anomalies of the eye as illustrated in the 'Transactions' of the Society. Trans Ophthalmol Soc UK 1898;18:1-16. 9. Valentin B: Die Korrelation (Koppelung) von Missbildungen, erl\l=a"\utertam Beispiel der Akrocephalosyndaktylie. Acta Orthop Scand 1938;9:235-316. 10. Martischnig E, Thalhammer 0: Akroceph-$ alosyndaktylie (Er\l=o"\rterungder Genese von Gesichtspunkt der Embryopathie). Helv Paediatr Acta 1952;7:257-271. 11. Gross H: Zur Kenntnis der Beziehungen zwischen Gehirn und Sch\l=a"\delkapselbei den turricephalen, craniostenotischen Dysostosen. Virchows Arch A 1957;330:365-383. 12. Hogan GR, Bauman ML: Hydrocephalus in Apert's syndrome. J Pediatr 1971;79:782-787. 13. Maksem JA, Roessmann U: Apert's syndrome with central nervous system anomalies. Acta Neuropathol 1979;48:59-61. 14. Stewart RE, Dixon G, Cohen A: The pathogenesis of premature craniosynostosis in acrocephalosyndactyly (Apert's syndrome): A reconsideration. Plast Reconstr Surg 1977;59:699-707. 15. Leonard CO, Daikoku NH, Winn K: Prenatal fetoscopic diagnosis of the Apert syndrome. Am J Med Genet 1982;11:5-9. 16. Tessier P: The definitive plastic surgical treatment of the severe facial deformities of craniofacial dysostosis: Crouzon's and Apert's diseases. Plast Reconstr Surg 1971;48:419-442. 17. Ortiz Monasterio F, Fuente del Campo A, Carrillo A: Advancement of the orbits and the midface in one piece, combined with frontal repositioning for the correction of Crouzon's deformities. Plast Reconstr Surg 1978;61:507\x=req-\ 516. 18. Raulo Y, Tessier P: Fronto-facial advancement for Crouzon's and Apert's syndromes. Scand J Plast Reconstr Surg 1981;15:245-250. 19. Patten BM: Human Embryology, ed 3. New York, McGraw-Hill International Book Co, 1968. 20. Friede H: Normal development and growth of the human neurocranium and cranial base. Scand J Plast Reconstr Surg 1981;15:163-169. 21. Zellweger H, von Muralt G: Zur Pathologie des Septum pellucidum im Pneumoencephalogram (PEG). Helv Paediatr Acta 1952;7:229-252. 22. Gross H, Hoff H: Sur les malformations ventricularies d\l=e'\pendantesdes dysg\l=e'\n\l=e'\siescommissurales, in Heuyer G, Feld M, Gruner J (eds): Les Malformations Cong\l=e'\nitalesdu Cerveau. Paris, Masson et Cie, 1959, pp 329-351. 23. Trzebicki J, Golabek R: Anomalies du septum pellucidum. Ann Radiol 1969;12:493-497. 24. Bruyn GW: Agenesis septi pellucidi, cavum septi pellucidi, cavum Vergae, and cavum veli interpositi, in Vinken PJ, Bruyn GW (eds): Handbook of Clinical Neurology. Amsterdam, North Holland Publishing Co, 1977, vol 30, chap 13, pp 299-336. 25. Norman RM: Malformation of the corpus callosum, in Blackwood W, McMenemey WH, Meyer A, et al (eds): Grenfield's Neuropathology, ed 2. Baltimore, Williams & Wilkins, 1963, pp 345-347. 26. Blank CE: Apert's syndrome (a type of acrocephalosyndactyly): Observations on a British series of 39 cases. Ann Hum Genet 1960;24:151-164. 27. Vollmer DG, Park TS, Cail WS, et al: Hydromyelia complicating Apert's syndrome: A case report. Neurosurgery 1985;17:70-74. 28. Crome L, Stern J: Pathology of Mental Retardation, ed 2. London, Churchill Livingstone Inc, 1972. 29. Ettlinger G, Blakemore CB, Milner AD, et al: Agenesis of the corpus callosum: A further behavioural investigation. Brain 1974;97:225\x=req-\ 234. 30. Gott PS, Saul RE: Agenesis of the corpus callosum: Limits of functional compensation. Neurology 1979;28:1271-1279. 31. Akelaitis AJ: A study of gnosis, praxis, and language following section of the corpus callosum and anterior commissure. J Neurosurg 1944;1:94-102. 32. Bogen JE: The callosal syndromes, in Heilman KM, Valenstein E (eds): Clinical Neuropsychology, ed 2. New York, Oxford University Press, 1985, chap 11, pp 295-338. 33. Loeser JD, Alvord EC Jr: Agenesis of the corpus callosum. Brain 1968;91:553-570. 34. Rakic P, Yakovlev PI: Development of the corpus callosum and cavum septi in man. J Comp Neurol 1968;132:45-72. 35. Leech RW, Shuman RM: Holoprosencephaly and related midline cerebral anomalies: A review. J Child Neurol 1986;1:3-18. 