Central Deafness Associated with a Midbrain Lesion...J Am Acad Audiol 15:133–151 (2004) 133 Central Deafness Associated with a Midbrain Lesion Frank E. Musiek* Lori Charette† Diantha

J Am Acad Audiol 15:133–151 (2004)

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Central Deafness Associated with aMidbrain Lesion

Frank E. Musiek*

Lori Charette†

Diantha Morse‡

Jane A. Baran§

AbstractCentral deafness has been linked historically to bihemispheric involvement ofthe temporal lobe, with more recent findings suggesting that compromise ofother cortical and subcortical structures can also result in this disorder. Thepresent investigation extends our understanding of the potential anatomicalcorrelates to central deafness by demonstrating that bilateral involvement ofan auditory structure within the midbrain can additionally result in this condi-tion. Our subject was a 21-year-old male with a subarachnoid bleed affectingboth inferior colliculi. Significant auditory deficits were noted for the middleand late auditory evoked potentials, while electrophysiologic measures of theperiphery indicated normal function. The patient was enrolled in a rehabilita-tion program for approximately 14 weeks. Although initially unresponsive tosounds, the patient regained most of his auditory abilities during the 10 monthshe was followed. This case documents the range of auditory deficits that maybe associated with damage to the inferior colliculi, and it profiles a hierarchi-cal recovery of auditory function consistent with test findings.

Key Words: Auditory evoked potentials, auditory processing disorder, cen-tral auditory disorders, central deafness, inferior colliculus

Abbreviations: ABR = auditory brainstem response; ALD = assistive listen-ing device; CT = computerized tomography; DL = difference limen; DPOAE =distortion product otoacoustic emissions; MLR = middle latency response;MRI = magnetic resonance imaging

Sumario La sordera central ha sido históricamente relacionada con el compromiso bi-hemisférico del lóbulo temporal, aunque hallazgos más recientes sugierentambién que el compromiso adicional de otras estructuras corticales y sub-corticales pueden producir este trastorno. La presente investigación amplianuestro conocimiento sobre la correlación anatómica potencial en la sorderacentral, demostrando que el compromiso bilateral de una estructura auditivadentro del mesencéfalo puede también resultar en esta condición. Nuestrosujeto fue un hombre de 21 años de edad con un sangrado sub-aracnoideoque afectó ambos colículos inferiores. Una deficiencia auditiva significativafue notada en los potenciales evocados auditivos tardíos y de latencia media,mientras las mediciones electrofisiológicas periféricas mostraron una funciónnormal. El paciente fue inscrito en un programa de rehabilitación durante 14semanas. Aunque con una falta inicial de respuesta a sonidos, el paciente

*Department of Communication Sciences, Neuroaudiology Lab, University of Connecticut, Storrs, Connecticut; †GaylordHospital, Wallingford, Connecticut; ‡Meriden, Connecticut; §Department of Communication Disorders, University of Massachusetts,Amherst, Massachusetts

Reprint requests: Frank E. Musiek, Ph.D., Professor, Department of Communication Sciences, 850 Bolton Road, Unit 1085,Storrs, CT 06269-1085; Phone: 860-486-3166; E-mail: [email protected]

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Central deafness is a relatively raredisorder but one that, if appropriatelydefined and investigated, can add

much to our understanding of the specificanatomical structures within the humanbrain that are involved in the processing ofauditory stimuli. Much of what is currentlyknown about the functioning of the centralauditory nervous system (CANS) has beengleaned from studies of patients withdocumented lesions of the brain (Damasioand Damasio, 1989). Investigations thatcorrelate specific auditory deficits with knownlesion sites serve to establish clear linksbetween auditory functions and theiranatomical correlates. Although significantadvances have been made on this front, theexact structures that compromise the CANSin humans have not been completelydelineated. This is particularly true of thecortical and subcortical structures thatsupport hearing. Additional studies ofpatients with CANS damage are needed tobuild upon the existing knowledge base thatdetails the neural substrate involved inhearing and hearing disorders, and patientswith central deafness provide uniqueopportunities to add to this knowledge base.

Individuals with central deafness oftenpresent with a rather dramatic auditorydeficit that is not commonly observed in other

patients with CANS compromise. Mostnotably, these patients often demonstrateinconsistent or no responses to sound (Hoodet al, 1994; Musiek et al, 1994; Murray andFields, 2001). Upon initial assessment, thesepatients may appear to have a peripheralhearing loss since pure-tone testing typicallyreveals a severe to profound hearing loss—a finding more commonly associated withcompromise of the peripheral hearing system.However, if objective test measures ofperipheral function are administered,compromise of the periphery is often ruledout, and central auditory system involvementis suggested. With additional testing (e.g.,middle and late auditory evoked potentials),the CANS involvement can be documented.Unfortunately, if such testing is notundertaken, then the central origin of thehearing loss is likely to remain unidentified.

To date there have been a number ofcase studies reported in the literature thathave clearly implicated bihemisphericinvolvement of Heschl’s gyrus as the likelyorigin of the auditory deficits noted in manypatients with central deafness (see Musiekand Lee, 1998). In their review of 33 cases ofpatients with central deafness, Musiek andLee (1998) found that bihemisphericinvolvement of the temporal lobe was acommon finding in most of these cases. This

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recuperó la mayor parte de sus capacidades auditivas a lo largo de 10 mesesde seguimiento. Este caso documenta el rango de deficiencias auditivas quepueden asociarse con una lesión en los colículos inferiores, y brinda un perfiljerárquico de recuperación de la función auditiva, consistente con los ha-llazgos en las evaluaciones.

Palabras Clave: Potenciales evocados auditivos, trastorno de procesamientoauditivo, trastornos auditivos centrales, sordera central, colículo inferior

Abreviaturas: ABR = respuestas auditivas del tallo cerebral; ALD = dispo-sitivo de ayuda auditiva; CT = tomografía computarizada; DL = umbral diferencial;DPOAE = emisiones otoacústicas por productos de distorsión; MLR = respues-tas de latencia media; MRI = imágenes por resonancia magnética


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observation lends some support to thecommonly held notion that damage to theprimary auditory areas (i.e., Heschl’s gyrus)of both hemispheres must be present in orderfor the auditory deficits typically associatedwith this condition to be present. Althoughbihemispheric temporal lobe compromise wasa common finding in the cases reviewed byMusiek and Lee, this site of lesion was notreported for all of the cases reviewed. Thus,the possibility of other lesion sites must beentertained. In addition, their review of thelesion sites for the 33 patients included intheir analysis indicated that multiple sites oflesion were involved in nearly every case,with other lesion sites including subcorticalstructures, the parietal lobe, the frontal lobe,the basal ganglion, the medial geniculatebody, and even the pons. With multiple sitesof lesions, it is difficult to determine whichsite, or combination of sites, may havecontributed to the central deafness.

