Effects of profound deafness on the plasticity of central auditory system

采用正电子发射断层扫描(PET)技术，对人工耳蜗术后、语前聋患者和正常受试者在噪声和语音听力过程中三个感兴趣区的脑活动进行了测量。在正常和语后聋受试者中，当听到噪声或语音时，初级听区的局部脑血流量(RCBF)增加约10%。只有语音增加了听觉关联区的rCBF，噪声增加了2%的rCBF，语音刺激增加了9%~16%的rCBF。因此，我们认为听觉关联区参与了语音识别，语后聋人工耳蜗者可能正在使用听觉关联区的正常语言网络。而在语前聋人工耳蜗组，噪声和言语引起的初级听区rCBF增加幅度均低于正常或语后聋组，分别为3%~6%和1%~3%，而听觉联想区的言语激活率明显低于两者。如果受试者在早期失去听力，中央听觉皮质神经网络的发育可能不完整或采取不同的过程。在所谓的语音获取期间，如果没有适当的语音刺激，用于口语识别的网络可能不会正常发展。据报道，在2岁和3岁左右接受人工耳蜗术的语前聋儿获得了良好的语音识别和产生能力。这类儿童的皮质语言网络是否发育正常，可能会在未来的PET研究中得到阐明。

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.