilateral ioss that is selectir.e {irr'uvords, i.e.. lexical decision of unilateral u,ordtargets is more accurate than of u.ord targetsacconrpanied bv dffircnt u,ord or nonr,'orcl ilis-tractors (Iacoboni and Zaidel. 1gg6). This ef-lbct is absent or dranraticallt'recluced in tliesplit brain (L.8.). Third. bilaieral presentatronof the same target speecls up RVF clec,isions ofr.r'ord targets in normal subjects (Nlohr et al..1994) but not in L.B. (Nlolir et al.. lgg,tarTaken together. the results suggest that thesplit br:Lin prevents the norlral inrplic.it slrar-ing oflexical resources behveen the hvo herrri-spheres, but nonetheless perniits irnplicittransfer of postlexical clecision codes.

\\reekes and E. Zaidel t1gg6) used a r.ersiorrof'the' Stroop task with spatialiv separate colorpatches and color r.r'ords and witli unirnanualrather than verbal responses. The spatial sep-aration pemrits a coniparison of the Stroop ef-fects u.ithin and bet'uveen tlre lienrispher"., onclunirnanual responses (pressilg one o{ t lrreekevs) penlit probing of either lrernisplrere.Both the spatial separation and the rrnirlanrralresponses dilute the Stroop effect but clo noteliniinate it (\\'eekes and Zaidel, 1996). BothN.G. and L.B. showed significant Stroop ef-fects u.ithin ancl between the hernispfieres(Za.del,1994; Weekes and Zaidel. unpublishecldata) .

Complex implicit facilitatory ancl inhibitonsubcallosal eflet,ts oc,cur irr <.overl orientirrg ofspatial attention using the Posner pariicligm o{'cueing in SRT (see Attention. above).

Finallv. perhaps the rnost drarnatic exampleof impl ic i t t ransler i r r t l re spl i t br idns is t l re err -liarrcecl redundant target effects (lnper-RTE )in SRT and choice RT (see Attention. above).Sorrre callosal patients shou. co-activation of cle-tection or identification o{'unilateral tilrgets bvl r i l a te ra l r , op ies i r r t l r e o t l r t ' r VF . r r r r r l t l r i s l i r i l sto occur in tlre rrrirltirl brail. It appears thatt l r e CC no r r r ra lh senes l o r r ru t l r r l a te o r i r r l r r l r i tsorrre of t l iese autornatic interactions.

In sunr. cornplete cerebral corlnuissurotolrn.r t l lous expl ic i t r rnd i r r rp l i t . i t t ransfer r , l in fo i -nration about klcation. orientation. size. anclllor.'ernent through the collicular visual s'n'stenr.T l rc le r r re l r r rge i r rd i r idr ra l d i f ferent , " . . I 'nr , -ever. in tl ie transfer of objec,t (shape) infonnil-

386

tiorr. (lcl lor infi lnnation is least l ikelv to trarrs_Ier. Response codes irr t. lroir.e tasks car alscltransl'er. er,en for abstrac,t tlecisions. Sorrre se-rnantic. especirrllv ii{Iectir.t . inforrnation c,rmtransler. ' f l ius,

it is trrit ic,al I irr t lre investigatorto assess tran.sfer belbrer rrreasrrring herni_spheric c,onrpetencre along sorne expeirrrentalvariable in tlre rl isc.orrnec.tetl lrernisli l iercs on ac'ir.se-lx-cirse basis.

PARTIAT DISCONNECTION

Tlie efl'ects o{'pilrtial disconnection are not r.,etcrirnpietelv lllrderstood. Sorrie crrnflict existsbehveen the sr-nrptorns ibilouinq surgic,al dis-connection and those follor.ving clisconnectiondue to traurnatic or cereltrovasc,ular acciclents.Sr.rnptorns tend to be nrore drirrnatic u,ith nat_ural lesiolrs. perhaps becarrse o{ associatecl ex-tracallosal darnage.

Anatomical (Aboitiz et al.. l9g2). phvsiolog_ical ((lhen. lg86), and beh:iviora7cllnical clata(see belou') suppoft the r.ierv thiit tiie CC con_tains rnoclalitr-. nraterial-. ancl lirn<,tion_specificc'lrannels {br conrmunicatiorr and corrtrir l t l iatinterconnect honrotopic, regiclns in the tr.vocerebral hernisplieres f Zrriclel et al.. 1990:Zaidel and Iacoboni. in press)(Fiq. 1,1_2). Theanteroposterior arrangenlent of t lrose channelsrespects the anteropostetirlr rrrrangentent oftlre corresponding cortical regions: gcling in ac'auclal-rostri i l cl irectiorr the'spleniuni' inter-c'orrnects ', ' isual cortices. the isthrrrus probablr,irrterconnc.cts aucliton. cortices and superiorteuiporal bbes, t ite posterirtr rnirlbodv inter_connects sotnatosenson- crrrtic.es. t lre arrteriorrnidbodv interconnects niotor cortices. ancl thegenu interconnects fronta] cortic,es. Aboitiz etal. (1992) compared tl ie rnrrnber clfsrna]i un_rnrelinated fibers that predoniinantlv inter_connect associiition cortex writh thc, nuntber o1rnvelinated fibers that predominantlv inter_( o ru re ( . t sens ( ,n r r ro lo r t . ode r . T l re i l b r r r r t lt 'or r rp lerr rerr tan r l is t r ihut ions f r r r t l re h"" h; . ;of fibers: srnall fibers predrlninate,l ;r, nrrte.icr.irncl posterior ciriiosal regions, u4rereas largefibers predorninated in tl-re posteri,,. nrl,jb,riil,ant l Io<.a lh in t l re poster ior sp lerr i r r ru. Assign_rrrerr t o l ' t . i r l los i t l t . l l rnnr , ls to s1let . i f i t . tasks l r i rsbarell been attenrptecl. []larke arrrl E. Zaidel

C L I N I C A I - N E L ] R O P S Y C H O L O C Y

(199.1) e.rplored tlre r,onjc.cturc (Galaburrla etal., l9g0) that t lte c.onnectiritr,of callosal chan-nels,is invt rseli progrrtional to i lre asynlrnetn,of the rno<lule that t l iev intercrlnnect. Us

'

botl i aratornicil l rrrorlrh.nretric, i,allosal,rrl] lsrrres and lateralize<l beliar.ioral t lnta in norrnalsubjec,ts. t lrev c,ont,luderl that lerical acc.ess rsltrocessecl irr srrperirir_posterior ternltoral re-gions that interconnect througlr t l ie isthrlus,rvhere:is phonetic perceptiorr is processed 111frontiil regions tlat inteicrrrnec,t throrrgh theanterior clillrisrtrn.

THE ANTERIOR COMMISSURE

Pirtients with c,onrplete callosotornl. sparing tlreanterior cornniissure are sairl to exlribit a [e;,_eralizecl but not the r.orrrplet" , l ir"nnn".i inusrnclrorrie (Sidtis et al.. tSStbt. Thev exhibitsornatosenson' auditon,, and, usuallr,, brrt nor,tlwavs. risrral rl is<.onnection. Lr,lt ir",;;,alexia,4rernianornia rnar. (Risse et ai.. lg7g) 9rrn: i l 'not (NlcKeer-er et a l . . lgg l )be present .Thev do not r'.xhibit olfacton, rlisc,onneciiorr(Risse et a l . . 1989).

DiVirglio et al. 119g9) {bund irrterherni-spheric inferoternporal iincl occipital pro.jec_tiorrs througlr the anterior cclnrnissure i lr i lr-rnans and srrggestetl thrrt thev rn:1.. mediatt,risuosenrantic inforrnation. Incleecl. I_aura_(lrotto et iil. (subntitted) describe a ca.lloso_torrrv patient. NLE., rvith a right prefrontal ie-sion u'ho rvas unable to read L\F rvords butc,ould narne sorne LVF pictures iurcl rniike se-nrantic decisions about LVF pictures. The au_tlrors attributed these .srtrptonts to risuose-nrantic transfer r.ia the anterior corrrrnissure irra patient u.ith LH speech.

THE SPLENIUM

Conrplete section of the spieniuni is necessan., r r rd suf f i r . ient f t r r r isr ra l d is t r rnrrer . t ion r \ tas_pes, 1948), but herniiinomia or herriialexia arenot invariably present. The splenium appeanto contain several di{Ierent channels. The pos-terior spleniurn rnav trans{'er nonr.erbaj risualinlorrnation, whereas the anterior spleniunrr nav transfer verbal r,is uai i nforrnation I Dania-sio and Danra.sio, lg83). The po.stenor sple-nium (and genu) lva.s severecl irr a Japanese pa-

T H I C A L L O S A L S Y N D R O M E S

c. CallosalSubdrvrsion

A Anterior third (rostrum,genu. & anterior body)

AB Anterior midbody

PB Posterjor midbody

I lsthmus

S Splenium

Figure 121-2. a.ll Scherne frrr paftitiorring the midsagittalcross-sectional area ol tlre lrurnarr urrpLrs callosurn'\\'itelson. 1989). B\\'. rninimunr bodl width: L. totalanterior-postcrior callosrrm length; S\\'. rn:xirnrrm splenial*rdth. c: Putative topographic relationships between fir.ecallosum subilirisions and corresponding coftical regionsare based on findings frorn the rhesus monkev ( Pandva an<l

CorrespondingCortical Region

Pref rontal, premotor, supplementary motor,poss ibly a nte rio r infe rio r parietal

Precentral, possi bly m i dtemporal

Postcentral, posterior parielal, possibly mid-temporal

Posterior parietal, superior temporal

Occipital, inferior temporal, ventral temporal,superior parietal

Sel tzer. 1986) and human (c lc ' Lacoste et a l . . 19E5). , .

Italicized cortical regions repr{.sent pott ntrallv positivelindings in the hurrran that rvere not lbund in tht'rhesus

rnonkcr'. Positive {inclings in the rhesus monkev were notIirund in tht' human case studied bi, Degos et al. (19E7).(Adapted from Clarke, 1990.)

387

tient u'ho attempted suicide u..ith an ice picli(Abe et al.. 1986). Tli is resulted in a more se-vere left henriaieria fcrr Kzrna (phonologicais('ript) tharr for Kanji (logographical script).Cohen and l)ehaene (1996) described :i patient\\'itll an infarct in the posterior lialf of the C(1.There u'as a <lisconneciion for Arabic digits anil{ilr nuurerositv but transfer fcrr apprirxirnatt:t r r t q r r i t u t l e o f t l r e t l i q i l s ,

THE ISTHMUS

Section of the isthnrus of the (lC usuallv'AL ' ra l r rL , r r r nd \ \ ' i r r r e r r . 198 \ ' l r r r t l r o t a l \ \ . a \ s,S r rq i sh i t a e t r r l . . l gg5 r resu l t s i r r a r rd i l on , [ i s -( ( ) l l rec ' t io l r . TI r is is l rest derr rorrs t rated lx tL

rnassive right ear advantage (left ear suppres-sion) in dichotic listening to stop consonant-\.ou'el svllables (see Audition). The anteriorspleniunl mav srlbsen'e auditon' ilterhemi-spheric transfer in sorne subjects (Sugishita eta l . . 1995 ) .

THE BODY

I-esions in tlie boclr. of the CC often result innrore or l"ss ser.eie tac'tile or ulotor cliscon-rtec't ion (Jeeves. 19791 Berit in ei al.. lgE4;\Iaver et al., 1988). Tacti le discxrnnection con-sists of failure of interhenrispheric tactile trans-f'er and results in ieft hand tactiie anonria. Sec-tion of the anterior bodv mai,'result in Lrft hand

CONSCIOUSNESS

Desc'artes t164g) bel iel.ecl t l iat t l re specialstmcturer for consciousness slroulc] l te . . in

t l reni idcl le," "n'est

nul lenient le c.t leur. ni arrssi tr irrrle c'en'earr, nrais se,rr lernelt la pl l is int6rieurerle ses part ies. qrr i est rrrre c.eftarrre glancle lbtpeti te, si tu6e r1ari .s l t t nt i l iert cle sa 5r11151i11i6.s."lernphasis irclcledl. [" i t is neither t l ie heirrt nortJre errt ire cerebmrn. but t l ie rnost interior ofi ts parts. rvhich is a cerlain ren-sriral l glancl si t_rratecl in the rrr iddle of i is s,rhsia,rt .e

"] N-o srrt .h

rnidl ine struc,ture. lrolver.er. exists (the pituitarv: r n t l p i r r e ; r l r r , , l o r r q e r l r e r r r q t . r . , . , L b l e r . i r r r t l i -dates ).

Eac'h discorrnected herri isphere. Dossessesttot onh a separ3te selson.-rrrotor lnterfirccwitlr the enrironnient. its orrnr perc.eptua.l,nrnestic. cognitive, and linguistic repertoires,brrt also a distinct personaiitv anrl distinct feel_ings. as well iis chtrracteristic preferences anclt l i s l i kes r la i ' , l r l . I99 ,1 , . T l r r rs . t l re hvo l re r r r i -splreres l iave sirni lar. but not iclentical. con_cepts of self, past and futrrre. farnil,,.. social cul_t r r r e . a r r c l l r i s t o n . S p e r n e l r r l . r I g T g r s t u c l i e r ltlie reactions o1' the hvo ciisconnectecl henii_spheres of L.B. alcl N.G. to pic,trrres of self .r e l a t i r e s . p e t s . r r r r r l l r e l , r n g i n g s . i r r r r l o f p u b l i r . .historical. anci religioris figures and person,ili-t ies [ - ro r r r t l r t ' en ter ta i l r r r ren t u r r r ld . T i re r fo r rnd

3BB

iipri l l i ia to rr.r l tal cor.rrnranrl (see above). Sec,_t ion ol the posterior. l tot lv rtrav result in lei tl r i r r r t l r rq l r rp l r i i r .

ANTERIOR CALLOSOTOMY SPARI NCT H E S P L E N I U M

Srrrgical sec,t ion o{ ' thc, anterirtr hvo_thircls o1'the CC nliil'par"adoxicalh. result in f-evr. or ncrr l i s r . o r r r r t . t . t i o n s v r r r p t o r r r s . . \ r r t l i t o n d i s r . o n n . t . -t i o r r r r r ; r r l r l p r e s e r r t , l e p t , r r r l i r r g , r r r t l r , , p o s t e _rior extent ol the lesion. Tl ierre nlav be nl i l ( lr lef ici t in birnanrial coort l i rrat iorr arr i i rr tact i leor ltotor transler. Nlernon for neur r,\rents nta\,i t ] s , r l r e i r r r p a i r e r l , ( l o r r l o n . l g g ( ) r . T l t i s t . o r r _trasts r,rritlr natural lesi<ns to tliose pafts, rvhichlnav prevent (fross-lnodal associations ancl mar..r , ' s r r l t i r Ie l i r r r r i la te r - i r l aqr i rp l r i r r i r r r r l i rp r iu ia .

C L I N I C A I N E U R O P S Y C H O L O C Y

a clrrir.acteristic sociill, p<llitic,al. personal, an(lsell-au'areness roughh co,nparalile in the hvosirles of'the siune subiect. l lr lrvever. Sclriffer etal t1998) probed r)rore cleeph into the p51_c:l ioloqicrai status ol the trvri lr",,, irph"."i ,rtL.B. and A.A. and li lrncl that ther lrrive differ-errt perspectives on tlre u,orlt l. especi:rlh. w,it lrregard io self-irrrage and clri lr lhorxi ,,,",,,,,.,er.Inlbnrial testing (E. Zaidet. rrnpublishecl datalsuggests that the DRH lias a rather conver)-tional sell--inli ige ("super ego"). ahrr kl I i l laffinitr' lbr conventional scenes anci stereohp-ical conc,epts (D.\\r. Zaiclel. tggOa: see Nlerrr-on' . above).

. The experience of clreams rnav be alfecterlbv comnrissurotornr, '. E. Zaidel foirrrcl that N.(lanrl L.B. {ronr tlie l,os Angeles series rlo norreport dreams (unpublisliecl clata). but Greerr-.,voocl et al. (1g77) {buncl nornial clrearn rerlortin sorne callosotoniy patients fiorn tlie ljart-nrouth series. Hoppe (1977) intenierved 12('ornnussurotornv patients and fbuncl that theirclrearns lacked conclensation. displacernent.and srlrbolization, ancl tliat their firnia.sies iver"rrnirnaginatir.e. utilitarian, anrj tiecl to realihTl re i r sr r r r l ro l izat i r r r rs \ \ 'ere ( .on( . retc . r l i .cr r r_sive. ancl rigcl.

Eaclr lienrisphere can adapt to nerl, sitrru-tions and solr.e cornplex reasorrrnq proll lerrrs(Zaiclel. 1981: Zaidel et al., Iggl). Af'ter sorrretesting experience witli p:itients. exalrinersspontaneoush, refer to the hvo herriispheres asif they were distinct people, e.g.. .,t lre

LH rvirsupset at t l ie RFI responses toclav." \\ 'hi le srr<,hrelerences nriiv be regarded as shofthand lirrpattenis of behiivior u.,ith specific lateralizetls t i r r r r r l i ar r r I responses. t l ter l ronet l re less exnr , , rsa strong phenomenologicai sense o{'hvo ro_existing strearn.s o{' conscictusness. Both herli_spheres can probably be sirnultaneouslv antl jrr-dependent l r ( r r r rsc ious: I roth carr s i r r ru l tarr , , -or.isll' possess conflicting wills so that tlre splitbrain can exhlbit hvo distinct, and possiblv irr-cr r r r rpat ih le. lo<. i o l r r rora l responi ib i l in ' lncohoni et r r l . . I g96rr ; hrr t see \ l l r .Kar rut t lNIacKav, 19f12).

Recognizing that the DRH is conscious pnr-r i r les i rdr l i l ior ra l er iderr t .e l l ra t langrrage is r r r r tne( essan for l r r r r r r i rn r .orrs t . i t r r rsr res i . \ l r , re u l r .portiint. using the split brain as a rnodel for thenormal nrincl. a nornral inclividual's cons('ious-

T H E C A L L O S A L S Y N D R O M E S

ness can then be r'ierved irs the net result o{'aninteraction anrong at least two distinct states ofconsciousness. The question tl.ren arises ulll'the nclrrnal person witli trn intact brain experi-ences consciousness as unified ratlier tharrdual. Spern' reasoned tliat normal conscious-ness is a higher ernergent entitl'that transcendsthe separate a\\'areness in the corinected LHanrl RH, supersedes thern in controllingthought ancl action, and integrates their actir'-ih. Instead, we argue that normal conscious-ness is also dual, u.ith paftially separate paral-lel processing in tlie hvo hernispheres thatsonietirnes results in subjective feelings o{ con-flict. This implies a dualitv of the mechiinismsfor consciousness (Bogen. 1995a, 1995b, 1997.2000). lvloreover, sorne nonnal subjects behar.elike split-brain patients during lateralized tests.thus demonstrating spontaneous rtr c\narrricl u r r r { i on r r l d i s , . onn . , . i i , , n r l a t . o l r o r r i e t a l . .I 996a).