One of the challenges in considering theavailable data on cases with central deafnessis lack of consistency in the terminology used.Investigators have used a number of termsto describe their patients, including “centraldeafness,” “cortical deafness,” “auditoryagnosia,” and “word deafness,” and in manycases the use of these terms have not beendefined fully. For example, “word deafness”has been used to describe a condition whereinpatients are unable to recognize words, butthe ability to perceive other auditory abilitiesis not necessarily addressed, leaving thereader uncertain as to the status of thisauditory skill in many of the patients studied.On the other hand, “central deafness” hasbeen used to describe patients with a varietyof symptoms and test findings, includingthose that demonstrate a complete lack ofresponse to sounds of any type (includingspeech), as well as others who show somereductions in hearing sensitivity (hence, notdeaf in a strict interpretation), but who showinordinately poor speech recognition abilitiesor other auditory processing abilities thatcannot be accounted for solely on the basis ofthe noted reduction of hearing sensitivity.

For our purpose we have chosen to usethe term “central deafness” to refer to acondition in which the followingcharacteristics are noted: (1) pure-tonethresholds may be absent or they may showsevere decrements in hearing sensitivity thatdo not have an origin in the peripheral

hearing system (this may change over time);(2) speech intelligibility is likely to be severelyaffected by the apparent compromise ofhearing sensitivity, and the extent of thespeech recognition deficit may be more severethan would have been predicted based upona consideration of the pure-tone thresholds;(3) objective measures of peripheral andbrainstem functions are normal unless thebrainstem is involved and contributing tothe central deficit; and (4) evoked potentialsthat assess electrophysiological responsesthat originate in the cortex or the radiationsto the auditory cortex show abnormalities.

As alluded to above, the current lack ofspecification of the anatomy of centraldeafness can be attributed to a number offactors. These include the following factors:(1) lesions are seldom specific to structuresof interest, (2) radiological evidence in thepast has not been exact enough to define theboundaries of damage in auditory system,(3) semantic differences in the terminologyused to describe central deafness haveprecluded precise comparison of the datasince it is difficult to define the patientpopulations in many cases, and (4) the use oflimited audiologic testing in manyinvestigations may have resulted in less thana complete elucidation of the nature and thefull extent of the auditory deficits in many ofthe patients studied. Fortunately, recentadvances in radiological imaging techniquesnow permit more careful specification of thelocation and precise boundaries of lesionswithin the CANS, and developments in thearea of electrophysiologic assessments havecontributed to the ability of the audiologistto document auditory deficits arising fromcortical and subcortical structures.

A careful review of anatomy of centralauditory deafness based upon the available(but qualified) empirical and hypotheticaldata would argue against the primaryauditory areas as being the only auditoryregions that could precipitate central auditorydeafness (see Musiek and Lee, 1998; Samsonet al, 2001). Other cases, with little or nodocumented involvement of the temporallobes, have shown that central deafness canresult from compromise associated withbilateral infarcts of the insula (Habib et al,1995), bleeds of the putamen (Nishioka et al,1993; Makino et al, 1998; Wakabayshi et al,1999; Taniwaki et al, 2000), third ventriclehydrocephalus affecting the thalamocortical


pathways (Shivashankar et al, 2001),bilateral medial geniculate body involvementassociated with a tentorial meningioma(Karibe et al, 2000), arteriovenousmalformation embolization involving theinferior colliculi (Vitte et al, 2002), and inferiorcolliculi destruction and medical geniculatebody degeneration associated with a pinealbody tumor (Masuda et al, 2000). The presentcase adds to the growing body of evidence thatindicates that compromise of auditorystructures outside of the primary corticalareas can result in central deafness.

CASE REPORT

History

This is a report of a 21-year-old collegestudent, who had been in good health with noproblems in hearing prior to the time of themedical condition that is described below.He was sent from the college to a localhospital because of severe headaches andvomiting. During his short stay at the localhospital, he became unresponsive and wastransferred to a large tertiary care hospital.At the second hospital, he became somewhatmore responsive, but he was combative andnonverbal. Key observations at this timeincluded unequal and minimally responsivepupils and purposeful movements to noxiousstimuli; however, the patient did not followcommands and was totally unresponsive toverbal stimuli. A computerized tomography(CT) scan at this time showed a subarachnoidbleed. Soon after admission, a diagnosis ofNeisseria meningitis was rendered. This raretype of meningitis, to our understanding, canresult in accompanying vascular lesions.

During the first two weeks following hismedical incident, the patient improved onmost fronts. He started vocalizing and sayinga few words, which were used appropriatelythe majority of the time. He was able to moveall extremities appropriately andpurposefully, and his mental status wasimproving. He communicated by writing ona pad, which he did reasonably well; however,he remained unresponsive to all sounds. Hewas soon transferred to a rehabilitationhospital and shortly after the transfer becamean outpatient. As an outpatient, he was seenover the next five months for audiologicalfollow-up and auditory therapy as his main

problem over this period of time was hishearing loss.

From a medical standpoint, the patientimproved markedly over the first six weeksof his outpatient treatment, and there wereno major concerns in this regard. However,he continued to be seen for audiological follow-up following his discharge so that anyadditional changes in his auditory functioncould be monitored. His schedule ofaudiological testing included a number ofevaluations that were completed over thefirst two months immediately following hismedical incident, and then subsequent tothis he was seen only periodically. The datareported in this study documents the resultsof most of the formal audiological evaluationsthat were completed over a 10-month period.Because the patient became fatigued quickly,especially during the initial six weeks, hehad to be brought back for repeated visits atvarious times to complete his audiologicalevaluations. In addition, the amount of timeavailable for testing was often limited due toa variety of circumstances. Hence, thetimelines for testing are not quite ascongruent as we would have liked, nor are theevaluations as extensive and complete in allcases as would have been desired.

