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Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 1*
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Functional+neuroanatomy+of+meditation:+A+review+and+meta?analysis+of+78+functional+
neuroimaging+investigations+
Kieran*C.*R.*Foxa,*,*Matthew*L.*Dixona,*Savannah*Nijeboera,*Manesh*Girna,*James*L.*Flomanb,*
Michael*Lifshitzc,*Melissa*Ellamild,*Peter*Sedlmeiere,*and*Kalina*Christoffa,f*
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a*Department*of*Psychology,*University*of*British*Columbia,*2136*West*Mall,*Vancouver,*
B.C.,*V6T*1Z4*Canada*
b*Department*of*Educational*and*Counselling*Psychology,*and*Special*Education,*University*
of*British*Columbia,*2125*Main*Mall,*Vancouver,*B.C.,*V6T*1Z4*
c*Integrated*Program*in*Neuroscience,*McGill*University,*3775*University*St.,*Montreal,*QC,*
H3A*2B4*
d*Neuroanatomy*and*Connectivity*Research*Group,*Max*Planck*Institute*for*Human*
Cognitive*and*Brain*Sciences,*Stephanstrasse*1a,*Leipzig,*Germany*04103.*
e*Institut*für*Psychologie,*Technische*Universität*Chemnitz,*43*Wilhelm_Raabe*Street,*
Chemnitz,*Germany*
f*Brain*Research*Centre,*University*of*British*Columbia,*2211*Wesbrook*Mall,*Vancouver,*
B.C.,*V6T*2B5*Canada*
**To*whom*correspondence*may*be*addressed*(at*address*a*above).*Telephone:*1_778_968_
3334;*Fax:*1_604_822_6923;*E_mail:*[email protected]*
*
*
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 2*
Abstract+
Meditation*is*a*family*of*mental*practices*that*encompasses*a*wide*array*of*
techniques*employing*distinctive*mental*strategies.*We*systematically*reviewed*78*
functional*neuroimaging*(fMRI*and*PET)*studies*of*meditation,*and*used*activation*
likelihood*estimation*to*meta_analyze*257*peak*foci*from*31*experiments*involving*527*
participants.*We*found*reliably*dissociable*patterns*of*brain*activation*and*deactivation*for*
four*common*styles*of*meditation*(focused*attention,*mantra*recitation,*open*monitoring,*
and*compassion/loving_kindness),*and*suggestive*differences*for*three*others*
(visualization,*sense_withdrawal,*and*non_dual*awareness*practices).*Overall,*dissociable*
activation*patterns*are*congruent*with*the*psychological*and*behavioral*aims*of*each*
practice.*Some*brain*areas*are*recruited*consistently*across*multiple*techniques*–*
including*insula,*pre/supplementary*motor*cortices,*dorsal*anterior*cingulate*cortex,*and*
frontopolar*cortex*–*but*convergence*is*the*exception*rather*than*the*rule.*A*preliminary*
effect_size*meta_analysis*found*medium*effects*for*both*activations*(d*=*.59)*and*
deactivations*(d*=*_.74),*suggesting*potential*practical*significance.+Our*meta_analysis*
supports*the*neurophysiological*dissociability*of*meditation*practices,*but*also*raises*many*
methodological*concerns*and*suggests*avenues*for*future*research.+
+
Keywords:+meditation;*open*monitoring;*focused*attention;*functional*magnetic*resonance*
imaging;*meta_analysis;*activation*likelihood*estimation+
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 3*
1.+Introduction++
Meditation*has*been*used*as*a*tool*to*train*the*mind*for*thousands*of*years*
(Anālayo,*2003,*Iyengar,*2005).*Broadly*speaking,*meditation*practices*involve*the*
monitoring*and*regulation*of*attention*and*emotion*(Lutz*et*al.,*2008b,*Tang*et*al.,*2015).*
Meditation*can*be*either*directed*outward*to*particular*objects*and*sensory*stimuli*or*
turned*inward*to*the*workings*of*the*mind*and*felt*experiences*of*the*body.*A*common*
principle*across*all*forms*of*meditation*is*that*through*specific*and*regular*practice,*the*
ability*to*monitor*and*regulate*mental_physical*processes*can*be*progressively*developed*–*
the*way*performance*on*any*other*cognitive*or*motor*skill*can*be*improved*with*practice*
(Ericsson*et*al.,*1993,*Slagter*et*al.,*2011,*Vago,*2014).*Interest*in*the*neural*basis*of*
meditative*practices*has*increased*enormously*over*the*past*decade,*and*mounting*
empirical*evidence*suggests*that*meditation*indeed*leads*to*or*is*associated*with*
significant*changes*in*cognitive*and*affective*processing*(Sedlmeier*et*al.,*2012),*as*well*as*
alterations*in*brain*structure*(Fox*et*al.,*2014)*and*function*(Cahn*and*Polich,*2006).**
Although*meditative*practices*now*garner*serious*interest*from*the*cognitive*
neuroscience*community*(Fig.*1),*meditation*still*tends*to*be*viewed*as*a*somewhat*
uniform*practice*(e.g.,*(Sperduti*et*al.,*2012).*The*umbrella_term*‘meditation’*encompasses*
a*wide*variety*of*distinct*practices*with*specific*goals*and*methods,*however.*The*varying*
methods*and*scope*of*particular*forms*of*meditation*include*focalizing*and*sustaining*
attention*(Wallace,*2006),*generating*and*maintaining*complex*visual*imagery*
(Kozhevnikov*et*al.,*2009),*improving*emotion*regulation*and*well_being*(Chambers*et*al.,*
2009,*Sedlmeier*et*al.,*2012),*and*deepening*compassion*for*others*(Galante*et*al.,*2014).*
Functional*neuroanatomy*of*meditation*
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Despite*the*diversity*of*meditation*practices,*few*behavioral,*clinical,*or*
neuroimaging*studies*have*directly*compared*meditation*styles*within*or!across*studies.*
As*such,*little*is*known*about*whether*functional*neural*differences*underlie*each*type*of*
practice*(although*see*(Lou*et*al.,*1999,*Manna*et*al.,*2010,*Brewer*et*al.,*2011,*Lee*et*al.,*
2012,*Tomasino*et*al.,*2013).*Although*mounting*empirical*evidence*suggests*that*these*
distinctive*psychological*practices*may*be*dissociable*at*the*neurophysiological*level*(Lutz*
et*al.,*2008b,*Travis*and*Shear,*2010a,*Josipovic*et*al.,*2011,*Tomasino*et*al.,*2013),*no*
comprehensive*overview*has*adequately*addressed*this*complex*issue.*We*therefore*
attempted*to*synthesize*the*large*and*rapidly*expanding*(Fig.*1)*body*of*work*on*the*
functional*neuroanatomy*of*meditation*practices*in*the*present*review*and*meta_analysis.**
Our*central*hypothesis*was*a*simple*one:*meditation*practices*distinct*at*the*
psychological*level*(Ψ)*may*be*accompanied*by*dissociable*activation*patterns*at*the*
neurophysiological*level*(Φ).*Such*a*model*describes*a*‘one_to_many’*isomorphism*
between*mind*and*brain:*a*particular*psychological*state*or*process*is*expected*to*have*
many*neurophysiological*correlates*from*which,*ideally,*a*consistent*pattern*can*be*
discerned*(Cacioppo*and*Tassinary,*1990).**
Supporting*or*disconfirming*this*prediction*through*empirical*synthesis*is*
challenging,*however,*because*at*present*there*are*few*(if*any)*‘objective’*third_person*
measures*that*can*confirm*engagement*in*a*particular*subjective*state*or*mental*practice*
(Lutz*and*Thompson,*2003,*Fazelpour*and*Thompson,*2015).*Current*investigations*
therefore*necessarily*rely*on*first_person*reports*that*a*specific*mental*practice*is*indeed*
being*carried*out*as*instructed*or*intended.*Acknowledging*this*difficulty,*we*reasoned*that*
if*meditation*practitioners*are*really*engaging*in*the*practices*they*report*to*be*–*and*if*
Functional*neuroanatomy*of*meditation*
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these*practices*engender*their*intended*effects*and*mental*states*–*then*distinctive*
patterns*of*brain*activation*and*deactivation*should*accompany*each*technique.**
In*line*with*our*hypothesis,*it*has*been*argued*that*various*categories*of*meditation*
are*characterized*by*differential*electroencephalography*(EEG)*signatures*(Travis*and*
Shear,*2010a),*cognitive_emotional*effects*(Sedlmeier*et*al.,*2012),*and*potentially*
neuroanatomical*alterations*(Fox*et*al.,*2014).*In*the*present*synthesis,*we*sought*to*build*
on*prior*reviews*and*meta_analyses*by*examining*the*possibility*that*comparable*
dissociations*might*exist*with*modalities*that*measure*cerebral*blood*flow*(positron*
emission*tomography;*PET)*or*blood_oxygenation*level*(functional*magnetic*resonance*
imaging;*fMRI).*Other*modalities,*such*as*EEG,*have*extremely*high*temporal*resolution*but*
very*poor*spatial*resolution*(or*vice*versa,*in*morphometric*neuroimaging).*Functional*
neuroimaging*methods,*on*the*other*hand,*are*unique*in*their*combination*of*good*
temporal*and*spatial*resolution.*This*allows*for*precise*localization*of*dynamic*changes*in*
brain*activity,*providing*unified*spatiotemporal*neurophysiological*data*that*could*prove*
critical*in*differentiating*one*form*of*meditation*practice*from*another.*
Taken*together,*our*central*aims*were*to:*(i)*comprehensively*review*and*meta_
analyze*the*existing*functional*neuroimaging*studies*of*meditation*(using*the*meta_analytic*
method*known*as*activation*likelihood*estimation,*or*ALE),*and*compare*consistencies*in*
brain*activation*and*deactivation*both*within*and*across*psychologically*distinct*
meditation*techniques;*(ii)*examine*the*magnitude*of*the*effects*that*characterize*these*
activation*patterns,*and*address*whether*they*suggest*any*practical*significance;*and*(iii)*
articulate*the*various*methodological*challenges*facing*the*emerging*field*of*contemplative*
neuroscience*(Caspi*and*Burleson,*2005,*Thompson,*2009,*Davidson,*2010,*Davidson*and*
Functional*neuroanatomy*of*meditation*
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Kaszniak,*2015),*particularly*with*respect*to*functional*neuroimaging*studies*of*
meditation.*
*
Figure!1.!!!The!rapid*increase*in*functional*(fMRI*and*PET)*and*morphometric*
neuroimaging*of*meditation*and*related*secular*contemplative*practices.+
*Functional*neuroimaging*(fMRI*and*PET)*study*counts*based*on*the*results*of*the*present*review;*morphometric*study*counts*based*on*our*previous*meta_analysis*of*this*literature*(Fox*et*al.,*2014).+!
!
1.1!Functional!neuroimaging!of!meditation:!The!need!for!quantitative!meta8analysis+
There*are*now*close*to*a*hundred*functional*neuroimaging*studies*of*meditation*
(Fig.*1)*–*but*can*any*conclusions*be*drawn*from*this*large*and*fast*growing*literature?*
Determining*reliable*neural*correlates*of*any*mental*process*is*a*difficult*task*under*the*
best*of*conditions.*This*is*all*the*more*true*when*the*mental*processes*in*question*are*
Functional*neuroanatomy*of*meditation*
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subtle*and*largely*subjective,*and*when*the*participants*employed*are*highly*experienced*
practitioners*often*operating*within*spiritual_religious*frameworks.*Despite*the*
voluminous*functional*neuroimaging*literature*on*meditation,*we*suspect*that*most*
researchers*would*be*hard_pressed*to*provide*a*clear*answer*to*the*ostensibly*simple*
question:*What*brain*regions*are*reliably*recruited,*for*instance,*by*focused*attention*
meditation?*We*expect*that*similar*challenges*would*face*researchers*seeking*to*describe*
other*common*categories*of*meditation.*Part*of*the*problem*is*that*despite*the*rapid*
proliferation*of*neuroimaging*studies*of*meditation*in*the*past*few*years*(Fig.*1),*neither*
narrative*(Rubia,*2009,*Tang*et*al.,*2015),*nor*meta_analytic*(Sedlmeier*et*al.,*2012,*Fox*et*
al.,*2014),*nor*theoretical*(Holzel*et*al.,*2011,*Vago*and*Silbersweig,*2012)*synthesis*of*
these*results*has*been*able*to*keep*pace*with*the*emergence*of*new*and*complex*data.*
Given*the*numerous*and*often*contradictory*results*reported*to*date,*researchers*
interested*in*the*neural*correlates*of*meditation*may*find*it*difficult*to*decide*among*
different*findings.*As*experts*on*meta_analytic*methodology*recently*framed*the*general*
problem*of*integrating*findings:**
How*should*scientists*proceed*when*results*differ?*First,*it*is*clear*how*they*should*not!proceed:*they*
should*not*pretend* that* there* is*no*problem,*or*decide* that* just*one*study*(perhaps* the*most*recent*
one,*or*the*one*they*conducted,*or*a*study*chosen*via*some*other*equally*arbitrary*criterion)*produced*
the*correct*finding.*If*results*that*are*expected*to*be*very*similar*show*variability,*the*scientific*instinct*
should*be*to*account*for*the*variability*by*further*systematic*work.**(Cooper*and*Hedges,*2009);*p.*4)**
It*is*in*this*spirit*of*systematic,*quantitative*synthesis*that*the*present*meta_analysis*was*
conducted.*
Although*the*coordinate_based*meta_analysis*we*employed*here*(see*Methods)*is*
far*from*the*perfect*(or*only)*method*of*achieving*this*kind*of*synthesis*(Salimi_Khorshidi*
Functional*neuroanatomy*of*meditation*
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et*al.,*2009),*it*is*a*major*improvement*over*narrative*(and/or*selective)*surveys*of*the*
literature,*which*often*lead*to*erroneous*conclusions*(Schmidt,*1992).*We*therefore*echo*
other*neuroscientists*in*arguing*that*quantitative*meta_analysis*of*neuroimaging*data*is*a*
potent*(indeed*necessary)*tool*for*better*understanding*the*neural*basis*of*mental*
processes*(Wager*et*al.,*2007,*Salimi_Khorshidi*et*al.,*2009,*Wager*et*al.,*2009,*Kober*and*
Wager,*2010,*Yarkoni*et*al.,*2010,*Hupé,*2015).*More*specifically,*meta_analysis*can*
provide:*(i)*a*less_biased*overview*of*an*evidence*base*than*a*simple*narrative*review*or*
qualitative*survey*of*prior*work*(Schmidt,*1992);*(ii)*specific*peaks*of*meta_analytic*
activation,*rather*than*just*broad*regional*results;*(iii)*statistically*significant*activation*
overlaps*across*studies,*instead*of*merely*indicating*broad*‘replications’;*and*(iv)*a*way*to*
mitigate*the*lack*of*statistical*power*caused*by*small*samples*found*in*many*neuroimaging*
studies*–*a*problem*especially*prevalent*in*the*study*of*meditation*practitioners,*where*
experienced*individuals*are*difficult*to*recruit.*For*a*deeper*discussion*of*the*limitations*of*
these*meta_analytic*methods,*however,*see*Section*5.11.**
* Moreover,*persuasive*arguments*have*also*been*made*for*a*move*toward*a*more*
‘cumulative’*science*that*focuses*on*broad*conclusions*drawn*from*dozens*or*hundreds*of*
independent*investigations,*as*opposed*to*‘critical*experiments’*from*isolated*but*
influential*studies*(Schmidt,*1992,*Yarkoni*et*al.,*2010).*Some*statisticians*have*gone*as*far*
as*claiming*that*“any*individual*study*must*be*considered*only*a*single*data*point*to*be*
contributed*to*a*future*meta_analysis”*(Schmidt,*1992);*p.*1179).*Without*endorsing*such*
an*extreme*viewpoint,*we*agree*that*a*careful*sifting*and*quantitative*synthesis*of*the*
research*conducted*to*date*will*help*to*advance*the*state*of*the*field.*
!
Functional*neuroanatomy*of*meditation*
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1.2!Four!general!categories!of!meditation!
Before*conducting*a*synthesis*of*the*meditation*neuroimaging*literature,*one*must*
ask*a*central*question:*How*are*meditation*practices*to*be*categorized?*There*is*growing*
consensus*that*at*least*three*broad*categories*of*meditation*techniques*can*be*discerned:*
focused!attention,*open!monitoring,*and*compassion*or*loving8kindness*practices*(Cahn*and*
Polich,*2006,*Lutz*et*al.,*2008b,*Brewer*et*al.,*2011,*Vago*and*Silbersweig,*2012,*Lippelt*et*
al.,*2014).*Similar*classification*schemes*appear*to*reach*back*centuries*to*early*Eastern*
treatises*on*meditation*(Harvey,*1990,*Lodro,*1998,*Goenka,*2000,*Wangyal*and*Turner,*
2011).*Although*a*few*broad*categories*do*not*begin*to*exhaust*the*subtleties*of*all*
contemplative*practices*(Niranjananada,*1993,*Singh,*2002),*there*seems*to*be*fair*
justification*for*a*tentative*division*along*these*lines*(Lutz*et*al.,*2008b,*Vago*and*
Silbersweig,*2012).*The*main*aim*of*this*review*and*meta_analysis*was*to*investigate*
whether*some*isomorphism*(even*if*a*complex*one)*can*be*discovered*between*
psychological*practices*and*brain*recruitment*(Cacioppo*and*Tassinary,*1990):*that*is,*are*
these*various*categories*of*meditation,*which*differ*markedly*at*the*psychological*level*
(Ψ),*in*fact*characterized*by*distinctive*patterns*of*brain*activation*and*deactivation*(Φ)?*
1.2.1+Focused+attention+meditation.!Focused!attention*meditation*involves*
directing*attention*to*one*specific*object*(e.g.,*the*breath*or*a*mantra)*while*monitoring*
and*disengaging*from*extraneous*thoughts*or*stimuli*(Harvey,*1990,*Hanh,*1991,*Kabat_
Zinn,*2005,*Lutz*et*al.,*2008b,*Wangyal*and*Turner,*2011).*Attention*is*directed*to*a*
particular*object*(most*commonly*the*sensations*associated*with*respiration),*and*
whenever*the*mind*wanders,*attention*is*redirected*to*this*target.*With*regular*training,*
the*ability*to*voluntarily*control*attention*without*being*distracted*appears*to*become*
Functional*neuroanatomy*of*meditation*
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progressively*enhanced*(e.g.,*(MacLean*et*al.,*2010)*and*less*effortful*(Wallace,*1999,*2006,*
Brefczynski_Lewis*et*al.,*2007).*In*particular,*focused*attention*meditation*may*lead*to*
three*types*of*improvements:*monitoring*the*locus*of*attention,*disengaging*from*
distraction,*and*shifting*attention*back*to*its*intended*target*(Lutz*et*al.,*2008b).*
* 1.2.2+Mantra+recitation+meditation.*Focused*attention*meditation*itself*may*be*
subdivided*into*distinct*practices,*or*distinguished*from*practices*that*appear*similar*at*
first*glance:*in*particular,*mantra!recitation!meditation*involves*unique*components*
(Travis,*2014).*Mantra*meditation*–*probably*best*known*in*the*form*of*the*widespread*
‘Transcendental*Meditation’*–*involves*the*repetition*of*a*sound,*word,*or*sentence*(spoken*
aloud*or*silently*in*one's*head)*with*the*goals*of*calming*the*mind,*maintaining*focus,*and*
avoiding*mind_wandering.*While*mantra*meditation*therefore*clearly*overlaps*with*other*
forms*of*focused*attention*in*regard*to*its*aims,*it*differs*in*that*the*object*of*focus*is*a*
voluntary*verbal_motor*production,*rather*than*naturally*arising*body*sensations*(like*the*
breath)*or*external*physical*objects*(such*as*a*point*in*space*upon*which*the*gaze*is*
focused).*Further,*mantra*meditation*appears*to*be*associated*with*neural*correlates*
separate*from*other*related*forms*of*focused*attention*practice*(e.g.,*(Lazar*et*al.,*2000,*
Shimomura*et*al.,*2008,*Davanger*et*al.,*2010,*Tomasino*et*al.,*2013)*–*although,*in*the*
absence*of*a*meta_analysis,*these*differences*remain*only*suggestive.*Although*mantra*
meditation*could*reasonably*be*placed*within*the*general*‘focused*attention’*category*of*
practices,*because*of*its*unique*elements*(most*notably*its*linguistic,*verbal_motor*
component)*we*examined*it*separately*here.*
1.2.3+Open+monitoring+meditation.+Open!monitoring!practice*typically*begins*with*
bringing*attention*to*the*present*moment*and*impartially*observing*all*mental*contents*
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(thoughts,*emotions,*sensations,*etc.)*as*they*naturally*arise*and*subside.*A*key*element*of*
this*practice*is*possessing*an*open,*accepting*attitude*toward,*and*learning*to*‘let*go’*of,*
mental*content*–*neither*resisting*nor*elaborating*upon*anything*that*surfaces*in*
awareness*(Harvey,*1990,*Walker,*1995,*Suzuki,*2003,*Kabat_Zinn,*2005,*Wangyal*and*
Turner,*2011).*In*contrast*to*focused*attention,*then,*in*open*monitoring*meditation*mental*
content*is*neither*evaluated*for*relevance*to*a*particular*goal,*nor*is*any*content*
suppressed.*This*‘non_elaborative’*mental*stance*cultivates*a*more*present_centered*
awareness*in*tune*with*the*moment_to_moment*experience*of*the*mind*and*body*(Anālayo,*
2003,*Farb*et*al.,*2007).*Somatic*and*visceral*body*sensations*are*often*a*prominent*feature*
of*this*present*moment*experience,*and*hence*interoceptive*and*exteroceptive*inputs*
generally*receive*greater*processing*in*open*monitoring*than*in*focused*attention*practices*
(e.g.,*(Fox*et*al.,*2012,*Kerr*et*al.,*2013).*Open*monitoring*meditation*can*also*sometimes*
serve*as*a*platform*from*which*practitioners*can*go*on*to*enter*subtler*states*of*non_dual*
awareness*(see*section*1.3,*below).*
1.2.4+Loving?kindness+and+compassion+meditations.+Loving8kindness*meditation*
(closely*related*to,*but*not*identical*with,*compassion*meditation)*aims*to*deepen*feelings*
of*sympathetic*joy*for*all*living*beings,*as*well*as*promote*altruistic*behaviors*(Harvey,*
1990,*Gyatso*and*Jinpa,*1995,*Kabat_Zinn,*2005,*Lutz*et*al.,*2008a).*Typically,*practitioners*
begin*by*generating*feelings*of*kindness,*love,*and*joy*toward*themselves,*then*
progressively*extend*these*feelings*to*imagined*loved*ones,*acquaintances,*strangers,*
enemies,*and*eventually*all*living*beings*(Harvey,*1990,*Kabat_Zinn,*2005,*Lutz*et*al.,*
2008a).*Compassion*meditation*generally*takes*this*practice*a*step*further:*practitioners*
imagine*the*physical*and/or*psychological*suffering*of*others*(ranging*from*loved*ones*to*
Functional*neuroanatomy*of*meditation*
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all*humanity)*and*cultivate*compassionate*attitudes*and*responses*to*this*suffering.*Both*
practices*share*the*long_term*goals*of*enhancing*sympathetic*joy*and*empathy*for*pain,*
which*are*viewed*as*trainable*skills*that*increase*altruistic*behavior*(Gyatso*and*Jinpa,*
1995,*Lutz*et*al.,*2008a).*Although*there*are*potentially*important*psychological*
differences*between*these*practices,*of*the*neuroimaging*studies*to*date,*the*instructions*
have*been*comparable:*participants*have*been*asked*to*generate*positive*emotions*(such*
as*loving_kindness,*well_wishing,*or*compassion)*directed*toward*others*and/or*generated*
in*a*non_referential*way*(see*the*supplementary*material*for*the*exact*instructions*in*each*
study).*We*therefore*grouped*the*available*studies*together,*reasoning*that*they*were*
more*similar*than*different:*despite*some*difference*in*instructions*and*implementation*of*
the*practices,*all*studies*involved*a*strong*focus*on*cultivating*positive*affect*directed*
outward.*We*acknowledge,*however,*that*differences*in*the*various*stages*of*these*
practices*(e.g.,*compassion*for*self,*vs.*a*loved*one,*vs.*a*stranger,*vs.*non_referential*
compassion)*might*very*well*be*resolved*at*the*neural*level*by*future*research**Note,*too,*
that*the*instructions*involved*in*the*studies*investigated*here*do*not*exhaust*the*possibility*
of*this*type*of*practice,*which*can*also*involve*complex*visualizations*and*a*focus*on*
spiritual*‘benefactors’*(Makransky*et*al.,*2012).*Further*research*is*clearly*warranted*to*
more*thoroughly*examine*the*many*variants*of*loving_kindness*and*compassion*
meditation.*
In*one*sense,*loving_kindness*and*compassion*meditations*could*also*be*considered*
a*form*of*focused!attention*in*that*they*often*focus*intensively*on*a*single*object*(the*person*
who*is*the*target*of*the*loving_kindness)*and*cultivate*a*consistent*emotional*tone*(to*the*
exclusion*of*other*kinds*of*affect).*Alternatively,*when*conducted*in*a*non_referential,*all_
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embracing*way*(extending*one’s*compassion*and*joyful*feelings*to*any*being*or*object*that*
arises*in*consciousness*indiscriminately,*or*even*cultivating*such*feelings*without*any*
object*whatsoever),*these*practices*could*conceivably*be*considered*a*form*of*open!
monitoring.*Nonetheless,*given*the*strong*emphasis*on*deliberate*cultivation*of*joyful,*
altruistic,*and*empathetic*emotions*that*is*fairly*unique*to*these*practices,*there*seems*
sufficient*justification*for*considering*them*as*a*separate*class,*worthy*of*investigation*in*
its*own*right.*
*
1.3!Other!forms!of!meditation!