I t tar r l le argrred t l ra t t onsr . ior rs l ress presup-poses adaptive problenr solving ancl complexcognition. anci that. otlier tliings being erpral.rnore complex cognition entails greater cou-sciousness. Since the CC is important for mocl-u lat ing r 'oqrr i t ion te.g. . \4 'eeke. rurr l E. Zai r le l .1995a,b. 1997). it follorvs that consciousness inthe unified brain is different frorn the sum ofeach consci<tusness of the hvo disconnectedItenrispiieres together. The normal CC permitshernispheric dorninance bv callosal inhibitionas rveli as interhemisplieric interaction bv cal-los i t l lar . i I i ta t ior r . Th ' r i . t l re c .ogrr i t ive reper lo i reo{'the r.rnified brain is richer than tlie.^suni ofthr: c'ognitive reperloires of the trvo cliscon-nectecl hemisoheres.

It is noteu,orthv that the hvo chronicalh.'clis-t r r t t t tecter l l rer r r isp l reres ger r r r i r lh do rot e i rg i rgei t t , r ' r 'd c 'orr l l i r ' t . T l r is rs p i r r l l r erTl r r i r ret l l , r ' t . lur r -ac'tt:ristic, RI{ passirih. LH ckintinanc'e. trncl attttilied svsterrr of rn<ltrir control. as u,ell iisrltarr:cl subcortic;rl stnrctures. I nterrrritntrirl cr rn-flict lras usuallr.beeri ollsen.ed in tlie acrrte staqef - t lI ( ) l l ( ) \ t i r r { s r r rq t t . l i l r [ i sc .o r r r re< . t io I r ru r t l i r r p i r r l i i J(ltsc()nnection chu. to natura] lesiorrs. as in casesof tlre alierr (anarc,hic,) liarrtl srrrdroure. Hou-cver . even in t l re t . l r ron i< . s laqe rve o l te r r e l r -trlttnter LH rlisbelief of intentional RII cnitout.

I r r s r r r r r . e i u . l r r l i s r . , r n r r t , t . t e r l l r t , r r r i s n l r e r c i s r tt t r o l l l ] , , f i r u l r , r l " l r n r i r r . t . o r r r n l e l , , u i t l ' r e r t n . -

389

sentations of t lre self and of the enrironrrielrrand the perceptual--cognitive repertoire to nia-nipulate tlierri. Eacli disconnected henrispliereis also separatelr- conscious. Hou' and u4reretheir separate sets of c.onsciousrress are inte-grated remains a niajor chtrllenge for cognitiveneuroscience. Especiallv prornising is a re-search progratl) airr-recl at characterizirrg theseif-concept in each disconnected (iincl nor-mal) hernisphere and discor.'ering liou'the in-teraction of the hvo gives rise to a r.rnifiecl in-diridual self-concept.

NOTES

L \\'herr rvc actually read Lr Beau. rve lind tllrt tht, rt'stof his sentence is "but this, in anv casL'. is insrrfllcicntto perrrrit rnore than a clinical suslticion of localizutionirr the CC. Most of thc tirnc. thcre is nothing of thesol1'' (p. 1370). And on the vt'n first page ol his exten-sirt afticlr', Lc Bem savs. 'Tht c.linical diagnosis o1these turnors is hartllv possible. lrer.turse the'rt is no r.al-krsal smri ronre ' 1p. 1365). Fi r ra] l r ' . in h is surnnran' hestates. "in

particrrlar thr.rr. is n,r clrrr.rc.teristir' rrtr.nt;rldel lc i t and no apr ix ia" ip. 1381L

REFERENCES

Abe. T.. Nakarnura. N., Sugishita. M.. Kato. Y.. andlu'ata. l\I. (1986). l'artial disconnection sr.n-r l r , , r r r t , f r , l l , , rv inq penet ra t i r rq s t ; rh w, , r rn t l o f lh , ,brairr. Err. Neur. 25:233-239.

Aboit iz, F.. Scheibel, A. B.. Fisher. R. S.. and Zaidel.t . (1992). Fiber cornposit ion ofthe hrunan cor-pus cal losurn. Brain Rcs.,598;143-15i1.

Agliot i . S., Tassinari , G.. ( jorbal l is. NI. (1.. anclIlerlucchi. (;. (2(XX)). Incornplete gustaton lat-eralization as shown bv analvsis oftaste cliscrinr-ina t io r r a f te r t a l l , , s , , t , , l t r . . J ( ' ( tgn . . \ i r rn , * r ' i . .12:238-215.

Agliot i . S.. Tassinari . C].. Fabri. \{ . , Del l ' t sct ' . NI.,

Quattr irr i . r \ . . Nl i inzorr i . T., ancl Be.rhrcchi. (1.

{2001 ). Taste lateral iw* ir the spl i t l tair. Eur INeurost ' i . , -1,3: l- t .

.{ .kelait is, A J (194.1-45). Strrdies orr the crirprrs cal-Iosurn. lVr l) iagnostic dvspriuia in epi leptics frr l-lorirrg parlial an<l c<rrnplett, section ol thr cor-

1'rrrs callosrurr. Arrt. J. Psycliutry l0):591-599.Alexandt'r . \ ' { . P. and \\ 'arren. } i . 1,. (19E8). Lrx.al-

ization ol callosal autlitor-u'pathrvavs: a (lT casestudr', Nt rrrrrlogrT,}6:802-80,1.

A l l rson . J . D . , \ {eador . K J , Lor ing . D. \ \ ' . .Figueroa. 11. t l . . and \\ i r ight. J. C. (2(X)()). Func-tional MRI ccrelrral ac'tivatiorr irn<l rlcactivatiol

390

< l r r r i rg l r r iqc r r r ro r . t , r r r t , r r t . \ ' n t ro log t151: I35t-12.

Al l isorr. ' l ' . . arrt l Zldel. l l . i l (XX)). Oornpletc trrr i_rnissurotornr. abol ishes interhrmispheric olf i rc_trrn' transfer. J. Ir f t . \ ' t t tr t t1t.st lclrol. Srtr. . 6:17l).

-\ l1ters. 13. J. ( lgj l6) Tlte rnt,nt:r l srrtr lrorne of trrrrurrs( ' l l l r ' . (1 ) r ' l ) r t s , . l r l l , , r r r r , \ r i , / , . \ ) r rn , l . p .s ry , . l t i r t -f r rT ,3 .5 9 i l -912.

Arnant l . l ) . (1 . . lnsar rs t i . l l . . a r r r l Crxv : rn . \ \ ' . \1 .(198.1). The conrnrissrrr ir l crrnnt,ct ions ol thenronkev hippocarnp:rl lirrmatiorr. J. Conp. \teu-ntl . 221;:)07 :): j6.

Aptrnan, l \{ . . I-erin. I l . . anrl Sent, l ic,k. t i . [ ] (1977)..,\le.-ria r.rithout agraphia in a left-hantl:cl patientri.r th lrrr rsopaqnosi a. \i,rr zrlr t gr 1 27 : 53,J-�i36.

Arguin. M.. l ,assorrde. Nl.. errattr ini . A.. I)el Pesce.N{.. Foschi. \ . , anrl papo. l (2(X)0). Dir. icled i .r_suospatial attention s\..sterlrs with total and itnrr_ri<>r cirlloscrtor tv. N eu rop s t l r:l t t ilo gi a 38 : 2g3-2g 1.

Baie.r l . I ' . . Ft irster, Cl., FirrJel. IL. Naegele, \ ,L,Fink, U.. and Kenn. U' ( lggE). \{agnetic reso_rrance inraging of norrnal and pathological u4ritern atter I n atr rr2ltion. ped i a tr. Ro d k, l. I B : Ig3_lgg.

Banks. (1.. Shoft. P.. M:rrt incz. A. J., Latcharv. R..Ratcl i l f . (1.. ancl lhl ler. F- (19S9). The Alierrhancl snclrorrle: clinical ancl postrrroftcm fincl_irrgs. rlrr.l. Neurol. 16:l\6_15g.

Barbize't . J . Degos. J. D.. Leerrne. A.. anrl Lerol, . A.( l ! l7E). Srrrdrorne, dr. r lrsr.,nrr<,t ion interh6lr i ._ph6rir lue nr..", l r ,rp., ,-* i . . t l iagorrrst iqrre anc()rtrscl une rrralatlie de \{archufava_l3ignarni. }ler..Neuni. (Pans ) I . :31 i1l_7\9.

l larbizet. J.. DLrizabo. 1,. . Rouchtrrt , ine,. A., l )egos.J. D.. anrl Poir ier. l . ( jgi1). . \hnlgi r le \ :ett_rttp.sqt:lnhtgie. Paris: Nlassrtrr.

lJarrett, T. \ \ ' (1969) Strrt l ies of the frrrrc,t ion of th.arrvgclaloid cornplt.x in f[ru.aco ttntlattu. Nett-r , , l t r r l r . l t , t l , ' , : i t t l ; l l . ) .

Bar les . K . . E l iassc ,n . J . ( i . . l , r r t scp . l l . L . . a r rc l Gaz_zaniga, \ l S. (1998). \{o<lular orgirnization ofcogrri t i r t s\-stenls tnaskecl bv interhernisphedr.inteqration. St'ienu: 2t0 :902-905.

Barnes. K.. Frrnnel l . NL (1. ancl Forvler. ( i . A.( i994). I lcmisphc.r ic coltr ibutions to the inte-gratiorr ol r..isual and aucliton, ir:firrrnation irrslreet.h pert.epl i ln. Pen., '1tt p*yt. l t , ,1thys. 5, i .633_6.11

Biivnes. K.. ancl ()az.zaniga. VL S. (20fi)). C.allosalclisconnectiorr. In Patiutt-Basul Appntaclrc,s toCognitit:e Ncunt.scienct:. Nf . J. t'arah and T. E.Feinberg ieds.). ( jarnbrir lgc. M.{: \ I IT press.pp. 327 rl3:l

Bar,rIes. K., Trarro. \ I . J.. Reeves. . . \ . G.. arrd Gaz_zaniga. \L S. ( 1997) Isolat ion o{ a r ight herni_sphere c'ogrritivt' svstem in a patrent rvith anar-

c t t N t c A l N E t . I R O P S Y C H O L O c Y

clr i (al ien) l tarrcl siqrr. . \ 'utrrryt.sr l t . lnloglzr r-: l I5!fI 173.

Bearclsrvofth, !1.. antl Zaidel. I) \ \ ' i l ! )94r. \ t t .rrr-on'tor f i lces in epi lcpt ic chi l t l rerr befirre arrt l ; i l ,ter rrni latcral. tentporal lohec,tontr. . / Ol ir t . I : . t l tIatroTtlrlclutl . 16 738-7.15.

l lert in. S.. Sahar. -{. . antl Nlosc,ori tch. \ .1. l l9E,l). In_tcrhern ispht 'r ic ' inl irrrn:rt ior i trarrsf er irr patjent.\uith lesions in tht ' trrrnk o{ ' the crrrprrs . , , ,11,,r, , , , ,\ et t rops q r.:holo gia 22 : GlI 6 | L

I lenton. A. L. (1962). The r. isual rr.r tention test as acorrstrrrctional praxis task. Ctnfin. Nutrol. !2,r + I - l D D .

Renton. A. I- . (1967). ( lonstnrct iorral apr- iuia and therninrrr hernisphere. Confin. \ ,eurol. 29: l_16.

Bentorr, A. L.. ancl l ,-ogel, \{ . L. t1962). Three-dirn ension al c'onstmctional ltrti-ri s. A rci. lierr rrr1.7 :j17_351.

Berlucchi, (1., and Aqliot; . S. ( ig9g). Inttrhenrr_spheric clisconnecton smdrorne. In Hanclbook ofClinir:al and Eryterimerrt al N utn ryt.s.r1 chrilo 91. C.Denes and L. Pizzartiglio (eds.). psy"},1,1,,OPress. East Sussex, pp. 6115-670

Berlucchi. Cl., Aglioti. S.. \{arzi. C A . anrl Ta.ssr-nari . (1. (199,5). ( i rryus cal losrrrn ancl sirnplt ,\.rsuornotor integr:rtiorr. \, eu n t7 t.s.r1 c lut kt gia ;).3.923-936.

Beukelrnan, D. R.. Fklvers. ( i . R.. anrl Su,ansolP. D. (1980) ( lerebral cl iscorr lect iol associaterlu, i th alte'r ior connnrtnicatirrg arten, Anelln,srl l :irnplications fbr e'valuation of svrnptorns. Arry'rPhy.s. trIed. Rclmbil. 6l:lr;23.

Bogerr, J. E. (1969a). The other side o1'the brain. LDvsgraphia ald clvscopia follotirrg cerelrralcorrrnissurotonl�. Rull. Los Angeles Neurol. Soc31:i3.�105.

Bogen. J. E. (I969b) The other side of the brainII: An appositiontil rnincl. Bull. Loy ,\ngelc.s Nu.t-rol. Sot:. 3.1. t35-i62.

Bogen. J. E. (1976) Language f inct ion in the shortterrn fbllorring cerebral corntnissurotornv. InCurrent Trends in :,r"euntlingui.stic.r. II. Avahan-\\rhitaker and N. A. \\'hitaker (ecls ). Nerv york:Acaclemic Press. 1'rp. fW-221.

Bogen, J. E. (1977). F-rrrther disc,ussion on spl i t-brairrs and hemispheric capabilitics. Br. I

phitSci. 2B:28I,2!J6.

Bogen, J li (1979). A svstematic qrrantitirtir.e studlof arrornia, tactik' cross-retrieval and verbalcross-cueing in the lone ternr f<rllorving completecerelrral cornmissurotoml'. Inrited adJress,Acadernv of Aphasia. Sarr Diego.

Bogen. J. Fi (1995a). ()n the nt,rrrophvsiologr.ofcorrsciousness. Part l: Or.e n.ieu . OonscionlCogn. 1:52-62.

T H E C A L L O S A L S Y N D R O M E S391

Bn<rn. S.. arrcl Jedrnak. (1. P (19;5) [ ts Tnnit lcs

rl t t T ran s.ft ft I rtt c rl il ni sph irirTrrr' PrLlis : \1 :rssot r

Ilrotlr'. B. A.. Kinner'. I{. Cl . Kkrman A S ' arrcl

Cj i l les. p. IL (1987). Serpence of cetrtr:r l ner-

xurs svste'rtt tnve'lination in httrnan intancr ' ]' IIt

autopsv stuclr' of rnvelination. .l \curttpotlnl

Erp. Neurctl 46:2El]-301

Bro,niev. S. NI.. and Dot\. R. 1,. [g!J5). Odor rt 'corl-

nititil rnernon'is better urrcler bilateral tharl uni-

lateral tt'st conditions Coftn 3l:2540

Clain. \ \ ' ' . S. ( i977). Bi later:r l interaction in ol{ irct iorr '

Nature 268:5(l-52.( lairns. IL R. (1952) l) isturbances of consciotrsrtess

uith lesions of the brair lstetrr arrd cl iertcephalotr '

Brain 7'5: i09-1'46(lambier. J.. Elghozi D.. ( lravelearr ' l ' ' ancl Ltrbet-

zki, C,. (19E'1). I{ert l isor]1i l tagttt tsie drrt i te t-t st ' r t-

titlent cl'alllptrtation par l6siorr gaLrchc solls-('or-

t icale. R6le de la t l iscolrnexion cal lettsr ' ' Rcr"

Neurol ( Pafis ) 1 10:256-262'( lasel l i , l i J. 11991) Recl iscortr ir tg tac't i l t 'aqnosia

l[at1o CIht. Proc 66:129 112(lhen. i l . IL ( l9f i6). Selective coryrus cai losotorrrr for

the treatment o{ intractable gerrc'ralized epilepsr'

Clnt. J. Neurowrg 1:79i '( l iark. (1. i l . . . , , td ( le{fen. Cl \ 'L i1969) ( lor lus cal-

Iostrtn surgen. at lcl recent ln( l ln()n: Rrain I l2:

l b ' ] I ' D .

( l larkt ' . F l . . ancl ( ) NI : r l ler" (1. 1) . r1968) Tlu ' I lurrmrt

Brain and Spinal Corrl . Llerkeler": Univt'rsitr" of

Cltrlifornia Press.( i larke. J. NI (1990). Interhernispher ic funct i<rns in

h.t,r-,r,r'ts, rel ationships betr"'een anatortlical trtea-

srrres ol the corptrs callosuln. behtlu'ioral l:rtcrarl-

ih' effects ancl cognitive profiles' l 'nprtblished

clirctoral dissefiatirin. I-lniversin+ o1' (lalifornia'

Los Angt les.( l l a r ke . J . \ I . . and Za i c l e l . E ( 1989 ) S i r np l t ' r eac -

tion tintes to lateraliztld flashes' v:rrieties of rrl-

terhernispheric cotntnulticatioll rotrtes Btzitr

I /2:8 '19-570( l larkt ' . J . \ '1 . . ancl Zaidel ' E (1994) Alratornical-

beharioral relatioriships: corpus t'allosrrllr lllor-

phorrrctn ancl l iern ispht : r ic spccia l izat iorr ' 1 lc-

har. Rruin Rgs. 6 i l ; lE5 -202'

( , larke. S. . Kraf is ik . R. . \ 'an I )er l 'oos ' [ l - i tnt l I r r -

r r ocen t i . ( l M i l 9E9 l . Fo rn r s l t t l d t neas l t r t s l r l

ac lu l t at rd c lew' lopinq ht t t r lar colr t ts cal los l t t t t : is

tht ' re st 'x t t i r l d i r l ror l l is l r r? . l Oorr tp \ : t ' r r r r r l J '9{) :

213 -2110( lrherr. L.. :rttcl Dchaclle. S. i 1996r (lerebral tlt'hvorks

tirr ttrurtbet'llloctlssittg; erirlt'rtcr' frc.'ttt tr t'tse' cll'

p<rsterior trallosal lesi<in N a r ntco st' 2 : I55- l'i 4

( l , r r lbal l is . \ l ( , . (19E'1) . I lumau lateral ih ' r r iat tcrs

<rf peciiqree. Belun:. IJrain Sci T:73'1-ill5'

Boqen. j . E. {1995b) On t lrc rreurophr-siologr o{'consc' iousness.