Magnetic Resonance Imaging (MRI)

At the beginning of his third week in thehospital, an MRI was performed. The MRIshowed infarcts at the superior leftcerebellum/occipital lobe and the left inferiortemporal lobe. Neither of these regions isconsidered “auditory.” However, in themidbrain, both inferior colliculi were almosttotally infarcted with some spread of thecompromise into the inferior aspect of thesuperior colliculi (see Figures 1a, 1b, and1c). A more specific radiologic interpretationindicated that perhaps there was lessinvolvement in the anterior or ventral aspectsof the colliculi than in the posterior aspect ofthe colliculi.

Informal Observations on Hearing

As mentioned earlier, hospital personnelworking with this young man noted noresponse to any sound on the part of thispatient for the best part of the first week ofhis hospitalization. Commencing toward theend of the first week of his hospital stay, and


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continuing for several weeks thereafter, thepatient claimed he heard a certain sound,yet other people in the room with him did nothear the sound. Beginning in his secondweek, the patient acknowledged hearing somesounds in his environment that were actuallypresent, but he could not identify the exactnature and/or the source of these sounds. Itappeared that the sounds that were heardwere relatively loud and of a broad spectrum.By the third week of his hospital stay, definiteimprovements in hearing were noted. Thepatient could hear voices, but he could notunderstand anything that was being said tohim. He stated that “voices don’t [didn’t]sound like voices.” He was speaking often, buthospital personnel noticed that his voice wasmonotone. Listening was a strain, and itfatigued him to the point where he oftencomplained about it. He continued to hearenvironmental sounds, such as a dish beingdropped and water running from a faucet, andhe seemed to be able to discern loud soundsfrom soft sounds. However, he continued tobe inconsistent in his identification of thesource(s) of environmental sounds. Thepatient additionally complained of extremedifficulty listening to people speak wheneverbackground noises were present. At this pointin his recovery, he was able to read slowly, andthis skill has continued to improve over time.

In the fourth week post–medical incident,the patient reported that he felt his hearingwas improving. He could hear voices on TVbut could not understand what was beingsaid. In general, the patient knew whenpeople were speaking but could not followspeech on a consistent basis. He stated thatriding in a car was a difficult situationbecause everything was too loud. He wasidentifying more environmental sounds andwas encouraged when he identified theclicking of high heels caused by someonewalking on a hard floor. There remainedsome disassociation between what the patientbelieved he heard and what sounds wereactually present in his environment. Heclaimed to be able to hear women’s voicesbetter than men’s, and he reported that hecould hear parts of his girlfriend’s voice on thephone. During this time period, the patientbegan to experience bilateral tinnitus (ringingtype sound), which he reported was worse inthe morning than later in the day.

In the time period from about 5 through12 weeks, the patient’s hearing continued to

Figure 1. Top: a transverse MRI view showing theinvolvement of both inferior colliculi (arrows), aswell as the left lateral aspect of the cerebellum. Itappears that there may be slightly greater areainvolvement for the right inferior colliculus com-pared to the left. Middle: a mid saggital MRI show-ing the involvement of the inferior colliculus (arrow).Bottom: a human brain specimen that emphasizesa posterior view of the pons, midbrain, and thalamus.The area inside the dashed box reflects the authors’interpretation of the involved anatomy in this study’ssubject. The region of involvement encompasses bothinferior colliculi and the inferior fringe of the supe-rior colliculi. Key: 1 = inferior colliculus, 2 = superiorcolliculus, 3 = brachium of the inferior colliculus, 4= medial geniculate bodies, 5 = fourth ventricle, 6 =cochlear nucleus area. Courtesy of W. T. Mosenthaland F. E. Musiek.


show steady improvement. He could nowunderstand several words, and this abilitygradually improved over time but was highlydependent on the patient’s being located ina quiet environment. Background noise, evenif of a low intensity (e.g., noise generated bya small fan), caused considerable problems inhis understanding of speech. He noted thathe heard better when he was activelyparticipating in a conversation compared towhen he was listening passively. He reportedthat speech seemed muffled and described hislistening experiences as if he were listeningto speech over a two-way radio transmitter.He could hear birds chirp but described thechirping of the birds as having a “robotic”quality. His therapist noted that his voicewas softer at this time, and possibly lessmonotone.

In the post–hospital admission periodfrom 12 weeks to 10 months, the patient wasseen only a few times formally. His ability tounderstand speech in quiet continued toimprove, and he was able to follow mostconversations. Complex and similar soundingwords remained difficult for him to correctlyinterpret and discriminate, and backgroundnoise continued to be a major detriment to hisaccurate understanding of speech. Thepatient’s confidence in communicationimproved considerably over this period oftime, and at this point in his recovery hehad gone back to college and appeared to bedoing satisfactorily with someaccommodations such as preferential seating.As part of his rehabilitation program, thepatient had been provided an assistivelistening device (ALD), which provided someassistance; however, there was somereluctance on the part of the patient to useit consistently as he did not want to becomedependent upon the device. The patient wasmotivated to act as if he has no problem atall and therefore downplayed use of the ALD,as well as some of the academicaccommodations that were recommended.His auditory behavior at 10 months after hismedical incident was similar to that of anindividual with a moderately severe high-frequency hearing loss. However, backgroundnoise continued to be a major problem, moreso than would be expected for a person withonly a moderately severe high-frequencysensorineural hearing loss.

PROCEDURES

Pure-Tone and Speech Audiometry

All audiological tests were conducted insound-treated rooms. Conventional pure-toneair- and bone-conduction threshold techniqueswere used to establish hearing thresholdsfor this patient; however, at times these hadto be modified to accommodate the patient’sneeds. Spondee thresholds were obtained onsome occasions using only a small subset ofspondees as indicated in the test resultssection. Speech recognition measures wereconducted using the Northwestern UniversityTest Number Six (NU-6). Speech audiometrywas carried out using monitored live voiceprocedures as this mode of presentationseemed most clinically feasible particularlyduring the early evaluations of the patient’shearing.

Immittance Audiometry

Tympanograms and acoustic reflexeswere derived in a conventional manner usinga GSI 1733 middle-ear analyzer. Acousticreflexes were measured both ipsilaterallyand contralaterally at 500, 1000, and 2000 Hz.

Otoacoustic Emissions

Distortion product otoacoustic emissions(DPOAEs) were derived for this patient.Levels (L1, L2) were 65 dB SPL and 55 dBSPL, and the f1 to f2 ratio was 1.2. The leftear DPOAEs were measured for frequenciesfrom 600 to 8000 Hz, and the right ear forfrequencies from 800 to 8000 Hz (the lowerfrequencies could not be measured in theright ear due to the presence of excessivenoise at these frequencies). Four distortionproducts per octave were obtained for each ear(see Smurzynski, 1994 for details of thisprocedure).