36. Kl\l=u"\verH, Bucy PC: Preliminary analysis of functions of the temporal lobes in monkeys. Arch Neurol Psychiatry 1939;42:979-1000. 37. Damasio AR, Van Hoesen GW: Emotional disturbances associated with focal lesions of the limbic frontal lobe, in Heilman KM, Satz P (eds): Neuropsychology of Human Emotion. New York, The Guilford Press, 1983, chap 4, pp 85-110. 38. Duyckaerts C, Derouesne C, Signoret JL, et al: Bilateral and limited amygdalohippocampal lesions causing a pure amnesic syndrome. Ann Neurol 1985;18:314-319. 39. Parrish ML, Roessmann U, Levinsohn MW: Agenesis of the corpus callosum: A study of the frequency of associated malformations. Ann Neurol 1979;6:349-354. Neurologic, Audiologic, and Electrophysiologic Sequelae of Bilateral Temporal Lobe Lesions Kennely J. Ho, MD; Paul Kileny, PhD; Daniel Paccioretti, MS; Donald R. McLean, MD \s=b\A 67-year-old woman with demonstrated intact peripheral and brain-stem auditory pathways presented with sudden deafness secondary to sequential bilateral temporal lobe infarcts. Initial examination revealed no behavioral response to sounds and a mild Wernicke's aphasia. Hearing gradually returned but auditory agnosia persists. Changes seen on the computed tomographic scan and the middle latency auditory evoked response over a seven-month period were analyzed and suggest that the peak component of the middle latency response arises from The generator source of the MLR in humans has not been clearly identi¬ fied.1 A myogenic source from overly¬ ing scalp muscles was ruled out as the MLR remained unaffected following administration of neuromuscular Heschl's gyrus. blocking agents.7-8 In an early review, Picton et al4 described several possible (Arch Neurol 1987;44:982-987) neural generator sources for the MLR: Auditory evoked responses have become useful clinical tools for the assessment of auditory dysfunc¬ tion. Recently there has been renewed Accepted for publication June 8, 1987. From the Division of Neurology, Department of Medicine, University of Alberta, Edmonton, Canada (Drs Ho and McLean); Glenrose Rehabilitation Hospital, Edmonton, Canada (Mr Paccioretti); and the Department of Otolaryngology, Head and Neck Surgery, University of Michigan Medical Center, Ann Arbor (Dr Kileny). Reprint requests to the Division of Neurology, Department of Medicine, 2E3.16 Walter Mackenzie Centre, University of Alberta, Edmonton, Canada T6G 2B7 (Dr Ho). interest in the audiologic and neuro¬ logie applications of scalp-recorded middle latency auditory evoked responses.13 The middle latency response (MLR) occurs within 100 ms following an effective auditory stimu¬ lus. In adults the most prominent and robust component of this response is a vertex-positive peak with a latency of 25 to 35 ms, usually labeled Pa.45 The MLR may be recorded over wide regions of the scalp but is usually maximal in amplitude over frontocentral head regions near the vertex.4·6 thalamus, primary auditory cortex, and.association cortex in the frontal, parietal, and temporal lobes. To fur¬ ther isolate these neural substrates, the effects of unilateral human brain lesions in various locations were studied. Patients with confirmed uni¬ lateral temporal lobe lesion but not frontal or parietal lesion demon¬ strated amplitude reduction or ab¬ sence of the Pa component of the MLR in surface recordings over the involved hemisphere.9 The observa¬ tion that the MLR was intact in uni¬ lateral anterior temporal lobectomies Downloaded From: http://archneur.jamanetwork.com/ by a Michigan State University User on 06/15/2015 further narrowed the source of the neural generators to the posterior temporal lobes.1·10 Additional analysis revealed that the midline recorded MLR was the sum of bilateral and symmetrical generators. A lesion in one temporal lobe may diminish, but usually does not abolish a vertexrecorded MLR due to contributions from the intact contralateral tempo¬ ral lobe.6·9 The routine use of a coronal chain of recording electrodes was emphasized in determining the rela¬ tive contributions from either tempo¬ ral lobe.1·9·11 