Part 2: Oonstrairr ing the sernatl-

tir, pr<rblem. Cttnsciuts. Cttgn 'l:l3i-1o5t

Bogen. J. Fl (1997) Some neurophvsiologic asPects

oJ' conscictttsness. .ssrnlrl Neurol /7:95-103

Bogen. J. E (1998). Phvsiological consequence-s oi

complete or partial cornmissurirl section ln Sur-

genl of the Thirrl Yettr'icle. *tl ed'. \l L l

Apuzzo (ecl.). Baltirnore: \\'illian-rs ancl Wilkins'

pp 167-1E6.Bogen. J. E (2(n0), Split-branr basics: rele"'ance lor

thc concept of one's other nrind. J. An Acad

Pn1 clun nal 26{ 2 rr3'1 1-i169

Boqen. J. E.. Fisher. E. D.. and \ 'oqel. P J (19651

(lerebral cotrttrissttrotontr": a seconcl case report

lATlA 191:I32lJ-1329.Boqen. J. [ ' ] . and ( lazzaniga. IU S. t1965). ( jerebral

t .r) lrnl lssl lrotot l lv lr l l l lAn: r l l i rr t tr herl l ispl lere

tlrttninartce ftrr certatlr visuospatial firnctitxrs /\t'u rr;,vr rg. 23; 39'1*1199

Boqen. J . E . . Schu l tz . l ) . I I . . and \ 'oge l . P J i IgEt r(,ornpletettess ol callosotornl' sltowrt bv rnaq-

tretic resotlttllce irnaging in the' lorrg term Ar-ry'r'

\arrrrl 1,5: |2(\3-l 205.

Bogerr. J. 1,. . ancl Yoqel. P. J. { 1962 r ( lerelrral cotrr-

rr issLtrototttr i r l lnart Bul l hts Arrgt lrs \eurol

Str ' . 27:769 I i2.Boqen. J. E.. and \trqt: I . P. J. (1975) Neurologic'sta-

tus in the lortq tt:nn follou"ing cerebral comrttis-

surotomv. lt I'ts Sqmlrrtnu"s rk' l)iscLtrtt'tt:tirtrt

CnlLeusti Cht': l"Hrnrnnr:. F \{ichel imd B Schoti

{ t'ds. ). Lv<rn : I lopital Neurologirpe' pp' 22i -25 |

Bossonr. 1.. Spern. R. \ \r . . and Arora. I I (1961) Di-

vrsion of -ernotiortal

beharior p:rttems in split-

brain nronkevs. Oaltet:h. 9ilil. Attrt' Rep p I2l'

Botez. \1. (197'1). Frontal lolre turtrortrs ln Hnrrr l-

hook tyf Cliricul Neun'Lttgr-/. \'ol lT In P JVinkerr ancl (1. L,. Bruvn. (eds.) North Hollancl '

pp. 213-1-26{}.Botez. \{ L. and Bost 'r t . J E r1976l The grasp re-

fler o{ thc firot antl relatetl phenorttetra in tht'

absence ol other reflerx ablorrnalities follouirIg

cerebr,r l cctt t t t t t isstrrotott lr ' Azfr l Natntl Scattt l

5"t '15:l--+6rl

Botez. \ l L. anrl oriqhel, E. (19;l r . Part ial discorr-

t t t 'x ion srrtclrott t t ' i t l att i r tnlr idextrotts Patiel l tI lmirt 91:161191.

lJrernt'r. I,'.. tlrihavt. J.. alrtl Arrtlri'-Balisarr-r. (l

r 19561 Pl*'siologie et pathtllogre clrr corps c'a]lerrx

,'\rllr. Stris.sls l'crrrrr1. Psqcltiatfit i'\::lI-Fj7Br ia r r r l . K . A . . an t l K le in . I l . \1 . 1 lgb l ) l s Posner s

' ' l rcutn' t l t t ' sattt t : as Treistt tat l s 'glrrt '?" Orl the

rt ' lut ior lr t ' t rvt 'etr r isttal ortett t i t lg arrd f i :attrrc i l r

t t 'qrat ior theon./. F"rp. I tsqchol Hurtt . Percr '1t l

I ' t r lonr t . .1.3;22b 2-11.

I)anclr. \ \ ' Fl ( lgt36). ep6lnf i \ .e el?(,r ience in case.s()r l)ut(.al t trnior. Arz./r. .Surg. .33:i9J6.D ; t r r r ; r s i , , . . \ H l 9 \ 5 , . T h t . f r , r r r t ; t l 1 , , h , , s . I r t C l i r t i _

cal .\-t'rtrtrytulr.lnlogq, 2nd r:d.. K. !1. Heilman

antl E. \ , t i l ,nst(. in. (e(ls. ) . \ ierv york: Oxfbrd Urri_rt.rsitv Press. pp 3t39-375.

l)arrasio. A. R.. Chui. I I . ( j . . Clorbett. . f . . and Kas_sel. \ . r lgbOl. I1)stcrior cal losal , ." t inn in o n,rrr_epileptic patit.nt. J. \-eurol. \,eurosttrg. f.,yrhia,tn1 .l:3 351_:)56.

I):rrrrasio.,{. R.. arrt l l )arnasio. }1. i lgg;l) The an:r_k;rr r drasi s ol' pr rre, aleriir. _\aa rrlr ) g l ( C: k, re kt d ),3.J 1573_15 r1

l!)art l i tsio. I I . . antl I)arna.sio. A. I t$79) . . Irar.4' .xic.,ear ert irct ion i l cl jc,hotic. l isterr ing: possi l l le, an,;rtornic' signifir,anc.r,. .\t,rarrlo gq * Ai+_Oi3

l)r:gos. . f D.. ( lrar. F.. I_orranr. i . . . . \rrsr lrrer. f , ( i . .

C I I N I C A L N E L ] R O P S Y C H O L O C Y

Poir ier. . f , , ancl Barbizet. .J. dgS71. I)osterior cal-losa l in l i i r c t io r t . Bra i r t i l0 . lLEs- l l ; l

I )el la Sala. S.. \{archc.tt i . O.. anrl Spirrnlcr. I j ( lggl1.Right-sidecl anarchic. (:Llien) hrirrtl: a longitrulinal"^tr rrh-, .\rcu n7r. s t1 r ; ht I o gi r t 2 t). I t I :l I I 2T .

I)el la Sala. S.. \ Iar<,hett i , C.. anrl Spinnler. I{ .(199'1) Th(, anarchic. hancl: a Irorrto_nresial srr, , ,ht

.Hancllxnk ttf ,\'tttrctpstlclult,!!1, I,,,/ g. ]Bol lcr. arrt l . f . (Jraf irarr te<l i i . . t ,nsie.. lun, Elr. _r.ier Scierrcr.. pp 21313-255.

Dencnberg. \r . I I . i l gE l ) . I l t ,rnispht,nc Iateral ih. rranirn:rls iurd the eflects of earir. t,rperit,nce. 8,.-hat:. Brnirt Scl. .1. t_-19.

Dennv-Bnrrvr. D. dgsE). The natrrre of.aprixiaJ. Nen:. tr[ent. Di:; 126.9.�32.

De Renzi. E. ( lgg2). l)i,srtrclers of Spact, Erpktrotiott

__ and Cognititttr. New, \irrk: ;Jhn t\.ilev l"a i r"

Descartes, R. (1649). Les passions a. t ,u,r," " i , ,

Descntle.y: Oeuxres r:t Littre,s iBlhliothFque cl"la pldiade). A. Bridoru<. (ed.). Gall i rna.,f . ' fSO.;p . i l 0 .

Dewson, J. I I . , I I f . (1g77). prel irninarv eridenc,e oi.henrr'spheric a.s\..rn metn. of. auditon. fi,""t,,,, i,,rn0nker .s . ln La t r ra l i :a l i t t t t i t t !h t . . \ i . , r , , , , , S , , ,_/ r ' l r . S . l l a n r a d e l , r l . , e d r . . \ r . u ) o r k \ r , : u J t . _nr ic Press , pp .63_71.

Dimond, S. J i1972). Tht: Dorhle Br-airt. Lor.t<Ion.( lh r r rch i l l L i r ings tone.D i r r ro r r t l . S . J . l9 i9 r per l i r r rnant .c h r rp i i l_hra in l r r r_

mans on lateralizecl vigilance task; Ci,rl.l. j;.13_50

Dirnond, S. J.. Bures. J.. Farr irrgtol. L.J.. arl lRrorrrvers. Fj. y. N,I. ri975). t-he',rr.. "f :.,;,,;;,;ienses fbr the Iateralization of isual l;r; i;;rnatt. At:tu psqchol.,39. 341_349.

Di!-irsilio. G . Cllarke. S.. pizzolato. G.. arrrlScha{Iner, T. (lg9g). Cortical regions ",:lnt.il,,,i_inq to thc anterior cornmissrrre irr rnan. LrTrBrain Rel. l2l : I-7.

Dof t . f f . L . . S tern . \1 . 8 . . l , fe i f le r . (1 . . Co l lo rnnS. l \1 . . an t l Hur t ig . IL L , lg92r U i la te ra l o l fa itorv dvsfirnction in earlv stage treated ancl rrrr_treated idiopathic parhnson's disease. /. Iarr,,iNeurosurg. psychiatry 55, 136_142.

Doh' R. \ \ ' . Negrio. N.. and yamasa, K. [973tThe-unrlateral engranr. Acta Nertroltiri. Erp. J . J . I I 1 - r ! ) i .

Doh'. R. \1'. and Or..ennan, \1,. Il. (lg77). \{nenrorritrole of firrebrain comrni.sstires in macarlues. InInterali:ation in the Nen.,uts St1stern. S. i{anrr,iet ai. (eds. ). Nerv lbrk: Acaclerniclpress. pp. 7,5.-\.\

Dotv. R..\\'.. Ringo. J L., anrl Lervine. I b. rfgUlInterhemispheric sharing of l isual menlon. rr lnra(.af lues. Bt ' lnr. l lnr ir t Ret. 2() ig_61.

I)ot, . R. L., Shaman, p.. and l)ann. ! I . (19&r. I)r, .velopment of the Universih of irennsvlrarr,r

392

( io rba l l j s . \1 . C . t t i )95) \ . i s r ra l in teqra t ion i r the. ) l t l l

l r r r r i r r \ r r r r r , ,1 r ,y , . l t r i t ,g t r r ; ; r f f ;_g jg( . r , r l ) , r l l i \ \ l ( . l ! . ) l ) \ l r r l e r l r e r r r i s p l r _ r i t . r r r r r r l r l

s ru r rn t i r t io r r in t l re , r l r r r r rcc o l t l r , , t r ,n r r rs t .a l lo_sr r r r r . Brz l r r I 21 . I igS_I \0 i

( l r r l ra l l i s . \1 . C . . and Serger r t . J . ( lg tb ) In raqen. i r r;r crrrrrrnissrrrotorrr izet l pati t ,nt. \-r , t t roltsty, l t , t l , t_g ia 26 1)_26.

( lo r l l r l l j s . \1 . ( . . . tu r r l T r r r r le l . C L r lgg3 l . The ro l t ,, , l t l r , . l i , r r , l r r , r i r rs1,rr r, ri<, i' r egrtrti... ffi il;;:r-, llli,I"l.(torbrr l l is. 1,. \1.. Fi.nthic, l , . l i ' , i l ,aplJ,. n f l . ,naLazz:.tnigtt . NI. S. i tgslgr. I l l t rsorl contorrr Der_ct,pt iorr ancl arnorlal boulrdan. crrrnple.t ion, eri_rlc'rrc,t, ol a tlissociatiorr fbikning i.nllor.,,n,rrr.J r n t_n m I t l' C o gt t it it t: j- a t ro.s t:ie t t t ;, rj I l. 48g466.(lritchlc.r'. \1. {l!ltl0) The anterior ",,."br"I nrt.l.r,ancl i ts srrr<. lronres. Brairt ,5j: 120-165.

( lrorr irr-( lolorrrb. : \ . ( I9E6h). Srrbqrrt ical transf.er o{.coEritir.e infbrrrratiol in srrbjects u.ith cornpletefrrrebrain conrrrr issurotornr.. Coricr 22:$g:EW.( lror r in -(lolorn b. .\. i I 9g6a ). F.iqrrre-l rac,kgnr,,n,l rr.._c,r'yrtron in riqht anrl lefi ht,nri.spherr,,s of hu,'nan

. r1 )n ln t i \ \ r l ro t r r r r r r r r r l l j , ,1 . t r p r . r r . , .1 t l i , , t t t r .gB_ l l )g

r , r ( 1 1 r l u - ( , r r l r l r l l r { . , 1 9 9 5 ) . S e r r r a n t i c , t r e . t r v o r k s i r rtlre dir irler I c.t. relrral h er rr rsph eres. f .r 11 r, lr,rr:, i S r:.i6.212-21s.

( l ro r r i r r - ( lo l rn rb . , { . . ( ja l r r ie l i . J D E. : rnc l Keane

fl f l r1l996) f n1phc,1t anri expl ici t ,"n,, , .r , ."_trit,r.al tithirr arrcl ircross the rlisconrec.te.l i,e.e_

._ brirl henrispheres. \ertropsrldtoltrg,l IO,ZSIZAZ.

I)arle L r\ . . . fones-Ciotrnan. \1.. Zi l t trn,. R. J anrtI tvans. .{ . C. r l99tl . I l rrnr:rn lrrai, t f i rnct lon dur_rrrg orlor encocl inq ancl rr:coqnrturn. r\ PET acti_r at iorr strrr ir . . _.1rrrr . \- . )- . Acad. Sci. g5.,5. iT2,5Tl.

l)rrhrrrt 'n- \ \ l lart j t . \ \ ' . . I lussing. _.\ . . ancl Str,rnr.\ \ ' I 1! l !2r I) isorclers ,rf c,alc,r l iat ior i , , ont nri . ll lat i t 'nts; spatral anrl verbal c.olrrponerrts. ' .vr:rr_rt t p s t 1 t l u tl tt gt a 2( ) : ll,j_15:1.

t . . ,

t . ' , ,

T H E C A L L O S A L S Y N D R O M E S

Srrrel l I t l r :nt i l ic at ion Tcst: a st irndarcl izecl rr r i-croenc'apsrrlate,cl test of olfacton' firrrction. P/rr7s-iol Belmr . .32 : 1b9-502.

Doh. R. \ \ ' , . Yarnasa, K.. and Negrio. N. (197i).

\leciiation ofrisrral fear ria the corpus callosurrr.Pntr:. Sot'. -\clrrr,rr:1. -l: 1()4.

Dorrrer. J. f , dc Ci i l96l ). C)hanges in r. . isual gnos-t ic f i rrct iorts artcl err iot iorral treharior l i r l louirgrrni lateral teriporal pole clarnage irr the spl i t .l rrain monker' . \ature 191:50-51.

Douner. J. L. de Cl. (1962). Interheniispheric inte'-graticrn in the visual svsteln. lt hterlu:ni,spltericReLation,s anrl Cerebral Doninantp. \'. B.l \{ountcastl t . iecl.) . Balt irnorc, Johns l loyrkirrsl lr i i 'ersrh Press. yrp. 6i.- I29.

Elrorr. R. t l990l. I /rc Dt 'r : l int utr l F-al l of Hott i-sl t lu:dc Spn:ial i :at iort. I I i l ls<lale . NJ: Lau'renc.eI lr l l rarrrn -{.ssociates.

f . l l .nberg . 1 . . and Spern ' . R . \ \ ' . ( lg79r . ( lapac i t r

l i rr holdirrg sustainerl attc.rrtron lbi louinq ctrnr-t tr issurotonir . C t t f te.r 1,5:.12 I Jl l l i .

Fi l l t 'nlrcrg L.. arrcl Spern. R. \1' . f 1980). Lateral izt 'clthusion ol attention in the cornrnissurotorrr izerl;rrrtl intact hrain. -Yau rop sqchologia / 6i,1I l,-1 I E.

l ' , sc rx r ro l le . R . . I laun ' . J J . ( i rav . F . . and I len in . I ) .1975t. Aspects rreuropirthologicpes dt:s l6sions

tl tr crrrps c'al lerrx. In Let Sryndrtnnes de I) iv:t trr-rt t ' r i r tr t Cal leu.se Che: L-IIonrlre. F. N{ichel andl l Sc'hott i t ' r ls.). Lvon: I l i rpital Neurologiqru,.p y r - 1 1 - 5 1

I ' .skt 'nazr. I l . ( lair i . \ \ ' S. t , ipsit t . !1. D.. ancl Nor-el ir R. A t lgEb) Olfacton'f irnct ioning and r:al-losotonrr': ir rt,porl ol trvo cases. )-ale J. Biol. tlttl.61 117_!'56

l, tht ' lberg. S i l95l r Clhanges in circrr lat ion throughtl ie antt,r irrr cerelrral af ien. Acla Psqchiatr. Narn t l 5up1t l i5 : l -21L

I ' ,ua tar . Z . \ { t ' l l . 1 , . . and Z : r ide l . E . i1990) . ( lon-(r( ' teress: rr<lrns. r 'erbs antl htrrr ispheres. (, 'or-I r ' r 26 :61 1-624.

I ' ,r ' i i i t rLr. 2.. arrr l Zaiclel. E. (199.1). l ,etter rn:rtclr i lgsithrr antl l r t 'hr. t ,er the cl isrrrrrnt 'c:ted herrr i-: l r l re r t s . Bra i r t Oogn. 95 :128 1117.