It*is*important*to*note*that*these*four*putative*categories*of*meditation*are*intended*
not*as*a*final*classification*scheme,*but*merely*as*a*first*step*toward*delineating*
quantitative*neurophysiological*(Φ)*correlates*associated*with*relatively*distinctive*
psychological*(Ψ)*practices*(Cacioppo*and*Tassinary,*1990).*There*are*several*other*major*
categories*of*meditation*that*have*been*investigated*in*some*preliminary*work,*but*that*
could*not*be*examined*meta_analytically*due*to*a*paucity*of*data.*We*nonetheless*sought*to*
examine*and*compare*our*meta_analytic*results*with*these*data*by*conducting*a*qualitative*
review*of*the*results*reported*to*date.**
Visualization*meditation,*for*instance,*involves*creating*and*sustaining*complex*
mental*imagery*for*extended*periods*of*time.*These*visualizations*typically*involve*
mandalas*or*yantras*(geometric*designs)*or*deities*or*patron_teachers*(Gyatso,*1981),*and*
experts*in*these*techniques*have*been*shown*to*have*enhanced*visuospatial*processing*
(Kozhevnikov*et*al.,*2009).*Nonetheless,*only*a*single*study*of*which*we*are*aware*has*
investigated*the*neural*correlates*of*any*form*of*visualization*meditation*(Lou*et*al.,*1999),*
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although*loving_kindness*and*compassion*practices*can*also*sometimes*involve*important*
visualization*components*(Weng*et*al.,*2013).*
Another*almost*uninvestigated*set*of*practices*based*in*yogic*traditions*involve*the*
withdrawal*of!the!senses!(pratyahara*in*Sanskrit;*(Iyengar,*2005).*These*practices*involve*
the*deliberate*detachment*from*or*blocking*of*sensory*inputs,*including*pain,*with*the*
eventual*goal*of*transcending*any*narrow*sense*of*self*or*personal*identity.*Although*this*
type*of*practice*shares*many*features*of*focused*attention*techniques*(e.g.,*a*highly*
selective*attentional*focus),*and*would*traditionally*be*practiced*alongside*them*(Iyengar,*
2005),*it*could*also*be*considered*a*practice*in*its*own*right.*However,*so*far*only*one*
study*has*investigated*neural*correlates*of*this*kind*of*technique*(Kakigi*et*al.,*2005).*
Non8dual!awareness!practices*are*another*example.*In*general,*the*aim*of*these*
practices*is*to*dissolve*or*attenuate*the*boundary*between*subject*and*object*(Josipovic,*
2010,*Travis*and*Shear,*2010b,*Dunne,*2011).*Although*this*kind*of*practice*bears*some*
resemblance*to*open*monitoring*meditation,*it*could*be*considered*a*distinct*practice,*and*
further*investigation*into*its*neural*correlates*would*be*a*welcome*follow_up*to*a*recent,*
seminal*study*(Josipovic*et*al.,*2011,*Josipovic,*2014).*
Finally,*another*suite*of*practices*aims*at*manipulating*or*enhancing*meta_
awareness*during*various*stages*of*sleep*and*dreaming.*Yoga!nidra*(literally*‘sleep*yoga’),*
for*instance,*involves*the*deliberate*dampening*of*sensory*inputs*to*induce*a*‘hypnagogic’*
state*(Mavromatis,*1987,*Hori*et*al.,*1994,*Hayashi*et*al.,*1999,*Stenstrom*et*al.,*2012),*so*as*
to*enhance*one’s*capacity*to*carry*out*visualization*and*relaxation*practices*(Saraswati,*
1984).*Dream!yoga*(rmi8lam*in*Tibetan;*svapnadarsana*in*Sanskrit)*practices*aim*at*
enhancing*meta_awareness*during*dreaming*(i.e.,*enhancing*so_called*‘lucid’*dreaming;*
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(Gackenbach*and*LaBerge,*1988),*and*are*particularly*prevalent*in*the*Tibetan*Buddhist*
tradition*(Norbu*and*Katz,*1992,*Mullin,*1996,*Rinpoche,*2004).*Other*techniques*even*aim*
at*maintaining*awareness*during*states*of*deep,*dreamless*sleep*(Aurobindo,*2004,*
Sharma,*2012).*We*are*aware*of*only*a*single*study*of*these*practices,*however*(Kjaer*et*al.,*
2002).*
+
1.4!Delineating!reliable!neural!correlates!of!different!meditation!practices!
Only*in*about*the*past*year*have*a*sufficient*number*of*studies*been*cumulatively*
reported*to*allow*for*a*reliable*meta_analysis*of*each*major*meditation*type*(including*
open*monitoring*and*loving_kindness/compassion*meditations).*Even*very*recent*meta_
analyses*have*been*forced*by*a*paucity*of*empirical*data*to*examine*only*focused*attention*
and*mantra*recitation*meditation*(Tomasino*et*al.,*2013),*or*to*group*all*practice*types*
together*(Sperduti*et*al.,*2012).*Other*meta_analyses*have*employed*less*theoretically*or*
empirically*grounded*categorizations,*such*as*basing*meta_analytic*contrasts*on*the*
religion*of*origin*for*a*practice*(Buddhism*vs.*Hinduism)*as*opposed*to*the*
phenomenological*content,*intended*goals,*and*behavioral*characteristics*of*the*practice*
itself*(Tomasino*et*al.,*2014).*
Here*we*present*the*first*meta_analysis*inclusive*of*four*major*categories*of*
meditation,*with*a*focus*on*elucidating*whether*ostensibly*distinct*forms*of*mental*
practice*activate*a*common*neural*substrate*(Sperduti*et*al.,*2012)*or*instead*show*
dissociable*patterns*of*underlying*neural*activation*and*deactivation.*Accordingly,*we*
conducted*four*separate*activation*likelihood*estimation*(ALE)*meta_analyses*using*263*
foci*of*peak*activation*from*26*independent*PET*and*fMRI*studies*involving*32*unique*
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experiments*(Tables*1*and*2)*to*examine*the*patterns*of*brain*activation*associated*with*
focused*attention,*mantra*recitation,*open*monitoring,*and*loving_kindness/compassion*
meditation.*Additionally,*we*examined*the*results*for*three*categories*of*meditation*that*
have*only*been*investigated*thus*far*in*a*single*study*each*(Table*1).*Because*this*paucity*
of*data*precluded*a*formal,*quantitative*meta_analysis,*we*qualitatively*reviewed*the*
results*for*each*practice*type*and*compared*it*to*our*other*meta_analytic*results*(Table*1).*
*
!Table!1.***Seven*meditation*categories*investigated*via*quantitative*meta_analysis*and*
qualitative*review.!
Meditation+Type+ Contributing+Experiments+(N)+
Contributing+Foci++A/D+(Total)+
Quantitative*meta_analysis*
Focused*attention* 7* 48/13*(61)*
Mantra*recitation* 8* 63/19*(82)*
Open*monitoring* 10* 45/29*(74)*
Compassion/Loving_kindness** 6* 36/4*(40)*
+++Totals* 31* 192/65*(257)*
Qualitative*review*
Visualization* 1* –*
Sense_withdrawal* 1* –*
Non_dual*awareness* 1* –*Note.*Some*studies*examined*multiple*meditation*types*and*therefore*contributed*to*multiple*analyses.*This*resulted*in*a*total*of*31*experiments*(contrasts)*from*the*25*independent*studies*included*in*the*quantitative*meta_analyses*for*the*first*four*categories*(see*Table*2*for*details*of*included*studies).*Further,*three*other*categories*of*meditation*were*also*examined*where*results*have*been*reported*from*only*a*single*study*to*date.*These*investigations*were*not*included*in*any*formal,*quantitative*meta_analyses,*but*the*results*were*nonetheless*examined*and*compared*with*our*meta_analytic*findings*in*a*qualitative*fashion.*A*=*activations;*D*=*deactivations.*+
+
!
!
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1.5!Are!the!effects!of!meditation!practices!on!brain!function!of!any!practical!significance?!
Determining*whether*there*are*any*consistencies*in*brain*activation*for*various*
styles*of*meditation*is*only*the*first*step.*A*logical*next*question*is*whether*activations*and*
deactivations*associated*with*a*given*meditation*technique*have*any*practical*significance.*
That*is,*what*effect*sizes*characterize*these*differences,*and*do*effect*sizes*vary*across*
particular*forms*of*meditation?*Note,*however,*that*practical*significance*is*not*a*fully*
objective*measure*–*typically*a*half_standard*deviation*difference*is*considered*a*notable*
effect,*but*this*boundary*is*essentially*arbitrary,*and*‘practical’*significance*does*not*
necessarily*translate*to*clinical*significance*or*relevance*(Rosnow*and*Rosenthal,*1989).*
An*additional*benefit*of*calculating*effect*sizes*is*that*they*can*be*used*to*estimate*
the*extent*of*publication*bias*in*a*field*(Egger*et*al.,*1997),*a*major*and*outstanding*issue*
across*the*social*and*neurobiological*sciences,*including*contemplative*neuroscience.*
Because*we*found*strong*evidence*for*publication*bias*in*morphometric*(anatomical)*
neuroimaging*studies*of*meditation*in*a*recent*review*(Fox*et*al.,*2014),*we*sought*to*
address*whether*or*not*such*a*bias*might*be*affecting*functional*neuroimaging*studies*of*
meditation*as*well.*The*second*central*aim*of*this*meta_analytic*synthesis*was*therefore*to*
provide*preliminary*estimates*of*effect*sizes*in*the*functional*neuroimaging*of*meditation*
in*order*to*assess*practical*significance*and*the*possibility*of*publication*bias.
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2.+Meta?analytic+methods*
!
2.1!Literature!review!
2.1.1+Search+strategy.+Three*authors*(KCRF,*SN,*and*MG)*searched*MEDLINE*
(http://www.ncbi.nlm.nih.gov/pubmed/),*Google*Scholar*(http://scholar.google.com),*and*
PsycINFO*(http://www.apa.org/pub/databases/psycinfo/index.aspx)*for*all*papers*
containing*the*word*‘meditation’*since*the*first*functional*neuroimaging*study*of*
contemplative*practices*was*published*(Lou*et*al.,*1999).*These*extensive*lists*of*articles*
were*then*refined*by*searching*within*results*for*studies*that*contained*any*of*the*words*
or*phrases*‘magnetic*resonance*imaging’,*‘MRI,’*‘neuroimaging,’*or*‘brain’*within*the*title*or*
abstract.*Of*the*remaining*results,*every*abstract*was*consulted*to*see*whether*the*study*
actually*employed*functional*neuroimaging*methods*to*study*meditation.*The*reference*
lists*of*each*study*found,*as*well*as*those*of*several*major*reviews*(e.g.,*(Holzel*et*al.,*2011,*
Vago*and*Silbersweig,*2012)),*were*also*consulted*to*ensure*that*no*studies*were*missed.*
2.1.2+Study+inclusion+and+exclusion+criteria.+All*studies*using*functional*
neuroimaging*to*investigate*some*form*of*meditation*were*considered.*By*‘functional*
neuroimaging’*we*mean*functional*magnetic*resonance*imaging*(fMRI)*or*positron*
emission*tomography*(PET)*studies*that*can*provide*details*about*the*specific*location*of*
brain*activations*and*deactivations.*Using*the*search*strategy*detailed*above,*a*total*of*78*
studies*served*as*the*initial*pool*of*data*to*be*reviewed*(see*Table*2*for*included*studies,*
and*Table*S1*for*excluded*studies).+
* In*order*to*ensure*the*most*rigorous*results*possible,*stringent*inclusion*criteria*
were*applied.*Studies*were*required*to:*(i)*report*specific*peak*foci*of*activation*in*either*
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Talairach*or*Montreal*Neurological*Institute*(MNI)*space;*(ii)*include*a*reasonable*sample*
size*(i.e.,*case*studies*of*single*subjects*were*excluded);*(iii)*involve*participants*who*
actually*practiced*meditation,*be*they*novices*or*long_term*practitioners*(as*opposed*to,*
for*example,*studies*involving*only*self_report*scales*of*‘dispositional’*mindfulness);*(iv)*
involve*actual*meditation*during!the!scanning!session*(as*opposed*to*having*meditation*
practitioners*engage*in*other*tasks*without*some*explicit*contemplative*element);*and*(v)*
involve*healthy,*non_clinical*populations.*Finally,*(vi)*only*reports*published*in*peer_
reviewed*scientific*journals*were*included*(results*from*conference*abstracts,*presented*
talks,*dissertations,*etc.,*were*excluded).*For*further*details*on*excluded*studies,*see*the*
Supplementary*Material*Methods.*
Ultimately,*about*one*third*(25*of*78)*of*the*examined*studies*were*included*in*our*
meta_analyses*(Table*2).*Given*that*some*of*these*studies*examined*multiple*categories*of*
meditation,*we*investigated*a*total*of*31*separate*‘experiments’*or*contrasts*of*interest*
spread*across*the*four*major*meditation*categories.*
2.1.3+Study+classification.+Two*coders*with*longtime*personal*meditation*
experience*(authors*KCRF*and*MLD)*independently*classified*all*included*results*as*
involving*focused!attention,*open!monitoring,*compassion*or*loving8kindness,*or*mantra!
recitation*meditation.*Concordance*was*nearly*perfect:*a*single*disparity*was*resolved*after*
further*discussion.*Several*studies*employed*multiple*practice*types*across*different*
sessions;*in*these*cases,*results*from*each*session*were*coded*separately*and*considered*
individual*‘experiments.’*Therefore,*the*number*of*‘experiments’*exceeded*the*number*of*
independent*studies*actually*included*in*the*meta_analysis*(see*Tables*1*and*2).*All*
classifications*for*included*studies*are*summarized*in*Table*2.**
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Further,*one*study*each*was*found*that*examined*visualization*(Lou*et*al.,*1999),*
sense8withdrawal*(Kakigi*et*al.,*2005),*and*non8dual!awareness*(Josipovic*et*al.,*2011)*forms*
of*meditation.*Again,*both*coders*(KCRF*and*MLD)*independently*classified*and*agreed*on*
these*categorizations.*Due*to*there*being*only*a*single*study*for*each*category,*these*
reports*were*not*included*in*any*formal*meta_analyses.*Nevertheless,*their*results*were*
qualitatively*reviewed*and*considered*in*comparison*to*our*meta_analytic*results*for*the*
other*four*general*meditation*styles*(see*Table*1).*
In*virtually*all*cases,*classification*was*straightforward*and*mirrored*the*
classifications*described*by*the*authors*of*the*studies*in*their*methods.*For*instance,*
phrases*such*as*‘concentration*meditation’*were*categorized*under*the*focused*attention*
category;*mantra*meditation*studies*were*easily*categorized*based*on*descriptions*of*
mantra*recitation*in*the*methods;*and*so*on.*Because*of*the*prevalence*of*classification*
schemes*involving*the*four*categories*described*above*(e.g.,*(Cahn*and*Polich,*2006,*Lutz*et*
al.,*2008b,*Travis*and*Shear,*2010a,*Vago*and*Silbersweig,*2012),*many*studies*in*fact*
explicitly*described*their*methods*using*these*same*(or*highly*similar)*terms.*
*
! !
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Table!2.***Studies*included*in*the*meta_analyses*(n!=*25).**
Study+ Practice++ N+(M/C)+ Tradition+ Expertise+ Average+Experience+Lou*et*al.*(1999)* OM*+*LK** 9/–* Yoga*Nidra* LTP* >5*yrs*Lazar*et*al.*(2000)* MR* 5/–* Kundalini* LTP* 4*yrs*Brefczynski_Lewis*et*al.*(2007)* FA* 14/16* Tibetan*Buddhist* LTP* 19000*hrs*&*44000*hrs*
Farb*et*al.*(2007)* OM* 20/–* MBSR* STT* ~42*hours*Lutz*et*al.*(2008)* LK* 16/16* Tibetan*Buddhist* LTP* 45*±*12.7*yrs*Shimomura*et*al.*(2008)* MR* 8/–* Pure*Land*Buddhism** LTP* >10*years*
Lutz*et*al.*(2009)* LK* 10/12* Tibetan*Buddhist* LTP* 40*±*9.6*yrs*Davanger*et*al.*(2010)* MR* 4/–* Acem*Meditation* LTP* >23*yrs*
Engström*et*al.*(2010)* MR* 8/–* Acem*Meditation*
and*Kundalini*Yoga* LTP* 1.17*yrs*
Manna*et*al.*(2010)* FA*+*OM* 8/–*Vipassana*
(Theravada*_*Thai*Forest*Tradition)*
LTP* 15750*hrs*
Brewer*et*al.**(2011)* FA*+*OM*+*LK* 12/13* Vipassana*
(Mindfulness)* LTP* 10565*±*5148*hrs*Gard*et*al.*(2011)* OM* 17/17* Vipassana* LTP* 5979*±*5114*Ives_Deliperi*et*al.*(2011)* OM* 10/–* MBSR* LTP* >4*yrs*
Kalyani*et*al.*(2011)* MR* 12/–* Om*mantra*recitation* LTP*+*STT* Not*reported*
Taylor*et*al.*(2011)* OM* 12/10* Zen* LTP*+*STT* LTP:*>1,000*hrs*STT:*1*wk*
Wang*et*al.*(2011)* MR* 10/–* Kundalini*yoga* LTP* ~20,000*hrs*Dickenson*et*al.**(2012)* FA* 31/–* Mindfulness/MBSR* STT* No*previous*experience;*brief*
meditation*induction*only**Hasenkamp*et*al.*(2012)* FA* 14/–* Various* LTP* 1386*±*1368*hrs*
Lee*et*al.*(2012)* FA*+*LK* 22/22* Theravada* LTP* FA:*5249*±*6192*hrs**LK:*7492*±*6681*hrs*
Farb*et*al.*(2013)* OM* 20/16* MBSR* STT* 49.2*±*4.3*hrs*Guleria*et*al.*(2013)* MR* 14/–* Soham*Meditation* LTP* 2088*±*320*hrs*Lutz*et*al.*(2013)* OM* 14/14* Tibetan*Buddhist* LTP* 27000*±*12500*hrs*Weng*et*al.*(2013)* LK* 20/21* Tibetan*Buddhist* STT* 5.9*±*0.5*hrs*Lutz*et*al.*(2014)* OM* 24/22* Mindfulness/MBSR* STT* Variable*Xu*et*al.*(2014)* FA*+*MR* 14/–* Acem*Meditation* LTP* 27*±*9*yrs*All*studies*employed*fMRI*except*for*Lou*et*al.*(1999),*which*employed*PET.*C:*controls;*FA:*focused*attention;*LK:*loving_kindness*or*compassion*meditation;*LTP:*long_term*practitioners;*M:*meditators;*MBSR:*mindfulness_based*stress*reduction;*MR:*mantra*recitation;*N:*sample*size;*OM:*open*monitoring;*STT:*short_term*training.*!!!! !
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2.2!The!question!of!baselines,!control!conditions,!and!tasks!engaged!in!during!meditation!
* One*potential*problem*is*that*even*studies*examining*a*similar*form*of*meditation*
might*compare*a*meditation*practice*to*very*different*baseline*or*comparison*tasks*and*
conditions.*However,*collapsing*across*numerous*different*baselines*or*control*conditions*
is*a*common*(in*fact,*usually*inevitable)*practice*in*meta_analyses*of*functional*
neuroimaging*studies*(Turkeltaub*et*al.,*2002,*Wager*et*al.,*2003,*Wager*et*al.,*2007,*Wager*
et*al.,*2009,*Caspers*et*al.,*2010,*Yarkoni*et*al.,*2010,*Tomasino*et*al.,*2013).+It*is*by*no*
means*a*problem*limited*to*the*meditation*literature.*Aside*from*the*heterogeneity*of*
conditions*across*studies,*meditation*is*also*often*investigated*during*a*given*task*or*form*
of*stimulus*presentation.*Although*typically*these*tasks*or*stimuli*are*equally*present*in*
the*baseline*or*control*condition*(and*therefore,*in*principle,*should*not*unduly*influence*
the*meditation*state*results),*the*potential*for*our*results*representing*interactions*
between*meditation*and*the*given*task*employed*should*be*kept*in*mind.*These*issues*are*
examined*further*in*the*Discussion.*
The*goal*of*the*present*synthesis*was*to*determine,*irrespective*of*any*incidental*
differences*in*comparison*or*baseline*conditions*and*tasks:*(i)*whether*differing*
meditation*practices*tend*to*reliably*recruit*differentiable*neural*networks;*(ii)*if*the*
differences*in*brain*activation*show*practically*significant*effect*sizes;*and*lastly,*(iii)*
whether*distinct*practices*exhibit*differing*mean*effect*sizes*(i.e.,*is*a*given*style*of*
meditation*associated*with*greater*differences*in*brain*activity*than*others?).*
!
!
!
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 23*
2.3!Reporting!and!classification!of!results!!
* All*peak*voxel*coordinates*are*reported*in*Montreal*Neurological*Institute*(MNI)*
space.*For*consistency,*for*all*studies*where*peak*voxels*were*originally*reported*in*
Talairach*coordinates,*we*used*the*WFU*Pickatlas*software*package*(Maldjian*et*al.,*2003)+
to*perform*a*nonlinear*transformation*of*Talairach*coordinates*to*MNI*space.*For*meta_
analytic*ALE*results,*region*classifications*follow*those*indicated*in*the*Multi_Image*
Analysis*GUI*(‘Mango’)*image_viewing*software*(UT*Health*Science*Center*Research*
Imaging*Institute)*used*to*display*our*findings*(see*Results*below).*For*additional*
precision,*the*Duvernoy*neuroanatomical*atlas*was*also*consulted*(Duvernoy*et*al.,*1991).*
!
2.4!Activation!likelihood!estimation!(ALE)!meta8analysis!