Auditory Brainstem Response (ABR)

All ABR testing was conducted using 100µsec clicks presented through TDH-39earphones to each ear independently at 85 dBnHL at a rate of 15.7 clicks per second unlessotherwise noted. Neuroelectrical activity wasrecorded from electrodes attached to the highforehead and each earlobe (one reference and


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one ground) and averaged over 2000 trials.Impedance across the electrodes wasmaintained at less than 5 kohm. Filter bandsfor the ABR were set at 150 to 3000 Hz witha 12 dB per octave roll-off. Responses wereanalyzed over a 10 msec time period.

Middle Latency Evoked Response(MLR)

The MLR was obtained using 100 µsecclicks presented through TDH-39 earphonesat 70 dB nHL at a rate of 8.7 clicks per secondfor each ear. For the initial test session,electrodes were placed at Cz and referred toeither A1 and A2; however, all subsequentMLR recordings were conducted withelectrodes at Cz, C5, and C6 with the samereferences. Impedance across the electrodearray was maintained at less than 5 kohm.In all cases the reference electrode was on theside of the head that was receiving the clickstimulus. There were 800 accepted trialsconducted for each run, and filtering was 20to 1500 Hz with a 12 dB per octave roll-off.The time period for analysis was 70 msec.

P300 Potential

The P300 was conducted in each earusing an odd-ball paradigm with 1000 Hzand 2000 Hz tones representing the frequentand rare stimuli, respectively. These toneshad a 10 msec rise and fall time and a 20 msecplateau and were presented at 70 dB nHLthrough TDH-39 earphones at a rate of 1.2stimuli per second. Electrical activity from thescalp was picked up by electrodes placed atFz, Cz, and Pz. Stimuli presentation rateswere set at 80% for the frequent stimulus and20% for the rare stimulus, and the totalnumber of stimuli to be accepted during eachrun was fixed at 300. Impedance acrosselectrodes was less than 5 kohm. Filteringwas set at 1 to 30 Hz with a 12 dB per octaveroll-off. The time window was 800 msec. Thepatient had to count the number of rarestimuli and report this number at the end ofeach run (a score of >80% correct behavioralcounting performance was required for theacceptance of an electrophysiologicalresponse). Responses from the rare andfrequent stimuli were averaged separately.The frequent stimuli yielded late potentialsN1 and P2, and the rare stimuli providedN1, P2, and P300 waves for analysis.

Intensity Discrimination

Intensity discrimination testing wasconducted in each ear for three frequencies(500, 1000, and 2000 Hz). Each test stimuliconsisted of the presentation of two tonesthat were delivered at either the sameintensity level or at different intensity levels,and the patient was asked to indicate if thetones were the same or different in loudness.Each tone was 500 msec tones in durationwith a 40 msec rise-fall time, and theinterstimulus interval between the twosuccessive tones was approximately 1 sec induration. Trials of equal versus differentintensities were presented at random. Thereference presentation level was fixed at 50dB HL; thus, in each test stimuli, one of thetones was presented at this intensity levelwhile the second tone was varied for thepurpose of identifying the smallest intensitydifference that the patient could recognize.The patient was required to achieve two outof three correct judgments at a particularintensity difference before going further. Thisprocedure was repeated several times, andthe average of difference limens (DLs)obtained was computed. At times thisprocedure had to be modified to accommodatethe patient. For example, on some days, morepractice items with large DLs were providedand/or the presentation approach was slightlychanged to allow a better orientation towardthe test.

TEST RESULTS

Basic Audiological Evaluation

The first formal audiological evaluationwas performed about two and one-half weeksafter admission. At this point, the patient’shearing had already improved considerablyfrom the first week; however, in spite of thisnoted improvement in hearing, pure-tonethresholds were difficult to obtain, especiallyat the low frequencies with a frequentoccurrence of false positives. This difficultywith the assessment of pure-tone sensitivitycontinued for most of the early evaluations,and to a lesser degree for later evaluations.One of the factors that contributed to thedifficulty with determining thresholds forpure tones was that the patient noted littleor no tonality in the stimuli; hence, the sounds


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were not distinctive. This was particularlyproblematic during the first few evaluations,especially for low frequencies and the rightear. Another factor that was likely to haveaffected his performance during this initialevaluation, as well as in other subsequentevaluations, was the difficultly that thepatient reported in maintaining his attention.At the time of his initial evaluation, a severelow-frequency sensorineural loss, rising to amild to moderate loss, was indicatedbilaterally (Figure 2). Speech audiometrycould not be obtained during this evaluationfor either ear, but tympanograms were ofnormal pressure, compliance, and shapebilaterally. Ipsilateral and contralateralacoustic reflex thresholds were grossly withinthe normal range for absolute thresholdlevels for both ears, but these thresholdswere at reduced sensation levels in referenceto pure-tone thresholds for both ears at 500,1000, and 2000 Hz.

The next formal evaluation wasperformed at three and one-half weeks. As canbe seen in Figure 3, there was a definiteimprovement in the hearing thresholds forboth ears. Spondee thresholds were obtainedbilaterally for the first time using selectedspondees; however, these thresholds wereelevated and in poor agreement with thepure-tone averages for both ears. Speechrecognition could not be tested at this timeas the patient could not understand even thecarrier phrase. Acoustic reflex andtympanometric test results remained normalbilaterally.

The next audiological assessment wasconducted at five weeks (Figure 4), andalthough it showed improvement at the midand high frequencies, the low frequencieswere difficult to assess. There was so muchvariability in performance at the lowfrequencies for the right ear that thresholdscould not be established. The patient claimedthat the low-frequency tones (especially forthe right ear) “sounded like the wind blowingtall grass in a field.” Speech recognition could


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Figure 2. The initial audiogram and acoustic reflextest results for a 21-year-old male with bilateralinvolvement of the inferior colliculi. Spondee thresh-olds and speech recognition could not be tested (CNT)for either ear (AU) at this time. Key: X, O = left andright ears, [ ] = bone conduction right and left sides,DNT = did not test, AU = both left and right ears, CNT= could not test, bone conduction was not tested at250 Hz.

Figure 3. An audiogram showing pure-tone thresh-olds, spondee thresholds for selected spondees, speechrecognition scores, and acoustic reflex findings. Theseresults were obtained at approximately three and one-half weeks following the patient’s hospitalization.



