Effects of profound deafness on the plasticity of central auditory system

点击翻译按钮获取中文摘要

Brain activities in three regions of interest during noise and speech sound hearing were measured in post-and prelingually deaf cochlear implant users and in normal subjects by using positron emission tomography (PET). In normal and postlingually deaf subjects, regional cerebral blood flow (rCBF) in the primary auditory area increased by about 10% with noise or speech sound hearing. Only speech sound increased rCBF in the auditory association area ; 2% rCBF increase for noise and 9 to 16% rCBF increase for speech stimulation. Consequently, it was suggested that the auditory association area is involved in speech sound recognition, and that postlingually deaf cochlear implant users may be using normal language networks in the auditory association area. In prelingually deaf cochlear implant users, on the other hand, both noise and speech induced rCBF increase in the primary auditory area was lower than in normal or postlingually deaf subjects ranging from 3 to 6%, and speech activation in the auditory association area was much less than in the oher two groups ranging from 1 to 3%. Development of neural networks in the central auditory cortex may be incomplete or take different courses if the subjects lose hearing in early life. Networks for spoken language recognition may not develop normally without appropriate speech sound stimulation during so called speech acquisition period. It has been reported that prelingually deaf infants who received cochlear implant around the age of 2 and 3 acquire good recognition and production of speech. Whether cortical language networks in such children develop normally or not may be elucidated in the future PET study.