* 2.4.1+General+methods.+We*used*a*quantitative,*random_effects*meta_analytic*
method*known*as*activation*likelihood*estimation*(ALE;*(Turkeltaub*et*al.,*2002,*Laird*et*
al.,*2005,*Eickhoff*et*al.,*2009,*Eickhoff*et*al.,*2012,*Turkeltaub*et*al.,*2012)*implemented*in*
the*software*program*GingerALE*2.1.1*(San*Antonio,*TX:*UT*Health*Science*Center*
Research*Imaging*Institute).+The*most*recent*ALE*algorithm*tests*for*above_chance*
clustering*of*peak*foci*from*different*experiments*included*in*the*meta_analysis*(Eickhoff*
et*al.,*2009,*Eickhoff*et*al.,*2012)*by*comparing*actual*activation*foci*locations/clustering*
with*a*null*distribution*that*includes*the*same*number*of*peak*foci*distributed*randomly*
throughout*the*brain.*Included*activation*foci*were*smoothed*using*a*full_width*half*
maximum*(FWHM)*Gaussian*kernel*dependent*on*the*total*sample*size*of*the*experiment*
from*which*foci*were*drawn*(larger*sample*_>*smaller*smoothing*kernel*–*empirically*
determined*by*(Eickhoff*et*al.,*2009,*Eickhoff*et*al.,*2012).*Resulting*statistical*maps*show*
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 24*
clusters*where*convergence*between*foci*of*activation*or*deactivation*is*greater*than*
would*be*expected*by*chance*(i.e.,*if*foci*from*each*experiment*were*distributed*
independently).+
2.4.2+Primary+neuroimaging+meta?analyses.+We*meta_analyzed*a*total*of*257*
peak*foci*of*activation*or*deactivation*drawn*from*25*studies*(Table*2),*involving*
31separate*‘experiments’*or*contrasts*(summarized*in*Table*1).*In*order*to*retain*a*
maximal*amount*of*information,*this*primary*meta_analysis*collapsed*data*from*between_
group*(long_term*practitioners*vs.*novices*or*controls)*and*repeated_measures*(the*same*
practitioners*pre_*and*post_meditation*training)*designs.*Although*only*a*small*amount*of*
data*came*from*short_term*training*(STT)*investigations*(6*of*25*studies*included*in*the*
meta_analysis),*nonetheless*this*difference*presents*a*potentially*confounding*factor.*We*
therefore*addressed*this*issue*by*performing*supplemental*meta_analyses*that*included*
only*investigations*of*long_term*practitioners*(see*Supplementary*Materials).**
Several*coordinate*foci*(n!=*7)*from*the*included*studies*fell*outside*of*the*brain*
mask*templates*used*with*the*GingerALE*meta_analysis*software*(1*focus*for*focused*
attention*activations;*4*foci*for*open*monitoring*activations;*and*2*foci*for*loving_kindness*
activations).*This*is*a*normal*occurrence*when*using*exclusive*meta_analytic*template*
masks.*The*total*number*of*foci*included*in*the*final*meta_analyses*was*therefore*250.*
Statistical*maps*were*thresholded*using*a*false*discovery*rate*(FDR;*(Genovese*et*
al.,*2002)*of*q*=*.05*and*a*cluster*threshold*of*k*=*100*mm3.*The*meta_analytic*software*
offers*suggested*minimum*cluster*thresholds*depending*on*the*number*of*studies*and*foci*
entered.*These*recommendations*centered*around*100*(generally,*between*88*and*132*
mm3),*but*differed*slightly*in*each*of*our*eight*meta_analyses*(activations*and*
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 25*
deactivations*for*each*of*four*meditation*categories).*For*consistency,*we*therefore*set*a*
standard*value*of*100*mm3*for*all*analyses.*Note*that*the*cluster*threshold*is*essentially*
arbitrary*and*does*not*affect*the*underlying*meta_analytic*analyses*or*results;*it*merely*
determines*which*meta_analytic*clusters*are*deemed*‘significant’*and*therefore*to*be*
reported*in*tables*of*results.*It*does*not*affect*the*underlying*meta_analytic*results,*which*
display*all*meta_analytic*activations*and*deactivations*regardless*of*cluster*threshold.*The*
full*meta_analytic*data*are*visible*in*our*supplementary*results*figures.*
To*display*our*results,*we*used*the*‘Colin’*template*brain*images*suggested*for*use*
with*GingerALE*2.1.1,*displayed*in*the*‘Mango’*software*package*(San*Antonio,*TX:*UT*
Health*Science*Center*Research*Imaging*Institute).*Maps*were*computed*separately*for*
activations*and*deactivations*for*each*meditation*category.*Activation*and*deactivation*
maps*were*then*concatenated*onto*a*single*template*brain*image*for*visualization*
purposes.*The*creation*of*the*final*figures*for*presentation*here*was*performed*in*the*
MRIcron*software*package*
(http://www.mccauslandcenter.sc.edu/mricro/mricron/index.html)*(Rorden*et*al.,*2007).*
!
2.5!Effect!size!meta8analysis!
In*addition*to*determining*which*brain*regions*were*consistently*activated*by*
various*meditation*practices,*we*sought*to*evaluate*the*magnitude*of*these*differences*(i.e.,*
their*effect*sizes;*(Cohen,*1992,*Lipsey*and*Wilson,*2001,*Sedlmeier*et*al.,*2012).*In*all,*17*
of*the*25*studies*that*met*our*inclusion*criteria*also*provided*necessary*and*sufficient*data*
to*allow*reliable*calculation*of*effect*sizes.**
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 26*
Although*the*calculation*and*comparison*of*effect*sizes*in*neuroimaging*studies*
faces*a*number*of*challenges,*simple*null_hypothesis*significance*tests*and*p_values*have*
come*under*harsh*criticism*as*well*(Schmidt,*1992,*Schmidt*and*Hunter,*1997,*Cumming,*
2012,*2013,*Hupé,*2015).*The*meaning*and*relevance*of*null_hypothesis*significance*
testing*and*associated*statistics*(such*as*t*and*F*statistics)*has*become*so*hotly*contested*
that*some*journals*have*outright*banned*reporting*of*such*values*(Savalei*and*Dunn,*2015,*
Trafimow*and*Marks,*2015).**
Bearing*in*mind*these*considerations,*we*concluded*that*effect*sizes*are*worth*
calculating*and*reporting*in*meta_analyses*of*neuroimaging*data,*so*long*as*these*serious*
limitations*are*noted*and*attempts*are*made*to*correct*for*them.*The*many*relevant*issues*
are*discussed*at*length*in*the*Supplementary*Methods*section.*
Briefly,*our*procedure*for*applying*these*corrections*was*as*follows:*After*
calculating*effect*sizes*directly*from*the*peak*or*maximum*t!or!F!statistics!reported*in*the*
original*studies,*we*then*adjusted*these*values*downward*to*approximate*more*
conservative*estimates*of*t*or*F*statistics*for*the*entire*cluster*of*significant*difference.*
Next,*we*further*deflated*these*values*to*account*for*the*inflationary*bias*of*effect*sizes*
derived*only*from*results*that*have*exceeded*stringent*statistical*thresholds*(Schmidt,*
1992).*In*these*ways,*we*aimed*to*provide*effect*size*estimates*that*more*closely*
approximate*true*effect*sizes.*It*should*be*noted,*however,*that*we*neither*claim*nor*expect*
that*this*procedure*is*ideal.*It*is*clear*that*some*deflation*of*reported*values*is*necessary*
(Schmidt,*1992,*Yarkoni,*2009,*Yarkoni*et*al.,*2010,*Hupé,*2015),*but*the*best*method*and*
optimal*degree*of*deflation*remains*unclear.*As*such,*our*methods*are*a*preliminary*effort*
to*produce*effect*sizes*that*are*more*accurate*than*those*produced*by*calculations*solely*
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 27*
based*on*t_statistics*reported*in*the*literature,*but*should*not*by*any*means*be*considered*
a*definitive*approach.*For*full*details,*as*well*as*specific*formulas*used,*see*the*
Supplementary*Methods.*
*
2.6!Estimating!publication!bias!in!meta8analytic!results!
+ The*bias*toward*publication*of*only*positive*(i.e.,*non_null)*results*is*a*serious*
concern*(the*‘file*drawer’*problem;*c.f.*(Rosenthal,*1979).*We*constructed*a*funnel*plot*
(scatterplot*of*effect*size*against*sample*size)*to*test*for*potential*publication*bias*in*our*
sample*of*studies*(Egger*et*al.,*1997).*Effect*sizes*were*calculated*as*described*above*and*
in*the*Supplementary*Methods,*and*plotted*against*total*sample*size*(meditators*+*
controls).*For*detailed*discussion*of*funnel*plots*see*Egger*and*colleagues*(1997).*For*other*
examples*of*their*use*in*meta_analyses*of*meditation*and*further*discussion*see*Fox*and*
colleagues*(2014)*and*Sedlmeier*and*colleagues*(2012).+
!
!
Functional*neuroanatomy*of*meditation*
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3.+Results+I:+Neuroimaging+meta?analysis+
+
3.1!Focused!attention!meditation!
* Meta_analysis*of*focused*attention*studies*resulted*in*2*significant*clusters*of*
activation,*both*in*prefrontal*cortex*(Table*3;*Fig.*2).*Activations*were*observed*in*regions*
associated*with*the*voluntary*regulation*of*thought*and*action,*including*the*premotor*
cortex*(BA*6;*Fig.*2e)*and*dorsal*anterior*cingulate*cortex*(BA*24;*Fig.*2a).*Slightly*sub_
threshold*clusters*were*also*observed*in*the*dorsolateral*prefrontal*cortex*(BA*8/9;*Fig.*
2c)*and*left*mid*insula*(BA*13;*Fig.*2e);*we*display*these*somewhat*sub_threshold*results*
here*because*of*the*obvious*interest*of*these*findings*in*practices*that*involve*top_down*
focusing*of*attention,*typically*focused*on*respiration.*We*also*observed*clusters*of*
deactivation*in*regions*associated*with*episodic*memory*and*conceptual*processing,*
including*the*ventral*posterior*cingulate*cortex*(BA*31;*Fig.*2d)*and*left*inferior*parietal*
lobule*(BA*39;*Fig.*2f).*A*detailed*series*of*slices*covering*the*entire*brain*is*presented*in*
Fig.*S1.*
* A*supplementary*meta_analysis,*excluding*studies*that*investigated*only*
practitioners*with*short_term*training,*yielded*nearly*identical*results*(see*Table*S2).*
*
**
! !
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 29*
Table!3.*Activations*and*deactivations*associated*with*focused*attention*meditation**
Region+ Cluster+Size+(mm3)+
Side+ Peak+Coordinates++(x,+y,+z)+
Peak+ALE+value+
Activations+
Premotor*cortex* 712* L* _36,*6,*56*(BA*6)* 0.0144*
Dorsal*anterior/mid*cingulate*cortex* 280* M* 2,*12,*32*(BA*24)* 0.0112*
Deactivations+
Posterior*cingulate*cortex* 152* M* _6,*_60,*18*(BA*30)* 0.0071*
Inferior*parietal*lobule* 144* L* _48,*_72,*30*(BA*39)* 0.0071*
!!!Figure!2.!Peak*activations*and*deactivations*associated*with*focused*attention*meditation*!
**(a)*Dorsal*anterior/mid*cingulate*cortex*(b)*Premotor*cortex/posterior*dorsolateral*prefrontal*cortex.*(c)*Sub_threshold*cluster*in*dorsolateral*prefrontal*cortex.*(d)*Posterior*cingulate*cortex.*(e)*Sub_threshold*cluster*in*mid_insula.*(f)*Inferior*parietal*lobule.*Warm*colors:*activations;*cool*colors:*deactivations.*See*the*supplementary*materials*for*a*detailed*series*of*slices*covering*the*entire*brain*(Fig.*S1).*!
3.!2!Mantra!recitation!meditation!
! A*meta_analysis*of*mantra*recitation*studies*revealed*seven*significant*activation*
clusters*(Table*4).*Activations*were*observed*in*regions*associated*with*planning*and*
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 30*
executing*voluntary*motor*output,*including*the*posterior*dorsolateral*prefrontal*
cortex/left*premotor*cortex*(BA*6/8;*Fig.*3d),*pre_supplementary*motor*cortex,*
supplementary*motor*cortex*(BA*6;*Fig.*3a),*and*putamen/lateral*globus*pallidus*(Fig.*3b).*
Other*activations*were*observed*in*regions*associated*with*visual*processing*and*mental*
imagery*including*the*fusiform*gyrus*(Fig.*3c),*cuneus*(BA*18),*and*precuneus*(BA*7)*(Fig.*
S2).*There*was*also*a*small*(but*non_significant)*cluster*located*within*Broca's*area*(BA*
44/6),*consistent*with*the*verbal*component*of*mantra*recitation.*A*single*cluster*of*
deactivation*was*observed*(Table*4)*in*the*left*anterior*insula*(BA*13)/claustrum*(Fig.*3b),*
a*region*associated*with*processing*viscero_somatic*body*signals.*A*detailed*series*of*slices*
covering*the*entire*brain*is*presented*in*Fig.*S2.*
* A*supplementary*meta_analysis,*excluding*studies*that*investigated*only*
practitioners*with*short_term*training,*yielded*nearly*identical*results.*The*only*notable*
difference*was*the*disappearance*of*the*single*deactivation*cluster*in*the*anterior*insula*
(see*Table*S3).*Although*ALE*implements*controls*for*sample*size,*another*concern*was*the*
inclusion*of*two*studies*with*very*small*sample*sizes*–*Lazar*et*al.*(2000)*with*n*=*5,*and*
Davanger*et*al.*(2010)*with*n*=*4*–*which*might*still*have*unduly*influenced*the*results.*We*
therefore*also*executed*our*analysis*with*data*from*these*two*studies*excluded.*This*had*
no*effect*on*the*pattern*of*deactivations.*All*remaining*clusters*of*activation*were*the*same,*
but*two*clusters*disappeared*from*the*results:*the*putamen/lateral*globus*pallidus,*and*the*
small*(112*mm3)*cluster*in*the*supplementary*motor*area.*
!
!
!
!
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 31*
Table!4.*Activations*and*deactivations*associated*with*mantra*recitation*meditation*
Region+ Cluster+Size+(mm3)+
Side+ Peak+Coordinates++(x,+y,+z)+
Peak+ALE+value+
Activations+
Premotor*cortex* 896* L* _30,4,*60*(BA*6)* 0.0137*
Supplementary*motor*area*584* M* 0,*12,*54*(BA*6)* 0.0111*
112* M* _4,*2,*68*(BA*6)* 0.0080*
Putamen/Lateral*globus*pallidus* 368* R* 28,*_16,*_6* 0.0111*
Fusiform*gyrus* 248* R* 40,*_26,*_30*(BA*20/36)* 0.0093*
Cuneus* 160* R* 24,*_86,*26*(BA*18)* 0.0082*
Precuneus* 152* L* _14,*_56,*54*(BA*7)* 0.0082*
Deactivations+
Anterior*insula* 192* L* _28,*25,*_7*(BA*13)* 0.0075*
!!Figure!3.!Peak*activations*and*deactivations*associated*with*mantra*recitation*meditation*!
!
(a)*Supplementary*motor*area.*(b)*Bilateral*deactivations*in*the*anterior*insula*(blue)*and*activations*in*the*right*basal*ganglia*(putamen*and*globus*pallidus).*(c)*Fusiform*gyrus.*(d)*Premotor*cortex.*Warm*colors:*activations;*cool*colors:*deactivations.*See*the*supplementary*materials*for*a*detailed*series*of*slices*covering*the*entire*brain*(Fig.*S2).*
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 32*
3.3!Open!monitoring!meditation!
! Meta_analysis*of*open*monitoring*studies*showed*five*significant*clusters*of*
activation*(Table*5).*One*cluster*was*located*in*the*insula*(BA*13;*Fig.*4d),*consistent*with*
awareness*of*ongoing*viscero_somatic*body*signals.*Other*significant*clusters*were*
observed*in*regions*associated*with*the*voluntary*control*of*action,*including*the*left*
inferior*frontal*gyrus*(BA*44/45;*Fig.*4b),*pre_supplementary*motor*area*(BA*32/6;*Fig.*
4a),*supplementary*motor*area*(BA*6;*Fig.*4a,c),*and*premotor*cortex*(BA*6;*Fig.*4*c).*
Smaller*(non_significant)*clusters*were*observed*in*the*rostrolateral*prefrontal*cortex*(BA*
10)*and*mid_dorsolateral*prefrontal*cortex*(BA*9/46)*―*regions*associated*with*cognitive*
control*and*metacognitive*awareness.*We*observed*a*single*significant*cluster*of*
deactivation*(Table*5)*in*the*right*thalamus*(Fig.*4d).*A*detailed*series*of*slices*covering*the*
entire*brain*is*presented*in*Fig.*S3.*
* A*supplementary*meta_analysis,*excluding*studies*that*investigated*only*
practitioners*with*short_term*training,*yielded*similar*results*(Table*S4).*Some*of*the*more*
salient*differences*are*outlined*in*the*Discussion,*below*(also,*compare*Table*5*with*Table*
S4).*
*
! !
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 33*
Table!5.*Activations*and*deactivations*associated*with*open*monitoring*meditation**
Region+ Cluster+Size+(mm3)+
Side+ Peak+Coordinates++(x,+y,+z)+
Peak+ALE+value+
Activations+
Supplementary*motor*area* 824* M* _6,*4,*60*(BA*6)* 0.0165*
Dorsal*anterior*cingulate*cortex/*pre_supplementary*motor*area* 368* M* _6,*18,*44*(BA*32/6)* 0.0110*
Insular*cortex*(mid/anterior)* 360* L* _44,*10,*4*(BA*13)* 0.0111*
Inferior*frontal*gyrus* 200* L* _50,*16,*14*(BA*44/45)* 0.0092*
Premotor*cortex* 104* L* _44,*10,*46*(BA*6)* 0.0089*
Deactivations*
Thalamus*(pulvinar)* 112* R* 17,*_24,*11* 0.0084*
!
Figure!4.*Peak*activations*and*deactivations*associated*with*open*monitoring*meditation+
+
(a)*Supplementary*motor*area*(larger,*more*superior*cluster)*and*dorsal*anterior*cingulate*cortex/pre_supplementary*motor*area.*(b)*Inferior*frontal*gyrus.*(c)*Premotor*cortex*(smaller*cluster*to*left),*and*supplementary*motor*area*also*visible*again*(center).*(d)*Activation*in*mid/anterior*insula*and*bilateral*deactivations*in*the*thalamus.*Warm*colors:*activations;*cool*colors:*deactivations.*L:*left;*R:*right.*See*the*supplementary*materials*for*a*detailed*series*of*slices*covering*the*entire*brain*(Fig.*S3).*!
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 34*
3.4!Loving8kindness!and!compassion!meditation*
Meta_analysis*of*loving_kindness*and*compassion*meditation*revealed*significant*
activation*clusters*in*3*regions*(Table*6).*Activations*were*observed*in*regions*associated*
with*awareness*of*bodily*sensations*and*feelings*including*the*right*anterior*insula/frontal*
operculum*(BA*13;*Fig.*5a)*and*secondary*somatosensory*areas*extending*into*the*anterior*
inferior*parietal*lobule*(BA*2/40;*Fig.*5b).*Additionally,*activation*was*observed*near*the*
parieto_occipital*sulcus*(BA*23/31;*Fig.*5c).*No*significant*deactivations*were*observed.*A*
detailed*series*of*slices*covering*the*entire*brain*is*presented*in*Fig.*S4.*
A*supplementary*meta_analysis,*excluding*studies*that*investigated*only*
practitioners*with*short_term*training,*yielded*nearly*identical*results.*The*only*significant*
difference*was*the*appearance*of*a*small*cluster*of*activation*in*the*left*somatosensory*
cortices*(see*Table*S5).*
!
! !
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 35*
Table!6.*Activations*and*deactivations*associated*with*loving_kindness*and*compassion*
meditation*
Region+ Cluster+Size+(mm3)+
Side+ Peak+Coordinates++(x,+y,+z)+
Peak+ALE+value+
Activations+
Anterior*insula* 512* R* 38,*22,*14*(BA*13)* 0.0135*
Parieto_occipital*sulcus* 344* R* 24,*_60,*18*(BA*23/31)* 0.0115*
Somatosensory*cortices/Inferior*parietal*lobule*
320* R* 54,*_26,*30*(BA*2/40)* 0.0101*
!!
Figure!5.!!!Peak*activations*associated*with*loving_kindness*and*compassion*meditation!
!
(a)*Right*anterior*insula/frontal*operculum.*(b)*Right*somatosensory*cortices.*(c)*Parieto_occipital*sulcus.*L:*left;*R:*right.*See*the*supplementary*materials*for*a*detailed*series*of*slices*covering*the*entire*brain*(Fig.*S4).*!
+ +
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 36*
4.+Results+II:+Effect+size+meta?analysis++
+ As*detailed*in*the*Supplementary*Methods,*we*derived*effect*sizes*(Cohen’s*d)*from*
studies*that*reported*t*or*F*statistics,*and*then*adjusted*these*raw*effect*sizes*for*the*severe*
inflationary*bias*that*influences*effect*sizes*in*all*neuroimaging*research.*From*our*
adjusted*effect*sizes*for*each*individual*reported*result,*we*then*calculated*mean*positive*
(+)*and*negative*(–)*effect*sizes*for*each*study*(and*for*each*different*practice*within*a*
study,*if*more*than*one*was*examined).*These*results*are*reported*in*Table*7.*We*then*
pooled*these*data*to*calculate*mean*(+)*and*(–)*effect*sizes*for*each*type*of*practice*(Table*
8).*Recall*that*in*total,*two*deflation*coefficients*were*employed*to*adjust*for*suspected*
inflation*bias.*Coefficients*of*0.697*and*0.60,*for*a*net*coefficient*of*0.4182,*were*applied*to*
the*effects*calculated*from*the*primary*reports.*Therefore,*in*order*to*obtain*the*
unadjusted*values,*simply*multiply*our*effect*size*results*by*2.391.*For*details*see*Methods*
section*2.5.*
+
! !
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MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 37*
Table!7.***Summary*of*adjusted*mean*effect*sizes*for*each*study*and*practice*type.!
Study+ Sample+(N)+ Practice+Mean+(+)+effect+size+
(Cohen’s+d)+Mean+(–)+effect+size+
(Cohen’s+d)+
Brefczynski_Lewis*et*al.*(2007)* 30* FA* 0.51* –*
Lutz*et*al.*(2008)* 32* LK* 0.33* –*
Lutz*et*al.*(2009)* 22* LK* 0.56* –*
Davanger*et*al.*(2010)* 4* MR* 1.48* –*
Manna*et*al.*(2010)* 8*FA* 1.56* _1.29*
OM* 1.25* –*
Brewer*et*al.*(2011)* 25*
FA* –* _0.71*
OM* –* _0.58*
LK* –* _0.68*
Gard*et*al.*(2011)* 34* OM* 0.46* –*
Ives_Deliperi*et*al.*(2011)* 10* OM* 2.03* _2.01*
Kalyani*et*al.*(2011)* 12* MR* –* _1.11*
Taylor*et*al.*(2011)* 22* OM* –* _0.79*
Dickenson*et*al.*(2012)* 31* FA* 0.49* –*
Hasenkamp*et*al.*(2012)* 14* FA* 0.67* –*
Lee*et*al.*(2012)* 44*FA* 0.56* –*
LK* 0.54* –*
Farb*et*al.*(2013)* 36* OM* 0.71* –*
Lutz*et*al.*(2013)* 28* OM* 0.58* _0.62*
Weng*et*al.*(2013)* 41* LK* 0.36* –*
Lutz*et*al.*(2014)* 46* OM* 0.51* _0.45*
++! !
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Table!8.*Summary*of*adjusted*mean*effect*sizes*by*meditation*practice*type!