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not be tested. The patient became veryfatigued during this evaluation, and hismotivation was dwindling.

The next audiogram was at 10 weeks(Figure 5). Pure-tone thresholds hadimproved to close to normal bilaterally atthis time and were in good agreement withthe spondee thresholds bilaterally. At thisevaluation, speech recognition could be testedfor both ears and in a binaural (diotic)condition for which the best score wasobtained. At approximately five months,speech recognition had improved into the80% range bilaterally as informalassessments during his rehabilitation periodwere conducted. He was discharged fromtherapy at five months. At 10 months he wasseen for assessment and showed essentiallya normal audiogram and speech testing(Figure 6). As mentioned earlier, however,he continued to experience difficulty withbackground noise.

Otoacoustic Emissions

Distortion product otoacoustic emissionswere administered approximately four weeks

Figure 4. An audiogram and speech recognitionresults at five weeks. The “?*” indicates the “bestguess” thresholds for the right ear at these frequen-cies as threshold criteria could not be achieved at thistime due to variability in responses and fatigue on thepart of the patient.

Figure 6. An audiogram at 10 months with spondeethresholds and speech recognition scores.

Figure 5. An audiogram, spondee thresholds, andspeech recognition scores for each ear and in the bin-aural (Bin.) condition obtained at 10 weeks.


after hospital admission. The left ear resultswere essentially normal for absolute DPOAElevels and DPOAE to noise floormeasurements for frequencies 600 through6000 Hz (Figure 7), whereas the right earresults were at normal absolute levels from800 through 2000 Hz, but at abnormal levelsfor the higher frequencies tested (Figure 7).The right ear DPOAE to noise floormeasurements were grossly normal for alltest frequencies (800 through 6000 Hz). Thepatient was anxious and tense during thisevaluation, and reliable measurements couldnot be made below 800 Hz due to excess noise.

Auditory Brainstem Response (ABR)

The initial ABR was performed at threeand one-half weeks and showed normal wavesI, II, and III bilaterally. It appeared that theIV-V complex was compromised for both ears.It is possible that wave IV could be normal,but the amplitude and morphology of V is notas would be expected for either ear (Musiekand Lee, 1995). The amplitude of the IV-Vcomplex is less than half the amplitude ofwave I bilaterally. This abnormal V-Iamplitude ratio highlights the compromise ofthe IV-V complex (Musiek and Lee, 1995). TheABR was evaluated several times over therecovery period up to 10 months but remainedessentially the same as shown in Figure 8.

Middle Latency Response (MLR)

The initial MLR was conducted at threeand one-half weeks and showed no readableresponse for either ear (Figure 9). A secondMLR derived one week later again revealedno repeatable responses for either ear. Thefirst follow-up MLR that showed a notablechange was derived at 24 weeks (Figure 10).At this time, a meager Pa wave began toemerge at essentially normal latencies forboth ears across all electrode sites. It wasdifficult to determine if an Na wave waspresent at this time, but it seems doubtful.


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Figure 7. DPOAEs responses for the left and right ears. The heavy solid line is the patient’s DPOAE levels;the thin solid line is the patient’s noise floor; the dashed line is the average noise floor; and the dotted line anddashed/dotted lines are 10th and 90th percentiles.

Figure 8. The initial ABR.


The Nb and Pb waves were absent. At 10months, the MLR was more noisy but showedsimilar responses to those noted at 24 weeks.

P300 Potentials

The P300 as well as the N1 and P2 latepotentials (as derived using an odd-ball

paradigm) showed no readable responses atfour weeks (Figure 11). An evaluation at 9weeks showed a P300 emerging for both earsacross all electrode sites (Figure 12). The P300was within the normal latency range for the leftear stimulation but was extended for the rightear stimulation. The P2 also began to emerge,though attenuated, at Fz and Cz electrodesites for both ears. The latency of P2 wasextended (240 msec), and an N1 was not seenfor any recording site at nine weeks. At 10months, the P300 increased in amplitude anddecreased slightly in latency across the Pz andCz electrode sites for both ears. The N1 and P2for both ears remained essentially the same forFz and Cz electrode sites; however, at 10months a P2 emerged for the Pz electrodeposition (Figure 13).


Intensity discrimination was measuredat 5 and 11 weeks. As depicted in Figure 14,there was considerable improvement inintensity discrimination over this period oftime. The right ear, which was the ear withpoorer performance at five weeks, improvedmore than the left ear. At five weeks, theright ear could not be assessed due to toogreat of a hearing loss. The patient performedbetter in the binaural condition for both testsessions (Figure 14). The cut-off for normal


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Figure 9. The initial MLR. Figure 10. An MLR obtained at 24 weeks.

Figure 11. The initial findings for the P300 as wellas late auditory evoked potentials (N1 and P2).


performance on this task is 2 dB for bothmonaural and binaural presentations.

REHABILITION PROGRAM

The aural rehabilitation programcommenced approximately one month

after hospital admission and continued ona consistent basis for about four and one-half months. Individual therapy sessionswere held once per week for one to one andone-quarter hours, and the patient’sperformance on the various therapy tasks

outlined below was monitored throughoutthis period. Task difficulty was governed tobe in the moderate range so that overall thetasks were not too demanding or too easyand the patient was either directly orindirectly provided feedback as to hisperformance during training procedures.The patient was also given therapyassignments to complete at home. Theseincluded such activities as auditorydirectives, discrimination tasks, andcritically listening to music. The descriptionof the formal therapy has been divided into


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Figure 12. Left and right ear results for the P300 and late auditory evoked potentials at nine weeks.

Figure 13. Left and right ear results for the P300 and late auditory evoked potentials at 10 months.

Left Ear Right Ear

Left Ear Right Ear


three time periods; early (approximatelythe first month), mid (approximately thenext two months), and late (approximatelythe last month and a half).

Early Therapy Sessions (with VisualCues)

One of the first therapy goals was towork on the patient’s vocal intonation as thepatient’s voice was monotone. Early therapyactivities additionally focused on havingthe patient respond appropriately tofundamental questions about himself.Therapy on identifying and discriminatingspeech and environmental sounds was amajor component of this therapy period.The patient was asked to make judgmentsas to intensity differences between and/oramong sounds both in formal and informalparadigms. In addition there was somework on speech reading and emphasizingthe use of visual cues. Much therapy wascentered around multimodality stimulationand associating cues across differentmodalities.