The effects of bilateral temporal lobe lesions on the MLR and on the cortical processing of auditory infor¬ mation have rarely been studied, in part due to the rarity of such cases. The few reports in the recent litera¬ ture have arrived at opposing conclu¬ sions with regard to the role of the primary auditory cortex in the gener¬ ation of the MLR.112·13 This report doc¬ uments the behavioral, electrophysiologic, and computed tomographic (CT) findings in a patient with bilateral temporal lobe infarctions presenting with sudden onset of cortical deaf- ness. Follow-up evaluations in this patient correlating clinical, MLR, and CT scan changes over time help clari¬ fy the neural substrates underlying the MLR. REPORT OF A CASE AND BEHAVIORAL ASSESSMENT A 67-year-old right-handed woman with previously normal hearing was admitted to hospital with sudden onset of complete bilateral hearing loss. There was no dizzi¬ ness, tinnitus, earache, recent upper respi¬ ratory tract infection, head injury, psychi¬ atric disorder, or exposure to ototoxic drugs or excessive noise. Her medical his- Fig 1.—Noncontrast computed tomographic scans in patient on admission (top left), at day 4 (top right), and at seven months (bottom). Arrows point to left primary auditory cortex in superior temporal gyrus. Note resolution of hypodensity in this area by seven months (hypodense is dark and hyperdense is light in shading). Downloaded From: http://archneur.jamanetwork.com/ by a Michigan State University User on 06/15/2015 ent but contained frequent word-finding difficulties and paraphasic errors typical of mild Wernicke's aphasia. An initially noted mild right/left disorientation, acal¬ culia, and finger agnosis resolved com¬ pletely in a few days. A left homonymous visual field defect was detected. Aside from slow imprecise left hand and finger movements and a mild left hyperreflexia, the motor examination results were nor¬ mal. There was astereognosis and tactile extinction of double simultaneous stimula¬ tion in the left hand. Cardiac auscultation revealed normal prosthetic valve sounds and a soft diastolic murmur. Echocardiog¬ raphy demonstrated a normally function¬ ing mitral valve prosthesis, slight dilata¬ tion of the left atrium, and no evidence of thrombus. Prothrombin time on admission was 20.8 s, with a control of 10.6 s. Eight days following admission the patient was able to perceive very loud noises, and several days later, testing revealed near normal hearing levels. Despite this, the patient was unable to make sense of anything she heard. Human voices and environmental sounds seemed "all mixed up together" or "like traffic noise." Over several testing sessions she was unable to identify human speech, musical tunes previously familiar to her, or common environmental sounds such as running water, a door slamming, or hands clapping. By seven months there had been a grad¬ ual improvement in her ability to discrim¬ inate speech, particularly in noncompeting Left-Hemisphere Infarct Right-Hemisphere Infarct Fig 2.—Top, Orientation of computed tomo¬ graphic (CT) scan slices at seven months; CT cuts are at 25° and spaced 5 mm apart. Middle, Reconstructed lateral views of left- right-sided lesions at seven months superimposed over left hemisphere. Bottom, Brodmann's cytoarchitectonic map over region of interest. ANG indicates angular gyrus; SMG, supramarginal gyrus; STG, supe¬ rior temporal gyrus; MTG, middle temporal gyrus; and ITG, inferior temporal gyrus. and tory was significant for an acute left hemi¬ paresis immediately following mitral valve replacement for mitral stenosis eight years previously. With improvement, a residual slight clumsiness of the left hand remained. Speech and hearing were unaf¬ fected at that time. Current medications included digoxin and warfarin sodium (Coumadin). Initial examination revealed an alert oriented woman who spoke in a loud, poor¬ ly modulated voice. She gave no indication of being able to detect any words or sounds and did not startle to loud noises generated by the examiner. Ear