Meditation+Type+Contributing+Experiments+
(N)+
Mean+(+)+effect+size+(Cohen’s+d)a+
Mean+(–)+effect+size+(Cohen’s+d)a+
Focused*attention* 6* 0.60!±*0.05* _0.85*±*0.09*Mantra*recitation* 2* 1.48* _1.11*
Open*monitoring* 8* 0.68*±*0.12* _0.69*±*0.14*Loving_kindness/compassion* 5* 0.44*±*0.01* _0.68*
All+practices+combined+ 21+ M+=+0.59+±+0.02+ M+=+?0.74!±+0.09+Mean*effect*sizes*±!95%*confidence*intervals.*Note*that*the*‘mean’*effect*sizes*for*mantra*recitation*are*based*on*only*a*single*study*each,*as*are*negative*effect*sizes*for*loving_kindness/compassion*meditations*(cf.*Table*7).*Accordingly,*no*confidence*intervals*are*provided*since*there*was*no*variance*in*the*estimates.*Note*that*a*total*of*21*‘experiments’*were*analyzed,*from*17*independent*studies*of*the*25*studies*originally*included*in*the*neuroimaging*meta_analysis.*The*remaining*studies*did*not*provide*statistical*data*that*allowed*for*calculation*of*Cohen’s*d.**++Figure!6.*Funnel*plot*showing*weighted*means*of*both*negative*and*positive*effect*sizes**
+The*two*anchor*lines*represent*the*means*for*all*(–)*and*(+)*effect*sizes*(_0.74*and*+0.59,*respectively)*weighted*by*sample*size.*Positive*effect*sizes*relate*to*brain*activations*during*meditation,*whereas*negative*effect*sizes*represent*brain*deactivations.*See*Tables*7*and*8*for*details.*+
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5.+Discussion,+future+directions,+and+conclusions+
+
5.1!Overview!
* The*ensuing*discussion*is*divided*into*three*broad*sections:**
(i)*First,*we*outline*and*interpret*the*various*results*from*our*meta_analysis*and*
qualitative*review*of*neuroimaging*findings*(sections*5.2_5.8).*We*synthesize*and*simplify*
all*of*these*results*in*a*single*summary*figure*(Fig.*7).*We*focus*on*the*clusters*that*
attained*statistical*significance*in*our*meta_analysis,*but*it*should*be*recalled*that*
significance*and*cluster*thresholds*are*ultimately*arbitrary*and*should*not*restrict*
discussion.*Some*‘significant’*clusters*are*difficult*to*understand*or*explain,*whereas*some*
non_significant*clusters*dovetail*extremely*well*with*the*stated*techniques*and*goals*of*a*
given*form*of*meditation.*We*therefore*endeavor*to*offer*as*integrated*and*impartial*a*
discussion*as*possible,*including*consideration*of*meta_analytic*activations*that*may*not*
have*exceeded*our*cluster*thresholds.*We*also*integrate*the*limited*findings*from*the*three*
meditation*categories*that*could*not*be*included*in*the*quantitative*meta_analysis,*for*the*
same*reasons:*preliminary*data,*even*if*tentative,*is*still*informative*and*relevant*to*our*
discussion.*In*a*similar*vein,*the*figures*in*our*Results*section,*for*the*sake*of*clarity,*focus*
on*the*most*reliable,*consistent*clusters*for*each*category*of*meditation.*However,*we*have*
presented*detailed*series*of*slices*in*our*supplementary*materials*in*order*to*clearly*
visualize*all*activations*associated*with*a*given*meditation*type*(not*just*those*that*
exceeded*our*cluster*and*significance*thresholds;*see*Figs.*S1_S4).*
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(ii)*Second,*we*discuss*the*results*of*our*effect*size*meta_analysis*(section*5.9),*and*
its*implications*for*the*‘practical*significance’*of*the*functional*neural*effects*associated*
with*meditation.*We*also*discuss*the*possibility*of*publication*bias.**
(iii)*Finally,*several*sections*(5.10_5.13)*outline*the*limitations*of*our*meta_analysis,*
the*relevance*of*these*results*to*clinical*conditions,*and*the*implications*for*future*avenues*
of*research.*
*
Figure!7.*Simplified*summary*of*all*meta_analytic*activations*and*deactivations.!!
Filled*circles*indicate*activations;*circles*with*downward*arrows*indicate*deactivations.*All*labels*are*approximate*and*intended*for*illustrative*purposes*only.*Medial*meta_analytic*clusters*are*arbitrarily*represented*on*a*right*hemisphere*view*merely*for*simplicity;*lateral*and*insular*clusters*are*represented*in*the*correct*hemisphere.*For*the*specific*location*of*each*cluster,*see*Tables*3_6*and*Supplementary*Figures*1_4.** **
!
!
Functional*neuroanatomy*of*meditation*
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5.2!Functional!neuroanatomy!of!focused!attention!meditation!
+ 5.2.1+Activations.+Focused*attention*meditation*was*associated*with*activations*in*
regions*associated*with*cognitive*control*and*self_reflection.*Directly*in*line*with*others’*
predictions*(Lutz*et*al.,*2008b),*we*found*activations*in*the*premotor*cortex*extending*into*
the*posterior*dorsolateral*prefrontal*cortex,*as*well*as*in*the*dorsal*anterior*cingulate*
cortex.*We*also*observed*a*slightly*sub_threshold*(88*m3)*cluster*in*the*dorsolateral*
prefrontal*cortex*(BA*8/9).*These*regions*are*frequently*activated*in*studies*of*cognitive*
control*that*require*monitoring*performance,*and*the*voluntary*regulation*of*attention*and*
behavior,*such*that*task_relevant*actions*are*selected*(Carter*et*al.,*1998,*Vincent*et*al.,*
2008,*Dixon*and*Christoff,*2012,*Dixon*et*al.,*2014a).*The*recruitment*of*such*executive*
brain*areas*is*consistent*with*a*contemplative*practice*consisting*largely*of*effortful,*
sustained*attention*with*a*range*of*regulation*demands.*For*more*details,*see*the*
Supplementary*Discussion.* *
5.2.2+Deactivations.+Consistent*deactivations*were*observed*in*two*major*hubs*of*
the*default*mode*network:*the*posterior*cingulate*cortex*(BA*23/31)*and*the*posterior*
inferior*parietal*lobule*(BA*39)*(Buckner*et*al.,*2008).*These*regions*have*well_established*
roles*in*mind_wandering*(Fox*et*al.,*2015),*and*in*particular,*episodic*memory*retrieval,*
simulation*of*future*events,*and*conceptual/semantic*processing.*Deactivations*in*these*
regions*suggest*that*focused*attention*meditation*may*diminish*spontaneous*thoughts*
regarding*past*and*future*events,*as*well*as*their*conceptual*elaboration.*Although*many*
regions*beyond*the*default*mode*network*are*implicated*in*mind_wandering*and*related*
spontaneous*thought*processes,*the*default*mode*network*nonetheless*plays*an*essential*
role*(Fox*et*al.,*2015).*For*more*details,*see*the*Supplementary*Discussion.*
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5.3!Functional!neuroanatomy!of!mantra!recitation!meditation!
! 5.3.1+Activations.+The*most*salient*activations*for*mantra*recitation*meditation*
were*in*the*motor*control*network,*including*Broca's*area,*the*premotor*and*
supplementary*motor*cortices*(lateral*and*medial*BA*6),*as*well*as*the*putamen*within*the*
basal*ganglia.*Consistent*with*the*goals*of*mantra*meditation,*these*regions*may*be*
involved*in*the*process*of*internally*generating*and*staying*focused*on*a*phrase*within*
one's*mind*(or*recited*aloud).+
* Particularly*interesting*was*a*small*cluster*in*Broca’s*area*(BA*44),*extending*
posteriorly*into*the*face/tongue*area*of*premotor*cortex*(BA*6).*This*area*is*well_known*
from*the*neuropsychological*lesion*work*of*Pierre*Paul*Broca*to*be*critically*involved*in*
the*motor*components*of*speech*production*(Broca,*1861).*Its*consistent*recruitment*
during*mantra*recitation*requires*little*comment.*
* Large*activations*were*also*observed*in*various*areas*of*the*basal*ganglia,*including*
bilateral*clusters*in*both*the*putamen*and*globus*pallidus.*Although*these*areas*play*a*clear*
role*in*‘reward’*(Schultz*et*al.,*2000),*they*are*most*strongly*implicated*in*highly_practiced*
motor*movements*and*habit*formation*in*general*(Yin*and*Knowlton,*2006,*Ashby*et*al.,*
2010).*In*a*broader*sense,*the*basal*ganglia*are*thought*to*aid*in*the*inhibition*of*undesired*
movements,*and*in*facilitating*the*smooth*execution*of*those*movements*that*are*desired,*
via*tight*reciprocal*connections*with*premotor*areas*(Chakravarthy*et*al.,*2010,*Stocco*et*
al.,*2010).*These*latter*functions*are*all*consistent*with*a*meditation*practice*that*primarily*
involves*the*deliberate*execution*of*a*highly_practiced*and*highly_specific*sequence*of*
motor*behavior*(whether*imagined*in*detail*or*recited*aloud).*For*more*details,*see*the*
Supplementary*Discussion.* *
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5.3.2+Deactivations.+An*interesting*pattern*of*deactivations*was*observed,*
suggesting*decreased*processing*of*external*sensory*(particularly*somatosensory)*inputs.*
Deactivations*were*observed*bilaterally*in*the*anterior*insula,*and*at*a*sub_threshold*level*
in*the*thalamus,*left*primary*somatosensory*cortex*(postcentral*gyrus;*BA*2),*and*left*
inferior*parietal*lobule*(BA*40).*All*of*these*areas*are*centrally*involved*in*processing*and*
awareness*of*somatosensory*and*interoceptive*information*(Penfield*and*Boldrey,*1937,*
Bonda*et*al.,*1995,*Craig,*2004,*2009).*Deactivations*were*also*observed*in*primary*
auditory*cortex*(BA*41)*and*in*the*posterior*area*of*the*superior*temporal*gyrus*(BA*22),*
both*well_known*to*be*involved*in*the*processing*and*comprehension*of*sounds*and*
language*(Galaburda*and*Sanides,*1980,*Demonet*et*al.,*1992).*
One*of*the*reasons*mantra*is*employed*is*to*heighten*the*effectiveness*of*focused*
attention*meditation.*The*implication*is*that*by*focusing*upon*a*single*salient*percept*(the*
mantra),*attention*is*more*easily*sustained*and*distractors*more*easily*ignored*than*
without*the*mantra*(Goenka,*2000).*The*observed*pattern*of*deactivations*is*consistent*
with*the*idea*that*mantra*aids*in*maintaining*a*sharp*focus*of*attention,*to*the*exclusion*of*
incoming*sensory*stimuli*and*awareness*of*one’s*own*body.*Deactivations*in*auditory*and*
language_comprehension*areas*are*also*intriguing*in*that*the*mantra*is*intended*as*a*tool*
for*focusing*attention,*but*is*not*usually*meant*to*be*understood*semantically.*!
5.4!Functional!neuroanatomy!of!open!monitoring!meditation!
* 5.4.1+Activations.+Open*monitoring*meditation*was*associated*with*activation*in*
regions*involved*in*the*voluntary*regulation*of*thought*and*action*(inferior*frontal*gyrus,*
posterior*dorsolateral*prefrontal*cortex/pre_motor*cortex,*and*dorsal*anterior*cingulate*
cortex/pre_supplementary*motor*area),*as*well*as*activation*in*the*insula,*a*region*that*
Functional*neuroanatomy*of*meditation*
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plays*a*key*role*in*interoceptive*processing.*As*all*of*these*areas*were*recruited*by*multiple*
meditation*techniques,*they*are*discussed*in*more*detail*below*in*Section*5.6*on*
‘Convergent*findings.’*
* Smaller*clusters*that*did*not*exceed*our*threshold+were*observed*in*left*
rostrolateral*prefrontal*cortex*(BA*10)*and*left*mid_dorsolateral*prefrontal*cortex*(BA*
9/46).*Together*with*the*dorsal*anterior*cingulate*cortex,*these*areas*constitute*key*parts*
of*a*‘frontoparietal*control’*network*(Vincent*et*al.,*2008,*Spreng*et*al.,*2010)*generally*
involved*in*cognitive*control,*that*is,*coordinating*and*monitoring*attention*to*both*
internal*and*external*channels*of*information*(Spreng,*2012,*Dixon*et*al.,*2014b).*Given*
that*open*monitoring*meditation*typically*involves*a*broad,*non_judgmental*attention*to*
any*and*all*mental*content*(including*information*from*the*outside*world,*from*within*the*
body,*and*also*internal*channels*of*thought*and*memories),*it*is*congruous*that*this*
practice*recruits*numerous*areas*from*the*frontoparietal*control*network.**
5.4.2+Deactivations.+Only*a*single*significant*deactivation*was*observed,*in*the*
right*thalamus,*and*a*sizeable*(albeit*sub_threshold)*deactivation*was*also*observed*in*the*
left*thalamus.*Interestingly,*in*the*supplemental*meta_analysis*(which*excluded*
practitioners*with*only*brief*training*in*this*practice),*these*findings*were*even*more*
salient*(Table*S5).*The*thalamus*is*the*key*relay*center*for*most*incoming*sensory*
information,*and*also*functions*in*‘sensory*gating’*(i.e.,*the*selective*filtering*out*of*certain*
sensory*signals).*Interestingly,*increased*intensity*of*sensory*gating*appears*to*be*
correlated*with*increased*activity*in*the*thalamus*(LaBerge,*1990,*LaBerge*and*Buchsbaum,*
1990,*Banich,*2004).*Therefore,*deactivations*here*suggest*decreased*sensory*gating,*an*
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interpretation*that*aligns*well*with*the*goal*of*being*open*and*receptive*to*sensory*stimuli.*
For*more*details,*see*the*Supplementary*Discussion.* *
!
5.5!Functional!neuroanatomy!of!loving8kindness!and!compassion!meditation!
5.5.1+Activations.+Loving_kindness*and*compassion*meditation*involve*cultivating*
positive*emotions,*such*as*joy*and*compassion,*as*well*as*prosocial*skills*and*tendencies,*
such*as*empathic*concern*and*altruistic*behavior.*They*focus*on*active*‘mentalizing’*in*the*
form*of*taking*the*perspective*of*others*and*imagining*their*emotional*experiences.*
Mounting*evidence*from*behavioral*studies*suggests*that*these*practices*can*be*effective,*
and*that*even*brief*training*in*compassion*meditation*can*increase*empathy*for,*and*
prosocial*behavior*toward,*others*(Leiberg*et*al.,*2011,*Condon*et*al.,*2013,*Kang*et*al.,*
2013,*Weng*et*al.,*2013,*Lim*et*al.,*2015).*One*study*even*found*that*compassion*
meditation_driven*changes*in*brain*activation*specifically*predicted*subsequent*
compassionate*behavior*toward*an*unknown*victim*(Weng*et*al.,*2013).**
Only*three*significant*meta_analytic*clusters*were*observed,*probably*due*to*the*low*
power*of*this*analysis,*which*involved*the*fewest*studies*(N*=*5*experiments;*see*Table*1).*
One*large*cluster*was*observed*in*the*right*somatosensory*cortices*(BA*2),*extending*into*
the*inferior*parietal*lobule*(BA*40).*A*similarly*located*(albeit*statistically*non_significant)*
cluster*was*observed*on*the*postcentral*gyrus*of*the*left*hemisphere,*centered*on*BA*43*
and*extending*into*BA*3.*These*parts*of*parietal*lobe*play*a*well_known*role*in*
somatosensory*processing*and*in*creating*a*unified*sense*of*the*body*(Penfield*and*
Boldrey,*1937,*Penfield*and*Rasmussen,*1950),+but*both*regions*have*also*been*implicated*
in*empathy*in*a*recent*meta_analysis*(Lamm*et*al.,*2011)*and*comprehensive*review*
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(Bernhardt*and*Singer,*2012).*Both*areas*are*also*consistently*implicated*in*the*perception*
of*pain*(Grant*et*al.,*2011,*Grant,*2014),*but*this*function*may*overlap*with*their*role*in*
empathy,*as*part*of*the*proposed*role*of*these*areas*in*empathy*may*be*in*specifically*
empathizing*with*the*pain*of*others*(Lamm*et*al.,*2011).*
Another*large*cluster*centered*on*the*right*anterior*insula,*which*has*previously*
been*implicated*in*quantitative*meta_analyses*(Lamm*et*al.,*2011)+of*the*neural*correlates*
of*empathy*and*theory_of_mind*(i.e.,*mentalizing).*Because*insula*activation*was*observed*
across*multiple*meditation*categories,*its*possible*role(s)*in*loving_kindness*meditation*is*
discussed*further*in*the*section*on*convergent*findings*(section*5.6).*For*more*details,*see*
the*Supplementary*Discussion.*
! 5.5.2+Deactivations.+No*significant*deactivations*were*observed;*for*more*details,*
see*the*Supplementary*Discussion.*!
)
5.6!Convergent!findings!across!meditation!categories!
* Relatively*few*regions*showed*significant*clusters*across*multiple*meditation*
categories,*supporting*the*central*hypothesis*of*this*paper*that*distinct*meditation*styles*
recruit*largely*non_overlapping*neural*networks.*Only*a*single*area*(insular*cortex)*was*
recruited*by*all!four*meditation*categories.*Some*additional*consistencies*across*
meditation*types*were*observed,*however;*each*area*is*considered*in*turn*below.*
5.6.1+Insular+cortex.*Meta_analytic*activations*were*observed*in*insular*cortex*in*
all*four*meditation*categories*explored*here.*For*focused*attention,*a*small*(non_
significant)*cluster*was*observed*in*the*left*anterior*insula,*as*well*as*a*somewhat*larger*
(also*non_significant)*cluster*in*the*left*mid_insula.*For*mantra*recitation,*a*very*small*
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(non_significant)*cluster*was*observed*in*the*left*mid_insula/claustrum.*For*open*
monitoring*meditation,*a*large*(significant)*cluster*was*observed*in*the*left*anterior/mid_
insula,*as*well*as*two*smaller*(non_significant)*clusters*in*the*right*mid_*and*posterior*
insula.*For*loving_kindness*meditation,*a*large*(significant)*cluster*was*observed*in*the*
right*anterior*insula.*The*insula*therefore*appears*to*be*reliably*recruited*in*two*categories*
of*meditation*we*examined,*and*shows*evidence*for*recruitment*in*the*two*other*styles.*
* These*findings*suggest*an*important*role*for*the*insula*across*numerous*meditative*
practices.*They*are*also*consistent*with*our*recent*meta_analysis*of*morphometric*
neuroimaging*of*meditation,*which*collapsed*across*many*meditation*styles*and*found*that*
differences*in*insula*were*the*most*consistent*structural*alterations*(Fox*et*al.,*2014).*
Although*the*insula*has*many*roles,*probably*the*most*consistently*replicated*and*
thoroughly*investigated*is*its*involvement*in*interoception*(i.e.,*monitoring*and*conscious*
awareness*of*internal*body*states,*such*as*respiration*or*heart*rate)*(Craig,*2004,*Critchley*
et*al.,*2004,*Craig,*2009,*Farb*et*al.,*2013)*as*well*as*empathy*(Lamm*et*al.,*2011)*and*
possibly*even*metacognition*(Fleming*and*Dolan,*2012).*Given*that*virtually*all*forms*of*
meditation*investigated*here*involve*some*degree*of*monitoring*of*the*body,*some*
awareness*of*respiration,*and*basic*metacognitive*monitoring,*universal*recruitment*of*
insular*cortex*is*not*unreasonable.**
* Insular*cortex*is*not*functionally*homogenous,*however:*there*is*evidence*that*the*
mid*and*posterior*insula*serve*as*‘primary’*interoceptive*cortex,*receiving*and*processing*
direct*interoceptive*inputs*from*the*thalamus*(Flynn,*1999,*Hua*et*al.,*2005,*Frot*et*al.,*
2007),*whereas*more*anterior*parts*of*the*insula*are*preferentially*involved*in*conscious*
awareness*of*interoceptive*signals*and*the*integration*of*this*information*with*one’s*
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higher_order*goals*and*emotional*states*(Craig,*2004,*Critchley*et*al.,*2004,*Critchley,*2005,*
Craig,*2009).*In*this*light*it*is*interesting*that*anterior*insula*was*recruited*in*all*techniques*
except*mantra*recitation*–*which*is*the*technique*least*focused*on*conscious*awareness*of*
the*body,*and*most*geared*toward*detaching*from*immediate*sensory*stimuli.*This*
interpretation*is*speculative,*of*course;*
for*more*details,*see*the*Supplementary*Discussion.* *
5.6.2+Premotor+cortex+and+supplementary+motor+area+(lateral/medial+BA+6).***
Three*categories*of*meditation*(the*exception*being*loving_kindness/compassion)*showed*
large*meta_analytic*clusters*in*posterior*dorsolateral*prefrontal*cortex/premotor*and*
supplementary*motor*cortices*(BA*6).*Although*these*areas*are*traditionally*considered*
‘motor’*regions,*a*wealth*of*recent*work*has*demonstrated*that*they*also*play*a*role*in*
many*cognitive*functions*(e.g.,*(Hanakawa*et*al.,*2002,*Tanaka*et*al.,*2005).*Specifically,*it*
has*been*proposed*that*these*areas*could*play*a*role*analogous*to*their*motor*function*of*
manipulating*objects*in*the*physical*world*–*namely,*the*mental*manipulation*of*
psychological*content*and*memory*(Hanakawa*et*al.,*2002).*Functional*neuroimaging*
studies*have*shown*activation*in*these*areas*during*a*variety*of*complex*mental*tasks,*
including*working*memory*(Fiez*et*al.,*1996,*Owen*and*Evans,*1996),*attentional*control*
(Hopfinger*et*al.,*2000,*Boussaoud,*2001),*mental*imagery*(Mellet*et*al.,*1996),*and*
conceptual*reasoning*(Rao*et*al.,*1997).*Given*the*apparent*role*of*these*regions*in*diverse*
higher_order*cognitive*functions*and*attention*regulation*–*the*core*of*all*meditation*
techniques*–*their*recruitment*across*numerous*styles*of*meditation*appears*reasonable.*
Speculatively,*then,*these*regions*may*interact*with*other*brain*areas*more*specifically*tied*
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to*particular*meditation*techniques,*assisting*in*the*intentional*regulation*of*attention*and*
other*cognitive*processes*specific*to*the*practice*at*hand.***
5.6.3+Dorsal+anterior/mid+cingulate+cortex.*In*focused*attention*and*open*
monitoring*meditation,*we*observed*significant*activation*clusters*that*bordered*both*the*
supplementary*motor*areas*(discussed*in*the*previous*section)*and*the*dorsal*anterior*
cingulate*cortex.*Congruent*with*these*findings,*consistent*structural*alterations*in*dorsal*
anterior*cingulate*cortex*were*observed*in*our*recent*meta_analysis*of*morphometric*
neuroimaging*of*meditation*(Fox*et*al.,*2014).*Despite*numerous*functional*roles,*the*
dorsal*anterior*cingulate*is*clearly*a*key*player*in*the*brain’s*ability*to*regulate*attention*
and*emotion,*as*well*as*monitor*performance*(Bush*et*al.,*2000,*Posner*et*al.,*2007).*
Activations*here*across*the*two*styles*of*meditation*that*most*explicitly*involve*such*
regulation*and*monitoring*is*therefore*sensible.*For*further*discussion,*see*the*individual*
sections*on*focused*attention*and*open*monitoring.*
5.6.4+Frontopolar+cortex/rostrolateral+prefrontal+cortex.+We*observed*a*fairly*
large*but*sub_threshold*cluster*of*activation*in*the*left*frontopolar*cortex*(BA*10)*for*open*
monitoring*meditation.*For*loving_kindness/compassion*meditation,*we*observed*a*small*
(non_significant)*cluster*in*the*superior*portion*of*left*frontopolar*cortex*(BA*10),*
extending*somewhat*into*the*dorsolateral*prefrontal*cortex*(BA*9).*Although*neither*of*
these*results*exceeded*our*stringent*significance*thresholds,*nonetheless*these*findings*are*
in*line*with*our*recent*meta_analysis*of*morphometric*(i.e.,*structural_anatomical)*
neuroimaging*studies*of*meditation*(Fox*et*al.,*2014),*and*therefore*warrant*a*brief*
discussion.**
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In*our*morphometric*meta_analysis,*we*reported*anatomical*increases*(e.g.,*
increased*cortical*thickness;*Lazar*et*al.,*2005)*in*this*area*across*three*fairly*divergent*
schools*of*practice*(Fox*et*al.,*2014).*This*region*is*known*to*play*a*key*role*in*meta_
awareness*and*metacognitive*capacity*generally*(e.g.,*(Fleming*et*al.,*2010,*McCaig*et*al.,*
2011,*Fleming*and*Dolan,*2012,*Fleming*et*al.,*2012,*Fox*and*Christoff,*2015)),*but*it*also*
appears*to*be*involved*in*the*evaluation*of*self_generated*information*(Christoff*et*al.,*
2003)*and*in*the*processing*of*complex*and*abstract*information*generally*(Christoff*et*al.,*
2001,*Christoff*et*al.,*2009).*Frontopolar*cortex*is*also*a*key*node*of*the*frontoparietal*
control*network*(Vincent*et*al.,*2008)*and*may*play*an*important*role*in*switching*
attention*between*external*and*internal*channels*(Ramnani*and*Owen,*2004,*Burgess*et*al.,*
2007).*The*specific*functions*of*the*frontopolar*cortex*in*various*forms*of*meditation*
remain*an*open*question.**
+
5.7!Other!meditation!practices:!Further!evidence!for!dissociability!at!the!neural!level!