Midtherapy Sessions (with andwithout Visual Cues)

In this therapy period, the patient wasasked to identify familiar voices and to try todiscriminate male from female voices. Workwas continued on identifying anddiscriminating environmental sounds that, forthe most part, were tape recordings thatprovided a wide variety of acoustic stimuli.Since the patient liked popular music, sometherapy procedures centered aroundidentifying songs and their artists. Thepatient also spent time repeating sentencesthat were presented to him in the presenceof background noise that was varied in terms of noise type and level. Toward theend of this therapy period, auditory trainingconsisted of identifying vowels, blends, andconsonants using Sloan’s (1986) materials.Discriminating homophonous words andcontrasting nonsense words with real wordsin both monaural and binaural listeningconditions was also conducted. The patientwas asked to read aloud and listen to himself,and intensity discrimination tasks werecontinued. Finally, a portion of the therapytime was often devoted to work on one-, two-,and three-step auditory directives.

Late Therapy Sessions (with andwithout Visual Cues)

At this point, the patient had madeconsiderable improvement, and, accordingly,the tasks were made more challenging.Discrimination tasks with similar soundingphonemes, consonant-vowels (CVs), vowel-consonants (VCs), and homophonous wordsbecame a major focus in therapy.Identification tasks involving the presentationof words and sentences in noise werecontinued, and the patient was also asked toidentify and correct words that werepurposely distorted in a sentence. The patientclaimed he had difficulty in group discussionsrecognizing when he was being spoken toand responding appropriately. He wasprovided training on using visual cues inthese situations to help him determine whenhe was expected to be part of the conversation.An assistive listening device (ALD) wasintroduced, and although the patientexperienced some success with this device, hewas not in favor of its long-term use. Shortlyafter the formal therapy sessions ended, the


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Figure 14. The intensity DL derived at 500, 1000, and2000 Hz in each ear at 5 weeks and at 11 weeks. At5 weeks the DL at 500 Hz could not be recorded forthe right ear.


patient went back to college with an ALD. Hewas also provided a note taker for his classes.

DISCUSSION

Cases of central deafness are indeed ararity. Usually most cases of central

deafness involve vascular damage to theprimary auditory area in both cortices(Musiek and Lee, 1998). Even more unusualis central deafness associated with lesions ofthe brainstem or subcortex. Unlike themajority of cases of central deafness thatresult from bilateral auditory cortex lesions,this case had healthy (auditory) cortical andsubcortical substrate. In this case, theauditory deficits noted were most likelyrelated to impulse disruption arising at themidbrain level, which deprived the cortex ofappropriate neural input from both sides ofthe midbrain. This case is one that showedrecovery of many, but not all, higher-levelhearing processes. By following this patientfor 10 months, information as to the natureof the recovery process was gained.

Informal and Formal Observations ofHearing: Course of Recovery

We believe there is a strong possibilitythat this patient may have been totallycentrally deaf during the first week to weekand a half post–admission to the hospital.Hospital personnel reported that the patientwas unresponsive to acoustic stimuli duringthis period of time. By the time the firsthearing test was completed at two and one-half weeks, the patient had recoveredconsiderable hearing ability, but he remainedessentially word deaf throughout the firstmonth following his medical incident. Sufficeit to say, the involvement of the inferiorcolliculi created a major deficit across allaspects of hearing.

The informal observations of thispatient’s hearing recovery reflected a logicalprogression, which began with the return ofthe ability to perceive simple sounds andincreased to the perception of more complexsounds (speech). Initially the patient could notdetect any sounds; however, within the firstweek he could detect sounds but could notidentify them. The detection and subsequentidentification of simple environmental soundswas followed by the recognition of morecomplex and less familiar acoustic stimuli. By

10 weeks post–hospital admission, the patientcould communicate reasonably well whenvisual cues were optimized, and the acousticenvironment was ideal. The patient’simprovement for hearing in poor acoustic(noisy) environments was minimal in thefirst few weeks after his medical incident, andeven at 10 months this continued to be amajor problem for this patient.

Formal audiological testing showed asimilar progression of recovery. The simpleststimuli, pure tones, were the first to showprogress in the recovery process and endedup in the normal range bilaterally. Thespondee thresholds eventually progressed towithin the normal range, as did speechrecognition ability although the latter didrequire more time. The evoked potentials,other than the ABR, showed improvementover time. However, none of the evokedpotentials recovered to normal status. Thisprogression of regaining auditory perceptionfor simple and then more complex processesis consistent with what has been reportedpreviously in the literature for patientsrecovering from CANS damage (Mendez andGeehan, 1988; Nishioka et al, 1993; Musieket al, 1994). The more complex the acousticstimulus, the more neural substrate isneeded. This has been well demonstrated indichotic listening paradigms in people withtemporal lobe damage (Kimura, 1961). Incases of central deafness, neural damage isextensive, and recovery of sufficient neuralsubstrate to support complex processingrequires an extended period of time (Mendezand Geehan, 1988).

This case opposes the classic conceptthat central auditory lesions do not affectpure-tone thresholds. This case and otherstudies on both humans and animalsdemonstrate that central auditoryinvolvement can result in the reduction ofpure-tone sensitivity (Heffner and Heffner,1986; Musiek et al, 1994; Murray and Fields,2001). Whether or not pure-tone sensitivityis affected by central auditory involvementdepends on the site and size of the lesionand how soon the hearing sensitivity ismeasured after the damage occurred (seeHeffner and Heffner, 1986).

An interesting observation made on thispatient, especially early on in the recoveryprocess, was that he would think that heheard sounds that really did not exist. Thisbehavior has been seen in centrally deaf


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patients before (Musiek et al, 1994). Wecannot be sure if this phenomenon occursbecause the sounds are imagined in somemanner, such as an auditory illusion orhallucination, or whether they are the resultof some other psychophysiological phenomenon.Nonetheless, the patient genuinely believed thesound(s) was indeed present in hisenvironment. The incidence of thismisinterpretation or illusion of sound appearedto decrease as the patient’s hearing improved.

Anatomy and the MRI

This case is one that has some ratherspecific neuroanatomy. Although there werelesions in other areas of the brain, the onlysignificant auditory involvement was at theright and left inferior colliculi. There mayhave been some “minor” involvement in themore caudal aspects of the superior colliculi,which may have some auditory function. Ithas been demonstrated that in some animalspecies the superior colliculus may have someauditory fibers. These, however, are in theminority (Irvine, 1986). Therefore, the lesionsite in this case is one that is quite specific,which helps in determining the role of theinferior colliculus on the various aspects ofhearing function studied in the presentinvestigation.