canals were clear and tympanic membranes intact. Communica¬ tion was attempted by written instructions and gesturing. The patient responded appropriately to simple written commands but inconsistently to more complex com¬ mands containing two or more steps. Spon¬ taneous speech and oral reading were flu- situations and when allowed to use visual lipreading (see the "Audiologic Assessment" section). A very mild resid¬ ual receptive aphasia was detectable at this time. cues such as CT Scan and Lesion Localization Admission CT scans of the head (Fig 1, top left) revealed a moderately large hypo¬ density in the right temporoparietal cortex and adjacent subcortical white matter con¬ sistent with an old infarct. In addition, a smaller area of hypodensity was seen in the left posterior superior temporal region including Heschl's gyrus (arrow). This leftsided lesion on repeated CT scanning four days later (Fig 1, top right) demonstrated areas of increased density indicating an evolving hemorrhagic infarct. At seven months, selective CT cuts were made utilizing sections 5 mm thick ori¬ ented 25° to the anthropologie baseline (Figs 1, bottom, and 2, top). This technique allowed for precise anatomic localization of the lesions using the templates of Gado et al14 as references. The older and larger right-sided infarct was seen to involve Brodmann's areas 41 and 42 (Heschl's gyrus), 22, 39, and 40. The smaller leftsided lesion at seven months included the majority of area 22 posteriorly and a small rim of the adjacent areas 39 and 42 (Fig 2, middle and bottom). Of interest is that area 41 of Heschl's gyrus on the left, previously noted to be hypodense on the admission CT scans, appeared to be normal in density at seven months. Other areas of the brain initially noted to be hypodense remained so on the subsequent follow-up scan. No abnormality was seen in the brain stem on any of the CT studies. Audiologic Assessment Audiologic tests two days following admission revealed absence of response to pure tones and speech (Spondee word list) at the output limits of the audiometrie equipment (Fig 3, top left). Tympanograms and acoustic stapedial reflex thresholds elicited by pure tone activators ranging in frequency from 500 to 4000 Hz were normal bilaterally. A repeated audiogram 15 days following admission documented considerable im¬ provement (Fig 3, top right). Pure tone thresholds at this time in both ears ranged between 10 and 20 dB hearing level (HL) across test frequencies, while acoustic sta¬ pedial reflex thresholds remained un¬ changed. Speech awareness thresholds were 15-dB HL bilaterally, consistent with the patient's pure tone thresholds. Howev¬ er, utilizing an open set of record speech materials (W22, lists IB and 2B), it was impossible to obtain any measurable speech discrimination. In addition, the patient was unable to identify any re¬ corded animal or instrumental sounds. Taken together, the audiologic test results indicated that the peripheral hear¬ ing apparatus, cochlear, and eight nerves were intact bilaterally. The marked dis¬ crepancy between speech awareness and speech discrimination suggested a central auditory lesion. At follow-up evaluation at seven months (Fig 3, bottom left), pure tone and speech awareness thresholds remained stable. Utilizing a closed set of recorded speech materials (California Consonant Test; Auditec, St Louis) and with visual cues eliminated, 60%- to 65%-correct discrimi¬ nation scores were obtained. The patient was able to recognize a few environmental sounds (eg, telephone, doorbell, and air¬ plane) but remained unable to recognize music. EVOKED POTENTIAL STUDIES Brain-stem auditory evoked responses (BAERs) were recorded with a vertex to ipsilateral earlobe electrode configuration and were elicited by broad-band rarefac¬ tion clicks presented at 70 and 80 dB normal HL (nHL) at a rate of 11.1 per second for 1024 sweeps. Two responses were obtained for each stimulus condition (Fig 4). The low- and high-pass filters were set at 150 and 3000 Hz, respectively. The