* In*the*Introduction,*we*noted*that*there*are*several*other*major*categories*of*
meditation*wherein*research*remains*too*sparse*for*inclusion*in*a*meta_analysis*(Section*
1.3).*These*categories*include*visualization!(generating*and*sustaining*complex*visual*
imagery),!non8dual!awareness!(eroding*the*boundary*between*subject*and*object),!and!
pratyahara!(dampening*of*sensory*inputs).*Neural*correlates*of*these*practices*have*been*
reported*in*isolated*studies,*and*interestingly,*provide*further*support*for*the*hypothesis*
that*distinct*psychological*(Ψ)*practices*are*likewise*dissociable*at*the*neurobiological*(Φ)*
level*(Cacioppo*and*Tassinary,*1990).**
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For*instance,*a*single*study*has*examined*the*neural*correlates*of*visualization*
meditation*(Lou*et*al.,*1999).*In*this*study,*practitioners*were*guided*through*“visual*
imagination*of*a*summer*landscape*with*forests,*streams,*and*meadows*with*cattle”*(Lou*
et*al.,*1999;*p.*100).*Although*this*particular*imagined*content*is*not*typical*of*visualization*
meditation*practices*(which*tend*to*focus*on*more*explicitly*religious*themes),*nonetheless*
the*results*are*telling.*Visualization*meditation*resulted*in*significant*recruitment*(among*
other*areas)*of*the*fusiform*gyrus*(definitively*linked*to*higher_order*visual*processing;*
(McCarthy*et*al.,*1997,*McCandliss*et*al.,*2003),*the*parahippocampal*gyrus*(linked*to*
visual*‘place’*perception;*(Epstein*et*al.,*1999),*and*nearly*universal*recruitment*of*medial*
and*lateral*occipital*areas*(Lou*et*al.,*1999).*Intriguingly,*primary*visual*cortex*(V1),*which*
is*not*required*for*the*creation*of*visual*imagery*and*visual*dreaming*(Solms,*1997),*was*
essentially*the*only*occipital*area*not*strongly*recruited*(Lou*et*al.,*1999).*These*results,*
although*drawn*from*only*a*single*study,*support*the*idea*that*practitioners*were*
successfully*engaging*in*such*a*visualization*practice.*More*importantly,*for*our*purposes,*
they*are*utterly*distinct*from*any*of*the*broad*patterns*of*neural*activity*reported*in*this*
meta_analysis,*further*supporting*the*contention*that*differing*mental*practices*have*
dissociable*and*identifiable*neural*correlates.*
* A*case*study*involving*a*single*highly_experienced*practitioner*engaging*in*a*
pratyahara*(sense_withdrawal)*practice*is*similarly*informative*(Kakigi*et*al.,*2005).*
Compared*to*painful*stimulation*when*not*engaging*in*meditation,*which*led*to*
recruitment*of*all*the*regions*commonly*implicated*in*pain*processing,*during*meditation*
there*was*a*marked*deactivation*of*these*classic*pain*areas,*including*the*thalamus,*
secondary*somatosensory*cortex,*insula,*and*cingulate*cortex.*Again,*none*of*the*four*
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practice*types*meta_analyzed*here*bears*much*resemblance*to*this*pattern*(and*open*
monitoring*seems*almost*antithetical*to*it*–*in*line*with*the*methods*and*motivations*
underlying*each*practice).**
* Finally,*a*single*study*investigating*non8dual!awareness*in*highly*experienced*
Tibetan*Buddhist*practitioners*reported*evidence*that*this*practice*decreased*the*anti_
correlation*between*activity*in*‘extrinsic’*and*‘intrinsic’*networks*of*the*brain,*which*are*
argued*to*mediate*attention*to*the*external*environment*and*internal*states,*respectively*
(Josipovic*et*al.,*2011).*The*authors*created*numerous*regions_of_interest*throughout*the*
brain*corresponding*to*an*‘extrinsic’*network*for*attention*to*external*stimuli,*and*an*
‘intrinsic’*network*thought*to*be*involved*in*internal*streams*of*thought*(which*roughly*
parallels*the*default*mode*network).*The*extrinsic*and*intrinsic*networks*are*thought*to*
show*anti_correlated*patterns*of*functional*connectivity*during*either*external*tasks*or*
attention*to*internal*streams*of*thought*(e.g.,*during*mind_wandering)*(Fox*et*al.,*2005).*
The*authors*examined*the*extent*to*which*this*anti_correlated*functional*connectivity*
might*be*attenuated*by*non_dual*awareness*meditation,*which*broadly*aims*at*reducing*
the*sense*of*a*division*between*external*and*internal.*During*non_dual*awareness*
meditation,*the*anti_correlation*between*these*two*networks*was*markedly*attenuated*
compared*to*either*focused*attention*meditation*or*passive*fixation.*The*authors*
interpreted*these*results*as*evidence*of*the*effectiveness*of*non_dual*awareness*practice*at*
dissolving*the*boundary*between*internal*and*external*experiences*(i.e.,*subject_object*
duality;*Josipovic*et*al.,*2011).*In*line*with*our*central*hypothesis*and*meta_analytic*results,*
the*authors*also*suggested*that*their*results*indicated*that*non_dual*awareness*practice*is*
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differentiable*at*the*neural*level*from*other*meditations,*such*as*focused*attention*and*
open*monitoring*meditation*(Josipovic*et*al.,*2011).*
* *Although*the*evidence*regarding*these*other*forms*of*meditation*remains*tentative,*
it*seems*clear*that*further*research*is*warranted*into*various*other*techniques*that*have*
not*yet*been*intensively*investigated.*Based*on*our*meta_analytic*findings,*as*well*as*the*
studies*just*reviewed,*we*suspect*that*future*work*will*discover*and*refine*dissociable*
neural*correlates*associated*with*these*various*psychologically*unique*meditation*
practices.*
!
5.8!Are!contemplative!practices!dissociable!by!electrophysiological!and!neurochemical!
measures?!
Virtually*all*of*the*meta_analytic*results*and*discussion*in*this*review*have*relied*on*
brain*signals*indicative*of*cerebral*blood*flow*(PET)*or*blood*oxygenation*(fMRI),*but*there*
are*numerous*other*ways*of*characterizing*brain*function,*most*notably*via*
electrophysiological*activity*(via*electroencephalography,*for*instance;*EEG)*and*at*the*
neurochemical*level*(i.e.,*the*tonal*and*phasic*rates*of*release*of*various*neurotransmitters*
across*different*areas*of*the*brain).*For*more*details*on*how*these*possibilities*have*been*
applied*in*meditation*research,*see*the*Supplementary*Discussion.*
!
5.9!Do!functional!neural!effects!associated!with!meditation!have!practical!significance?!
! Our*effect*size*meta_analyses*found*that*the*four*primary*categories*of*meditation*
examined*were*all*associated*with*approximately*‘medium’*effect*sizes*(mean*Cohen’s*d*=*
0.60*for*activations*and*_0.74*for*deactivations;*for*details*see*Tables*7*and*8).*Although*we*
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find*these*results*both*reasonable*(in*magnitude)*and*encouraging,*we*reiterate*that*the*
‘meaningfulness’*of*effect*sizes*is*ultimately*arbitrary*even*where*their*use*is*highly*
developed*(e.g.,*in*the*behavioral,*social,*and*medical*sciences;*Cohen,*1992).*This*is*all*the*
more*true*in*neuroimaging,*where*their*calculation*and*interpretation*are*poorly*
understood*(see*Supplementary*Methods).*Nonetheless,*some*general*observations*can*be*
made.*
* First,*positive*and*negative*effect*sizes*(representing*activations*and*deactivations*
associated*with*meditation,*respectively)*are*similar*in*magnitude*(Tables*7*and*8;*Fig.*9).*
This*is*in*line*with*our*meta_analytic*neuroimaging*findings*(where*brain*deactivations*
were*nearly*as*common*and*significant*as*activations)*and*supports*the*idea*that*the*
successful*execution*of*a*particular*meditation*may*depend*as*much*on*which*brain*areas*
are*disengaged*as*on*which*are*actively*recruited.*
! Second,*the*approximately*‘medium’*magnitude*of*the*effects*suggests*that*the*
functional*neural*effects*of*meditation*result*in*roughly*a*one_half*standard*deviation*
increase*or*decrease*in*brain*activity,*relative*to*various*other*baseline*conditions,*or*
novices*attempting*to*execute*the*same*practice*as*experts.**
* Third,*differing*meditation*categories*showed*largely*similar*mean*effect*sizes*–*
roughly*one*half*to*two_thirds*of*a*standard*deviation*(Cohen’s*d*~0.50*–*0.67;*see*Table*8).*
The*exception*was*mantra*recitation,*which*appeared*to*result*in*larger*effects*for*both*
activations*and*deactivations*(Cohen’s*d!>*1.0).*This*apparently*large*difference*is*highly*
questionable,*however:*first,*these*‘mean’*(+)*and*(–)*effect*sizes*across*studies*are*in*fact*
simply*mean*effect*sizes*for*a*single*study*each,*as*only*two*studies*contributed*to*the*
effect*size*meta_analysis*for*mantra*recitation*(see*Tables*7*and*8).*Moreover,*the*two*
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studies*that*contributed*(Davanger*et*al.,*2010,*Kalyani*et*al.,*2011)*have*among*the*
smallest*sample*sizes*of*any*studies*we*investigated*here*(see*Table*7).*This*makes*these*
reports*highly*susceptible*to*the*inflationary*biasing*of*effect*sizes*we*discussed*at*length*
in*the*Supplementary*Methods.*We*therefore*conclude*that*it*would*be*highly*premature*to*
argue*that*mantra*meditation*results*in*larger*effects*than*other*forms*of*meditation*
practice.*A*more*plausible*interpretation*is*that*inflationary*bias*was*larger*in*these*
studies,*and*the*true*effect*size*of*mantra*recitation*is*in*fact*comparable*to*the*other*
practices*examined*here.*
* Fourth,*a*funnel*plot*(scatterplot*of*effect*size*vs.*sample*size;*Fig.*6)*showed*a*
conspicuous*dearth*of*null*results*or*small*effect*sizes*(even*after*our*multiple*deflationary*
adjustments*of*originally*reported*effect*sizes),*for*both*‘positive’*effect*sizes*(brain*
activations)*and*‘negative’*effect*sizes*(brain*deactivations).*The*simplest*interpretation*of*
these*results*is*that*fairly*serious*publication*bias*(i.e.*non_publication*of*null*and*‘non_
significant’*findings)*afflicts*this*field.*Even*if*meditation*always*and*truly*results*in*
significant*effects*on*brain*activation*or*deactivation,*given*that*78*functional*
neuroimaging*studies*had*been*published*at*the*time*of*writing,*we*would*expect*at*least*a*
few*null*results*to*have*been*obtained*and*reported*simply*by*chance*alone.*An*alternative*
(albeit*related)*explanation*is*that*smaller*effect*sizes*were*not*observed*precisely*because*
of*the*inflationary*bias*inherent*in*neuroimaging*reporting*of*effect*sizes*(see*section*2.5).*
Although*this*possibility*presents*at*least*as*large*a*problem*as*does*publication*bias,*it*
shifts*the*emphasis*from*the*limitations*of*the*current*scientific*publication*model*(which*
places*undue*emphasis*on*‘positive’*findings)*to*the*limitations*of*neuroimaging*data*
analysis*and*reporting*practices.*In*either*case,*the*lack*of*reported*small*or*null*effects*in*
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this*literature*(even*after*our*severe*deflationary*procedures)*suggests*bias*at*some*stage*
of*study*design,*analysis,*or*reporting.**
That*said,*for*both*negative*and*positive*effect*sizes,*the*expected*funnel*plot*
pattern*was*generally*observed:*that*is,*with*increasing*sample*size,*the*variability*among*
effect*sizes*reported*decreased*drastically;*and*notably,*the*most*extreme*effect*sizes*were*
always*reported*in*studies*with*the*smallest*sample*sizes.*This*suggests,*encouragingly,*
that*despite*potential*publication*bias*or*inflationary*bias*due*to*neuroimaging*analysis*
methods,*nonetheless*studies*with*larger*samples*tend*to*converge*on*similar*and*more*
reasonable*(medium)*effect*sizes.*Although*such*a*conclusion*is*tentative,*the*results*to*
date*(Fig.*6)*suggest*that*a*sample*size*of*approximately*n!=*25*is*sufficient*to*reliably*
produce*effect*sizes*that*accord*with*those*reported*in*studies*with*much*larger*samples*
(up*to*n!*=*46).*
!
5.10!Meditation,!the!brain,!and!clinical!disorders!
* Although*the*central*aim*of*this*meta_analysis*was*to*better*delineate*the*neural*
correlates*of*meditation*in*healthy*practitioners,*the*potential*effects*of*meditation*on*
various*physical*and*psychological*clinical*conditions*is*of*enormous*interest*(Gotink*et*al.,*
2015)*and*therefore*warrants*a*brief*discussion.*To*our*knowledge,*only*five+studies*to*
date*(Table*S1)*have*examined*the*relationship*between*meditation,*brain*activity,*and*
clinical*disorders*of*some*kind.*One*study*investigated*social*anxiety*disorder*(Goldin*and*
Gross,*2010)*and*another*bipolar*disorder*(Ives_Deliperi*et*al.,*2013);*one*examined*
patients*with*breast*cancer*(Monti*et*al.,*2012);*one*involved*chronic*tobacco*smokers*
during*a*period*of*abstinence*from*smoking*(Westbrook*et*al.,*2013);*and*one*recruited*
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patients*with*mild*cognitive*impairment*(Wells*et*al.,*2013).*The*heterogeneity*of*these*
investigations*precludes*any*quantitative*meta_analytic*procedure,*but*nonetheless*these*
preliminary*explorations*are*a*very*important*step*toward*examining*the*potential*of*
meditation*to*ameliorate*such*conditions,*as*well*as*understanding*the*cognitive*and*
neural*mechanisms*by*which*these*improvements*might*take*place.*Considering*the*fairly*
ample*evidence*from*psychological*research*that*meditation*can*have*salutary*effects*on*
affective*characteristics*(Sedlmeier*et*al.,*2012,*Goyal*et*al.,*2014),*further*investigations*
into*its*potential*benefits*for*clinical*conditions,*and*the*brain*mechanisms*related*to*these*
benefits,*are*of*paramount*importance.**
*
5.11!Meta8analytic!limitations!
First,*it*should*be*reiterated*that*the*four*categories*employed*in*our*synthesis**
combined*meditation*practices*which,*although*similar,*are*not*necessarily*identical.*
Moreover,*there*are*several*other*major*categories*of*meditation*that*could*not*be*
quantitatively*examined*here*(e.g.,*non_dual*awareness*and*sensory_withdrawal*practices),*
due*to*the*paucity*of*empirical*data*to*date*(see*Section*1.3).*
Second,*despite*inclusion*of*all*eligible*studies*to*date,*the*present*analysis*relies*on*
relatively*few*research*reports*(n*=*25;*see*Table*1).*We*also*combined*results*from*long_
term*practitioners*with*those*of*novices*undergoing*short_term*training*in*an*effort*to*
include*all*available*data*(see*Table*2).*This*may*be*problematic*because,*as*noted*earlier,*
the*diverse*goals*of*meditation*practices*can*take*considerable*time*to*be*realized.*It*might*
therefore*be*expected*that*the*distinctions*between*brain*activation*patterns*driven*by*
particular*forms*of*meditation*may*be*even*sharper*among*expert*vs.*novice*practitioners,*
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or*that*brain*activity*in*novices*might*otherwise*influence*or*drive*the*effects*observed*
here.*To*mitigate*these*concerns,*however,*we*conducted*a*series*of*four*supplemental*
meta_analyses*where*we*excluded*studies*of*short_term*meditation*training,*and*found*
little*evidence*that*this*was*the*case.*Meta_analytic*results*for*each*meditation*category*
employing*only*long_term*practitioners*were*negligibly*different*from*our*main*meta_
analyses,*except*in*the*case*of*open*monitoring*meditation.*In*the*case*of*open*monitoring*
meditation,*the*general*pattern*of*results*was*also*similar,*but*the*precise*locations*and*
significance*levels*of*various*clusters*were*different*(for*details,*compare*Table*5*with*
Table*S4).+
Third,*study*methods*and*practitioner*samples*were*highly*heterogeneous.*Both*
meditation*and*baseline*conditions*differed*considerably*across*studies*(even*within*a*
single*meditation*category),*as*did*meditation*experience*level*(even*among*expert*
practitioners).*
Fourth,*numerous*and*serious*difficulties*attend*the*calculation*and*interpretation*
of*effect*sizes*in*neuroimaging*data.*Our*results*in*this*sphere,*and*their*bearing*on*the*
question*of*the*‘practical*significance’*of*meditation’s*effects*on*brain*function,*need*to*be*
viewed*in*light*of*the*many*caveats*and*limitations*we*have*discussed*at*length*in*the*
Supplementary*Methods.*
Future*work*may*be*better*able*to*mitigate*many*of*these*limitations*by*directly*
examining*multiple*forms*of*meditation*within*the*same*practitioners*and/or*within!the*
same*study,*and*using*more*homogenous*baseline/control*conditions*(e.g.,*Brewer*et*al.,*
2011).*Such*an*approach*would*control*for*many*of*the*potential*confounds*that*plague*
comparison*across*different*studies,*conducted*by*different*researchers,*investigating*
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different*samples*of*practitioners.*Taken*together,*the*present*results*should*be*
interpreted*with*caution:*a*clearer*understanding*of*the*major*categories*of*meditation,*as*
well*as*their*subtler*subdivisions,*awaits*further*research*undertaken*with*more*directly*
comparable*methods,*baselines,*and*populations.*
!
5.12!Other!methodological!challenges!in!the!neuroimaging!of!meditation!
* Other*major*concerns*have*less*to*do*with*meta_analytics*or*statistical*issues,*but*
rather*relate*specifically*to*the*investigation*of*meditation*practitioners.*Several*important*
themes*are*outlined*here.*
* 5.12.1+Lifestyle+variables.+The*first*concern*is*the*general*and*unknown*effect*of*
lifestyle.*Highly_experienced*meditation*practitioners*are*likely*to*have*more*meager*
(calorie_restricted)*and*more*vegetarian*diets;*are*less*likely*to*have*children*or*long_term*
regular*employment;*and*probably*sleep*less*than*the*average*person*(Britton*et*al.,*2014).*
These*are*just*a*few*major*examples;*an*array*of*other*factors*might*be*relevant.*Different*
meditation*traditions*emphasize*such*factors*to*varying*degrees,*and*it*is*certainly*
conceivable*that*major*differences*in*diet,*stress,*and*sleeping*patterns*could*have*effects*
on*brain*structure*and*function.*Control*subjects*in*the*studies*meta_analyzed*here,*
however,*typically*only*control*for*simple*variables*like*age,*sex,*and*sometimes*
handedness,*and*are*therefore*unable*to*account*for*these*lifestyle*variables.*Until*these*
and*other*factors*are*carefully*controlled*for,*the*potentially*confounding*effects*of*non_
meditation_specific*aspects*of*the*contemplative*lifestyle*cannot*be*ruled*out*or*fully*
understood*(Fox*et*al.,*2014).*
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* 5.12.2+Pre?existing+differences+in+brain+structure+and+function.*A*second*
general*concern*is*the*possibility*of*pre8existing!differences*in*brain*structure*or*function*in*
advanced*meditation*practitioners*(Fox*et*al.,*2014).*Given*the*rigorous*and*peculiar*
demands*of*spending*thousands*of*hours*in*solitary,*minimally_stimulating*environments*
and*unusual*(for*Western*practitioners)*and*often*painful*physical*postures,*it*seems*
highly*likely*that*long_term*contemplative*practice*may*preferentially*attract*persons*with*
a*proclivity*toward*solitude*and*sustained*attention*to*inner*mental*life.*Support*for*this*
hypothesis*comes*from*a*recent*study*that*was*able*to*predict*subsequent*practice*of*two*
different*forms*of*meditation*(mindfulness*and*compassion)*from*baseline*brain*activity*
alone*(Mascaro*et*al.,*2013).*Cross_sectional*studies*(which*form*a*large*part*of*this*meta_
analytic*dataset)*cannot*control*for*such*pre_existing*differences.*On*the*other*hand,*
studies*involving*short_term*training*of*novices*in*pre_post*designs*cannot*examine*the*
potentially*subtle*effects*that*long_term*and*committed*practice*may*have*on*brain*
function.*Future*work*will*have*to*strike*a*balance*somewhere*between*the*limitations*of*
these*two*general*approaches,*and*further*studies*of*pre_existing*(and*potentially*
predictive)*differences*in*brain*structure*and*function*in*meditation*practitioners*would*be*
highly*beneficial*(cf.*Mascaro*et*al.,*2013).**
5.12.3+‘Overshadowing.’*A*third*and*major*concern*is*what*we*call*
‘overshadowing’*–*the*possibility*that*a*practitioner’s*background*experience*with*a*variety*
of*meditation*techniques*might*color*the*neurophysiological*results*obtained*during*the*
brief*‘state’*investigations*of*isolated*meditation*techniques*that*are*typical*of*the*
experiments*examined*here.*This*issue*is*discussed*further*in*the*Supplementary*
Discussion.*
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5.12.4+Enduring+trait+differences+in+brain+and+cognitive+function.*Closely*
related*to*the*overshadowing*effect*are*unknown*trait*differences.*By*‘overshadowing’*we*
mean*the*possibility*that*accumulated*trait*differences*might*overshadow*(or*interact*
with)*brain*activations*and*deactivations*directly*associated*with*a*brief,*induced*state!of*
meditation*in*neuroimaging*investigations.*But*although*these*putative*trait*differences*are*
a*potential*confounding*factor*for*our*purposes*here*(investigating*meditation*state*
effects),*enduring*trait*changes*are*an*explicit*goal*of*most*meditation*traditions,*and*are*a*
worthy*object*of*study*in*their*own*right.*Here,*we*chose*to*exclude*such*studies*from*our*
meta_analysis*(criterion*iv;*see*Methods*section*2.1.2),*mainly*because*of*the*enormous*
methodological*challenges*involved*in*synthesizing*across*so*many*disparate*tasks*and*
contemplative*traditions.*Although*our*meta_analysis*was*also*affected*by*differing*
baseline/comparison*conditions,*and*potentially*also*an*‘overshadowing’*effect,*
nonetheless*the*meditation*states*investigated*were*constant*and*consistent*for*each*
analysis*(focused*attention,*mantra*meditation,*etc.).*The*major*challenge*facing*any*effort*
to*synthesize*trait*effects*associated*with*meditation*practice*is*that*even*this*limited*
homogeneity*(constant*meditation*states,*despite*differing*samples*and*comparison*
conditions)*is*absent.*Not*only*is*there*great*heterogeneity*among*the*tasks*on*which*
meditation_related*traits*are*being*investigated*(e.g.,*emotion*regulation,*perceptual*
discrimination,*etc.),*no*consistent*meditation*state*is*being*induced,*and*the*practitioners*
employed*will*invariably*possess*heterogeneous*contemplative*backgrounds*with*respect*
to*the*proportion,*and*absolute*amount,*of*time*spent*in*various*different*practices.*One*
way*to*begin*to*examine*such*trait*differences,*which*sidesteps*these*problems,*would*be*
Functional*neuroanatomy*of*meditation*
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to*compile*data*on*long_term*practitioners*during*the*‘resting’*state,*for*instance*measuring*
changes*in*functional*connectivity*at*baseline*(in*the*absence*of*any*task*or*stimuli).*
+ 5.12.5+Integration+of+functional+neuroimaging+methods+with+behavioral+
measures.+As*we*discussed*in*our*previous*meta_analysis*of*morphometric*neuroimaging*
studies*of*meditation*(Fox*et*al.,*2014),*alterations*in*brain*structure*and*function*are*of*
little*value*(beyond*basic*scientific*interest)*if*they*are*not*accompanied*by*changes*in*
behavior*or*cognitive_emotional*experience*and*wellbeing*(Fox*et*al.,*in*press).*We*discuss*
this*issue*and*some*of*the*findings*we*reviewed*related*to*brain_behavior*correlations*in*
the*Supplementary*Discussion.*
!