I "a l rn \1 . . l )o lo rara . O. . Qr ra t t r in i . A . . Sa l \ ( ) l in i . I r . .l ) t ' l P t ' sce . \ t . anr l N{anzor i . T . (1999r . Ro l t ,o { 't l te corytrrs cal losrrs in tht. sol l tr tost 'nson actirat i , r r ; , , 1 , ; , , i p s i l ; r l l r ; r l t . , . r , , 1 , r ; , 1 t o 1 1 , . r : a r r I \ l H lst i tr l l oi c 'al losotorl izt,r l paticl ts. I i tr . .1. \ ' t ,r t-t,:'-t I I ll9{l_,ll!19.1.

l "a r i t l r \ [ . J . . (Jazzar iga . N l . S . . I lo l t z rnan. J . l ) . . anr lKoss l , " r . S \1 . (1985) . A lc { i henr isp l r r . re bas islrrr visrral l t t ,rr tal i rrragt 'nl \ tr l r-op.rr7t: lut l . t tgi t tJ . j 1 1 5 _ l L 5

l " r ' i r l x , rq . ' l - F , . . Sch i r r t l le r . R . J . . ( i l a r ragan. \ . ( ) .

: i r r r l I Iabr . r . 1 , . l ) . 1 i992) . Ts .o i r l i t .n hant l s r r r_t lrorrrt 's. \ ' tat rt I o gt 1, j2 : Ig-2q.

393

F-ergrrson. S. , \1.. Rarpoft. \{ . . and ( lorr ie. \ \ ' . S.(19E5). Ncrrropsvchiatr ic obsenatiorrs on l)e-havioral consequences of corprrs callosurrr sec-tiorr for seizure control. ln EpileTtstl and tlrc Cor-p1ts (:al loslnn \{. . , \ . Reeve-s ied.). \eu' York:Plenurn Press. pp. 501-51.1.

Fessarrl . A. E. (195't). \{ec.hirnisrns of nenous irrt t . ,qratrcrrr irncl consc'iorrs eptrience. ln Bruin l[ct'lranisrrt,s aru! ('.otL\ciousn?.\.\. J. F. I)elafiesnaveted. L Springlield. IL: (1. (1. Thorna^s. pp. 2t){I-236.

Fisher. (1. \{ . 11963i. Srrrrrnetr ical rnirror rn()\ 'e-rrrents arrcl left ideornotor apra-ria. Trarts. An.\eunrl. A.sror ' . 88:? l -{-216.

Foi-r. ( . . . an(l I l i l lenrard. I ' . r 1925). Les srrrt lrorne.t le lartt \r t ' c6rFbralr urrtr-r i t ' t i r t , . I ' - , t trcl , lmlt '20 209-232

F-rarcks. J. 13.. Srnith, S. \ ,1.. and \\ 'arcl. T lr l . t 19iJ5,.The use ol goggles f irr tcst inq hernispht,r i i 'asvrrrrne'trr'. Brrl1. P.n1 clutr t. Sot. 23 : 18i -!.E6.

F-ranco. L., and Spern', R. \ \ ' . (1977). I lenrispherclateralization frrr cognitive processing of geornt'

tw. N eunytsyclnlogiu -1,5. I07-l 1.1.Franz, E. A.. El iassen, J. (. . . Ivn'. R. l l . . arrd ( laz-

zaniga, NI. S. (1996). Dissociat ion ol spatial antltr :rnporal col lpl ing in tht: birnarnral rnoverncrtsof callosotomv patients. Psychol. Sr',. 7:306 310.

Franz, l l A.. \ \ 'aldie. K. E.. and Snrith, !1. J (2000)The elfect of calkrsotorrn'orr novel versus farriil-i r t r h i r r r a r r r i l i a t l i o r t s : a n e ' r r r L l d i s s r x i a t i o n l r c -hveen controlled anrl arrtornatic processes? PsrT-clnl. St: i . 1l :82 l \5.

Fuiks, K. S.. \ \ 'y ler. A. R.. I lerrnann. B. P.. arrciSomes. (] . (1991). Scizrrre (xttconl€' l inrrr ante-nor and cornplete corprrs callosotonrv fsee corn-r r re r r l s l . / . . \ ' c t rn ,surg 7 ' l :573 7 , \ .

F'unnell . N{. Cl.. ( iorbal l is P N{.. and ( iazzaniga.

\,{ . S. (1999). A defici t in perceptual rnatc}r ingin the lef i hemispherc ol 'a czrl losotorrn patient.N europ,sqchologia,37 : 1163 1151.

Irrrster. J. N{. (1969). 'llrc Prefrcntal C)oftet: Anat-ornq, PhqsiLtlogy antl Natnryt,ryr:hologl o.f theFntntaL Lr.rlz,. Neu' York: llirven Press.

F'rrstr:r. J. V\{. (1997). N-ehvork rnentor.r'. Trend.t N,nrnryi. 20:151459.

( la i r ro t t i . (1 . . N{ ice l i . (1 . . a l t I Oa l tag i rc r re . ( ] . ( l !177) .( .lon strr rcti or r:rl apr.rri a ir r i r,{i trrai n -rlunt:rqed pa-t i t ' r t t s : i t p iannr r rg r l i so rd t ' r ! C tu l t t l , l ) .109-1 t5 .

( la la l r t r r r la . - , \ . l \ ' 1 . . I losen ( ; . I ) . . :u r r l Sher rnan.(;. F. (1990). Indi ' , ' idrral variabi l ih ir i cof l icarl or-g ; r r r i z : t l i , r l r : i l s l r ' l r r l i o r r s l r i p l r r i r r a i r r l i r t r r t i l i h ; r r r r lirrlrlic'atirns to firrrctiort. \'t'unrytsrychctLogia 28:529-.5.16

(lal ir . D. (197,1). Irnpl icat iorrs { irr psvchiatn ot le,{tdnd r iglrt cerehral special izat iclrr. Arclt . ()att .

P.sLlclrlutrtl 31:572 5ii3.( la l in . I ) . . l ) ia r lo r r t l , R . . anr l I le r ron . J . {19 i7 ) . De-

394

velopnr( , r l t o l crosse( l an( l uncrosse( i tact i lc lo_cal izat io l on the f ingers. Bnin Lurtg. . l .56E_5g0

, t , , l l ' ] ; .11.: fohnstone. J.. Naktl l . t . . . n, ' , , t I lerron. Ji1979) I)(. \L, loprlrent o1 tht, capar. ih f irr tact i ieirrtonration transfi .r l rehvet,rr ht,rr i isphcres inrrorrrral clr iklr t , l . .Scl lrrr, tOl. I3rl()_ j3: j2

( larc, ia \ ler l inl . \{ . R.. arrr. l Cair. \ \ . . S ( ig,!2r Bi-lateral i l t t 'qrut jorr in t l re trrrrurrorr chenric.alserr se. /r/r17 rlol . lJ t: I t r t t:. :g. 3..l!j_.r15:l

( la r rh rer . I l . . a r r< l l l rou . re l l . I l . I I r l9g6) Ik , r r r r_sphr:r ic ( lonrrnurr icat ion l latten.. \ , .{ \ IC.. I jostorrl ' r r r . l ro l , ,g r S ln i t . r .

()azzanigtr. \'I. S. i lg70) 7-ltc Ri:;cctetl lJrzlrr. \.el.I 'ork: Appleton.

()azzaniqa. \1. S. dgST). I)err.eptrrai ancl atterrt ionalprocess(,s l i r l lou"ing c.al losal sec,t ion in hrrrnirn".N eu n ;p.t t1 c lu lo qia 2,5 ; I I 9* l rlil

Gazza.ni5a. -\{.

S.. Bogen, J. E.. ancl Spern.. Il. \\,.( 1962). Sonre frrnct ional effects oi.scct ioning thecerebral comrnissrrres in nran. prot.. Natl . ) .cart..Sci. t.' S..4. tB: 1765_1769.

,t"i':iij{". ,\t S . I}oqen, J Ii., and Sperrv, R. \\:.(l96tl). l,ateralitv effects in sorrresthesis {ollorv_ing cerelrrtr l corrrrnissurotornv n rran.,\ .ctr-r,'l ).\t/'l k'l (,{iu t . 209 . 2 | i.

"y1y:l ,NI S.. tsogen. J r, t . . ancl Spern.. R \\ , .(1965). Obsen.ations or: r.isual peri.eption afterilisconnerion o{ the cerebral le,r,ispheres ir:.rnan. Brain 88:221 236.

{}az'21.r.y11 M S ' B'sen. J. E . anci sperrr. R. \\.'i 1967) Dr.spr:r_ria firllolring dir.isiori ,,f ih" ""..-lrrzrl cornrnissurcs. Arclr. Neurol. l6 606_612.

()azz.anigt l \{ . S.. and Frtet lrnan, I l (1973) Ob_:en at iorrs on r isrral pro(.ess(.s after posterior r.rr l_I r r ra f se t . t ion . \ ' "u r t , l r )g t l j3 r I 126. I I3o

()azz;Lltiga. \1. S.. antl LeDou.r. J Fl. [97ti) I.lu, Irt_tu'gratecl J1ln11. \c,rv york: Iilenrrrr press.

C L I N I C A I N F U R O P S Y C H O L O C Y

( ieschu i r r<1 . \ . . a r r t l Kap lar i . F l . ( l962 l . . . \ | r11ar rct,rebral decorrnec.t ion srnt lrorrre: n p.a. l i ,ui ln,.reprrrt . Irrrrr logtl 1 2.6i5_6hi.

( l l ickstein. \ I . , Arora. I I . . , \ . . anrl Spern,. f i . \1( l96tl) . Dclnt,rLrt,sporrse pt,rf i rrrrrarrt ,e f i>lLnr,ing rpt ic. trac,t st ct ion. rrrr i lateral f iorrtal lesior.ancl cont nt issr rrotort, j6. I l , l r .

,) / . ( |ont\t . I ' l t t1.r iol . P.tr1t: l t t i

( io l< l l r t ' rq . (1 . . \ la re r . \ i . I I . . a r r t l - l -oq l i : r . . f t , . ( l9 ! lNledidl frontal crrrtex inf)rct ion u,,,1 th,, nl i" , ,hancl sign. , \rr:h. \ . t trnt l , lg.6g:l{ ig6.

( loldstein. K. (1t108) Zrrr [ ,ehr3 r lrr r | ,r rrrr,-krrjschen Apra-rie .l phtlsiol \,ttrrl Xli.li,5,I 6 9 - l \ ; < . i t l r l l r r l l r i o n r r r r r l . f e , h r r ; r k i l V i 5 l

( ) r r l d s t e i r r . K . , I g 3 9 [ 1 t , . < ) 1 . . a 1 1 i r , , , . \ - * \ , , r 1 ,Amt r ican Book Co.

Clordon. II. \'t'. (1973) \k,rbal an<l rron_r.erbal cere-b^rirl processing irr nran frrr arrditiorr. fhesis, (;aj-ifornia Institute of' Tc,chnologv.

(lrrdon, H. \t'. (1975). Oonrparisin ol'ipsilateral antlcontralateral auditory pathrvays in "allor,,,n_r",,t ioned patientr br, , ,s" ,r f n.. :rpunre_ti ,ne tecl -ni<1rre. ;VezrrT tsq clnlo gia 13, g_l S.

( lordon. I I . \ \ ' . ( lgg0). Right hernisphere c()mpre-hc.nsion of verbs in patients wlth crxnplete f.|reDrarn conrrnissrlrotornv: use of. the dichotic.

:."11]":l ."rd man ual perform arr ce. B rai r t La n q:

I I :76-86.Gordon. I I . \ \ ' (1990) Netrropsvcholoq.ical setlue-

I:ie of partial of partial .l.r,r,n,,rru.,rtun,".' L,I I u r.u, l I n u' k, t f . \ ' e t t r t t 1 t . t t I cl 1 1,1,,4y. \ ' , ,1. l . F-. tJol l , r: rn t l j . ( l r r r l rnar r . - r l s . . , \ rns te r r l i r r t r : E lser i , , r . p1 :tJ5_97.

( lorclon. FL \\ ' . . and Spern.. R. \1' . 11969). Laterai_iz i r t io r r o { , r l la t . to rv perc ,ep t ion r r r th r . s r r rg r t .a l l rreparaltr l h.rrr ispheres .f rnarr. . \ 'crtr, ,1t. try,. l t , , l , ,-giu 7:1II-120.

Grrrvers. \\'. R. (1903). A llanual of Diseases o.f tlu,\7n r r r r * . \ ys te t t t . \ ' , ,1 . 11 ,21 , ,1 , ,d ph i la t le lnh i : rP . B lak is lon s Sor r an t l Cr , .

Greenrvood, P.. \\'ilson. D. H., and Cliuzaniqa.\,1. S. (1977). Drezrnr report fol lowing comrnis-surotonrv. Cofter I3:3I I_3]r,6.

( lr i isser. O. J.. and Landis, T. (1991). \r isual Ag.rutsias and C)ther Di,sturbance,s of \ti.sual pt.ctlttion anrl C ognititn. l,ondon: \Iacmillan press

Clur, R. E.. Clrr. R. C., Srrssrnan. N. M.. O,Conrror.\1.,J.. and Ver' . NL I,{ . ( lgg4). Flernispheric con-trol of the',r'riting hanci: the effect of calosotomrin a left-harrder. \ 'crtr, , logy 3,/.90J_90S.

Ilarnilton, C]. R. (1977) In.,,estigations of perceptualand ninemonic late.raliz:rtion in monkevs. In 1-al-lral i :ot i t) t t in thc .\ t .n.t4ts SVslrrn. S. i larnatl , , tal . (eds.) New,York: Acaderri ic press, pp..15Ji!

l larni l ton. C. R.. and Verrneire. B. A. ( lgE2) ] Iemi-spheric differences in split-brain morlkevs lean).

()trzzanisa. \1. S.. anrl Spern.. R \\ ' . (1966). Simrrl_tanc,ous clor r blt, di.^r.n rn j n ation response {irllou. _ins brain lrisr.ction. pryclrort. Sci ):26I-�262.

(lersh. F.. and l):un:xio. .-\. R. (l96l). pr:r-xis and rwit_ins of the lcfi hancl rnar. he sen,ecl bv differentcallosal path*.iws. .,lrr:1. t- t:u ntl. jB:634_S36.

(]eschu. ' ind. D. IL. Iacrrboni. \{ . . l leca. }L S1ud:l

D \\ ' . . CJloughesr.. T., and Zajdel, E(1995). The al icn I iand sr.nclrone: interhenri-sllhc.nc rnotor clisconnection clue to a lesiotr inthe rridbodr.ol the corpus callosunr. \,etrrrlogy,1,5:802-808

(lesc'hwincl. \ . {196.1). T}re cleyel6pmclt of thclrrairr ancl the er..olrrtjon uf lnng.,*g". In Mort,,gmy:h Scfic.s orr Longuage and Lir'tgrti;;tics, \/o!.l : . ( . I . f \ 1 . \ t r r : r r t r e c l . . . \ \ . a s l r i n g t o r r . l ) ( . :Oeorgetourr L.'nivcrsitv I)ress, p1t. t,fS_IOg

(lesc.hrvind. \i. r 197-l). Selett,:rt pu)err r,,, Lon|ung,and t l tc Brzlrr. Boston: Reiclel.

T H F C A L L O S A L S Y N D R O M E S

i rr{ serlrrerrt ial cornparisons. \nro1t.t t lchologin

J(i ;691$98flarni l torr. (1. R.. arrt l \ /errneire. B. r\ . t I986). l ,o-

calization of vi sual firn ctions rvith partialh' split-brain mrrrrkevs. In ?tlo Henispheres-Ont:Brain: Furtt:tic,ns of the Ooryus CalLovtnt.l- l rpore. ancl \1. Pti to. and H. H. Jasper (eds. ).

\eu'\ i rrk: Alan R. Liss. pp. 315 33:1.l lamil ton. (1. R.. and \/ t- .rrneire. B. A. (196E). ( lonr-

plenrentan' hemispheric spccialization in mon-keys. Sciettce 249: I 691-169.1.

l larnad. S., Dotv. R. \ \ ' . . Ckrldstein. L.. Jalnes, Ianrl Krautlrarrrer. (1. t 1977). Lutcral i ;at ion in t lv\r,n'ol,s S t 1 ste nt . , \- . es' York: Acadernic Press.

l larnrgton. A. (19E7). tr ' ledic' i rrc. JIhul, atrcl t ln 'Dtnl le Bruin. Prirtce'ton. \J; Princeton Univcr-sih Press.

IIetat 'n. I I . . ancl Ajuriaguerra. J. (196:11 l .e:f t Hard'rrlncr.s. \elr' I'ork: (]nrne irrrrl Stratton.

l l t jcat,rr. IL. arrd .\ssal. (1. (197()). A corrrparison o{

crnstructivr rleflc'its fbllou'ing right and lt'fi

herrr isphent lesiotrs. Neuntpgr: lut l t tgia f):281)-

30rlI I t icaeri. I [ . . l ) t ' Agostir i . \1.. arrt l \ lotrzotr-] \ I i t t t tes.

A. ( I98l ). ( lerebral organizatiort i rr ieft-hantl t ' rs.Bnt i t t Lang 12 :261 28-1

I Iear l . t l . i1926. repr i i l ted ln 19631. Aphas ia a ru lKintlred Ditordcrt rlf specclt. \ir1. 1. \tri \irrkrI I af irer.

I lei lnran. K. N1.. Borve'rs. D.. \ 'alelrstern. E.. atrcl\ \ 'atson. R. -f . ( lgEi). l lernispace antl henrispa-tial ncglect. ln \trl'rrylrrT,siohtgirti arul Neu-ropstltlutiltgical .{sprt't,s of Spatial NegLect.F, N{arc Jeannerorl ancl (ecls. ). Amsterdarn:pp l l5 - I5 { )

I le i l rnar . K . \1 . . ( lo r le . J . \1 . . ( ionver i . E . I r . , anc l( lesch*irrd. \ . i19711). Apr:r-xia and agraphia i la le{ l-harrdt,r ' . l }rairt 96:21 2E.

l le i l rnan K. \1 . . and Van l ) r ' r i Abe l l , T . (19F i0rRight herrr isplrt ' re clominanct, f i rr attention: t l rctt techanisr rrs rurt ler lr ir g lrcrnispheric' i tsvn nne'trres o{ irrattentior (nt,qlect). \ ' i t rologrl 30.:\27-�rl:10

I l t ' l hq t , . J . I l . r l99 l l r . I le r r r i sp l re r ic asvmrnr , tn :rr lrat s r ight arr<l ul iat s ir . f i . ( larrbridge. N' l . ' \ :I Ian arcl [ ]nivt 'rsi t l l )r t ss.

