AUDITORY CORTICAL RESPONSES IN HUMANS WITH PROFOUND UNILATERAL SENSORINEURAL HEARING-LOSS FROM EARLY-CHILDHOOD

We recorded auditory evoked magnetic fields from five patients with pr ofound unilateral sensorineural hearing loss from early childhood, usi ng a 122-channel whole-scalp neuromagnetometer. The stimuli were 50-ms 1-kHz tone bursts delivered to the healthy ear at interstimulus inter vals (ISI) of 1, 2, and 4 s. As the normal-hearing controls, four pati ents had shorter latencies of N100m, the 100-ms response, over the hem isphere contralateral to the stimulation than over the ipsilateral hem isphere. With 1-s ISI, three patients had, instead of N100m, a deflect ion of opposite polarity at about 100 ms (P100m) after the stimulus on set. A 10-year-old patient had a prominent P100m response, did not pro duce a clear N100m at any ISI, but had a clear N50m at the 4-s ISI. Fo ur patients had bilateral N200m deflections peaking about 200 ms after the stimulus onset; the fifth patient showed N200m over the right hem isphere. N200m was also observed in the three youngest controls in bot h hemispheres. The ISI dependence of N100m amplitude and latency was s imilar in controls and patients. The amplitudes and latencies of N200m did not show any ISI dependence. In patients, the appearance of P100m -N200m deflections of auditory evoked fields, normally present in chil dren, is more pronounced than in controls. The defect apparently delay s the development of N100m, possibly by interfering with function of c allosal connections.