AUDITORY CORTICAL RESPONSES IN HUMANS WITH CONGENITAL UNILATERAL CONDUCTIVE HEARING-LOSS

We recorded auditory evoked magnetic fields from 6 patients with conge nital unilateral conductive hearing disorder with a 122-channel whole- head neuromagnetometer. The stimuli were 50-ms 1-kHz tones delivered t o the better ear at interstimulus intervals (ISIs) of 2 and 8 s at two different intensities (50 and 70 dB HL). As in normal-hearing subject s, the amplitudes of N100m, the 100-ms response, were larger in 5 pati ents and the latencies were shorter in 3 patients over the hemisphere contralateral to stimulation. However, in one patient N100m peaked alr eady at 61 ms over the contralateral hemisphere and amplitudes were la rger over the ipsilateral hemisphere, possibly reflecting reorganizati on of the auditory pathways. In 3 patients the latencies were shorter over the ipsilateral hemisphere. The effects of ISI and intensity were similar over both hemispheres and did not differ from those in contro ls. It seems that congenital unilateral conductive hearing loss does n ot necessarily lead to any gross disturbances in the human auditory co rtex.