5.13!Summary!and!conclusions!
The*present*meta_analysis*is*the*first*to*report*dissociable*patterns*of*brain*
activation*and*deactivation*underlying*four*major*categories*of*meditation*(focused*
attention,*mantra*recitation,*open*monitoring,*and*loving_kindness/compassion*practices),*
and*provides*suggestive*evidence*for*the*dissociability*of*three*additional*meditation*types*
(visualization,*sense_withdrawal,*and*non_dual*awareness*practices).*Our*synthesis*
provides*preliminary*evidence*for*largely*dissociable*neural*substrates*which,*broadly*
speaking,*are*consistent*with*the*methods,*aims,*and*putative*psychological*results*of*the*
practices*examined.*Collectively,*these*results*suggest*that*while*several*regions*may*be*
equally*involved*in*many*forms*of*contemplative*practice*(Sperduti*et*al.,*2012),*
differences*in*neural*activity*greatly*outnumber*similarities.*Commonality!across!
meditation!categories!is!the!exception!rather!than!the!rule.*Importantly,*deactivations*
almost*always*accompany*activations*(though*they*are*usually*fewer*in*number,*less*
Functional*neuroanatomy*of*meditation*
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substantial*in*terms*of*cluster*size,*and*less*consistent*across*studies*in*terms*of*peak*
likelihood*value).*This*suggests*that*for*the*effective*execution*of*various*meditation*
practices,*disengaging*particular*brain*regions*may*be*nearly*as*important*as*engaging*
others.**
After*careful*corrections*and*adjustments*for*suspected*inflationary*biases,*effect*
size*meta_analysis*suggests*that*meditation*practices*tend*to*yield*approximately*medium_
sized*effects.*These*results*suggest*that*meditation’s*relationship*with*brain*function*may*
be*practically*significant,*but*there*appears*to*be*a*long*way*to*go*in*the*statistical*theory*of*
neuroimaging*before*these*findings*can*be*interpreted*with*confidence.*Moreover,*it*is*
imperative*that*neuroimaging*investigations*of*meditation*begin*to*rigorously*relate*
findings*to*behavioral*and*self_reported*outcomes,*in*order*to*understand*how*(and*to*
what*extent)*these*changes*in*brain*activity*are*related*to*actual*cognitive_affective*change*
and*benefits*in*practitioners.*
Many*have*understandably*viewed*the*nascent*neuroscience*of*meditation*with*
skepticism*(Andresen,*2000,*Horgan,*2004),*but*recent*years*have*seen*an*increasing*
number*of*high_quality,*controlled*studies*that*are*suitable*for*inclusion*in*meta_analyses*
and*that*can*advance*our*cumulative*knowledge*of*the*neural*basis*of*various*meditation*
practices*(Tang*et*al.,*2015).*With*nearly*a*hundred*functional*neuroimaging*studies*of*
meditation*now*reported,*we*can*conclude*with*some*confidence*that*different*practices*
show*relatively*distinct*patterns*of*brain*activity,*and*that*the*magnitude*of*associated*
effects*on*brain*function*may*have*some*practical*significance.*The*only*totally*
incontrovertible*conclusion,*however,*is*that*much*work*remains*to*be*done*to*confirm*and*
build*upon*these*initial*findings.*
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 64*
Acknowledgments*
We*thank*Dr.*Antoine*Lutz*and*Dr.*David*M.*Fresco*for*very*helpful*discussions*of*
the*methods*and*results*of*this*meta_analysis.*We*also*thank*Dr.*Norman*Farb*for*
providing*further*details*from*previously*unpublished*data*that*contributed*to*the*effect*
size*meta_analysis.*This*work*was*supported*in*part*by*Natural*Sciences*and*Engineering*
Research*Council*(NSERC)*Vanier*Canada*Graduate*Scholarships*awarded*to*K.C.R.F.*and*
M.L.;*NSERC*Canada*Graduate*Scholarships*awarded*to*M.L.D.*and*M.E.;*a*University*of*
British*Columbia*Affiliated*Doctoral*Fellowship*awarded*to*J.L.F.;*and*NSERC*and*Canadian*
Institute*of*Health*Research*(CIHR)*grants*awarded*to*K.C.+
+
+ +
Functional*neuroanatomy*of*meditation*
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Westbrook*C,*Creswell*JD,*Tabibnia*G,*Julson*E,*Kober*H,*Tindle*HA*(2013)*Mindful*attention*reduces*neural*and*self_reported*cue_induced*craving*in*smokers.*Social*cognitive*and*affective*neuroscience*8:73_84.*
Yarkoni*T*(2009)*Big*Correlations*in*Little*Studies:*Inflated*fMRI*Correlations*Reflect*Low*Statistical*Power_Commentary*on*Vul*et*al.*(2009).*Perspectives*on*Psychological*Science*4:294_298.*
Yarkoni*T,*Poldrack*RA,*Van*Essen*DC,*Wager*TD*(2010)*Cognitive*neuroscience*2.0:*building*a*cumulative*science*of*human*brain*function.*Trends*Cogn*Sci*14:489_496.*
Yin*HH,*Knowlton*BJ*(2006)*The*role*of*the*basal*ganglia*in*habit*formation.*Nature*Reviews*Neuroscience*7:464_476.*
**
* *
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 75*
+
•+SUPPLEMENTARY+MATERIAL+•+
+
Functional+neuroanatomy+of+meditation:+A+review+and+meta?analysis+of+78+functional+
neuroimaging+investigations+
Kieran*C.*R.*Foxa,*,*Matthew*L.*Dixona,*Savannah*Nijeboera,*Manesh*Girna,*James*L.*Flomanb,*
Michael*Lifshitzc,*Melissa*Ellamild,*Peter*Sedlmeiere,*and*Kalina*Christoffa,e*
*
a*Department*of*Psychology,*University*of*British*Columbia,*2136*West*Mall,*Vancouver,*
B.C.,*V6T*1Z4*Canada*
b*Department*of*Educational*and*Counselling*Psychology,*and*Special*Education,*University*
of*British*Columbia,*2125*Main*Mall,*Vancouver,*B.C.,*V6T*1Z4*
c*Integrated*Program*in*Neuroscience,*McGill*University,*3775*University*St.,*Montreal,*QC,*
H3A*2B4*
d*Neuroanatomy*and*Connectivity*Research*Group,*Max*Planck*Institute*for*Human*
Cognitive*and*Brain*Sciences,*Stephanstrasse*1a,*Leipzig,*Germany*04103.*
e*Institut*für*Psychologie,*Technische*Universität*Chemnitz,*43*Wilhelm_Raabe*Street,*
Chemnitz,*Germany*
e*Brain*Research*Centre,*University*of*British*Columbia,*2211*Wesbrook*Mall,*Vancouver,*
B.C.,*V6T*2B5*Canada*
**To*whom*correspondence*may*be*addressed*(at*address*a*above).*Telephone:*1_778_968_
3334;*Fax:*1_604_822_6923;*E_mail:*[email protected]*
*
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 76*
Supplementary+Methods++!
Further!details!regarding!excluded!studies!
About*two_thirds*(52*of*78)*of*all*studies*did*not*meet*with*one*or*more*of*our*
inclusion*criteria*(Table*S1).*This*fact*should*not*be*considered*an*indication*of*the*poor*
quality*of*these*studies;*only*a*small*minority*was*excluded*because*of*methodological*
problems*(details*in*Table*S1).*Many*studies*were*excluded*simply*because*their*design*or*
analyses*were*not*amenable*to*our*meta_analytic*methods*and*questions,*with*criteria*(i)*
and*(iv)*accounting*for*the*vast*majority*of*exclusions*(Table*S1).*For*instance,*many*
studies*were*excluded*because*they*did*not*have*participants*actually*engage*in*meditation*
practice*in*the*scanner:*these*studies*were*interested*instead*in*the*effect*of*prior*
meditation*training*on*the*neural*correlates*of*various*other*tasks*during*scanning,*
whereas*our!interest!was!in!neural!correlates!of!the!meditation!practices!themselves.**
Mantra*recitation*bears*some*resemblance*to*prayer,*but*differs*in*several*
important*ways.*For*example,*mantra*recitation*is*typically*impersonal*(the*practitioner*
may*not*even*know*the*meaning*of*the*words*being*recited,*which*are*often*in*an*ancient*
and*unfamiliar*language,*such*as*Sanskrit),*whereas*prayer*often*involves*a*personal*
request*with*meaningful*content.*Mantra*recitation*is*also*often*recited*in*a*manner*that*
deliberately*matches*the*recitation*to*the*rhythm*of*inhalation*and*exhalation,*thus*
drawing*attention*toward*interoceptive*information,*whereas*prayer*does*not*typically*
have*this*component.*Therefore,*the*handful*of*studies*that*have*investigated*various*
forms*of*Judeo_Christian*prayer*(e.g.,*(Schjoedt*et*al.,*2009,*Schjoedt*et*al.,*2010)*were*not*
included*in*our*analyses*here.*
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 77*
Several*other*studies*pursued*the*question*of*meditation*training’s*relationship*to*
various*clinical*conditions*and*the*brain.*Despite*the*high*value*of*such*studies,*their*
inclusion*would*present*a*serious*confound*to*our*meta_analytic*results*and*so*these*
studies*too*were*excluded.*On*the*other*hand,*many*studies*(16*of*78)*were*excluded*
because*they*did*not*report*full*tables*of*voxel*coordinates*of*peak*difference*for*the*
contrast*of*interest*(meditation*>*some*other*condition).*Although*some*of*these*studies*
might*have*been*excluded*in*any*case*(for*a*variety*of*other*reasons),*nonetheless*the*
failure*to*report*full*voxel*coordinates*represents*a*serious*and*unfortunate*loss*of*data*for*
meta_analyses.*
*
Instructions!given!in!loving8kindness!and!compassion!meditation!studies!
* * Likely*the*category*in*our*meta_analysis*with*the*greatest*potential*for*variation*
among*studies*is*the*loving_kindness/compassion*group.*Upon*reviewing*the*instructions*
given*to*participants*in*these*six*studies,*however,*we*found*that*overall*the*similarities*
greatly*outweighed*the*differences:*broadly*speaking,*all*studies*had*participants*generate*
positive*emotions*(loving_kindness,*well_wishing,*compassion,*etc.)*toward*others*and/or*
in*a*general,*non_referential*way.*Here*we*reproduce*the*exact*instructions*given*in*each*
study*for*the*reader’s*convenience.*
*
•*Lou*et*al.*(1999):*“…experience*of*joy*and*happiness*in*abstract*form*(i.e.,**not*related*to*
external*events*or*facts).”*
•*Lutz*et*al.*(2008):*“During*the*training*session,*the*subject*will*think*about*someone*he*
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 78*
cares*about,*such*as*his*parents,*sibling*or*beloved,*and*will*let*his*mind*be*invaded*by*a*
feeling*of*altruistic*love*(wishing*well_being)*or*of*compassion*(wishing*freedom*from*
suffering)*toward*these*persons.*After*some*training*the*subject*will*generate*such*feeling*
toward*all*beings*and*without*thinking*specifically*about*someone.*While*in*the*scanner,*
the*subject*will*try*to*generate*this*state*of*loving*kindness*and*compassion.”*
•*Lutz*et*al.*(2009):*Same*as*Lutz*et*al.*(2008).*
•*Brewer*et*al.*(2011):*“Please*think*of*a*time*when*you*genuinely*wished*someone*well*
(pause).*Using*this*feeling*as*a*focus,*silently*wish*all*beings*well,*by*repeating*a*few*short*
phrases*of*your*choosing*over*and*over.*For*example:*May*all*beings*be*happy,*may*all*
beings*be*healthy,*may*all*beings*be*safe*from*harm.”*
•*Lee*et*al.*(2012):*Specific*instructions*not*provided,*but*described*as*“very*similar”*(p.*3)*
to*those*used*in*Lutz*et*al.*(2008)*and*(2009).**
•*Weng*et*al.*(2014):*“Participants*practiced*compassion*for*targets*by*1)*contemplating*
and*envisioning*their*suffering*and*then*2)*wishing*them*freedom*from*that*suffering.*They*
first*practiced*compassion*for*a*Loved*One,*such*as*a*friend*or*family*member.*They*
imagined*a*time*their*loved*one*had*suffered*(e.g.,*illness,*injury,*relationship*problem),*
and*were*instructed*to*pay*attention*to*the*emotions*and*sensations*this*evoked.*They*
practiced*wishing*that*the*suffering*were*relieved*and*repeated*the*phrases,*“May*you*be*
free*from*this*suffering.*May*you*have*joy*and*happiness.”*They*also*envisioned*a*golden*
light*that*extended*from*their*heart*to*the*loved*one,*which*helped*to*ease*his/her*
suffering.*They*were*also*instructed*to*pay*attention*to*bodily*sensations,*particularly*
Functional*neuroanatomy*of*meditation*
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around*the*heart.*They*repeated*this*procedure*for*the*Self,*a*Stranger,*and*a*Difficult*
Person.*The*Stranger*was*someone*encountered*in*daily*life*but*not*well*known*(e.g.,*a*bus*
driver*or*someone*on*the*street),*and*the*Difficult*Person*was*someone*with*whom*there*
was*conflict*(e.g.,*coworker,*significant*other).*Participants*envisioned*hypothetical*
situations*of*suffering*for*the*stranger*and*difficult*person*(if*needed)*such*as*having*an*
illness*or*experiencing*a*failure.*At*the*end*of*the*meditation,*compassion*was*extended*
towards*all*beings.*For*each*new*meditation*session,*participants*could*choose*to*use*
either*the*same*or*different*people*for*each*target*category*(e.g.,*for*the*loved*one*category,*
use*sister*one*day*and*use*father*the*next*day).”*
++Supplementary!neuroimaging!meta8analyses!
In*order*to*address*the*potential*confound*of*collapsing*across*studies*investigating*
long_term*practitioners,*and*those*involving*novices*undergoing*short_term*training,*we*
executed*a*series*of*supplementary*meta_analyses*where*all*studies*involving*short_term*
meditation*training*were*excluded.*This*allowed*us*to*ensure*that*the*potentially*large*
differences*observed*in*novices*learning*meditation*for*the*first*time*were*not*driving*our*
meta_analytic*results.**
Five*of*the*26*included*studies*involved*analyses*of*practitioners*engaging*in*short_
term*meditation*training*only*(Farb*et*al.,*2007,*Dickenson*et*al.,*2013,*Farb*et*al.,*2013b,*
Weng*et*al.,*2013,*Lutz*et*al.,*2014)*and*were*excluded*from*the*supplementary*meta_
analyses*(for*details,*see*Table*2).*Another*study*mixed*long_term*practitioners*and*
novices*in*its*sample*(Kalyani*et*al.,*2011)*and*did*not*report*results*separately*for*long_
term*practitioners,*and*was*therefore*also*excluded.*Another*study*also*employed*both*
Functional*neuroanatomy*of*meditation*
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long_term*and*short_term*practitioners*(Taylor*et*al.,*2011),*but*here*the*novice*
practitioners*served*as*the*comparison*group,*and*therefore*the*results*reported*from*this*
study*remained*valid*for*inclusion*in*the*supplementary*meta_analyses*(the*study*used*a*
between_group*design,*comparing*brain*activity*in*highly_experienced*practitioners*to*a*
less*experienced*group*–*consistent*with*the*other*reports*included*in*the*meta_analyses).*
Ultimately,*six*studies*were*excluded:*one*each*from*the*focused*attention*
(Dickenson*et*al.,*2013),*mantra*meditation*(Kalyani*et*al.,*2011),*and*loving_
kindness/compassion*(Weng*et*al.,*2013)*analyses,*and*three*studies*from*the*open*
monitoring*meta_analysis*(Farb*et*al.,*2007,*Farb*et*al.,*2013b,*Lutz*et*al.,*2014).*To*
anticipate*our*findings,*these*exclusions*generally*had*only*negligible*impact*on*our*meta_
analytic*results,*and*are*therefore*reported*below*in*the*Supplementary*Materials*Results.*
*
+Effect!size!meta8analysis:!Discussion!of!challenges,!methods,!and!equations!used!+
Should*effect*sizes*even*be*calculated*from*neuroimaging*data?*Intensive*debate*is*
ongoing*and*has*not*yet*provided*any*definitive*answers*(Kriegeskorte*et*al.,*2009,*Vul*et*
al.,*2009,*Friston,*2012).*There*appear*to*be*at*least*two*major*recurring*concerns.*The*first*
is*that,*typically,*only*maximum*t_statistics*are*reported*in*neuroimaging*analyses.*These*
statistics*represent*the*most*extreme*peak*for*the*voxel*showing*the*greatest*difference*
among*an*entire*cluster*of*significantly*different*voxels*–*the*rest*of*which*all*have*smaller*
(yet*still*significant)*t_statistics.*Therefore,*the*maximum*(or*‘peak’)*t_statistic*is*
necessarily*an*overestimate*of*the*average*cluster8wide*t_statistic,*which*is*rarely*reported.*
A*straightforward*(albeit*approximate*and*preliminary)*solution*to*this*problem,*which*we*
have*employed*before*(Fox*et*al.,*2014),*is*presented*below*(see*Section*2.5.6).*In*general,*
Functional*neuroanatomy*of*meditation*
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the*approach*is*to*adjust*(i.e.,*deflate)*the*calculated*effect*sizes*based*on*maximum/peak*
statistics,*so*that*they*are*more*conservative*and*more*representative*of*the*expected*
cluster8wide*values.*
A*second*major*concern*is*that*meta_analyses*of*mean*effect*sizes*should*also*
include*all*null*(non_significant)*results.*Null*results*are*rarely*reported*in*neuroimaging*
studies,*however.*Including*all*results*is*important*because*statistically*‘significant’*results*
need*not*be*large*in*magnitude,*particularly*if*sample*size*is*large:*with*a*large*enough*
sample,*even*very*small*differences*between*groups*that*are*trivial*for*practical*purposes*
can*yield*small*p_values*that*exceed*arbitrary_but_conventional*significance*thresholds*
(e.g.,*p*<.05).*Effect*size*meta_analysis*aims*to*comprehensively*include*even*non_
significant*results*for*the*simple*reason*that*an*effect*can*be*large*and*practically*
meaningful,*but*still*fail*to*attain*an*arbitrary*statistical*significance*threshold*due*to*small*
sample*size,*large*variability*in*the*data,*or*a*host*of*other*reasons*(Schmidt,*1992,*Schmidt*
and*Hunter,*1997).*By*impartially*including*all*reported*results*(regardless*of*statistical*
‘significance’)*effect*size*meta_analysis*aims*to*estimate*the*magnitude*of*true*effects*
relatively*independently*of*sample*size*or*arbitrarily*chosen*‘significance’*valuations*
(Schmidt,*1992,*Schmidt*and*Hunter,*1997).**
The*problem*is*that*standard*procedure*in*neuroimaging*studies*is*to*set*an*
arbitrary*significance*threshold*and*report*only*differences*that*exceed*this*value.*Such*a*
practice*produces*an*overwhelming*bias*toward*reporting*‘positive’*over*null*results,*a*
broader*problem*in*essentially*all*fields*of*research*(i.e.,*the*‘file*drawer’*problem;*
(Rosenthal,*1979).*Effect*sizes*based*solely*on*results*that*have*attained*statistical*
significance*(e.g.,*p*<*.05)*will*inevitably*overestimate*the*true*effect*size*(Schmidt,*1992).*
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 82*
This*appears*to*be*all*the*more*true*for*‘underpowered’*studies*with*small*sample*sizes*
(Kraemer*et*al.,*1998).*
Noting*that*the*failure*to*publish*overall*null*findings*plagues*neuroimaging*
research*as*much*as*other*fields,*an*additional*problem*is*whether*to*report*within8study*
null*results.*Typical*neuroimaging*subtraction*contrasts*involve*thousands*(or*tens*of*
thousands)*of*independent*t_tests*across*the*many*voxels*in*the*brain.*Clearly,*reporting*all*
non_significant*results*would*be*impractical,*and*reporting*effect*sizes*for*only*a*small*
number*of*voxels*may*therefore*be*an*“unavoidable”*practice*in*neuroimaging*(Friston,*
2012).*For*this*same*reason,*peak*t_statistics*for*a*given*significant*cluster*are*usually*the*
only*values*reported:*unique*t_statistics*for*each*voxel*in*a*cluster*are*not*usually*reported*
because*this*could*still*amount*to*tens*or*hundreds*of*individual*results*to*be*listed.*
Therefore,*there*seems*to*be*fairly*reasonable*justification*for*the*practice*in*neuroimaging*
of*not*reporting*within8study*null*results*(and*even*significant,*non_peak*results*within*a*
cluster).**
Unfortunately,*this*approach*(a*practical*but*crude*solution*to*a*very*difficult*
problem)*introduces*an*unknown*amount*of*inflationary*bias*in*the*mean*effect*sizes*for*
neuroimaging*studies.*Monte*Carlo*simulations*suggest*that*this*inflationary*bias*becomes*
increasingly*large*at*more*stringent*significance*thresholds*(Lane*and*Dunlap,*1978,*Brand*
et*al.,*2008)*–*and*unfortunately,*highly*conservative*family_wise*error*corrections*are*the*
norm*in*neuroimaging*studies.*Although*various*cross_validation*methods*have*been*
suggested*to*correct*for*this*bias,*these*methods*necessarily*employ*some*of*the*data*for*
validation*and*only*the*remaining*portion*for*estimating*effects*themselves,*and*are*
therefore*bound*to*miss*an*unknown*number*of*effects*(Friston,*2012).*
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 83*
Theoretical*arguments*have*been*made,*however,*that*this*problem*may*be*less*
severe*in*neuroimaging*than*(for*instance)*behavioral*or*clinical*investigations.*Due*to*the*
high*cost*of*neuroimaging,*studies*almost*always*involve*small*sample*sizes*(typically,*N*=*
10_20).*Indeed,*for*the*studies*included*in*the*present*meta_analysis,*samples*were*as*
small*as*just*4*subjects*in*one*repeated_measures*design*(Davanger*et*al.,*2010),*and*the*
mean*sample*size*(including*controls)*across*all*included*studies*was*only*~22*subjects*
(see*Table*2).*The*argument*is*that*smaller*sample*sizes*actually*have*the*benefit*of*
rendering*it*less*likely*that*sample*size*alone*will*drive*‘significant’*effects*(Friston*et*al.,*
1999,*Friston,*2012).*But*this*reasoning*only*goes*so*far:*stringent*significance*thresholds*
for*the*t_tests*upon*which*the*effect*sizes*are*based,*combined*with*low*statistical*power,*
will*nonetheless*produce*inflations*of*the*reported*effects*compared*to*the*true*effect*size,*
due*to*an*unintentional*publication*bias*toward*‘significant’*results*(Schmidt,*1992,*
Yarkoni,*2009,*Yarkoni*et*al.,*2010,*Hupé,*2015).*Additionally,*underpowered*studies*are*
more*likely*to*demonstrate*issues*with*replicability*and*reliability,*presenting*a*challenge*
to*developing*a*robust*evidence*base*in*any*field*of*research*(Cumming,*2012,*2013).*
Calculation+of+effect+sizes+(Cohen’s+d).+Wherever*possible,*we*used*studies’*t8
statistics*of*group*differences*between*brain*activations*of*meditators*vs.*controls,*or*of*
meditation*practitioners*before*and*after*short_term*training,*to*calculate*an*effect*size*
(Cohen’s*d)*for*each*result,*using*Equation*1*(Ray*and*Shadish,*1996):+
! = !! !!!+ !
