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，测量了人工耳蜗植入后和语前聋患者及正常人在噪声和言语声听觉过程中三个感兴趣区域的脑活动。在正常人和语后聋受试者中，噪声或言语声听觉使初级听觉区的局部脑血流量（rCBF）增加约10%。只有语音刺激使听觉联合区的rCBF增加，噪声使rCBF增加2%，语音刺激使rCBF增加9%~ 16%。因此，有人建议，听觉联想区参与语音识别，和语后聋人工耳蜗用户可能使用正常的语言网络中的听觉联想区。而在语前聋人工耳蜗植入者中，噪声和言语诱发的初级听觉区rCBF增加均低于正常人或语后聋受试者，范围为3 ~ 6%，听觉联合区言语激活明显低于其他两组，范围为1 ~ 3%。如果受试者在早期失去听力，中央听觉皮层的神经网络的发育可能是不完整的，或者采取不同的课程。在所谓的语音获取阶段，如果没有合适的语音刺激，口语识别网络可能无法正常发展。据报道，大约在2岁和3岁时接受人工耳蜗植入的语前聋婴儿获得了良好的识别和言语产生。这类儿童的皮质语言网络是否发育正常，可能在未来的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.