I l t ' rrrrrr. f . ier l .r . i 1980). \ ' r ,rrnr1t:; t1t ' l t t logrl of ' Lcft,l !urrk'dtt t :ss. Acarlerrr ic Pr-r 'ss: Ncu York.

I l i ros r ' (1 . . K i r i . ' l ' . . a r r r l N{ r r rakar r r i . F l i 1977) . : \ l t ' r iar i i thorrt aqraphia assoc' iatt ' t I si th r iqht oct ' ipi t i r ilesrrrr. . / \ ' r ,rrr i ,1. I ' rrrrr;srurg P,sr1t ' l : .utnl 1():22522;

I lo l t z r r ra r r . I . I ) . ( I961) . I t r te ra t ' t ions behveer r < :o r t i -t i r l rrrr l sulrcoft iciLl visrral areas: c'r icl t ' rrce f i l t t thtt t t t :ur trrrnnrjssrrrotorrrr 1;attents. \ ' i , r iott l i l 's: .1 E0 l 5L : l

395

Iloltzrnan. J. D.. Sit l t is. J J \ ir lpe. B. T.. \ \ ' i lsort

l) . IL. arcl ()a' tztrniqa. \1. S i1981). l) issocia-

tiorr ol spatial itrlirrmation ftrr stinrrrlus localiza-

tion and the control of irttentiotl. Brain 101'

861-872tloppe. K. l l (1977). Spl i t hrains antl psvc'hoanalr '

sis. P,ulchoanaL Q 16.221t-214.I loppe. K.. ancl Bosen. J. F.. (1977). Aleri thvnria in

12 comrnissrtrotornized patients. Pulchother'

Psy choso r rt. 28 : 116-155.Ikrrel. J. A.. and Keating. E. ( l (1972). Recovert

frorn a partial Kliiver-Bttcv srrldrorrre in thc

rnonkel- produced bl cliscotttrectittll:. J Oorrt1t

Pltrysiol. Ptycltol. 79: 105-l 1'1

l lrrrrrrnel. T.. \{ohatrtntadiarr. I ' . . antl Kol lal. (1.

(199E). Handeclrtess is a t leterr l l ini t lg lactor i l l

lateral ize<l olfactc>n r l isc'r inl in:rt ior l Olu:rrt

.Scnsc.s !'3. 5.1 1 -5,1.1

l lrrppt,r l . I" . . ' \ . I l9E1). Nlertron irr spl i t- l rrain pa-

t ients: ir corttparist l t t * i th r lrgarl ic att t l t t 's ic ' st ' r t-

clronres. Cr;r1r',t -l 7.3011 3 i I .Iacr.rborr i . M.. t-r ied. I . . and Zaidel. E. (199"{). ( lal-

iosal transrnision tirne befirrc ancl afier partialc'orn rr issrrrotornv. Nctr rotrTr o fi '5 ; 2521 -2521.

Iacolroni. \{ . . Pt i to. . \ . . \ \ i 'ckes. N. \ ' . . an<l Zaidel.F.. (2(XX)). I 'aral lel visrurnotor proccssing in thespl i t br:r in: <rrf t ico-subcorl ic 'al i t t t t ' ract ions.Rrain 123;759-76,().

lacolxrni. \1.. I iar-rrrarr. J.. and Zaidel. E. {1996a).Lefi brain savs \('s. right brain savs no: ll()rltltl-

t ive r lrral i tv in the spl i t l rrain. In Totcarr l a Sci-

cntific Rrtsis o.t''Cttnciottstu:,ss. S. R. Ilarneroil.A. \ \ ' . Kasniak. and A. (- ' . Scr>tt (eds.). ( jarn-

lrridge. \{r\: \IIT I'ress, pp. 197-202.Iacrrlxrni l\f .. Saver J. L.. arrd Zaidel, E. (1996b). Sec'

oncl r.isrrirl svstt'trt ancl blintlsight: eviclt'nce from

sirnpie reaction tirnes to bimodal (auditon and vi-

sual) stinruli. Lur .1. l"aroL. 3 (Su1rytl.,5l:167-l6E

l:rcrrbortr. Nl. . antl Zait lel . Fl. (1995). Channels of tht '

corprrs c'aliostun: evi<lt:nce frrlrrr sirnple rt'acrtiotl

tinles to later:rlized flirshc's in the norrrral arld the

spl i t l rrain. 1]ruirt l l8.779 7E6.Iacohoni. NL. anrl Zaiclel. E. (1996). I ler l ispht:r ' ic

indept'rrdt'rr<t' itt rvttt'cl re'trognitiotl: t'ri<lence

l iorrr rrni lateral arrcl bi latel 'al prt:sentir t iot ls.l l ru i r t I ' a r tg .5 ' i 121 l '10 .

Iaco l ro r r i . \1 . . a r rc l Za i t le l . f i . (199! l l T l rc c rosset l -

rrrrcrossctl t l i l { i ' r t :nce irr sirt t l l i t ' reactiott t i l } lcs to

latt ' ral izcd arrthton st irntr l i ls t tr t t : t t t t t ' l ts l tre ol

irr t t ,rhertr ispltef i t trattstt t ission t i t l te: evicletrc'e'

{ iorrr tht ' spl i t l rrain. Etp Rruirt Rcs. l2E:121

421lutolroni, N'I . . arrt l Zaiciel. E. ( irr press.t. Stahlt 'anc' l

variable aspects of cal losal chattt tr ' ]s ' I tssotls

f r<rrr partial disc onnectiort. ht l'lu ParuLlel

lJrain: Thc Cogrritit;e Neunt:r:iou:rt of tlrc ()or-

396

ptts Call()r1tn' ln. E. Zai<lel anrl \ I . Iacobori (eds.)(Jarnlrr ir lge. \ IA: \ I IT prt,ss.

1p. 301_1106.Intr i l igakrr.. [ . . I Ianaf1. I l . r \ . . ani i l . t i , ,h,. ' l . t . . t tggSt

r\ patient srrf ler ing frolt r lanrage to thc,poste_rior poft ior i ol the corprrs cal l i rrr, ,n , . , , , , ' , r , ,r , ,"i terns in both visrral f ields lrrrt cannot reportrvhe'tht 'r thcr. :rre thc sanre ,, . di f f" .r , , , t . ' ,Si, . .\ nt n t.: r' i. .\l ).et r. :]6 : 517 0.

lronsiclt ' . R.. arrcl Crrttrnirc,hcr. \ I . 1 lg2i l) . - fhe crrr-

lrus cal losrrrn arrr l i ts trnnorrr s. Brrt ir t ,52:1124E:J.h.rr ' , R B.. Frarz. E. A.. Kingstole, 1.. ful_. i ,rr .

.J. (1. ( 1996 ). The pRp eflect firllo$ing c.iljr,*n,,,,,r.,rrncoupling of lateralizt.ri re.sponse .rl.1., 7 Ayr.I'sqchol. Hurn. pentVr pejii,ttt. 21 463_ig0.

Ir. 'n ' . R. 8.. and l{zrzelt ine. E. (19g9). Subcort ical lo_cus of ternporal coupling in the binranrral move_rnents of a callosotontr.patient. Hrznt. Moxe. Sci.lB:315-375.

fackson_. J. I l . a1t,74). On the natrrre of the ci lral i tvof thc. brain. fled. press Cirrular. 1,1.9, ;i,';;.lleprinte<l in Brairr 1915. and in Seteteiivrit-ings of Jtfin Hughlings Jacktort. \/o1.9. I. Tar.l,,;.(ed. ). Lonrlon: Floclr ler arrt . l St()uehton. ' ig.32:;p.t29_1.15.

.facobsen. (1. F.. anrl \Jissen. I I . U. ( l9r l7). Stucl iesofcerebral firnc.tion rn priuratt s. I\.: The effectsof fiontal lobe lesions oi the clelar.,ed "fr""l"ri.,,habit. in^rron ke's. rI Cr rr27r rtr, 1., i,,t i, ji,,,i."i s,t 0 t _ l 1 2

Jt 'eves, NL .{. I lgTg). Sorrre l i rnits to interherni_spheric inteqration in c:rses ol 'cal iosal agenesisand partial crrrnmissrrrotrrntt.. Itt Stntcturt: antlF'ttnctictn tt' C erebral O r t t tttrti.t.stt res. I. S. R,rrr;li.-\L \l'. van IIof. ancl G. Berlucchi (.dr.). ;;il_rnrire: ( inir. t rsih, park press. pp. 4qg*/.74.

I , r r r l 1 n , T . H . l , r r t c h i n q . t ; H . . a , r t l V i l n . r , f . D ./ 1 9 9 \ f . , . r r t r t r l l i r t r t i r r r r s a r t , i r r a d e r l r r a t e l r c 0 n _trolled br. instructions nlon", l.pli"ati,r;r';;.shrdring cerebral asvrnmetrv. e J

'Eyt pstlchol.

,5lA:371-391.

C L t N t C A L N E U R O p S y C H O L O C y

krsrrnr agerresis u i th b i lateral langrrage rsp15,-\ e l l t i r t i o l | : pos i I r r r 11_s111 j15 i , , , , _ t , , , n , r qa rph , , r , , , , , 1

nerrropsvchological f int l inqs. l t t t [ \ : , r ;y , ,1r i 56.275-282.Kirrgstone, A.. Enrrs. f { , \ langun, Cl. R.. and (Jaz.

zaniga. NL S. (1995). Grrided ,. isul l l s.arch i" alel i henrispherr: pr)cess tn ,pt i t- t , .uin f , , t in,, t ,Psrychctl . Scl. 6. I l_I21. - r"-r! ! '

k i r r s h , ' r r r n * . . \ 1 . . ; r r r r l B r r r t r . . H . r l 9 \ 7 . . s | , ; 1 1 , n , r .

;]i:l'il:li;:;within hlocks ')t trials ilr t,u"

Klouda. R. \'., Robin. D. .{., Graff_Radibrd. \ Hand (,.ooper. \\'. E. (l93lJ). The ,,rt" "i."it,,rli::i1":t,,T, in speer.h prosorlv Broin I),j,,,x3,5:154-17 i.

Koha rakawaT . . Endo . I l . . Avabe_Kanan ru ra S r ,

:nlgait T, yarn agrrchi. v . rir.,,"rri, i, l.i"a.]'Saito S, and Ogarr.a H. r lg96r. Th" p, i ; ; ; ;"-t t t( ,n- area irr hrrrrran cerel,ral ", , . t" , , t , , ,11", i i ,*rnagnetoencephalographr,. N eu rosr:i. t*tt i ltii55_158.

Kuhn, T. S. [962). The Stntctrtre of Stierttific &t.-.

olutio-rrs. (,-hicngo: Universitv .{,'Chi;;;';;rr'Kumar, S. (1977). Short_terrn memon. d;. n ;,,,;'erbal tactual task afier cerebral ;"r.;rr,;r-

tc>rny.. C orter 13:55_6 1.Lambert, A. J. (1993). Attentional interaction in thr

sp l i t -h ra in : e r ider r t .e f . , ,m, , "qo11r . f n ; r , ; ;\1ttr, ,7tsyrh,, lngfu 3l. j l3-�321. I "" ' \

LaPlane, D.. Levasseur, ! I . , pi l lorr, B., Dubois. l lBtrulac. M., Nlazover, B.. Tran Drh 4.. ;;,;;.G., Danze. F., and Baron. J. C. i lggg) Ob.;r,sive-crrmpulsive antl . ther i , .hari , ,ural . .hanl . ,rr.r th lr i lateral basal qanglia 1"r i , , , ' r , gro,,,- ;1: '699_725

Lashle_r'. K. (1929). Brnin Mecltartisnrs arrl lnkllt.

, f",,,r. ..Ch.it.aqt_r: Universih. o[ Chit.aqo presr

Lashte . r . K , /1951 repr in ted in Ig6 i r . Theprob len ,ot scnal order in hehar.ror. In Cen.hral .llrcha.nisnts irt Behaxior, L. A. Jeffress (ed. ). Neu,l.oriI lafner, pp. l12.

La.ssonde, I,{. (19g6). The facilitaton. inflrrenc, olthe corpus <.al losurn on intrahenrisph"n.: pn,cessing. In Turt Heni,sphere,s_Ont, lJratnFutctions o.f the Coryu,s ballosurr. F l_epn.M. Pti to, and IL I I . Jasper (eds,). Ne*, i i rr lNan R. Liss. pp. 385_401.

Lauro-Grotto, R- Tassinari, G., and Shallict T(submitted ). Interhemispheric transfbr ol rrrrraj.sernantic inibrmation in the callostornized lrnrrr

Lausberg, I{.. Cmz, R. F , Kita. S., Zairle}. ll . arvjPtito. .{

.(in press). pantomirne to r,isual pn,v,ltation of objects: left h:rnd dvsprzxia rritit rrrrri.plete callostornv. Braht.

Le Beau, J. (1943). Sur Ia chirurgie cles tume,un rJrrcorps caileur. Linion trt ed. C a rt. 72 : 13tr>-13\I

t . ,

t . ,

Joseph. R. (1986). Reversal ofcerebral dominancelirr lanSrage and enrotron in a corpus calloso-tomv patient. J. \eurol. );rrrr,,.rrrrg. psychiatnl19:628-6:)J

fornt. R. -J. (197.1) The corpus cal losrrrn: histon.o{.thought regarclins its fiinction. I, i";r;r;;r'p;;;r;,I)isconnectiort artd C erehral Futtt.tiort. \,f'Ki";-bournc, ancl \ \ ' . L. Smith tecls.t . Sprinei i" l j . i i

- C. ( i . Thornirs. pp l l7_125.

Jont. R. I ( i977) hrattention srrr<lromes in spl i t_lrrairr rnan. In Heni_Inatteritttrt arrl HentisTthereSTter: ial i :at iort. l l . . \ . \ \ .e. instein ancl R. p F""a_l:rnd (ci ls.). \eu.york: Rar.. t ,r prrss.

Irp 3.3_i;Ktssltr. J.. I{uber. \1.. parvl ik. C; . I leiss. ir f n- ,r l

Nlarkonitsch. I l . J. {1991). Oornpler *; ;( . r r , \ s - j l r t r .g r . l t i r , r r t l . l i t , i t s i r r a c l rse , , f , r r .p , , , , .n i_

t i

r )

I )

l l

i ' ,

I

T H E C A L L O S A L S Y N D R O M E S

l,r'bnur. Y. (1990) .\firli,vrt Lonrlon: \\'hrrrr.

[ ,eDrnrr. J. ! i . Risst ' . O, L Spnnger. S. P.. \ \ ' i lsol.I) . I f . . and (.) i t : tzaniga. \ I S {197;) Ooqnitronucl crrrnrtr issrrrotorn\ ' . Brain 1()0:57-�1(1|4.

l , t .hr lan. R. A. \ \ ' . {1976). The harrcledness of rhe-sus nronker..s. II: (loncurrent reaching. (,'or1cr

./ .1. 190-196.lriguarda. R.. Starkstein. S.. ancl Befthier. Ivl

t1969). Anterior cal losal haemorrhage: a part ialinterhemispheric disconntct ion srndrome.I l r t t i r t I l2 l ( )19 l ( r r l ;

l ,er in. IL S.. Eisenberg. IL N{.. and Benton. A. 1,.reds.). (199L't. I'rorttal. Lolx: Iiurtction antl Dq*function. Nes'York: Oxford Universih, Press.

I l r r n . l l . S . . ( l r l d s t c i n . F ( . . G l r o s t i r r e , S . \ ' .\ \ 'einur. l : t . L.. ( lrofford. \{ . J.. ancl Eisenbt,rgIL I\{ . (1987). I lernispheric disconnectiorr sn-tlromt persistirrg after arrterior cerebral artenrr lcnn sf r r ntptr I rc. \ ' ct trr,r t t r4c n-1 2 / \r l I -53\.

Len. J. I197-1). Cerebral asvrnnrctr ies as rrranifestecli r r sp l i t -h r i r i r r r r ran . In Ht . r r t i . :1 t l t r ' r i r - I ) i t t . , , r t r t . , . -ti()n ilnd Ctrehral Fnnction. l{. Kinslrourne arrcl\ \ ' I- . Sni i th (e.ds. ) Springfield. IL, C. ( l .J 'homas. pp. 165 t,$.

Len J. ancl Trevarthen. ( i . (1977). Perceptual. st:-t t tarrt ic anrl plurnetic aspects of elenrenttrn' lan-guage proccsses i l spl i t- l rrarn patients. Brnlrr100:1( ' t5-I16.

[,en J.. Trevafthen. O. and Spern.. R. \ \ ' . {1972).I)r'rc'eption ol bilateral chirlenc. {lgrrrt,s lbllorr-irrg henrispl reric deconnectio n. B rain 9,5:6 I -75.

Irrr ' - \ 'alensi. J. ( Igl0) Lt 'Coryts Calleut tparis the,ses -1.1E1. Paris: (1. Stt: inhei l .

l , r ' r R. ( i . . arrd I ln'den. \1. P. (1932). r\ dissocia-tion ol right ard lefi he.rrrisphenc efiects fbr rt.cognrzing cnrotiolal tone anrl verbal crntent.Ilrain Cogrr. Li)-9.

l ,hr:rrnit te. F. l lg6i l) . . .ut i l izat ion bchariorrr. ' . ancl i tsrelat ion to lesions of the irontal lobes. l l rzirrl()6:2:1i,255

l, lrerrnrtte. F.. l \{arteau. l l . . Serdam. N.{.. arrd( ihcdnr . F . i tg77) . S igns o f i r r te rhern ispher ic .thscr;nnectiorr in Nlarchia{ava-Bignarni ci iseasr,.. \r-r ' l r \crro1. 3J:281.

[ .h t ' r r r r i t te . F - . . ] , i l k r r r . l ] . . Scrc lanr . NL (1986r . t l r r -rtr i l l al l tor)ol lrv iurd the frontai lobes, Parl I : Ir it trr t torr arrcl utt l izat iorr behalior: a nerrropsvcho,lrr l lcal stu(h o1 75 patients. , \nrt. \ , t :uroL. l !) .ri2ii_rlrl.1.

l . r ( 'p r r . r . . l l . i l g00) . l )as Krarkhe i tsb i ld derAprir-r i t , I rrurtorisclrt ' Asrrr r lrol i t ' ) arr l ( lnrrrt l eir rcsFafles vor cirrseit iger: Aprir-r ie. ] Iormtusst ' l t rPvlt l i r f tr Ntttnl 8 lE2 lgi

[ . i t 'P r r ranr r . I l . . u r r t l N laas . o . t190 i ) Fa l l r ,o r l i r ks -setttgcr Agraphit rrncl .{.pra-rie lrt'i rechtsseitigerLahrrrrrng . l Pulchol. Naurt, l . t() :214-22i.

