Sound-induced activation of auditory cortices in patients with inner-ear hearing loss

Abstract

Studies on sound-induced activation of auditory cortices in patients with inner-ear hearing loss were reviewed. First, we recorded auditory evoked magnetic fields (AEFs) by presenting 1-kHz pure tone at four different intensities in normal subjects and in patients with inner-ear hearing loss. Increment of dipole moment of N100m was more rapid according to the stimulus intensity in patients compared with that in healthy subjects. Next, we measured AEFs by presenting white noise and speech-related sounds. AEF responses in patients were less dependent on the acoustic structure of the stimuli than in normal subjects. Although the N100m moments were larger in the right hemisphere in normal subjects, such interhemispheric differences were not identified in the patient group. In the third study, we made two word lists, well-perceived and poorly perceived words, and measured rCBF during their monaural presentation. Well-perceived words activated bilateral temporal lobes and left angular gyrus (AG), while poorly perceived words activated only the temporal lobe contralateral to the stimulated ear and little or no activation was observed in AG.