!!*********(1)**
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 84*
In*this*equation,*t*is*the*value*of*the*reported*peak*t_statistic,*and*ne!and*nc*are*the*sample*
sizes*for*experimental*(meditation)*and*control*groups,*respectively*(see*section*2.5.3*for*
justification*of*the*use*of*this*equation*with*repeated_measures*designs).*
Occasionally,*where*only!F_statistics*were*provided,*effect*sizes*were*calculated*
using*the*online*Practical*Meta_Analysis*Effect*Size*Calculator*(Lipsey*and*Wilson,*2001)*
maintained*by*the*Campbell*Collaboration*(available*at:*
http://www.campbellcollaboration.org/escalc/html/EffectSizeCalculator_Home.php).*
Studies*reporting*only*p8values*or*Z!scores*were*not*included*in*the*effect*size*meta_
analysis*because*of*the*inherent*difficulty*of*calculating*effect*sizes*from*these*statistics*
without*access*to*original*datasets.*
Calculating+effect+sizes+for+repeated?measures+designs.+Many*of*the*studies*
examined*here*involve*some*form*of*repeated_measures*design,*in*that*they*compared*
brain*activation*in*meditation*practitioners*with*these*practitioners’*own*brain*activity*
during*different*tasks*(e.g.,*resting*and*not*meditating)*or*at*various*time_points*(e.g.,*pre_*
and*post_training*in*a*meditation*technique).**
Although*fairly*simple*solutions*for*calculating*effect*sizes*from*t_statistics*derived*
from*repeated_measures*designs*have*been*proposed,*unfortunately*the*information*
required*to*do*so*(namely,*the*correlation*between*the*scores*being*compared*in*the*t_test)*
is*almost*never*reported*(Dunlap*et*al.,*1996).*Using*Monte*Carlo*simulations,*however,*
Dunlap*and*colleagues*(1996)*have*shown*that*use*of*the*standard*effect*size*formula*for*
between_groups*designs*only*very*minimally*affects*the*results,*compared*to*the*corrected*
formula*they*advocate*(their*Equation*3).*We*therefore*used*the*standard*formula*(our*
Equation*1)*for*calculating*effect*sizes*for*repeated_measures*designs.**
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 85*
Positive+vs.+negative+mean+effect+sizes.+After*calculating*effect*sizes*for*156*
unique*results,*both*positive*(+)*and*negative*(–)*mean*effect*sizes*were*calculated*for*each*
of*the*22*experiments*from*18*studies*(Table*S2).*We*did*not*pool*positive*and*negative*
effect*sizes*together*because*the*dependent*variables*(brain*activation*or*deactivation,*
respectively)*have*no*intrinsic*‘valence’*or*value.*Increased*brain*activity*is*not*necessarily*
‘good’*and*decreased*activity*not*necessarily*‘bad’*–*and*vice*versa.*As*a*result,*pooling*
positive*and*negative*effect*sizes*would*have*had*the*result*that*any*study*reporting*both*
activations*and*deactivations*associated*with*meditation*(of*which*there*were*many)*
would*tend*toward*a*mean*effect*size*of*zero.*This*would*suggest*no*practically*significant*
effects,*an*obviously*unwarranted*interpretation.*The*nature*of*most*functional*
neuroimaging*subtraction*(t_statistic_based)*contrasts*requires*that*activations*and*
deactivations*cannot*both*be*reported*in*exactly*the*same*area*of*the*brain*(although*they*
could*be*proximate):*a*study*reporting*both*positive*and*negative*effects*in*meditation*
practitioners*is*not*suggesting*that*the*overall*effect*of*meditation*approaches*zero*for*a*
given*brain*area.*Rather,*the*results*suggest*that*meditation*leads*to*increased*activation*in*
some*parts*of*the*brain,*and*decreased*activation*in*other*areas*that*are*non8overlapping*
(whether*these*are*distal*or*proximal).*
Mean+effect+size+for+different+meditation+categories.*Combining*mean*effect*sizes*
from*each*experiment,*we*further*calculated*mean*effect*sizes*by*meditation*category*
(focused*attention*vs.*mantra*recitation,*and*so*on)*to*investigate*whether*particular*
meditation*practices*have*differential*effects*on*brain*activation*and/or*deactivation.*In*
line*with*the*recommendations*of*Schmidt*et*al.*(2009),*we*calculated*95%*confidence*
Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 86*
intervals*for*mean*effect*sizes,*to*provide*an*estimate*of*their*precision,*following*
equations*8*and*10*in*Sedlmeier*et*al.*(2012).*
Adjusting+for+inflation+of+effect+sizes+due+to+reporting+of+t?statistics+only+from+
peak+voxels.+Standard*procedure*in*neuroimaging*research*is*to*report!peak*t*or*F*
statistics*only,*which*by*definition*are*the*extreme*(maximum)*values*for*a*given*cluster*of*
significant*difference*between*groups.*Mean*t_statistics*for*an*entire*cluster*of*significant*
differences*are*rarely*reported.*The*effect*sizes*we*calculated*therefore*represent*the*peak,*
maximum*effects*for*each*given*cluster*of*results;*the*actual*mean*t8statistics*for*entire*
clusters*are*necessarily*lower.*Therefore,*our*results*necessarily*overestimate*the*effect*
size*of*the*cluster*as*a*whole.+
In*our*recent*meta_analysis*of*morphometric*neuroimaging*studies*of*meditation,*
we*attempted*to*mitigate*this*inflation*problem*by*examining*a*single*study*in*which*both*
effect*sizes*based*on*peak*t_statistics*and*those*based*on*mean*t8statistics*for*the*entire*
cluster*of*significant*difference*were*reported*(Fox*et*al.,*2014).*This*allowed*us*to*
approximate*the*inflationary*bias*caused*by*reporting*of*only*peak*vs.*entire*clusters*of*t_
statistics,*then*adjust*(deflate)*the*mean*effect*sizes*from*other*studies*accordingly.*We*
found*that*average*cluster*t_statistics*were*about*half*(~57%)*of*the*value*of*the*peak*t_
statistics*for*a*given*cluster*(Fox*et*al.,*2014).**
Unfortunately,*reporting*of*both*peak*and!cluster_wide*t_statistics*is*similarly*rare*
in*functional*neuroimaging*studies*of*meditation.*We*are*aware*of*only*one*study*involving*
meditation*practitioners*that*reports*both*types*of*results*(see*Table*1*in*(Grant*et*al.,*
2011).*This*study*did*not*meet*our*inclusion*criteria,*but*this*was*simply*because*actual*
meditation*practice*(which*we*sought*to*meta_analyze)*was*not*engaged*in*during*MRI*
Functional*neuroanatomy*of*meditation*
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scanning*(see*Table*S1).*Instead,*putative*trait*differences*in*highly*experienced*
practitioners*were*examined.*That*said,*given*that*this*study*contrasted*experienced*
meditation*practitioners*with*control*subjects,*it*provides*a*starting*point*for*ascertaining*
the*degree*of*inflationary*bias*caused*by*calculating*effect*sizes*solely*from*peak,*rather*
than*average,*t_statistics*for*a*given*cluster.**
Accordingly,*although*we*consider*this*step*absolutely*critical*to*gaining*a*more*
accurate*assessment*of*neuroimaging_related*effect*sizes,*our*only*option*was*to*base*our*
deflationary*adjustment*on*data*from*a*single*study.*The*average*t_statistics*(absolute*
value,*ignoring*sign)*reported*in*the*study*by*Grant*and*colleagues*(2011)*were*2.952*for*
cluster_wide*results*and*4.236*for*maximum*t_statistics*(see*Table*1*in*(Grant*et*al.,*2011).*
These*results*suggest*that*cluster_wide*t_statistics*are*approximately*70%*of*those*
reported*for*maximum*t_statistics*(2.95/4.24*=*0.697),*roughly*in*line*with*our*prior*
efforts*to*deflate*effect*sizes*in*morphometric*investigations*of*meditation*(i.e.,*57%;*(Fox*
et*al.,*2014).*
Assuming*a*roughly*comparable*difference*between*cluster*and*peak*effect*sizes*for*
other*studies,*we*adjusted*all*our*effect*sizes*accordingly,*deflating*them*to*69.7%*of*their*
original*value.*We*readily*acknowledge*the*real*and*significant*limitations*of*this*approach,*
particularly*the*uncertainty*surrounding*the*amount*of*inflation*for*which*adjustment*is*
required.*Whether*our*adjustment*(deflation)*of*effect*sizes*is*too*conservative,*too*lenient,*
or*approximately*accurate,*remains*to*be*seen,*pending*development*of*better*
understanding*of,*and*better*tools*for*assessing,*practical*significance*in*neuroimaging.*For*
present*purposes,*however,*we*considered*this*approach*preferable*to*reporting*effect*
sizes*that*are*guaranteed!to*be*overestimates.*Despite*its*limitations,*our*approach*
Functional*neuroanatomy*of*meditation*
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provides*a*more*conservative*estimate*of*practical*significance*in*the*functional*
neuroimaging*of*meditation*than*would*be*provided*by*unadjusted*effect*sizes.**
Adjusting+for+inflation+of+effect+sizes+due+to+selective+reporting+of+statistically+
significant+results.+There*have*long*been*serious*and*effective*efforts*to*account*for*Type*I*
statistical*errors*(false*positives)*in*psychological*research*in*general,*as*well*as*in*
neuroimaging*research,*where*massive*numbers*of*multiple*comparisons*(often*thousands*
of*tests)*are*the*norm.*However,*this*sustained*effort*to*control*for*the*rate*of*Type*I*errors*
has*been*paralleled*by*a*serious*failure*to*control*for*the*rate*of*Type*II*errors*(false*
negatives)*–*that*is,*the*chance*of*failing*to*detect*a*true*effect*when*one*is*indeed*present*
(Sedlmeier*and*Gigerenzer,*1989,*Schmidt,*1992).*Among*many*other*concerns,*one*
important*consequence*of*this*situation*is*that*if*results*are*reported*only*when*they*
exceed*a*given*statistical*significance*threshold*(which*is*the*case*in*nearly*all*
psychological*and*neuroscientific*research),*there*will*tend*to*be*a*bias*toward*reporting*of*
effect*sizes*larger*than*the*true*effect*–*and*this*problem*appears*to*be*particularly*true*of*
underpowered*(small*sample)*studies*(Lane*and*Dunlap,*1978,*Kraemer*et*al.,*1998).*This*
is*because*the*initial*criterion*for*publication*and*reporting*(results*exceeding*a*given*
statistical*significance*threshold)*inevitably*leads*to*the*over_reporting*of*larger*group*
differences*that*are*merely*a*result*of*sampling*error*(which*increases*in*smaller*samples)**
–*and*these*apparently*larger*group*differences*will*be*accompanied*by*correspondingly*
large*(and*inflated)*effect*sizes*(Lane*and*Dunlap,*1978,*Schmidt,*1992,*Brand*et*al.,*2008,*
Simonsohn*et*al.,*2014).*
Several*statistical*procedures*have*been*suggested*to*quantitatively*account*for*this*
inflationary*bias,*including*Egger’s*test*(Egger*et*al.,*1997)*and*the*popular*Trim*and*Fill*
Functional*neuroanatomy*of*meditation*
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method*(Duval*and*Tweedie,*2000b,*a).*However,*more*recent*investigations*suggest*that*
unadjusted*averages*of*effect*size,*as*well*as*the*trim_and_fill*method,*produce*markedly*
inflated*estimates*of*the*true*effect*size*(Simonsohn*et*al.,*2014).*And,*unfortunately,*
methods*such*as*Egger’s*test*(Egger*et*al.,*1997)*or*the*p_curve*method*(Simonsohn*et*al.,*
2014)*rely*critically*on*values*for*the*standard*error,*or*precise*p8values*(respectively)*–*
neither*of*which*is*routinely*reported*in*neuroimaging*studies.*Therefore,*we*addressed*
this*problem*by*employing*a*different*method.*We*deflated*effect*sizes*based*on*the*
general*expected*inflationary*bias*across*study*designs,*as*outlined*in*numerous*
theoretical*and*Monte*Carlo*simulation*studies.*
For*instance,*assume*a*true*effect*size*of*d*=*0.50*(typically*found*in*many*
interventions,*and*considered*‘medium’*size*(Cohen,*1992)),*and*a*significance*threshold*of*
!!=*.05*(which*is*the*threshold*employed*in*virtually*all*of*the*studies*we*examined).*Under*
these*conditions,*and*assuming*a*normal*distribution*of*observed*effects,*then*theoretically*
speaking*the*minimum*effect*size*required*to*attain*significance*is*~0.62,*and*the*average*
of*all*effect*sizes*that*will*be*reported*as*significant*is*~0.89*–*nearly*double*the*true*effect*
size*(Schmidt,*1992).*From*this*theoretical*perspective,*the*true*effect*is*approximately*
56%*the*size*of*the*effects*that*have*are*reported*because*they*exceed*a*given*statistical*
significance*threshold*(Schmidt,*1992).*Recent*years*have*seen*more*comprehensive*
efforts*to*quantify*the*bias*due*to*reporting*of*only*significant*results,*and*have*yielded*
similar*conclusions.*One*study*employing*100,000*Monte*Carlo*simulations*found*that*for*a*
true*effect*of*d*=*0.50,*the*mean*observed*effect*size*(from*significant*results*only)*was*
0.66*–*32%*larger*than*the*true*effect*(Brand*et*al.,*2008).*True*effects,*under*these*
conditions,*are*therefore*approximately*76%*the*size*of*those*that*are*reported.*Although*
Functional*neuroanatomy*of*meditation*
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this*is*considerably*less*inflation*than*suggested*by*others*(e.g.,*Schmidt,*1992),*these*
authors*assumed*a*total*sample*size*of*N!=*76,*which*is*considerably*larger*than*samples*
employed*in*most*neuroimaging*experiments,*including*the*studies*investigated*here*
(Table*2).*As*already*noted,*this*inflationary*bias*will*tend*to*increase*with*decreasing*
sample*size*(Lane*and*Dunlap,*1978,*Kraemer*et*al.,*1998),*so*the*estimate*of*Brand*et*al.*
(2008)*is*likely*too*lenient*for*our*purposes.*In*a*more*recent*investigation,*simulations*
showed*that*for*a*true*effect*size*of*d*=*0.50*the*average*reported*effect*size*was*around*
0.82–0.85,*depending*on*sample*size*and*whether*fixed_*vs.*random_effects*models*were*
employed*(Simonsohn*et*al.,*2014).*This*corresponds*to*true*effects*that*are*approximately*
60%*the*size*of*those*reported*based*only*on*statistically*significant*results.*
* Importantly,*the*size*of*the*true*effect*has*marked*effects*on*this*bias:*the*difference*
between*true*and*reported*effect*sizes*is*much*greater*for*smaller*true*effects,*and*
becomes*increasingly*negligible*when*true*effects*are*large*(Simonsohn*et*al.,*2014).*For*
purposes*of*our*effect*size*adjustments,*we*assumed*a*‘medium’*effect*size*of*d*=*0.50*and*
employed*the*0.60*ratio*reported*by*Simonsohn*and*colleagues*(2014),*which*appears*to*
us*to*provide*the*most*reliable*and*up_to_date*estimate*of*this*potential*bias.*We*reiterate,*
however,*that*depending*on*the*actual*size*of*the*true*effect,*this*bias*may*be*greater*or*
smaller*than*the*0.60*coefficient*we*employ*here.*Further,*the*adjustments*employed*here*
were*meant*mainly*to*ensure*that*the*conclusions*we*report*do*not*represent*egregiously*
inflated*effect*sizes.*Our*specific*deflation*coefficients*should*be*considered*merely*
preliminary*and*very*much*open*to*amelioration*by*future*empirical,*theoretical,*and*
statistical*simulation*research.**
Functional*neuroanatomy*of*meditation*
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Further+caveats+regarding+effect+sizes+in+neuroimaging.+Even*given*the*various*
corrections*discussed*above,*another*concern*is*the*interpretation*of*effect*sizes.*The*
interpretive*guidelines*laid*down*by*Cohen*(1992)*were*intended*for*the*behavioral*
sciences,*not*neuroimaging,*and*even*in*the*behavioral*sciences*questions*are*raised*as*to*
their*utility*(Rosenthal,*1996).*Although*it*seems*reasonable*to*use*similar*guidelines*(e.g.,*
the*general*assumption*that*a*one_half*standard*deviation*difference*between*groups*is*
meaningful*and*of*practical*significance),*rigorous*discussion*and*elaboration*of*these*
ideas*has*not*yet*been*undertaken*in*the*field*of*neuroimaging.*Even*in*the*behavioral*and*
social*sciences,*the*interpretation*of*effect*sizes*as*‘small,’*‘medium,’*or*‘large’*is*ultimately*
arbitrary*(Cohen,*1992).*Moreover,*the*true*‘practical’*significance*of*an*effect*depends*on*
many*factors*beyond*magnitude*alone.*Small*effects*can*be*of*large*practical*importance*if*
the*construct*in*question*is*highly*valuable*or*meaningful,*such*as*when*investigating*life_
or_death*outcomes*(Prentice*and*Miller,*1992,*Vacha_Haase*and*Thompson,*2004).*
* Despite*these*limitations,*there*have*already*been*efforts*to*calculate*and*interpret*
effect*sizes*in*meta_analyses*of*neuroimaging*studies*(e.g.,*(Kempton*et*al.,*2008,*Fox*et*al.,*
2014).*The*benefits*of*reporting*effect*size*information*appear*to*greatly*outweigh*the*
drawbacks*inherent*in*their*calculation*and*interpretation*for*neuroimaging*studies.*We*
therefore*calculate*and*report*effect*sizes*here*to*provide*a*general*sense*of*the*magnitude*
of*brain*activation*differences*reported*in*meditation*practitioners,*but*we*emphasize*the*
need*for*caution*in*interpreting*these*results.*
+ +
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MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 92*
Supplementary+Results++Table!S1.***Studies*excluded*from*meta_analyses*(N!=*53).*
Study+ Reason+for+exclusion+(Khushu*et*al.,*2000)* Original*publication*not*locatable*(Ueda*et*al.,*2000)* Original*publication*not*locatable*(Bærentsen*et*al.,*2001)* No*voxel*coordinates*reported*(Kjaer*et*al.,*2002)* Only*regions_of_interest*examined;*dopamine*release*measured*(Ritskes*et*al.,*2004)* No*voxel*coordinates*reported*(Kakigi*et*al.,*2005)* Single*subject*case*study*(Khushu*et*al.,*2005)* Original*publication*not*locatable+(Liou*et*al.,*2006)* No*voxel*coordinates*reported*(Orme_Johnson*et*al.,*2006)* No*voxel*coordinates*reported*(Creswell*et*al.,*2007)* No*meditators*involved;*only*'dispositional'*mindfulness*scored*(Holzel*et*al.,*2007)* Only*regions_of_interest*examined*(Kozasa*et*al.,*2008)* No*voxel*coordinates*reported*(Pagnoni*et*al.,*2008)* Only*regions_of_interest*investigated*(for*contrast*of*interest)*(Beauregard*et*al.,*2009)* Meditation*experience*ambiguous*(Baerentsen*et*al.,*2010)* Multiple*meditation*types*pooled*in*analysis*(Engström*and*Söderfeldt,*2010)* Single*subject*case*study;*no*voxel*coordinates*reported*(Farb*et*al.,*2010)* No*actual*meditation*engaged*in*during*scanning*(Goldin*and*Gross,*2010)* Clinical*population*(social*anxiety*disorder)*(Short*et*al.,*2010)* No*voxel*coordinates*reported*(Grant*et*al.,*2011)* No*actual*meditation*engaged*in*during*scanning*(Jang*et*al.,*2011)* No*actual*meditation*engaged*in*during*scanning*(Josipovic*et*al.,*2011)* Only*regions_of_interest*examined*(Kilpatrick*et*al.,*2011)* No*actual*meditation*engaged*in*during*scanning*(Kirk*et*al.,*2011)* No*actual*meditation*engaged*in*during*scanning*(Xue*et*al.,*2011)* No*voxel*coordinates*reported*(Zeidan*et*al.,*2011)* No*voxel*coordinates*reported*(Allen*et*al.,*2012)* No*actual*meditation*engaged*in*during*scanning*(Desbordes*et*al.,*2012)* No*actual*meditation*engaged*in*during*scanning*(Froeliger*et*al.,*2012a)* No*voxel*coordinates*reported*(Froeliger*et*al.,*2012b)* No*actual*meditation*engaged*in*during*scanning*(Hasenkamp*and*Barsalou,*2012)* No*actual*meditation*engaged*in*during*scanning*(Klimecki*et*al.,*2012)* No*actual*meditation*engaged*in*during*scanning*(Kozasa*et*al.,*2012)* No*actual*meditation*engaged*in*during*scanning*(Monti*et*al.,*2012)* Clinical*population*(breast*cancer)*(Pagnoni,*2012)* Only*differences*in*skewness*of*fMRI*signal*reported*(Garrison*et*al.,*2013a)* No*voxel*coordinates*reported*(Garrison*et*al.,*2013b)* No*voxel*coordinates*reported*(Goldin*et*al.,*2013)* Clinical*population*(social*anxiety*disorder)*(Hagerty*et*al.,*2013)* Single*subject*case*study*(Ives_Deliperi*et*al.,*2013)* Clinical*population*(bipolar*disorder)*(Klimecki*et*al.,*2013)* No*actual*meditation*engaged*in*during*scanning*(Mascaro*et*al.,*2013a)* No*actual*meditation*engaged*in*during*scanning*(Mascaro*et*al.,*2013b)* No*actual*meditation*engaged*in*during*scanning*(Paul*et*al.,*2013)* No*meditators*involved;*only*trait*mindfulness*scored*(Prakash*et*al.,*2013)* No*meditators*involved;*only*trait*mindfulness*scored*(Taylor*et*al.,*2013)* No*actual*meditation*engaged*in*during*scanning*(Wells*et*al.,*2013)* Clinical*population*(mild*cognitive*impairment)*(Westbrook*et*al.,*2013)* Quasi_clinical*population*(abstinent/craving*smokers)*(Zeidan*et*al.,*2013)* No*voxel*coordinates*reported*(Garrison*et*al.,*2014)* No*voxel*coordinates*reported*(for*contrast*of*interest)*(Kirk*et*al.,*2014)* No*actual*meditation*engaged*in*during*scanning;*meditation*style*not*reported*(Josipovic,*2014)* No*voxel*coordinates*reported;*preliminary*data*only*(Ding*et*al.,*2015)* No*actual*meditation*engaged*in*during*scanning*
Functional*neuroanatomy*of*meditation*
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Table!S2.!!*Supplementary*meta_analysis*of*focused*attention*meditation*(excluding*studies*
involving*short_term*meditation*training).*
Region+ Cluster+Size+(mm3)+
Side+ Peak+Coordinates++(x,+y,+z)+
Peak+ALE+value+
Activations+
Premotor*cortex* 800* L* _36,*6,*56*(BA*6)* 0.0144*
Dorsal*anterior*cingulate*cortex* 304* M* 2,*12,*32*(BA*24)* 0.0112*
Deactivations+
Posterior*cingulate*cortex* 152* M* _6,*_60,*18*(BA*30)* 0.0071*
Inferior*parietal*lobule* 144* L* _48,*_72,*30*(BA*39)* 0.0071*
!**
*! !