patient was quietly asleep during the ini¬ tial recording on day two. The MLRs were elicited by 60-dB nHL clicks presented monaurally to left and right ears sequentially at a rate of 9.1 to 9.7 per second. The electroencephalogram was differentially amplified (40000 times) and band-pass filtered (5 to 1500 Hz, 12 dB per octave). Each response consisted of the summation of 2000 accepted sweeps (grand average of two responses each consisting of 1000 accepted sweeps) with a duration of 102.4 ms. Responses were recorded simul¬ taneously at three scalp locations in the Downloaded From: http://archneur.jamanetwork.com/ by a Michigan State University User on 06/15/2015 Audiogram Frequency, c/s 125 250 500 Frequency, c/s 125 1000 2000 4000 8000 3000 6000 750 1500 10- 10 o 0 10 10 - 20 20 250 500 1000 750 »- 2000 1500 4000 3000 *=k~<& 8000 6000 & - 30 30 - 40- 40 50 50 60 60 70 70 80 80 A · 90 A~A ± A A 100110 A- 90 100 110 · SAT Speech Discrimination Legend Day 2 No Response 0% (Open Set) Q Left Ear Day 15 15 dB (Both Ears) 0% (Open Set) X : Right Ear 7 mo 15 dB (Both Ears) : 60% to 65% : Acoustic Stapedial Reflex Thresholds (Closed Set of Words) Fig 3.—Results of audiologic assessment on day 2 (top left), on day 15 (top right), and at seven months. SAT Indicates speech awareness threshold. coronal plane as follows (10- to 20-electrode system): vertex (CJ; right and left central electrodes just above the sylvian fissures (C6 and C5, respectively). All active electrodes were referenced to common linked earlobe electrodes. During testing the patient was awake and resting com¬ fortably. For comparison purposes, Fig 5, top, illustrates MLRs elicited by left and right ear monaural stimulation from a normal subject recorded as described above. Ver¬ tex-positive peaks at 29.6 ms for left ear stimulation and 30.8 ms for right ear stim¬ ulation corresponded to the Pa component of the MLR. While the responses recorded at various electrode locations exhibited the same latency characteristics, the Pa peak amplitude was larger at the vertex than at the supratemporal electrode sites. Mean Pa latency obtained from five neu¬ rologically normal individuals was 27.7 ± 2.1 ms SD for the left ear and 27.8 ± 2.2 ms for the right ear. Mean Pa amplitudes were 0.96 ± 0.48 pV for the left ear and 0.94 ± 0.49 mV for the right ear.11 RESULTS The BAERs recorded on day two in our patient are illustrated in Fig 4. The configuration and the latency measurements obtained (both inter- peak and absolute) were within nor¬ mal limits bilaterally, suggesting intact brain-stem pathways for audi¬ tory information. Subsequent BAERs recorded during convalescence utiliz¬ ing the above technique as well as with simultaneous MLR recordings remained essentially unchanged. The MLRs were first recorded 15 days following admission (Fig 5, mid¬ dle). With right ear stimulation, no activity was recorded beyond the auditory brain-stem response complex over the right hemisphere and at the vertex. Over the left hemisphere, the brain-stem response complex was fol¬ lowed by a postauricular muscle reflex5 and a small (0.28 µ ) vertexpositive peak with a latency of 33 ms. This latter peak over the left hemi¬ sphere was evident with both left and right monaural stimulation and prob¬ ably represented a delayed and mark¬ edly attenuated Pa component of the MLR. The MLRs recorded at seven months (on the same date as the audi¬ ologic evaluation illustrated in Fig 3, bottom) are shown in Fig 5, bottom. At this time a vertex-positive poten¬ tial with a latency of just over 35 ms was evident at all electrode locations and was thought to represent a slight¬ ly delayed Pa component of the MLR. Its amplitude was largest (0.61 µ, ) over the left hemisphere (C5) with both left and right ear monaural stim¬ ulation. COMMENT The human auditory cortex is lo¬ cated in the posterior superior aspect of the temporal lobes bilaterally and the primary auditory cortex resides in the transverse temporal gyri of Heschl on each side. At the cortical level, hearing is bilaterally