Brain Function in Patients with Hearing Loss

The most frequent complaint of individuals with hearing loss is poor understanding of spoken language. Recent findings in the study of the function of brain, the final site of language recognition, examined among individuals with hearing loss are as follows. In prelingually deaf children, language recognition usually does not improve much with input from cochlear implant, but we experienced one case who showed apparent activity in the auditory association areas in the brain by PET several years after cochlear implantation. This indicates the possibility of new formation of the neural networks for language recognition in the temporal lobe. Examining patients with dysacusis by MEG, we observed an interesting tendency. The response of these individuals to noise was comparatively large, resulting in diminution of differences in the brain response between noise and language. In PET studies of patients with cochlear hearing loss, we failed to observe significant activation in the right hemisphere by language stimulation. Thus, degree of activation of the right temporal lobe by language stimulation may be utilized as one of the indices for the estimation of language recognition or effects of hearing aids in patients with hearing loss. In the future, clarification of the mechanism of hearing loss and development of its treatment are expected from the viewpoint of language recognition in the brain.