Close inspection of the MRIs may indicatethat there was less damage at the moreanterior aspect of the colliculi. If this was infact the case, it may explain why there wasbetter hearing at the high frequencies thanat the low frequencies. The tonotopicarrangement of the inferior colliculus hasbeen shown to progress from high to lowfrequencies in a posterior to anterior manner,with high frequencies located deep in themidbrain (Merzenich and Reid, 1974). If thedeep substrate was damaged less, it mayhave allowed the coding and progression ofthe high-frequency stimuli up the remainderof the auditory pathway. The severe damageto the low-frequency region of the inferiorcolliculus may have prohibited frequencycoding at this level and may have also eitherstopped or disrupted the rostral flow of low-frequency impulses to the thalamo-corticaltract. This may also explain why the patientreported during testing that the low-frequency pure tones did not sound tonal.

Auditory Evoked Potentials

Major damage to the inferior colliculusposes a situation that is of interest to the ABR,MLR, and late potentials. It was once thoughtthat the inferior colliculus was the majorgenerator of the ABR wave V. Studies onhumans during neurosurgery changed thisthinking (Moller, 1983; Moller et al, 1995).Current thinking is that wave V may have aslight contribution from the inferior colliculus,but that it is primarily generated by thelateral lemniscus (see Hall, 1992). This caseadds information to what is currently knownabout the wave V generator site. Theradiology shows that the damage was limitedto the inferior colliculus and possibly theinferior portion of the superior colliculus butthat the pons was spared in this patient.Although wave V is present, it is clear thatthe waveform morphology is somewhatcompromised. This finding was repeated anumber of times. Therefore, it appears thatin this patient wave V may have somecontribution from the inferior colliculus inaddition to contributions from neuralstructures located more caudally. The ABR IV-V complex is clearly distorted in spite of thefact that wave IV can be discerned from waveV. In addition, the IV-V complex issignificantly smaller in amplitude than waveI in both ears. This finding has often beenconsidered an indicator of a brainstem orretrocochlear lesion (Musiek and Lee, 1995).The early waves of the ABR are normalbilaterally indicating good neural integrity inthe region of the caudal pons.

It is interesting to note that the ABRwaveform did not change over time and hencedid not reflect the improvement noted in thepatient’s behavioral hearing. Thisdisassociation may be related to severalfactors. The auditory fibers in this area(midbrain) may have recovered to somedegree and rerouted themselves around thedamaged area, or new fibers may have beenrecruited to assume some of the functions ofthe damaged neurons. It has been shownthat the inferior colliculus has the ability toreorganize rather quickly when deprived ofperipheral input (Wang et al, 1996). In thispatient, this new or recovered neuralsubstrate may have supported the processesnecessary for the improvements noted in hisauditory behaviors but not have achievedthe neural synchrony or dipole orientation


necessary to generate a normal ABR wave V.We also know there is not a direct relationshipbetween behavioral hearing and the ABR(Worthington and Peters, 1980). Hence,behavioral changes may be reflected indifferent measures than the ABR. The ABR isdependent on neural synchrony, and perhapsthe fibers responsible for this synchrony didnot change but, rather, the change may haveoccurred in neural substrate not involveddirectly in the generation of the ABR.

The MLR that was recorded at three andone-half weeks showed no readable responsefor either ear at the Cz recording site. At 24weeks there clearly was some recovery of theMLR with the Pa wave visibly discernable forboth ears and across three electrode sites(Cz, C5, C6). The tracings from the right earappeared to be slightly more synchronousthan those derived from left ear stimulation.Although there was some definite recovery at24 weeks in the MLR waveform morphology,it did not continue to improve noticeablybeyond this time as waveforms at 10 monthswere similar to those noted at 24 weeks. Theimprovement in the MLR waves would againsupport the notion that synchronous impulsesbegan making their way to the thalamo-cortical regions of the brain (see Kraus et al,1994). In the initial MLR, this may not havebeen the case. Again, the neural pathways inthe midbrain may have recovered or beenreorganized to allow synchronous impulses toreach the generators of the MLR. Withoutsome form of recovery or auditory plasticityoccurring, it appears that bilateral damageto the inferior colliculus may precluderecording an MLR. Besides the auditorythalamo-cortical pathways, the MLRwaveform may be dependent on the reticularformation (see Kraus et al, 1994). Therefore,it may be possible that compromise or a“shutting down” of the reticular formationmay have compromised the MLR. There wasno asymmetry for the MLR waveforms acrosselectrode sites, indicating that the “effect”was bilateral. This is consistent with thelesion site being bilateral and symmetrical.It is also interesting to note that the MLRimproved without any change in the ABRlate waves (IV-V). Therefore, one mightconclude that the MLR change was notdependent on the same subcortical/brainstemsubstrate as the ABR at least in this case. Inthis regard, it has been shown previously

that an MLR can be present with an absentABR (Squires and Hecox, 1983).

The P300 as well as the N1 and P2 latepotentials were absent at the Cz recording siteat the initial evaluation, and there wasessentially no difference between the frequentand rare waveforms. However, at nine weeksthe P300 did emerge along with rathermeager N1 and P2 complexes across allelectrode sites for both ears. The latepotentials all appeared to be delayed inabsolute latency. As with the MLR, theselate evoked potentials may have initiallybeen absent due to the lack of synchronousinput secondary to severe bilateral CANSdamage at the midbrain level. The emergenceof the N1, P2, and P300 potentials at nineweeks may indicate (as with the MLR) thereestablishment of a functional neuralpathway in the midbrain that could providesynchronous input to the subcortex andcortex. It seems important to point out thatwithout this “reestablished pathway,”whether it is associated with recovery,plasticity, or some other phenomenon, therewould be no cortical or event-relatedpotentials. What this suggests is that thedisruption of neural impulses at the level ofthe midbrain can deprive the cortex of thenecessary input needed to generate itspotentials. It additionally suggests that thereis no other major pathway from the brainstemto cortex other than that which coursesthrough the inferior colliculi that can providethe synchronous input to the subcortical andcortical pathways needed to generate themiddle and late potentials.