397

l,rrck. S J.. I l i l lvard. S. A.. \ langun. ( i R.. and ( laz-

zaniga. tr l . S. { lgEg). Inclcpendent hr.rrr isphenratterrtiorral svstens rrrt'diate visual searc'h insplit-brnin patients. N attt rt 312 :51!1515.

\ ' lac'Kal ' . D. \1 . ancl N{acKar' . \ ' . I l9E2l. Erpl ici t dt-alogue l>etrveen left arrcl right half-sr.'sterns o1'split brains. N ature 29,5 :690-691.

\{angun. G. R., Luck. S. J.. I ' � lager. R.. anrl Lofius.\\ : (1994). \{onitoring the i isual urrrkl: henrr-spheric asvmmetries and srrhcortical proc'esses ilattentiorr. .1. Cogn. l\teuntsci. 6:26i 2ii

\ Iarchett i . (1. and Della Sala (199E). Diserrtangl ingalien hand and anarchic hancl. (,i.'g. \'europstl-t :hiatry 3(3i:191-207.

\Iargol in, D. I . ( I9S4). The nerrropstchologr'ofu.r i t-ing ancl spel l ing: sernantic. phonoloqical. nrotor.and perceptual processes. Q J Erp l'sryt'lnl.;]6 159-1E9.

N{arie. l ' � . (1906. reprinted in 1971). The third lef ifiontal conrolrrtion plavs no spr.cial roie in tht'frrnct ion o1' langrraqe. Senmine trI id 26:211-21i.Reprintecl in Pierrr: JIarit,'.s Papers ott Speer:ltI) isorders. \{ . F. ( lole an<l \{ . ( lolc ' (r 'cls.). NeuYork: Hafirer. pp. 51 71.

\{ark. \ i . \ \ ' . . \ , IcAlaster. R., ancl Lase.r. K. 1,. (1991I.

Bilateral alicn hand. it"eurology 1l(Supp I ):302Marzi. (1. A.. Bisiacchi. l ' . . ancl \ icolett i . R. (t99l l

ls interhenrispheric trarrsler of ' , isuonrot<tr in-lbrrr-ration zrsvrnmetric? Flridence lronr a rnr.tu-an :rlvsi s. \' cuntTts t 1 c ht I t t gi a 29 ; 1 16:), 1 | i i .

I larzi. Cl. A.. Srr iani:r. N.. Nlaft irr i . (1.. ( ianrbina. (1..

Tonrel leri . ( i . . Palamara. A.. Alt :ssanrlnri . F.. anrlI'rior. \{. r 1996). Irnplicit reclundiurt-tarqets eflectin r.isrral extinction. \' aropsq chol.o gia 3'1 :9-22.

\ laspes. P. E. (1948). Le srrdrome erp6rinrentaichez I'homnre de ia secti<xr du spl6nium chr coryscnl lerr,r, alerie r isuel le pure herninnopisrlue. RerNerrrol. (Paris). 80:100-1 13.

Maver, E.. Koerrig. O.. Panchaucl. A. (198E). Tac-tual extinction rrithout anonria: ericlerrct: o1'attentional luctors ir a patient u.'ith a prrrtialcalkrsal clisconuection. )'t'euntpsqcltoLtgin 26.85 1-86u,

NlcKeevcr. \ \r , F.. Sul l ivan. K. F.. Ftrgrrson. S. NL.and Ralport. l\{. (1gFtl ). Trpical cerelrral }rerni-sphere cliscorrnectiorr rk,{icits lbllou.ing crrrpusciillr.rsurn sectron despitt. sparing o{ the' antt rior'(1 ' rnnr iss l r re . . \ ' 1 11y , ' : , t * ry t l t , t l " ' J i , t l ! ) : l l i 157 .

\{cNabb. A. \ \r . . Carrol l . \ \ ' . N{.. and \ l :rstagi ia.F . 1 , . (19EE) . "A l ie r r h : r r r l " anc l ioss o l b io r r ran-rr:r l crxrrcl irrat ion af ier tkrnt inant arrterior ct 'rr :-lrral arten' tcrriton' irrlarction. /. \utrui. \'ertnt-surg. P.u1clfiatn1 5 J :21t-222.

\ lc 'sularn, N{. NL t lgEl). A cort ical nehrrrrk f irr <l i-rected attention and uni l :r teral ncglcct. Anr?.\utrol. 10::]09 325.

398

\ l t ' s r r l : l r r . \ 1 . \ I I I ! j ! ) ( ) ) . La roe -sca i c r r eu rocogn i t i vench r r r r ks r Ln t l r ] i s t r i i r r r t t , r l p roc , r , s s i nq i i r . , , t t en_t ion. l ;Lrrr1tragr, . ,u, ,1 , , , , , , , , ,ur . . . { r i r t \ i rur l ;1. JE.l ! ; r j l J

\ l t , v , r l l - [ i . . Ro r i ch t S . . i r n t i \ \ i r r c , i t . c ] r ou . . sk r . ( , .I l !J ! )5 r . ' fopogral)h\ .

of l j l rers in t l re hrrrnatr urr-p r r s t u l l os r r r r r r r r e r l i a t i ng i r r t t , r h t , r r i sp l r e r i c i nh i -l r i t i r r r r i r t , t t . r , r ,n the rr rotor c,ot t ices. \ t t r t . \ , t , t t ro[ .l,i::l(i0- rl6t).

- \ l ic , l re l . l i . . rut t . l I ) t , ronl t , t . F- . i lg75i . Ext inct iorrgar rc l re ar r t t ,s t r l ichot i r l r r t , : l t js ior r h6rr t rsph6r i t luerru lds iorr t r r rnrnissrrr - . r i , , ! l r r /_r , r St i , t , l r , , , ,u,sr l t ' I ) iuor tnt t iot r ( ' ( l l ( .u\ t . ( ,1t , . : L Hrt t r t t ru. . b, .\ l i < . h t ' l anc l l l . S l l r o t t r l t l s . ) L r r r n : I l 6p i t a l \ e r r -r o l og i r l r r e . pp . E5 l l i .

.Ui l ler .J r l9E2). Dir . idet l at tent iorr : cr ic lence torcoac' t ivat iorr n.r t l r rer l r r r r t l iur t s ignals. Cogn. pst l_cl tc , l . l . t ;2t i 219.

\ l i lner . A I ) . . ancl Grxr t la l t , . \L , { . (1995). . f l rc \ , i -

snal Rrai t t i r t . . \ t : t i t t r t . ( )x lbxl . LIK: Oxf i r rc l L. ln i_vers i t r .Pr lss.

\ I i lner . B . arr t l Tar lor . t , { 1g72 ) Right_henr ispheresrrpenor ih in tact i ie pat tern_re(,oqni t iun af terc.ereIrr i r l t r r r r r r r issrrrotomr. : er ic lenc,e f r r r norr_ver l r : r l r r rerrror- t . \er t r t4t tyc l toktgio I 0: I , IE.

\ l i i r rer . I l . . - f : l lor .

1, . a, r r . l . ; , , , , ,1s_Ci, r rnan, \ { .( ] lb !10I . I_essons f rorrr c ,er t bral crr rnrrr issurotorn\ , :i l l r ( l i t ( )n. : r t t t ,nt ion. l rapt ic rnernon.. turd, , isrra lirnagr:s in verbal associatrve learrring. In BrainFurt t ' t io t t .s anr l Ciru i ts , ,1 ' t l t t ) I i r t r l . ( j . B. Trc,_Varthe| ( t , t l . ) . ( janrbr i r lq, , . UK, Carnbr jdge Uni_versitv Press. pp. 293_t)03.

\ ' l i lner . 11. . Tar. lor . L. . ancl Spern. . R. \ \ , (196E), Lat-r . r a l i zed s r rpp ress ion , , f t d i t l l r , r t i r . a l l r , r . " r " * " . tr l ig i ts af ier crrr r r rn issrrru i srct i r r , i r r , ; ,J , , ; , r ; ; ; . ,1 61. I 6.1_ I t6

\ l inqa: , -z i r r i . ( ; . ( 1922) l ) t r l l r t lker t . l : ler l in : Spr in{er_\ e d i l q .

\ l o i r r . 8 . . P r rh e rn ru l l e r . F . . l l a r r na r r . J . . anc l Za i c l e l .F. . l l99-1ar. l l terhernisphenc crxrperat ion c lur_ing ler ical proc. t .ss ing is rner l iater l in . the corpusc'a l losrrrn: t , r . i r lerrce, I rorn , r spht_brain pat iJnt .. \ - t 'u nt n '7 to r l l , \ 1 . L7 -21.

\ lohr. 8. . l , r r lvernrrr l ier . F- . . ancl Zaic le l . E. Igg4b)Lerical rlt'c'ision afier le{i. right arrcl bilateral rrreserr tat iorr o1 f i rnc, t i rxr words. content rvords^anr lr ron- l r r r t ls : er ic l t ,nce fbr interhernispher ic inter_ac.tior r. _\ r,rln1 t s, q c I u t lo giu ,3, j 1 05_ l t4.

\ l lers. R. E. i l956) Functiorr of. the c,oryrrs cal lo_surn in irr terr icular transfer. t l rain 79:i5g_363.

-\ lvers, R. E.. :rrrt l Spern.. R. \ \ ' . r195:l). Interoculartr i insfer of r isrral l i rrnr r l isc.r irrr inatiol habit incats alt i ,r ser,t ion o{ t}re,optic,chiasnra and cor_lrrrs c. ir i losurn. .- \nat. Rt,c. I l5.3i l-n:) i2.

\ lvt rs. l l . 1.1.. rrrrd Spcrn,. l i . \ \ ' (1956l. Interhenri_sphr, l .r( . corrrrnrirr ic,at ion throrrqh tht, crrrpus cal_

C L t N t C A L N E U R O p S y C H O t O C y

I , , s l t r t r , n rn , . r r r , r r r i r . t .a rn _or e r hehver t r t l re [ "p ,_slr l ' . rer. . l rr . /r . . \ i r l i , / . ptrtr . l r i r t tnl Vt :gi_irn"

\ l rc rs . l . J . an< l Sp. rn . H i r tg r5 , In t * rh .^ , , .sp l re r i t t .o rn r r r r r t r i r . r r t ion a l ie r s t , r { ion , ,1 tho f i , r , .brain c<rrrrmiss tres. C)t n1 er 2 l. 2qg_260.

\a ik l r . \ . lggg ' . S ; r r r r r . , r i l f f e r r . r r t j r r r lqerner r ts a l r l r r rt h r ' , l i r ' t . t i r r . r r r , i , r , l , , r r r , , f . , p 1 r . . , , , ; _ , " ; ; l ; ; ; ; ;st imuli after corrrrrr issgia:)7.485Jg3.

; t trot<ttt t \" \ i turopsqtholo'

Naikar, N.. arrcl Corbal l is. LI. C. i t996). perc,eDti.nof apparent rnotion :rcross the rr"tinal ,i,ll;"1,;;;-lrtrr.jng cornrrrissrrrotonr\,. N "rr rr rTr rrl rtrol,, /A' li;.t297_309.

Nar.en. D. (1g77). Forest be{irre trees: the prece_dencr o l q l , rha l {u r t r r res in r rs r ra l n . rc , l r l , , , ,(1 , '4 t .psyc lu , l 9 rb3_3t3 .

r i " i ' ' I

Nebe's, R. D. (197i) . pr jor i tv . of thes l ) h ( , r r . i n co rn rn i ss r r r o l o rn i ze ( l l nanception of part-rvhole relatiolts.333_349

minor henri-for the prr-Cofter ll

Ncbes. R. D (1974). llr.rnispheric specializ.iition irjcommissurotomized man. psychLtl. Bull. B l, L | +\ e h e s . R D . . a r r t l S p e r n . . H . \ \ . , 1 9 ; l , I l " , ; ;spnen(. cle(,onne(.t ion sr. lrdr,rnre u. i th t .erelrralbirth injury.. in the dorninant arnr ,."r. i;;;rop s y chob gia 9. 217 _259.

Overman. \ \ , . I{ . , ancl l)oh,, R. \ \ . . r igg2). I lerrrr.spheric spe.cialization displavecl f,l. rrl"" fu,t ,,,,,lry macaqrres firr analvsis ,rf' f"""r. I,",r,;,,rr;;,t ' h t l r t { i t t 20 . t l r } - I : \

Pandva, D. N.. and Rosene. D. F, ( l9IJ5). Sonre ob-s ( rna t to l l s o r r t ra je t , lo r ies and t , ,pograp i r r , r lctrrnrnissrrr ir l I ihers. lrr Epi lrpty ur,, ' l th,. ( : , , , . tu,,C al I t t . , r t r t t . .- \ . ( i . Heei.es, "d. r. i . .r , . \ . , ,r1, pl"nl,u,Press, pp. 2l-39.

Pashler, H.. Luck. S. L.. Hi l lvard, S A.. I lanqulG. R., O'Brien. S.. :rncl ()azzaniga. \I S {1995Seqrrential operation of disconnec,tecl cerelrral

! "^tl,]T!"*r i n spli t- brai n patien ts. ); eu rn rq r,,t

5,2381_2381Paters<xr, A.. and Zangu,i l l , O. L. ( lg4d). Disor<icrr

ol \ tstrat spat.e perception assoc.iaterl rr i th lesrr,rrrof t l re r ight <.erehial hemispherr. Broirt hi331-356.

Phelps, E. A.. Hirst, \\'., and Geuzanrga. \l S(1991). Defic;ts in recall follorving partial anrlcornplete commissurototnt. Cereb. (jo*t lgi-.{98

Pipe \1. r l99l r. Der.elopmerrtal t ,hang.r irr l )rrqr.r

_ tr rcaf ization. .\' eu rt,7 t.* y c I n l, ryi a 29. 33g_j"l 2.I'lorrrde, G.. and Spern. R. \\,. (19g4). lrft henrr-

sphere inrrrlvement rn Ieft spatial neqiect liorrrright-sided lesions: a commissurotomv stutlrBrain l()7.98-106.

Poeck, K. (l9iJ.4). lieuropsr.,chologicai tlenrorrstr.r-tion ol splenial interhernisphenc tliscrrrrncclrori

T H T C A L L O S A L S Y N D R O M E S

rn a case of "optic

anotllii i. \europsyt:holouiu

22:707-il:JPoffenberger, A. (1912). Reaction t ime to ret i l ral

stimulation r'vith special relerence to the tirne

lost in conduction through nervolls centers.

Art:h. Psqclnl. 23:I-73.

Pollmann, S. (i996) A pop-olrt induced extinction-

like phenomenon in neurologicalh' intact srrb-

jects. N ett rop sy cholo gia 34 : 413125

Polirnann, S.. and Zaiclel. E. (i99E). The role of tlrc

corpus callosum in','isual orienting: i niportance

of interhemispheric visual transfer. Neuropsrl'

clnlogia 36:763-ii1.Polhnann, S., and Zaidel. E. (1999). Redundtrncv

qarns for visual search after conlplete comntis-

surotomv. N enrLtp ry chokt gq I 3 :216-256'

Poncet. \{ . . Al i Ch6ri{, A.. ( lhorrx. M.. Botrdo-rrre-

sques. J.. ani l Lherrnit te. F. (1978). Etrrde nerr-

ropsvchologique cl'trlr s\r clrotne de clFcot r rteriot t

culleuse totale a"'ec h6nriant4rsie IatFteralt'

horrionrrne droite. Rcc. Neurol. (Pari,s) ll:633

65r1.Posnrr. NI. I (19fJ0). Orienting ol attention. Q

I L-.xp. Psqchol. .:32:j-25Posner. \{ . I . , ancl Dehaene, S. (1994). Attentional

Irehvorks. Trends N euntsci. 17 :15-79.Proverbio, A. N1.. Zani. A.. ()azzirniga. N{. S, and

Mangun. (1. R. (1994). ERI' and RT signs ol a

nghtw'ard bias for spatial orienting irr a split-

brain patient. Neuroreport 5 :215i -2461.

399

Ree'r ' t 's. A. (1. (1991). Behavioral changes f ir l lor i ' ing

corprrs callosototnt'. Irt AtlL,urtces itt \eumktgr1'

\ i t . 55. D. Snrith. D. Treirnan. and N{. Trirrble

(eds.). Nerv York: Rar.'en Press. pp. 293 300.

Rerrter-Lorenz, P. A. ( in press). Paral lel processiug

in the bisected lrrain: irnplications lor callosal

functions. ln E. Zaidel and M. Iacoboni (eds.)

Tlrc Parallel Brain: Tlrc Cognitiue Neuntscit'nce

o.f tlrc Coryus Callosun. (lambridge. NlA: I\IIT

Press, pp. 3'11-35'1Reuter-Lorenz, P. A . and Fenclr ich. R. (1990) Ori-

enting attention across the vertical merritlian: t'r'-

iclence frorn callosotornv patients. J. Cogrt. Nctt'

rosci. 2:232-236.Rerrter-Loreriz. P. A.. Nozau'a. O . Oazzarl iga. Nl. S..

ancl I lughes. I I . C (t995) Fate o1'negle'ctccl tar-

gets: a chror)ornetric attalvsis of redunciant tar-

qet eflects in the bisected lrrain. /. Et:rt I'sqt:hol.

H urn. Pent:ytt. Perfonn. 2 I :21'l'-23(1.

