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We recorded the auditory-evoked fields in five patients with psychogenic hearing impairment and ten healthy controls. The maximum N100m peak amplitude and latency were measured under 1000 and 2000-Hz tone burst stimuli in each ear. The mean N100m amplitude in the patients was smaller than that in the controls. Especially, regardless of the side of stimulation, the mean amplitude in the left-hemisphere was significantly smaller in the patients than in the controls, except for the 2000-Hz stimulus condition in the left ear. There was no significant difference in the latency of the N100m peak between patients and controls. We attribute the findings of attenuation of the N100m amplitude to the peculiar auditory perception in patients with psychogenic hearing impairment. Concerning the cause of this finding, we suggest two possible mechanisms: inhibitory auditory processing and attention deficit.

Auditory evoked magnetic field (AEF) is known to be suitable to separate left and right hemispheric activities while auditory evoked potential is not. To evaluate cortical auditory function in ten patients with temporal lobe gliomas, we measured AEF for monaural tone stimuli using a helmet-shaped 66-channel MEG system. Latency of the N 100 m, the most prominent peak with a latency around 90 ms, was measured in the hemisphere contralateral to the stimulus onset. In five patients, the N 100 m latency was within our normal range (mean +/- 2 s.d.). In these five cases, tumor was located in the anterior or the inferior part of the temporal lobe. We observed significant delay of the N 100 m latency in four patients and disappearance of the N 100 m in another patient. In the later five patients, tumor extended to the superior and posterior part of the temporal lobe. AEF can be used to evaluate cortical auditory function noninvasively in cases with temporal lobe gliomas.