As with the MLR, it has been reportedthat late evoked potentials can be obtainedeven when the ABR is absent or severelycompromised (Squires and Hecox, 1983).However, in these cases one must entertainthe possibility that there may have beensome plasticity factors involved (as discussedearlier) and that perhaps even with an absentABR the inferior colliculus could have beensufficiently intact to conduct the neuralimpulses required for the generation of thelate potentials. It is well known that theinferior colliculus is the main synaptic stationof the brainstem pathway and that when itis severely damaged input to the next levelwill be drastically reduced (van Noort, 1969).It is reasonable to assume that since theinferior colliculus is larger than any of themore caudal auditory brainstem nuclei and


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since most of the ascending fibers from themore caudal nuclei synapse at the inferiorcolliculus, damage to the inferior colliculuswould have a greater effect on input to thecortex than damage to the lower brainstemstructures (see Pickles, 1988 for review).Given this scenario, it is logical to assume thatinferior colliculus damage of a severe degreewould have greater influence on thepropagation of mid and late potentials thanthe lack of an ABR. Hence, it is our belief thatthe mid and late potentials (and otherauditory processing at cortical levels) arehighly dependent on the integrity of theinferior colliculi and that if CANS function atthis level had not improved in this patientover time that the mid and late potentialswould have remained absent throughout theperiod that this individual was followed.

The lack of “normal” auditory evokedpotentials at 10 months was more consistentwith the patient’s symptoms than were theresults of basic pure-tone and speech testing.The patient still had problems hearing innoise and in other complex listeningenvironments. It could be that the evokedpotentials and listening in noisy backgroundsrequired a level of auditory processingsophistication not yet supported by a partiallyrecovered neural substrate. These findingsclearly support the importance of usingelectrophysiologic measures to documentauditory difficulties in many patients withCANS involvement.


Intensity discrimination was measuredat five and 11 weeks. At five weeks the rightear could not be tested due to poor thresholdsensitivity and inconsistent responses at thefrequencies tested (500, 1000, 2000 Hz). At11 weeks, there was a rather markedimprovement in the patient’s performanceat all frequencies, with the most significantchange noted at 2000 Hz. In addition, a clearbinaural advantage for the intensitydiscrimination task was observed. A similarbinaural advantage was also noted duringspeech recognition testing in this patient, aswell as in other centrally deaf subjects(Musiek et al, 1994). At 11 weeks, the patient’sintensity discrimination, although noticeablyimproved, was not normal, and this mayhave been the key reason why the speechrecognition scores remained poor at this time.

We believe there is a relationship amongabnormal difference limens (DLs) for intensityand frequency and poor speech recognitionscores. If the intensity (or frequency)discrimination is so poor that one cannotrecognize changes in intensity (or spectralinformation) from phoneme to phoneme, thenspeech perception will suffer. Cranford andcolleagues (1982) in an investigation ofpatients with temporal lobe lesions showedincreased DLs for frequency in ears that alsodemonstrated reduced speech recognitionscores. This was especially evident when thetone duration used in the DL test wasrelatively brief. We also know of at least oneprevious case of a patient with word deafnessin which the DLs for frequency were foundto be extremely large (Musiek et al, 1994). Atthis time it is not possible for us to indicatewhether this is a common finding in patientswith central deafness since few of the previousinvestigations reported in the literature haveundertaken this type of assessment. Withadditional testing, a clear relationshipbetween intensity and frequencydiscrimination abilities and speechrecognition performance may be documented.

Rehabilitation

The rehabilitation program for thispatient focused primarily on auditory trainingwith some work on language use and theutilization of visual cues. It is difficult toknow how much of a roll the therapy playedin this patient’s auditory improvement.Certainly much of the patient’s progress wasrelated to spontaneous recovery given thetime period over which most of the progresswas made. However, it is known that recoverycan often be enhanced by stimulation and bypresenting tasks to the central nervoussystem that challenge it (see Musiek andBerge, 1998, for review). It is therefore likelythat the patient’s improvement was positivelyaffected by the therapy activities in which heparticipated. The patient’s progress intherapy is reflected by the increasedsophistication in the tasks from the beginningto the end of the formal sessions. At thebeginning, the patient’s identification anddiscrimination had to do with gross, highlydifferent environmental sounds. At the endof therapy he was working on differentiatingwords, phonemes, and CVs that were highlysimilar in their phonetic features. There is


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evidence that auditory training can improveauditory abilities related to discriminationand temporal processing (Recanzone et al,1993; Kraus et al, 1995a, 1995b; Tallal et al,1996), as well as other higher-level linguisticprocesses. Therefore, it seems likely that thetherapy did make a contribution to thispatient’s recovery.

SUMMARY

There are a number of key observationsfrom this study that may be of interest to

the clinician and investigator. To ourknowledge, this is the first report of a case ofcentral deafness associated with damage toboth inferior colliculi. The audiological testingof this patient demonstrated a wide range ofauditory deficits associated with profounddamage to both inferior colliculi. Thesefindings were consistent, for the most part,with those noted for other cases with centraldeafness originating from other structureslocated more rostrally within the centralauditory nervous system. The most notabledifference was the observation ofabnormalities of wave V of the ABR. Althoughsuch abnormalities would not be expected incases with compromise of cortical orsubcortical structures, these abnormalitieswould also not have been predicted for thepresent case based upon our currentunderstanding of the generator sites for theABR waves (Moeller, 1983). This findingsuggests that at least in this case the inferiorcolliculus contributes to some degree to thegeneration of wave V of the ABR. Also ofinterest in this case was the observation ofa hierarchical course of recovery with thepatient demonstrating the ability to processsimple acoustic stimuli and tasks before hecould process auditory functions related tomore complex acoustic stimuli and tasks.Unlike his performance on pure-tone, spondeethreshold and speech recognition testing, hisperformance on other tests such as auditoryevoked potentials and intensitydiscrimination did not recover to normalvalues at 10 months. This may indicate adisassociation in the physiologic bases ofthese different types of tests and/or thatthese types of tests have a different level ofprocessing sophistication. Finally, this caseadds to the growing body of evidence thatcentral auditory involvement can affect pure-tone sensitivity.

Acknowledgment. A special thanks to MicheleAbrams, Rosemarie Russo Ghezzi, Arlene Schwartz,Paula Bacolini, Alyse Sicklick, Jacek Smurzynski,and the Hitchcock Foundation for help and supportwith this study.

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Central Deafness Associated with a Midbrain Lesion...J Am Acad Audiol 15:133–151 (2004) 133 Central Deafness Associated with a Midbrain Lesion Frank E. Musiek* Lori Charette† Diantha