repre¬ sented, although each temporal lobe receives a greater input from the con¬ tralateral ear.15 Unilateral lesions of the auditory cortex do not cause an elevation of hearing thresholds. Bilat¬ eral temporal lobe lesions, however, are known to produce a continuum of deficits ranging from auditory agno¬ sia for speech or nonspeech sounds, with relatively normal hearing thresholds, to rare cases of cortical Downloaded From: http://archneur.jamanetwork.com/ by a Michigan State University User on 06/15/2015 1(1.8) V(6.1) III (4.4) \ Right Ear Left Ear / - 80 dB 70 dB í__^ -I_I_1_ -j_ _i_ Left Ear 1(1.8) 111(4.1) V (6.2) 0.25 /iV |\ \ c>V%a-vv 80 dB 70 dB t_^ Right Ear J_ _i_ -J-1-1_1_ 10 ms Fig 4.—Brain-stem auditory evoked responses elicited by 80-dB and 70-dB normal hearing level clicks on day 2. Fig 5.—Middle latency auditory evoked responses with left and right monaural stimulation and recording from left central (C5), vertex (C,), and right central (C6) electrodes. PAMR indicates postauricular muscle 0.5 mV 50 ms reflex. deafness characterized by markedly elevated pure tone thresholds.16 There are over 20 well-documented cases of cortical deafness in the litera¬ ture,13·1726 usually the results of isch¬ emie infarcts in both temporal lobes at different times,17·18·20"23·25 as in our case. A unique case of cortical deaf¬ ness due to bilateral thalamic lesions has recently been published.29 The patient in this report sustained an earlier right-hemispheric infarct that destroyed the primary auditory cortex but produced no apparent hear¬ ing deficit. However, following an acute left-hemispheric infarct that involved the remaining primary audi¬ tory cortex, a state of profound deaf¬ ness resulted. A mild receptive apha- sia correlated with involvement of the adjacent Wernicke's area on the left. The location of the new infarct on the lower bank of the sylvian fissure, its later evolution to a hemorrhagic lesion, and the existence of a potential source of emboli from a prosthetic heart valve suggested an embolie mechanism. The audiologic assessment includ¬ ing normal tympanograms, acoustic stapedial reflex thresholds, and BAERs ruled out the presence of sig¬ nificant middle ear, cochlear or eighth nerve, or brain-stem causes for the profound hearing impairment. The marked discrepancy between the awareness and discrimination of com¬ plex sounds including speech follow- ing the progressive return of hearing in the second week suggested a central auditory lesion. The evolution from a state of cortical deafness (or extreme lack of awareness of any sounds) to a state of auditory agnosia for speech and environmental sounds has been noted by others.17·18·20·25 However, ana¬ tomic correlates of this change have not previously been demonstrated, to our knowledge. In our patient there was a brief interval of no more than two weeks between the initial absence of any response to pure tones and speech (at the limits of the audiometrie equip¬ ment) to a state characterized by nor¬ mal hearing sensitivity yet marked impairment of speech recognition. Downloaded From: http://archneur.jamanetwork.com/ by a Michigan State University User on 06/15/2015 was followed by gradually improving discrimination of both speech and environmental sounds over the ensuing weeks and months. This course of events suggests rapid and early reversibility of damage to the left primary auditory cortex but a more limited recovery in the adjacent auditory association cortex. Indeed, comparing the CT scan on admission to that obtained at seven months, one sees that the initial hypodensity in This Heschl's gyrus on the left had subse¬ quently become isodense in keeping with some return of viability to the primary auditory cortex (arrows, Fig 1, top left and bottom). This initial hypodensity likely represented edema and reversible ischemie change rather than infarction. On the other hand, persistent hypodensity noted in area 22 at seven months is taken to repre¬ sent infarction in the adjacent audito¬ ry association cortex. There has been