Risse. (1.. Ciates. J.. Lrrncl. ( i . , Nla*vel l . l i . . and

Rtrtrerts. A. (1989). Interhernispheric transfer in

patients u'ith incomplett: sectiotl of tht' colpus

callosrrtrr. Arch. N eurol. 16:13i 413

l l issc, G. L., Lt 'Doui. J.. Springer. S P . \ \ ' i lson'

I). Il.. and ()azzttniga, N{. S (1978). The antcrior

crlrnmissure in rnatl: functional variatiolr in a nlui-

tisen son' srstern. ;\kzrrrp s q cl nkt gi a I 6: 23-3 I

Rivest. J.. Oavanagh, P., and Lassonile. N'{ t199'1)

Interlrernispheric clepth judgrnt:lt N eurttp srl -

choLogirt 32:69-i6.Rohertson. L. (1.. and Lamb. M R. (1991 ) Neu-

ropsvcl'rological contributions to theories of parV

rvholt' organization (,irgn Psyclutl 23:299-330'

Robertson, 1,. (1., Larnb. M. l l . ' and Knight ' R. T'

(f988). Ef{-ects of lesions of temporal-parietal

junctiorr on perceptual and attent'ional process-

ing in hutrt i t trs. l . Neuntsci. B:3757-:1i69'

Rotrertson, L. C., Larnb. \{ . R. and Zaidei ' E'

(1993). Interhemispheric relat ions in processing

hicrarchical patterns: evidence from normal trncl

cornrnissttrtrt<rrrrized subjcct s. N euntTt s q c l nlo grl

7:325-312.Rost 'rre. l) . l - . . antl Virt t Floeserl. G \\r , (1987)' Thtr

hippocarnpal firrrnation of the primate lrrtritr' In

Cen:bral Coftt'r. E. (i. lones alrd A. Petcrs(eds,). Ne'rv York: I'lentrrn Press- pp. :315456'

l loss. t l , D., and Rush. r\ ' J (1981). I) iagrrosis anrl

ncrrtoartatottt ical c<rrrelatt 's ol del lressiorr irr

lrrain-danragecl Patients. Art'Jt Gert Prydilatnl

,ll8: 13,1.1-135'1l irss. E. D.. and Stervad. R. M. (19E1). Akinetic

rnutistn fionr ll'pothaliinric darttage: srlc'cessfrrl

treatrnent with dopalnirre agcmists. \'utroLogt1

,31: l4r l5-1439.Itr lr t 'ns. A, I l . . F-roehl ing. B.. Slatt ' r . (1 . an<l An-

tlersott. D (19E5). I-efi ear suppressiorl oll vcr-

Pujol, J.. Junqucl. Cl., Ventlrel l . P.. ( larci ir , l ' . .(Japdevi la, A.. and Mart iV:i lal ta. J. L.. ( f991).

l-eft-ear ertinction in patients r.vith MRI Periven-tricular lesions. N at rt4tsy <:holo gia 29 : 17 7 -1 81.

Quattrini, A.. Del Pesce. NL, Provinciali. L.. Clc-sarano. R., Oftenzi. A., Pagg, A.. Rvchl icki. F.Fioravanti . P., and Papo. L (1997). Mutisrn in 36

patients s'ho untlenvent callosotomv for drug-rr:sistant epilepsr'. J. Neuro,vrg. Sci. 'l.l;9il-96

Ranrachandran. V. S.. ( lronin-( lolonrb. A., and N' lv-ers. J. J. ( l9t i6). Perception 0{ apparent tnotiottlrv cornmissurr)tolnv patients . N rfiun' 32() : 356-:159

Rarr. S N{.. lJemardin. 1,. . Leo, (1. J.. El l ingtcm. L."Rvan. S. B . and tsurg. L S ( lgEg). ( ierelrral dis-tlnnection irr rnultiple scienrsis: relationship toatrol lhv of the corpus cal losurn. , \rr: l t . \euntl ..16,918_920

Ravrnond, F., Lt jcxrne. P.. and l , l rrrrnit te. J (190fi)T t t r t te t t rs r l r i t , , r1 , r t a lh . r r r . F . t t , t ;1 ' lu r l , / S i l l ] 565 .

Rarport. M.. Fergrison, S. NI.. ancl ( lrrne. \ \r . S.t l9tj3). Outconres ancl inclicatiors of corpus cal-losttrn section {br intrirctairlt' seizrrre control.Appl. N europhasiol. 16:17 -51

Reeves. A. (;. (e<l i't rg61). EpileTt,stl urrl the coryrtsCallovun. Nc'w York: Plt'nrun l,rcss.

400

bal cl ichotic tests in patir .nts *, i th rnrr l t iple scle_rosis. Anrr. \'r,uni. 1,!:.159--lfiil

Rrrclgc. P.. arrd \ l ,arr ington. I l . K. r l99l). Sclectivtirnpainrrt ,nt of nternon. i tncl r isiraj perception irrsplenial trrnrorrrs. IJrairt I l . l . : l l9_: i60

Sass. K. J.. [ ,e'r :cz. T.. \ \ i ,sten.clr l . M.. Novellr . .l l - A . Spcncer . D . D. an t l K i r r r . J . I I . (1991 l ) .Th t ' r r t ' r r ra l s r r l rs t ra t r , , , f ,n , : , r , , , , .1 in rpa inne. r r trlernor.-traterl ll., the intrirc.aroticl arnobarbitalprocedrrre. . \n.h. \ : t :uol. , lg: lE_52.

Sass. K. J.. Nrx't , l l r . . R. A.. Spence.r. l ) . I) . . anciSpenc.er. S. S. { tgg0). postcal losotornv iarrquagt,irnpairrnents irr patients uith crossed cerebraldorrinancr'. J. tueun tsurg 72 :gi-g}.

Sa." 'aki, I l . . and l)alezios. y. (1999). l4C_deoxr-glrrcose rrappirrq of the nronker. hrain duringreaching to risrral tarqets. prog. )lettrohiol. ,58;.173-540

Sarvtrguc,hi. T.. and (blclrnan_Rakic. Ir . S. ( l99l). Dlclopanrint' receptors in pre{rontal corterx: irr_rrrlr.'enrerrt in rrrrrking nre ntort,. Science 2Sl.g17_950.

Schaltenbrand. (; . i l964). l) iscussion. In CrebralLocal.izrttiott ancl Orgurti:atiort. C. Scha,_tenbrancl and C. N. \ \ i rolstr- (eds.). Nlacl isor,.Unir-r.rsi t t of \ \- iscon.sin prt,ss. p..11.

Sc'hif ler. F.. Zai<lel. E., Bogen. j . . u,, .1 Chasan_Taber. S. a1998). Dif l 'erent psr.chologicir l statusirr the hrrr herrr ispheres ol two spl i t_brain pa_tients.,,\:r,u rr;1 t.s t 1 t: hiat n1 s- t :u rt ryt s y t: h ol. B el t)tx\atro[. 1].15]r-IE6

Schott, B..Tri l let. \1.. Nl ichel. F.. arr<i Tornmasi, M.iI97.1). Lc Srndronre cle r l iscorrr iexion cal lerrsec.hez Iur.bidextre t,t le g.rrche,r. tr, I",; i;r;:d ro t ru: s de I )i.s tt n t Leio n C all au t, C I u, : L. H o ni ne.F-. \ ' f ichel an(l B. S(,hott (erls.). Lron: I{6pital-\errroloqirlue, pp. ;3-1:3-l).1fi.

Sc'hrl .artz. \1. F.. Rced. E. S.. Montgorne,n,. \L.Pa i rncr . ( , . . and Maver . N . IL ( lgg l ) . The quan_titative rlc,scription of uctiorr rlisorqanisatirir af_t t , r I r r a i n ( l a n l r { e : l r t , t r s e s l r r d r ( . . , , g r r . . \ i , u _nrysyr:hol. S. 3El-.11,1.

sersent. . t . i l9B3). t ini f ied respons(, to bi lateralhernispheric st imrrlat ion bv ir spl i t-brain patierrt .Nahtre 305.3(X)-802,

s( 'rgent. J (19u6). Subcort ical c<iorcl ination of henri_slthere actir.itv in comrnissurotornizecl patients.Rrain 109::J57,:)6g.

Sergent. J. i t987). A neu-look at the, hurnan spl i tltrain. Rrttirt I i0. l:l71-I3g2

Sergcnt. J. (1990) Frrrt ir .e ir .rcrrrsi6ns int. bicarneralrninds: integratir.t :rrrcl coordinating role of sub_crrrt ical stnrc,trrrt ,s. Brain I I , : ] .537-ui66.

Serqent. J f lgglr. proc.tssing of spatial relat ionsrr i thir arrr l l r t 'hveen the discrrnrrer,tet l cerebralher r r i sph t ' res . Bra in I I J l02 i - l0 . l r l .

C L I N I C A L N E U R O P S Y C H o L o C Y

se\.'rnour. S. 8.. llerrter_l,ort nz. Ir. ,,\., iurtl (iivzzulfgn,NL S. [994) Thl rlisconnectiorr srrclrome: l]n5;(.lindings reaffirrrrecl. Rntitt t l7:l0S-11B

Slral l ict ' . T.. Burqess. p. \ \ ' . . Schr>n. F.. an<l lJaxter.D. I .L (1999) Thc origins of rrt i l izat ion behirr,-icnr. Rrain I I2: l5ET.biE9E.

Sidt is. f . J. ( lgt jS) Dichotic l isterr ing al ier comrnrs_srrrotorlr\'. ln Ilanrllxutk of'

lit.httic Listt,rtittgTlu'on1, )Iethot!.s arul Rel(ur(.|t. K. llug,lnhl r",i ,

. \ r . r r ) , r r k : J o h r r \ \ ' i h , r l r r t l S r , r r s p p . I { l l _ l \ J

Sidt is. I J.. Sacl ler. A. Ft. and Na-ss. R O.irglg). i ; ; ,lrle clisconnectiorr r,f1i:cts rcsulting fnrm infiltrat-in g trrrn ors. N eu rt ry t s q c h o Lo girt 2 7 : I I 1-r_1 120.

Sidtx. J [ , \ 'olpe. B. T.. I lol tznrtrn. J. D.. \ \ , i lsorr.D. IL, and ( iazzaniga. \1. S. ( l9, la) C.iognit iveinteraction after stagecl callosal section,' E,.r_dence lbr transf'er of'sernantic actir.ation. Sciertrr,212.:l+1-:Jq6

Sid t is . J . J \o lpc . B T . . \ \ ' i l s , r r r . D . I l . . Ravnor rN{ . , Cazzan iga , M. S . ( lgg i l r r Vanah i l i t v in ng ; tIremisl lhere larguage l irnt. t iorr , ,1i", "ol irr" l r l , l_tion: evidence for a continuum ofgenerative ca_pacitr,. /. Neurosci. 1.323_331.

Sirnernitskaia, rr-. Cl. . and Ruma. \ ' . C. r lgEg). N{enr_ow disorders in le.sions of the corpus callosrrrrrin rnan [in Rrrssian]. Zh. \,qs,slt. \tct:t.. Dt:iot. IrrtI P Padota 39;995-1002.

sine. R. D.. Sorrf i . r \ . . arrd Shah. \ , I . ( lgg.l) . The cal_losal slrclronre: irnplications for stroke. .lrdrPhq.s. Med. 65;606-6I0.

Sobel. N , lrrabhakaran. \,.. Ilartler., C A..De.srnond. J. E., Glover, G. IL, Sul l ivan. Fl. \ ,arnd Clabriel i . J. D. ( lggg). BIincl snrel l : brain ac._tivation inducetl bv an rrnde.tected air_brrrnr,clrernical. l l rain I 2i( pr 2 ),209_�217

Sparks. R., and ( le,schri . ind. N. i l96g). Diclrot jc i is_terring irr nran after section of rreoc<trtical conr.rnissures. Cofter 4:3- L6.

Sparks . R. ( ioodq lass . H. . and ) ,J i t , k r , l . B . r l9 i0 r In_s i la te r r r l \ ( , rsu i i ( \ ) l r t ra ia t t , ra l t , r t in t t ion in , i r_chotic listening f'rorn hernispheric lesions. Cor_ter 6:219-260.

Speedie, 1,. J,, C--oslett. IL B.. and Heihran. K. \ t .( 1984). Repetition of aflective prosodv in nriredf rarrs<'ort ic.al aphasia. Ar,. l t . . \ 'ei tr , , l . _t t .26\_27(l

Spence. S. J.. Zaidel. E.. and Kasher. A. (1990). Theright hemisphere cornmunication batten.: rr,.s r r l t s f ro rn t r r r r r rn iss r r ro to r r r r pa t ten ts o r rd n , lnn" lsubject.s reveal onlv pa.tioi .ight hemisphere

_ contribr,rtion. J. Clin. Etp. Natrops;ychtt. l2.i2l3

Spencer, S. S., ( lates. J. R.. Reeve.s. A. R.. Spenctr.D. D.. \{anrr, l l R F. . and Roberts D. r_t9birCorprrs callosurn section. In Surgiutl Trt,atnu,nt' , . f lhc Ep i ! , ,1 t . , ia . r . J . Er rg" l . f r . ,ed . , . \eu . ) i , rk .Ruver r l ' ress . pp {25 !J+ .

Spencer. S. S.. Spencer, D. D . \ \ ' i l l iamson. p l)

\ l

3Et

$f

ii.

$:

I H i C A L L O S A t S Y N D R O M E S

Sass. K. J.. Novelh. R. A,. arrcl \{attsol. R. l l .i i988 ). (irrpus callosotonn firr epilepsr . I I.\europsrclrol<rgical outcorne . N ea rolog1,38 : 2l26

Sperrv. R. \1'. (1961). Cerebral org:uriziition ancl bt'-ltarior. Science I 33: 17 19-175i.

Sperry'. R. \\". (1964). The great cerebral comrnis-strre. Sci. .4n 210:12-52.

Sperrv. R. \ \- . (1968). Nlental unih'fol lo* ' ing surgi-cal disconnection of the cerebral hernispheres.

l,ofic.r \eq,york: Ra.,.en press.Sugislr i ta. \ i . . Otorrro. K.. \ 'anrazaki. K.. Shimizu. I I

Yoshioka. \1.. anrl Shinohara. A ( 19g5), Dichotic

Han:. Lect. 62 :293-:)23.Spern. R. \ \r . (1970) Perceptior in the abserrc.e of

the leocortical commissures. A,ssr.;c. Re,r. ,\rcnllent Dis. 18: 123-13E.

Spern. R \\ ' . (197'1). Lnteral sptcial izat ion i ' thesurgicalh separated hel i ispheres. In,\ :r : trr ;-,stience 3rd Studq Pntg.. F. O. Schrnitt anclF (1. \ \ i rrden (e<ls.). Oanrbridge. \ IA: \{ lTPress. pp. 5-19

Sp"..t R \\'. (1982). Sonre e{}ec.ts of clisconnectingthe cerebral he. rn isph eres. S r :itt t t t, 2 I 7 ; l 22i'.�1 226.

Spern, R. \ \ ' . . and ( l lark. Fl. (1949). Inter<nrlartransler o{'risual cliscrirnination habits in tt,leostfrsh Phqsiol. Z,nl. 22:372-37\

5pn1 R \\'. anti Ciuzafiga. N,l. S (1967). Langrageiirllrxving suryical discorrnectior.r o{ tht, henri-spheres. In Braht Mecluuistrts ()nderlryinq Spt:ecltard kutguage. (i. II \{illikan arrcl F. L l)arlere r l r \ r . r r ' \ i r r . l : ( , n r r r r . a n d S t r a l - l o n . p p . l i i - l r + .

Spern. R. \ \ ' . . Ciazzaniga. \ l S.. antl l logen. J. E.i1969). Interhenrispheric relat iorrships: the rreo-crtrtical cornmissures: s\,rrdr()mes of hernispheredisconnection. In tlandbook of Clinical Nerrrol-ogr', Vol. .1. Ir. J. Vinken ancl Cl. \\r. Bruvn eds.

, \o r th I lo l lan t l , pp . 2 i3 -29{ )

rpern'. R. \ \ ' . . Zaidel. E.. and Zaidel. D. (1979). Sel lrerrrgnition ancl social awareness in the decon,necterl nrinor hemisphert:. Neunrytrychologia17 153_166.

Spnnger. S. P.. ancl ()azzaniga. \{ . S. (1975). Dj-chotic testinq ol paftial and complete split-brain

,.. subjetts. N et n^op,;ty'l u tlt t gia I 3 i7 1 -3+6.

: r ta tn r r . J . S . . Rosen. S . (1 . . and Goc lo t t i . A . (1977) .Lateralizatron o{ firnc.tions in the rrionkt,r.'sf r r , t r l a l r r r r t I r I t t L t l l t n t l i i t r t i r t r t i r t l l t r . \ ' , . r - r , , rASrystern. S. I lar lac l . R. \ \ ' . I )oh. . 1, . ( io ldstein.

] .Jayncs. ant l (J . Krarr tharrrer (eds.) . Neu, yor i ,

.. Acaclernic Prt'ss. pp. ll85-.102.

starkstei r r . S. l l . . I ler th ier . \ { , 1, . . Fer lorof} . p. . I , r icc.T. R. . ant l Robinson. R. (1. {1990) , {nosognosia, t t t t l r r r i r i r t r r l e p r t , s s i o r r i l r I I r a t i e r r l : r i i t l r t , r r r .I r r r r r as r . r t l ; r r l I s i o r r s . \ ' , l r r r , / , , g17 / / / : l : i S0 l . ] \ l

Str rss. D. T. . ancl Bensorr . I ) ! ' . ( lgrJ6) Tl r t I - ror ta l

101

listening irr paticnts ni ih part ial sectiorr ol thec<rryrrrs c:r l losul;rt . Bnti t t 1 l S. l1l-J'2i.

Sugishita. \{ . . and Yoshioka. l \ ' I . r l9E7t. \ , isual pro_cesses in a hentizrlcxic patient uith poste,rior cal-l<rsal section. NeuroltryclnLogiu 25;J2g 33g.

Srrgishita. Nl.. \ 'oshioka, \ ,1.. antl Karvamrrra. tr{.( l9iJ6). Recoven' f iorr herl ialexia. Rrain l-arrg.,9i 106-1 I 8

Sr rssmiur . \ i . \ { . . ( } r r r . R . (1 . . ( i r r r . R . E . . andO'(ltmnor. \.1. J. ( l9tj3) Nftrtrsrn as zr consequencerrf call<rsotornr,. J. \' euts u rg.,59:5 I "1-5 i g.

Su'eet. \ \ ' . H. {1945). Seeping jntracraniurl anerrn.snrsintulat ing neoplasrn, srrt<lr, ,rrre ot t l re corluscallosu nr. Arch. N eu ntl. p,s t 1 chi a t ry I 5. 56_l ()l

Tabibnia. A.. Kee-Rose. K.. Ilickels. \\'.. arrcl Zaidel.E. (200I). Ilenrispheric specializahon. t"rnotirxr.iurd alexithr,mia. Cogrt. Neuntv.i, Soc. Nxtr. B:30.