Functional*neuroanatomy*of*meditation*
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Table!S3.!!*Supplementary*meta_analysis*of*mantra*recitation*meditation*(excluding*studies*
involving*short_term*meditation*training).*
Region+ Cluster+Size+(mm3)+
Side+ Peak+Coordinates++(x,+y,+z)+
Peak+ALE+value+
Activations+
Premotor*cortex* 896* L* _30,4,*60*(BA*6)* 0.0137*
Supplementary*motor*area*584* M* 0,*12,*54*(BA*6)* 0.0111*
112* M* _4,*2,*68*(BA*6)* 0.0080*
Putamen/Lateral*globus*pallidus* 368* R* 28,*_16,*_6* 0.0111*
Fusiform*gyrus* 248* R* 40,*_26,*_30*(BA*20/36)* 0.0093*
Cuneus* 160* R* 24,*_86,*26*(BA*18)* 0.0082*
Precuneus* 152* L* _14,*_56,*54*(BA*7)* 0.0082*
*!**! !
Functional*neuroanatomy*of*meditation*
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Table!S4.!!*Supplementary*meta_analysis*of*open*monitoring*meditation*(excluding*studies*
involving*short_term*meditation*training).*
Region+ Cluster+Size+(mm3)+
Side+ Peak+Coordinates++(x,+y,+z)+
Peak+ALE+value+
Activations+
Temporopolar*cortex* 160* L* _45,*19,*_30*(BA*38)* 0.0075*
Insular*cortex*(mid/posterior)* 160* R* 45,*_20,*13*(BA*13)* 0.0075*
Pre_supplementary*motor*area* 152* M* 0,*8,*64*(BA*6)* 0.0080*
Deactivations*
Thalamus*(pulvinar)*128* R* 17,*_24,*10* 0.0084*
112* R* 17,*_30,*4* 0.0083*
Parahippocampus* 104* R* 24,*_32,*_9*(BA*27/35)* 0.0086*
* !
Functional*neuroanatomy*of*meditation*
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Table!S5.***Supplementary*meta_analysis*of*loving_kindness/compassion*meditation*
(excluding*studies*involving*short_term*meditation*training).*
Region+ Cluster+Size+(mm3)+
Side+ Peak+Coordinates++(x,+y,+z)+
Peak+ALE+value+
Activations+
Anterior*insula* 632* R* 38,*22,*14*(BA*13)* 0.0135*
Parieto_occipital*sulcus* 376* R* 24,*_60,*18*(BA*23/31)* 0.0115*
Somatosensory*cortices/Inferior*parietal*lobule* 376* R* 54,*_26,*30*(BA*2/40)* 0.0101*
Postcentral*gyrus/*Somatosensory*cortex* 104* L* _60,*_8,*20* 0.0083*
!**+ +
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Supplementary+Discussion+
*
Functional!neuroanatomy!of!focused!attention!meditation.!
Activations.+If*focused*attention*meditation*so*often*involves*strong*focus*on*a*
visual*stimulus*or*the*interoceptive*signals*associated*with*respiration,*why*were*
activations*not*observed*in*visual*or*interoceptive*cortices?*Small*(non_significant)*clusters*
of*activation*were*in*fact*observed*in*the*lateral*geniculate*nucleus*of*the*thalamus,*which*
processes*and*relays*visual*information*(Casagrande*and*Norton,*1991),*as*well*as*in*the*
left*insula,*a*major*center*for*interoceptive*information*processing*(Critchley*et*al.,*2004,*
Craig,*2009,*Farb*et*al.,*2013a).*These*clusters*can*be*seen*in*the*detailed*supplementary*
data*on*focused*attention*meditation*(Fig.*S1).*One*reason*these*clusters*may*not*have*
been*larger*is*due*to*the*heterogeneity*of*the*studies*included*in*the*meta_analysis.*That*is,*
whereas*effortful*cognitive*control*along*with*attention*to*and*suppression*of*internal*
thought*streams*were*likely*common*across*these*studies,*activations*related*to*the*
particular*object*of*attentional*focus*may*have*been*too*disparate*to*attain*meta_analytic*
significance.*
Deactivations.+The*specific*role*of*the*posterior*cingulate*cortex*in*meditation*has*
been*explored*more*extensively*in*a*recent*study*examining*practitioners*from*diverse*
contemplative*backgrounds*(a*mix*of*Zen,*Catholic,*Theravada*Buddhist,*and*Tibetan*
Buddhist*practitioners).*Participants*engaged*in*a*focused*attention*meditation*where*the*
object*of*focus*was*the*breath*(Garrison*et*al.,*2013a).*Following*an*fMRI*scan,*participants*
described*the*subjective*qualities*of*their*meditation*that*corresponded*to*a*feedback*
graph*depicting*the*time*course*of*activity*from*their*posterior*cingulate*cortex*throughout*
Functional*neuroanatomy*of*meditation*
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the*scan.*It*was*found*that*deactivation!of*the*posterior*cingulate*cortex*was*associated*
with*qualities*of*meditation*described*by*terms*such*as*‘concentration’*or*‘undistracted*
awareness’*(Garrison*et*al.,*2013a).*The*converse*was*also*true:*activation*of*posterior*
cingulate*cortex*was*associated*with*subjective*distraction*and*poor*quality*of*focus*during*
meditation*(described,*e.g.,*as*‘distraction’*or*‘distracted*awareness’)*(Garrison*et*al.,*
2013a).*Another*study*from*the*same*group*reported*similar*findings*(Garrison*et*al.,*
2013b),*which*are*in*line*with*our*meta_analytic*results.*
*
Functional!neuroanatomy!of!mantra!recitation!meditation!
Activations.+Activations*were*also*observed*in*the*fusiform*gyrus*(BA*20),*cuneus,*
and*the*anterior*precuneus*(BA*7),*in*a*location*almost*identical*to*a*cluster*observed*in*
our*recent*meta_analysis*of*brain*structure*differences*in*experienced*meditation*
practitioners*(see*Fig.*2g*in*(Fox*et*al.,*2014).*Both*clusters*were*observed*in*a*putative*
‘anterior’*subregion*of*the*precuneus*with*strong*connections*to*somatomotor*cortices*and*
insula,*which*may*play*a*role*in*coordination*of*motor*behavior*as*well*as*the*generation*of*
motor*imagery*(Hanakawa*et*al.,*2003,*Malouin*et*al.,*2003,*Cavanna*and*Trimble,*2006).*A*
speculative*role*for*anterior*precuneus,*then,*may*be*in*assisting*in*the*overt*or*mental*
repetition*of*the*mantra.*Alternatively,*or*in*addition*to*this*interpretation,*the*activation*of*
the*precuneus*as*well*as*the*fusiform*gyrus*and*cuneus*may*indicate*that*practitioners*
evoke*visual*imagery*along*with*mantra*repetition.*Detailed*subjective*reports*will*be*
necessary*to*more*fully*elucidate*the*processes*activated*during*mantra*recitation,*and*by*
extension*the*meaning*of*these*activations.**
+
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Functional!neuroanatomy!of!open!monitoring!meditation.!
Deactivations.+Many*other*smaller*(non_significant)*clusters*of*deactivation*were*
observed.*One*deactivation*that*accords*well*with*the*goal*of*open*monitoring*meditation*
was*located*in*the+rostromedial*prefrontal*cortex*(medial*BA*10)*–*as*opposed*to*the*
cluster*of*activation*observed*in*lateral*BA*10*(see*Fig.*S3).*A*central*goal*of*open*
monitoring*is*to*dampen*the*tendency*to*become*ensnared*in*one’s*thoughts*and*emotions,*
and*to*not*turn*isolated*mental*content*into*extended*streams*of*self_referential*thinking*
(Goenka,*2000).*As*medial*prefrontal*cortex*has*been*so*consistently*implicated*in*these*
kinds*of*mind_wandering*(Fox*et*al.,*2015)*and*self_referential*thought*(Northoff*et*al.,*
2006),*a*simple*explanation*is*that*its*deactivation*represents*the*successful*execution*of*
open*monitoring*(Farb*et*al.,*2007).**
Consistent*with*this*explanation*are*other*small*(non_significant)*clusters*of*
deactivation*observed*bilaterally*in*the*subgenual*anterior*cingulate*cortex*(or*
ventromedial*prefrontal*cortex;*BA*25)*and*bilaterally*in*the*medial*temporal*lobe*(BAs*27,*
28,*and*36,*including*the*hippocampus)*–*both*of*which*are*similarly*implicated*in*the*
default*mode*network*(Buckner*et*al.,*2008)*as*well*as*mind_wandering*and*related*
spontaneous*thought*processes*(Fox*et*al.,*2015).*Also*consistent*with*such*an*
interpretation*were*small*clusters*of*deactivation*bilaterally*in*the*posterior*cingulate*
cortex*(BAs*23,*29,*30,*and*31),*likewise*involved*in*the*default*mode*network*(Buckner*et*
al.,*2008)*and*mind_wandering*(Fox*et*al.,*2015).*All*of*these*regions*of*course*play*many*
other*roles,*but*nonetheless*the*widespread*deactivation*of*so*many*important*default*
network*hubs,*which*are*consistently*activated*during*mind_wandering*(Fox*et*al.,*2015),*
is*suggestive*of*a*lowered*frequency*of,*and/or*a*decreased*involvement*in,*one’s*thoughts.*
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Various*other*small*clusters*of*deactivation*were*also*observed,*for*instance*in*the*
left*lingual*gyrus*of*the*occipital*lobe*(BA*18/19).*We*have*previously*found*the*lingual*
gyrus*to*be*consistently*recruited*during*both*nighttime*dreaming*(Fox*et*al.,*2013)*and*
waking*daydreaming/mind_wandering*(Domhoff*and*Fox,*2015,*Fox*et*al.,*2015),*and*
lesions*to*this*region*eliminate*all*visual*imagery*in*dreams,*while*sparing*the*dream*
experience*itself*(Solms,*1997).*In*line*with*our*suggestions*regarding*deactivation*of*
default*network*areas,*it*may*be*that*open*monitoring*dampens*the*visual*imagery*so*
characteristic*of*mind_wandering*during*normal*waking*(Fox*et*al.,*2013),*as*well*as*during*
formal*meditation*practice*(Austin,*1999).*
*
Functional!neuroanatomy!of!loving8kindness!and!compassion!meditation!
Activations.*A*notable*but*non_significant*cluster*of*activation*was*observed*in*the*
anterior*cingulate*cortex*(BA*24),*very*near*to*a*meta_analytic*cluster*reported*in*a*meta_
analysis*of*empathy*for*the*pain*of*others*(see*Fig.*2*in*(Lamm*et*al.,*2011)).*This*cluster*
was*located*in*a*more*anterior*location*than*those*identified*in*the*other*types*of*
meditation.*As*with*somatosensory*cortices*and*inferior*parietal*lobule*(discussed*above),*
this*area*is*also*consistently*implicated*in*pain*perception,*particularly*its*affective*(as*
opposed*to*sensory)*component*(Grant*et*al.,*2011).*Similarly,*then,*this*area*might*play*
overlapping*roles*in*imagining*the*pain*and*distress*of*others,*as*well*as*empathizing*with*
their*pain*and*distress.*
Deactivations.+No*significant*deactivations*were*observed,*and*very*few*non_
significant*deactivations*were*apparent*(Fig.*S4).*As*noted*above,*however,*our*meta_
analysis*of*loving_kindness*and*compassion*meditations*was*based*on*the*fewest*
Functional*neuroanatomy*of*meditation*
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experiments*and*smallest*number*of*foci*(Table*1),*and*therefore*had*lower*statistical*
power*than*the*other*meta_analyses.*The*relative*lack*of*activations*and*deactivations*in*
this*form*of*meditation*practice*more*likely*reflects*this*meta_analytic*limitation*rather*
than*any*inherent*feature*of*the*practice*itself.*More*research*is*therefore*needed*to*better*
illuminate*the*activations*and*deactivations*associated*with*this*group*of*meditation*
practices.!
!
Convergent!findings!across!meditation!categories*
+ Insula.*The*relatively*stronger*(and*statistically*significant)*recruitment*of*the*
insula*in*open*monitoring*and*loving_kindness/compassion*meditation*is*further*
consistent*with*the*character*of*these*practices.*These*practices*tend*to*focus*heavily*on*
awareness*of*the*body*and*emotions*(open*monitoring),*or*empathy,*mentalizing,*and*
perspective_taking*(loving_kindness/compassion).*For*open*monitoring,*there*is*growing*
evidence*that*practitioners*who*heavily*emphasize*this*practice*show*heightened*
interoceptive*and*exteroceptive*bodily*awareness.*Support*for*this*enhanced*awareness*
comes*from*multiple*methodologies,*including*behavioral*(Fox*et*al.,*2012),*physiological*
(Sze*et*al.,*2010),*magnetoencephalographic*(Kerr*et*al.,*2013),*and*fMRI*(Farb*et*al.,*2007,*
Farb*et*al.,*2013b)*research.*
Beyond*body*awareness*and*interoception,*the*insula*is*also*reliably*implicated*in*
empathy*and*the*perspective_taking*or*mentalizing*that*empathy*often*entails*(Lamm*et*al.,*
2011,*Bernhardt*and*Singer,*2012).*The*significant*insula*cluster*observed*in*loving_
kindness*and*compassion*meditation,*then,*suggests*an*alternate*function*that*the*insula*
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might*serve*in*meditations*involving*empathy,*imaging*the*pain*and*suffering*of*others,*
and*the*cultivation*of*compassionate*and*prosocial*responses*to*this*distress.*
Although*further*speculation*about*the*insula’s*particular*function(s)*across*various*
types*of*meditation*seems*unwarranted*at*this*early*stage,*both*morphometric*meta_
analysis*(Fox*et*al.,*2014)*and*the*present*functional*meta_analysis*agree*that*it*plays*an*
important*role*across*several*forms*of*meditation*practice.*
*
!
!
Are!contemplative!practices!dissociable!by!electrophysiological!and!neurochemical!measures?*
One*group*has*attempted*to*integrate*EEG*findings*from*across*many*meditation*
styles,*and*similar*to*our*claims*here,*argued*that*various*forms*of*meditation*are*
preferentially*associated*with*differing*electrical*rhythms*in*the*brain*(e.g.,*theta,*beta,*
gamma,*and*so*on)*(Travis*and*Shear,*2010).*Others,*however,*have*suggested*major*
commonalities*in*EEG*signatures*across*many*different*meditation*styles*(Lehmann*et*al.,*
2012).*Whether*these*findings*can*be*integrated*with*the*current*arguments*from*blood_
flow*or*blood_oxygenation_dependent*measures*remains*an*important*question*for*future*
research*and*meta_analytic*synthesis.*
The*ability*of*positron*emission*tomography*(PET)*scanners*to*investigate*the*
activity*of*particular*neurotransmitters*and*neuromodulators*has*hardly*been*exploited*in*
meditation*research.*A*single*study*examining*yoga!nidra*using*PET*has*reported*increased*
dopamine*release*during*this*form*of*practice*(Kjaer*et*al.,*2002),*but*to*our*knowledge*no*
research*has*followed*up*on*these*initial*findings.*Various*meditation*practices*consistently*
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lead*to*subjective*changes*in*relaxation,*levels*of*alertness*and*vigilance,*engagement*in*
visionary*and*dream_like*experiences,*and*so*on*–*all*of*which*are*known*to*be*heavily*
driven*by*changes*in*levels*of*various*neurotransmitters*and*neuromodulators*(Perry*et*al.,*
2002).*As*such,*there*is*good*reason*to*believe*that*both*the*tonic*and*phasic*activity*
profiles*of*various*neurotransmitters*might*vary*markedly*across*different*practice*
categories.*Given*the*paucity*of*research*to*date,*however,*these*remain*open*questions*to*
be*addressed*by*future*research.*
*
!
!
Other!methodological!challenges!in!the!neuroimaging!of!meditation*
‘Overshadowing.’+As*discussed*in*the*Introduction,*we*assumed*a*one8to8many*
logical*relationship*(Coombs*et*al.,*1970,*Cacioppo*and*Tassinary,*1990)*between*a*given*
psychological*meditation*state*(Ψ)*and*its*diverse*neural*correlates*(Φ):*one*form*of*
meditation*practice*(e.g.,*focused*attention)*would*be*accompanied*by*numerous*(many)*
but*hypothetically*consistent*neurophysiological*responses.*If*a*given*meditation*state*is*
strongly*colored*by*a*practitioner’s*contemplative*background*(experience*with*a*variety*
of*other*meditation*techniques),*however,*then*this*assumption*no*longer*holds,*and*the*
relationship*assumes*a*many8to8many*form,*making*it*much*more*difficult*to*draw*any*
reliable*conclusions.**
Unfortunately,*it*seems*likely*that*this*is*the*situation*in*at*least*some*of*our*sample:*
as*already*noted*(Table*1),*some*investigators*had*the*same*sample*of*practitioners*engage*
in*multiple*meditation*techniques*in*the*same*study.*This*was*possible*because*many*
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practitioners*are*familiar*with,*and*have*long*practiced,*multiple*techniques.*Clearly,*the*
particular*ratio*of*experience*with*different*techniques*will*vary*among*individual*
practitioners,*and/or*practitioners*from*differing*meditation*traditions,*adding*an*
additional*(and*unknown)*degree*of*heterogeneity.*For*instance,*some*traditions*focus*
heavily*on*mantra*meditation*practice*(e.g.,*Transcendental*Meditation),*although*their*
practitioners*may*of*course*also*be*familiar*with*other*practices.*Other*traditions*(e.g.,*
Theravada*Buddhist)*tend*to*focus*more*on*open*monitoring*techniques.*The*central*point*
is*that*these*various*emphases*are*largely*unknown.*When*a*practitioner*participates*in*a*
neuroimaging*study*and*is*asked*to*engage*in*a*particular*practice*for*a*short*period*of*
time*(usually*only*a*few*minutes)*in*a*brain*scanner,*their*traditional*contemplative*
background*and*the*emphasis*they*have*placed*on*various*techniques*over*their*years*of*
practice*may*greatly*influence*their*manner*of*meditation*practice*(and*the*concomitant*
neural*correlates*investigators*record*and*report)*–*but*these*diverse*contemplative*
backgrounds*are*rarely*investigated*or*reported*(typically,*total*hours*or*years*of*
meditation*experience*is*the*only*data*collected).*Although*total*hours*of*experience*is*a*
useful*preliminary*measure,*the*incredible*diversity*of*meditation*techniques*clearly*calls*
for*more*detailed*measures*in*future*work.*
Integration+of+functional+neuroimaging+methods+with+behavioral+measures.+In*
our*previous*meta_analysis,*we*noted*that*numerous*studies*attempted*to*directly*link*
brain*structure*changes*to*behavior*change*or*scores*on*various*self_report*measures,*but*
almost*all*of*the*reported*correlations*were*statistically*marginal*and/or*statistically*non_
independent.*Among*the*present*pool*of*studies,*a*few*have*reported*modest*correlations*
between*meditation*expertise*(i.e.,*total*hours*of*practice)*and*differences*in*brain*
Functional*neuroanatomy*of*meditation*
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activation*during*a*given*meditation*state*(e.g.,*(Lazar*et*al.,*2000,*Brefczynski_Lewis*et*al.,*
2007,*Farb*et*al.,*2013b).*Few,*however,*have*related*brain*activation*differences*during!
meditation*states*to*actual*behavior,*or*even*to*self_report*questionnaires*(e.g.,*for*anxiety*
or*mindfulness):*of*the*26*studies*included*here,*only*four*correlated*their*findings*with*
behavioral*outcomes*other*than*meditation*experience*or*expertise.*We*acknowledge*that*
this*is*an*extremely*challenging*problem:*of*innumerable*potential*outcomes,*what*
behavior*should*be*measured?*What*self_report*questionnaires*should*be*considered*the*
most*relevant*and*reliable?*Can*reliable*correlations*be*obtained*with*the*small*samples*
typical*of*neuroimaging*studies?*Is*activation*during!the*meditation*state*even*the*relevant*
independent*variable*–*i.e.,*should*these*correlations*instead*be*sought*using*baseline,*trait!
levels*of*brain*activity,*outside*of*the*meditation*practice*itself*(see*5.12.4)?**
* As*noted*above,*however,*several*of*the*more*recent*fMRI*studies*have*attempted*to*
integrate*neuroimaging*findings*with*behavioral*measures*other*than*just*meditation*
experience*itself*(Lee*et*al.,*2012,*Lutz*et*al.,*2013,*Weng*et*al.,*2013,*Lutz*et*al.,*2014).*For*
instance,*Weng*et*al.*(2013),*in*a*study*of*compassion*meditation,*reported*that*those*with*
greater*brain*activation*in*dorsolateral*prefrontal*cortex*and*inferior*parietal*cortex*during*
the*meditation*were*more*likely*to*redistribute*funds*more*equitably*in*an*economic*game*
they*subsequently*participated*in.*This*study*therefore*demonstrated*not*only*that*
compassion*meditation*training*leads*to*differential*neural*responses*to*the*suffering*of*
others*and*to*increased*altruistic*behaviors*in*an*economic*game*–*it*also*linked*these*
findings*together,*providing*evidence*that*specific*contemplative*training*leads*to*changes*
in*brain*activity*changes*which*in*turn*are*related*to*meaningful*behavioral*outcomes.*This*
multifaceted*approach*remains*rare,*but*provides*a*model*for*future*research,*which*can*
Functional*neuroanatomy*of*meditation*
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(and*should)*integrate*neuroimaging*measures*with*behavioral*and*first_person*report*
outcomes.+
Further,*several*of*the*studies*excluded*from*our*meta_analysis*that*examined*‘trait’*
differences*in*meditators*(Table*S1)*or*that*employed*meditation*in*clinical*populations*
have*also*assessed*various*outcome*measures*as*correlated*with*their*neuroimaging*
results*(Table*S1).*However,*we*hasten*to*reiterate*the*caveats*we*have*raised*before*
regarding*such*correlational*analyses*(cf.*Fox*et*al.,*2014):*for*instance,*correlation*
coefficients*are*highly*unstable*with*small*sample*sizes*(Glass*and*Hopkins,*1970),*and*
efforts*to*correlate*neuroimaging*findings*with*behavioral*measures*are*highly*susceptible*
to*‘circular’*or*non_independent*analysis,*which*can*grossly*inflate*correlation*coefficients*
(Vul*et*al.,*2009,*Hupé,*2015).*Nonetheless,*in*order*for*the*neuroimaging*of*meditation*to*
move*beyond*cartography*of*brain*activation*differences*and*toward*an*integrative*science*
linking*psychological*training*with*brain*and*behavior,*these*methodological*and*statistical*
difficulties*will*need*to*be*overcome.*
**+ +
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Functional*neuroanatomy*of*meditation*
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Figure!S1.***Activations*and*deactivations*associated*with*focused*attention*mediation.**
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Functional*neuroanatomy*of*meditation*
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Figure!S2.***Activations*and*deactivations*associated*with*mantra*recitation*mediation.**
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Functional*neuroanatomy*of*meditation*
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Figure!S3.***Activations*and*deactivations*associated*with*open*monitoring*mediation.**
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Functional*neuroanatomy*of*meditation*
MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 117*
Figure!S4.***Activations*associated*with*loving_kindness*and*compassion*mediation.**
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