one previously reported case25 in which the authors described a patient with bilateral temporal lobe lesions in whom an initially absent cortical evoked re¬ sponse subsequently returned. Unfor¬ tunately, no latency measurements were reported to determine whether these were middle or long latency potentials. In our patient the Pa com¬ ponent of the MLR was barely detect¬ able on the left (C5) and absent on the right (C6) on initial testing two weeks following the left-sided infarct and shortly after pure tone thresholds had returned to normal (15-dB HL). When MLRs were measured again at seven months, an increase in the amplitude of Pa was noted, especially over the left hemispheres (C5), along with a slightly prolonged latency. Drawing a parallel between the improvement seen in the CT scan in Heschl's gyrus and the improvement noted in the MLR, we suspect that Heschl's gyrus (approximately Brodmann's areas 41 and 42) may be the generator site of the Pa component of the MLR. An alternative possibility is that the Pa component of the MLR originates from further afield in the auditory association cortex of area 22. This possibility is not as attractive, since the CT scan at seven months demon¬ strates that much of this area had been destroyed, nor is the MLR likely to arise from frontal or parietal opercular regions, association cortices, or the medial geniculate body of the thalamus, as these structures had been spared from the beginning. Direct mapping of the human audi¬ tory cortex during operative proce¬ dures provides further support for this localization.27·28 Vertex-positive potentials with a mean latency of 32.2 ± 4.1 ms, labeled P2, were obtained with greatest consistency from recording electrodes directly over the transverse temporal gyrus (of Heschl),27 whereas recording elec¬ trodes situated over the adjacent lat¬ eral surface of the superior temporal gyrus (area 22) and the frontal and parietal opercula gave rise to relative¬ ly longer latency potentials, which were labile, variable, and small. Subdurally located electrodes28 recorded maximal amplitude auditory evoked responses with a major positive peak latency of 28.8 ± 0.3 ms when elec¬ trodes were placed parallel to the sylvian fissure adjacent to its halfway point corresponding to the region of Heschl's gyrus. Our findings support the suggestion that the Pa component of the MLR in humans is a bilaterally generated response arising from the primary auditory cortex in Heschl's gyrus. It demonstrates that Heschl's gyrus is important in the basic perception of sounds, while the adjacent auditory association cortex probably mediates higher-level, more discriminatory roles in speech and sound perception. The case also demonstrates that corti¬ cal deafness can evolve over time into a state of auditory agnosia and that this change can be followed by clini¬ cal, anatomic, and electrophysiologic correlations. Additional study of clini¬ cal cases with unilateral and bilateral cortical lesions combining careful electrophysiologic techniques with precise anatomic localization using CT, magnetic resonance, or autopsy findings would help to shed further light on both the components of the middle and late latency auditory evoked responses and the cortical pro¬ cessing of auditory information. References 1. 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Woods DL, Clayworth CC, Knight RT, et al: Generators of middle- and long-latency auditory evoked potentials: Implications from studies of patients with bitemporal lesions. Electroencephalogr Clin Neurophysiol 1987;68:132-148. 27. Celesia GG: Organization of auditory cortical areas in man. Brain 1976;99:403-413. 28. Lee YS, Lueders H, Dinner DS, et al: Recording of auditory evoked potentials in man using chronic subdural electrodes. Brain 1984; 107:115-131. 29. Motomura N, Yamadori A, Mori E, et al: Auditory agnosia: Analysis of a case with bilateral subcortical lesions. Brain 1986;109:379-391. Downloaded From: http://archneur.jamanetwork.com/ by a Michigan State University User on 06/15/2015