Tanaka. Y., Irr 'asa. I l . . ancl \ i rshida. \L (tgg()). Dr-agonistic tlvspra,ria: case report and rrovernerrt-related potentials. \ erz rolog q 10 : 657 -GGl

Tenllouten. \1.. D.. I Ioppc. K. I) . . Bogen, J. E.. ancl\ \ 'al ter. D. O. (1l9E6) Aleri thrrnia: an cxpen,mental stutlv of cerebral comrnissurotornv pd-tients ancl normal control subjects. Atrt. J. p.u1,r ' l t t t t tn1 i . / .3 312 : ] t6

Jirrnaiuolo. F.. Pti to. NL. Marzi. (1. A.. I)arrs. T.. arrdPti to. A. 11997). Bl inclsight in hemispherec_toritized patients as revealcd bv spatial srlrtna-ti<rl ac'ross tlte veftical rnericlian. Brain 120:795-E03.

Torlr i ls( ' l r . J (1954) Size. t l istr ibution. ancl nrrrnberof fibres in tht: human corprrs callosrtnt. Artat.Rec. I19:7-19.

'Iornasch, J. (1957). A rluantitatir.'e analysis of the hu-

rnarr antcrior cornrnissure. Atta Arwt. 30:902_906Trarno. M. J.. and Bhanrcha, J. J (1991). Nlrrsical

prirning bv the r ight hemisphere post-cal loso-tcrnr.'. ;\'tz rop,ny:ho b gia 29:3 1.1-325.

Treisrnan. A. NL. and Gelader. Cl. ( lgE0). A f i ,ature-integration theon. o{ attention. Cogn. p.ryr:lul12:97,1:J6.

Trescher, FI. I I . . arrd Ford. F. R. (1937) Clol loi t l cvstr r l the t l r i r r l ver r t r i< le : r r .por l r r l a t as r , : op l ra l i v r .rernoval uith section of posterior ltal{ of corprrscal l<rsrrrn. Arth. Neurol. Psqclt iatnl 37:g\g, l)73.

Tnl 'artht,rr. ( j . (1965). Functional interactions be-hver,n thc cerclrral hcrrr isphcres of the spl i t-lrrairr rrronker'. l'n I'ttttr:tiort.t tl' tlu, Ctnlnts Cal-/o.r l l r . I . l . (J. ! i t t l i rrger (t , t l . I . Lonrlrrr: ( i l rurc,hi l l .pp. 21--1{)

J'rt ,rartht 'rr . (1. i t991). Inte,qrat ir . .e l i rnct ions of thect'relrra] c.omrrissures. ln flrndbook tlf Nttrrt,ytsr1cluil.ogy, \1o1. 1: Tlp Coilunissurotouti:.cdRrairr, R. I) . Nt,bes (ecl.). Oxl irrd: Elserier. pp.-19-E3

l 'revaftht:n. (1., ancl Spcrn.. R \\ ' ( lg7l3). perc,e-p-

402

tual unitr. of the arnbient i , isual f ield in hrrrnalrcolr rn i ssr r rotom',' patir-rrts. I) ra i n l) 6 :517 -87 0.

Trope. I . . Fishrnerrr. B.. Grrr. l l . C.. Srrssntarr. N. \{ . .anrl ( lrr . l t . E. ( lgET) Contralaterr l anrl ipsi lat_eral <.ontrol of' lingers firllori.irrg c_.alLrsotornr..)i at n'p s r I cht io gia 2,5 : 2ti -29 l

Trr l ler. B.. l rrr l Kelso. l . , \ . ( lglg) Flnrironrnerital lr .speci l ict l pattents of rtrolerrrerrt crxrrt l ination inrrorrnal unrl spl i t- l rrain srrbjt ,cts. l)qt. Brait t ke.s.;5 306Lrl16

'I ' rvi tchr, l l . T. E. ( l t)5I). The restoratjorr o{ 'rnotor

frrnct ion fbl lor," ing hern\r leqia irr rnan. Brajrr71.113_180

Tzavara-s. A.. I l6caen. IL. and Lt. Bras. H. ( lg7l)Trorrbles cle la reconnaissalrct du r.isage hunrainet lat6ralisation h6rnisph(.rirpe l6sionielle chezles srr jets gauch ers. \, eu ntps y c lt Lt Lo gi a 9 : 47 EJ7 7 .

Van Kleek. M. i lg8g). Hernrspht,re t l i f ferenc,cs rnglobal r.'t'rsus local processing of hierarchical r,i_sual stirrruli tl normal subjects: nerv datti and trrneta-analvsis of prel'ious strrclir:s. Neurop,stl_r:lnlogitt 27. 1165,1 178.

\blpe. B. T. (1982) ( lort ical mtchanisms invol,, ,eclin prirxis: obsen.ations lbllorving partial and corn_plete section of tht. corTrs cal losrun in man.\: ttr ro kt grl,Jrr 6-15-650.

\\-arren. . f . NI.. ancl Nonnernan. A. J. {1976). Th(,search f irr cerebral dorninanct, in nronkevs. Arirr.\ ' . ) Arzrl . Sr ' i . j t r / . . i ; l ! l l - l

\\rarrinqtorr. F,. K. it969). Constnrctional apra-ria.I{atuthook tf CLinical Neurohlogy, t,ol. i. y

1.Vinken arrd (1. \ \- . Bnrrn ecls. North Hollancl,pp. 67-93.

\\ 'arnngton. Fi. K.. Jarnes, NL. an<i Kinsboume, M.(1966). Dra*ing disabi l i tr . in rel i i t ion to lateral_i l r o l t r . rehra l les io r r . l J l r i r r \9 :5 : l \2 .

\ \ 'artenberg. I t . i1953). Diagnostic ' l -est l i r t Neurol-

ogr7. (Jhici igo: Yearbrxrk Prrbl ishers.\\ 'atson. R. T.. and l lei lman, K. lU. ( lg8i]). Cal losal

apra-ria. B rai n I 06:39110:f .\ \ 'eekes. N.. Pti to. A.. ancl Zaidel E. (subrnit ted).

Perceptrral and hernispheric relationships in a hi-t'rarchical perception task.

\\ 'eekes, N. Y., and Zaidel, E. (1995). The effects <>fhorrnonal and psvchological ler.els of rnasculirr-itv in f'enrales on nerrropsvchologic'al function-ing. /1\,S 1 I75.

\Veekes. N. Y. ancl Zaidel, E. {1995). The effects ofsteroid horrnones on interhernispheric interac-tions: Behr.een- anci 1,,'ithin-s'.rbjects analvses./IN.S 1; IE7

\\. 'eekes, N. Y.. Camsi. l ) . . and Zaidel. E. r 1997). In_terhc rnisph eric relations i n hierarch ictrl percep-tion: A seconcl look. -\.arrop,sryt'hologia 3,5:37- l.

\ \ ' tekes. )r l . \ ' . and Zaidel. E. 11997). The effects ofrnascul initv anrl rrrenstnral sttrqe, on cognit ion./IN.S ,l rt5

C L I N I C A I N F U R O P S Y C H O T O C Y

\\ ' t ,ekes. N. Y.. and Zaidcl. E. (1996). The effects ofprocedrrral variations on lateralized Strrxlp ef_f'ects. Brrzlri (irgn. .31. 308-:3i30.

\\ 'est, S. Ll. . ancl l)otv, R. L l lgg5). lnf lrrence ofepilepsv ancl ternporal lol.re resection r>n olfac_ton, lirnction. Epi|ep,sia 36:53lil2.

\\rigan. :\. L. (13.1.{). The l)rralitv ol the Nlinrl. I,rxr_don: Lrxrgnrar, Ilrorur. Green antl Longnans. Re-prrblishecl irr 1985 bv Joseph Sirnorr. \{alibu. (.A

\\'ilson. (1. L.. Isokarvir-Akesson. NL, Babb, T. t,iurcl ( irandall . P. I t . (1990) Frrnctional connec,tions in the human ternporal lobe: I. Analt,sis ollintbic svsterrr pathrvar.,s using nerrronal actii.in,cvoked bv e'lectrical stirnulation. Erp. Brain Rc.s82:279-292.

\Vilson. C. L., Isokar.va-Akesson. \1.. Babb. T. I. ,Engle. J. J.. Cahan. L. D.. and Crandall . andP. H. (1987). A comparative view,of local and irr-terhemispheric limbic pathwavs in humans: anevoked potential anajvsis. In FuntlanwntalMechanisnt.s of Hunan Brain Funclion l. EneleJr. r"d. r. \ t .u. \ i rrk: Raven press. pp U i_f, f

\\rilson. D. IL, Cluiver. C.. \\'addinetou. M . un,l (;32.zaniga. \L (1975). Disconnection of the ceretx,r:r.lhemispheres \eurobgy 25;1l4g,I 153.

\\ i lson. D. I I . . Reeves. A.. Clazzaniga. \ ,L. ancl Crri-ver, C. (1977). (lerebral cornmissurotornv lirrcu1-t rol ul i r tt racl ;Ll,le st,izu rt,s. \' er t rr,!r V.!l ; ;( l,\_ ; I 5

\\ , ' i lson. S. A. K., and l lmce. A. N. (1940) . \ 'nrrrr l_ogt1, \/ol. 1. Baltirnore: \\rilliams and \\'ilkins.

\\'itelson, S. F. (197.1) flemispheric speciaJizationfor linguistic anci nonlinguistic tactual percep_tion using a dichotomous st imulat jon techniqrr i ,Coftex 10:3,17.

\\ / i telson. S. F. (19S9). I{and and sex dif ' ferenccs irrthe isthmrrs ancl genu of the human corprrs cal-losurn. Brain I 12:799-835.

\\'ittling, \\'. ( I990). Psvchophvsiologic:rl correlates ofhuman brain as\urn('tn*: blood pressure chanqt,sduring lateralized presentation of an emotionallrladen film. .\euro1tsy, lu'lt'gia 2B:J57-JI0

Yakovlev, P. I . , and Lecours, A. R. (1967) The rnvei.ogenetic cvcles of regional maturation of thebrain. In Regional DeteloTtment of the Brain inEadq Life. A. Minkorvski, (ed.). EdinbrrrghBlackwell, pp 3-70.

Yamadori, A.. Nagashima, T.. and Tamaki. \(1983). Ideogranr rvriting in a disconnection sur-drome. Brain [,ang. -19:3,16-356.

Zaidel. D.. and Sperw. R. \ \r . (197,1). \ Iernon inr.pairment afier commissurotomv in man. Brarrr97:263-2i2

Zaidel. D.. and Spern'. R. \ \ ' . (1977) Sorne lrrnq-term motor ef}ects ol cerebral comrnissrrrototnrin man. Neuropsychologia I 5:193-201.

Zaidel. D. \\r. (1990a). Long-term semantic nr{'n}.on' in the hvo cerebral hemispheres. ln Bmrt

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T H E C A L L O S A L S Y N D R O M E S

?iratits and Functitnt,s o.f the ltind, C. Tre_varthen led.). Nerv Ynrk: Carnbridge Universih.,Press. pp. 266 2S(l

Zaidel. D. \\'. (1990b). Nlern6rv and spatial cogni-tion fbllowing comrnissurotorrrr.. ln Handhook ctfNeumpsqchology, yol 4. F. Boller and J. Graf_rnan (eds.). Amsterdam: Elser, ier. pp. 15I_166

laidel. D. \\/. (Igg3). Vieu,of the lvorld ironr a split-b rain pe rspecti v e . In n\ eu rolo gic al B ou rcl ari) s o.fReali ty. E lvL R. Critchler,(eds.). London: Far_rand Press . pp . l6 l -1 i4 .

Ziirlel. D. \\' (1994). \\-orlcls aparl: pictorial sc,_rnantics in tht left ancJ right c,erebral hernr_spheres. Curr. Direct. psychol. .Sci ,3:5_6.

Zardel. E. ( i973). Linguist ic cornpetence ancl re-Iatecl iirnctions in the right hemisphere of rnanfollouing commissurotomv and Lemispherec_tonr' . Ph.D. thesis, Cali fomia Inst i tute of Tc,cl,_rroloqr'. I)isscrtation Abstracts Intentational.rl.1 :235{ )B ( Linir.ersih, N{icrofilms 73_26. .16 I ).

Zaidel. F,. r1975). A techni<pe l irr presenting later-;rlized vrsual input u,ith prol,,nged exposure. \ri_\ ir ' r , 1: l . \ / i .2\3- 259.

Zaidel. E. ( i976). Aud;ton.vocabulan. of the r ighthernisphere lirllorving brain bisection orIte nridr:corticrit i<.sn. Cl o rtex I 2 : 1g I -2I L

Zardel E. r 1977). Linilateral auditon. language corrrprehensiou on tht token test firllolr,ing cerebralcrrr lrrnissrrnrtorlv and hernispherectornv. \ .crr_rtrysychohryia I D.l- l i .

Zardel. E. r l97Ea). Ooncepts ofcerebral dorninancein the split-brait. In Cerebral Curekttes of Cort-scitnts Experienr.:r,. It. Buser ancl A. Rougeul-BLrser (eds.). Arnsterdarn: Elser.ier. pp 263-2g1

Z:ridel E (lg78b). Lexical organization ln the rightherrrisphere. In Oerehral Correlates oJ' C)tn-sr:iotts Experiertcr. P. Buser and A. Ror_rgeul,I}rser (ecls. ), Anrsterdiirn: Elsovier. pp. 263_2f1,{.

Zajdel. E. (1981). I lernispheric intel l igen'cc, the cascol the Ravel Progressive Matrices. ln Intel.li-gtrt .cc artr l Leuntirtg. \L lr . Frieclnttrn. J. p. Das.arrt l \ . () ' ( lonrror (t : t ls.). ) ,Je*. york, p]enurriPn,ss. pp. 5:l,l512.

Zaidel. F, I 1962r Reading in tht,disconnecterl r ightiienrisphert': al :rphasir>krgical perspectir.r.. IlDt1t lcxirt \ t ' r tronal. Cogrt i t i t c untl Lit tgtt is,t i t ; . \ , ;_7tt ' r ' t .r . ) ' . Zottcrnrarr (ed.r. 1;r11,.<o1 lrt ,rgarrrorrl ) ress . pp . f i7 91 .

Z n i r l , l E . l g \ : l I ) i s t . o r r r r r . r . t i o r r s r r r r l r r r r n , . l s unrorl ' l l i rr lateral ih cf l t 'cts irr t l i r rrornial brain.In- C e rt'bru I I I t,ntisplrc: re A,rynnnrt n1. lrldhod.Tluttt 'q and Appli t .at iott . J. I lel l ige rerl .) . Nes\ r , r k l ' r r r , . q e r l ) l ) f , 5 - l i l .

Za ld . l F . . l99 l . I l r i , . r . l r r r r r i spp l r t .nc t r i r r rs le r i r r t l r .

403

split brain: Iong-terrl status following cornpletecerebral commissrrroto ntt . I n B rai r t A,n1 ntntetn1 .R. J. Daridson and K. I luqhdal (eds.). Cam_bridge. \{A: MIT Press. pp. 491-532

Zaidel. E. (1998a). Language in the r ight hemi-sphe're follos.'irrg calkrsal disconnectior. InHandbook of Nenrolingul,sfjr:,s. B. Ster.nrner. andIl . $hitaker (eds.). San Diego: Acaclemic.press.pp. 369-3ti3

Zaide'i, E. (1998b) Stereognosis in the chronic splitbrain: hemispheric diffircnces. ipsilateral con_trol and senson'integratior across thc, rnicllinc.!\' eu rcp x 1 ch oht gia 36 : I033-l0li .

Zaidel. E. (2001). Hemispheric special izat iorr l i rrlanguagc in the split brain. In Handbutk o.f Ncu-rop.sychologtl, 2nd ed.. \'ol. 2. Lurtgttugt arrclAplrctsia, R. l len'rdt ivol. ccls.). F Boller arrcl J.( lraf inan (series ecls.). Elserier: Arnstert lanr. pp.393_4 I 8

Zaiclel. E.. Clarke. J. NI. and Srl 'crrobu. B r1990)IIernispheric incicpenclenc'e: a paracliqur case firrccrgnitive neuroscience. 7n \eunthiology rlfHigher Cognit i t t , Funtt iorts. A. B. Scheilx, l anclA. F. \\'echsler (eds. ). Net'l'ork: Cluilfirrci pres,,pp 297-355.

Zaidel. E,, :rncl Frazer, R. E. (t977) A unir.e.rsal hal i-fie'ld occhrder for lateralitr. research. CaltechBi , , ! Ar t r t . , l i r7 r . l l i l 3 \ .

Zaiclel, E.. and Iacoboni. N{. ( in press.). Senson.mo-tor integration in the split brain. In Tlte parullelBrain: Thc Cogtitixe Nettntscitttce of tln Cor-pus Callo.sunt, E. Zaidel ancl M. Iacoboni (eds.).Massachrrst,tts: MIT Press. pp. 3lg-336.

Zaidel. E.. ancl Peters. A. M. ( lglJl). phonologicalencoding and icleographic reading bv thr. dis-connected riqht hemispherc: tr.o caser strrdies.Brairt Lang. 11:205-231.

Zait lel , E., Zaidel. D. \ \ ' . . ancl Bogen. J. E (1990).'festirrg

the conrnrissrrrotolt\, patient. In lreu-ronrcthod.s. \tol. I,':t: \tcttrttpsqcltdogrT. A. A.Boultorr. (1. B. Baker anrl \{ . I l isruck {ecls.).( l l i f ion. NJ: IJLrnrana l ,ress. pp 1,17-201

Zaidel. E.. Zaidel, D. \ \ , . . alr l Spern. R. \ \ ' . (19E1 ).l,t'fi arrcl riglrt ink'lligerc(,: (.:$r,strrclies of llaverr'sProgressivr \{atrices lirlk xrirrq I rrain bisectior r ar rr Iherrridccorticati<.r.'t. Crtrlt't I 7. 16i IE6.

Zakl. l ) , H.. ancl Parrlo- J. \ ' . ( lgg7). Ernotiorr. olfirction. anrl the hutrarr ann.gdala, anl.qrlala ac.-tivation during aversir.e olfic'torl stirnulatiorr.Pnu ' . \a1 ! \ r ' r r r l . 5 r ' i . t .S . . \ . 9J : - l I l9 -J l2 l .

Zttrtrre. R. J.. and Jones-Ciotrnan. IVI. (1g91). I l rr-rnan olfacton discrirninatiorr aficr rrnilaterall iorrtal <rr tenrporal kr lrectornr ' . Rrain l l l tpt1A ) .71_5. { .