Categorical perception mechanism in the auditory cortex and its plasticity

基于PET（正电子发射断层扫描）对正常听力者、内耳听力损失者和深度耳蜗使用者的口语加工中枢机制的研究结果，我们认为听觉皮层的分类知觉神经网络可能位于上颞叶皮层和中颞叶皮层的中部。对人工耳蜗编码的扭曲和不完整的语音信号的感知可能需要语音处理网络的过度活动，在这种情况下被强烈激活的颞中回中部可能在分类感知中起重要作用。据报道，颞中回神经元的兴奋性反应与某些音素或韵律特征没有密切联系，退化的和不完整的语音信号可能是基于粗糙编码识别的语音信号，在粗糙编码中，由一群更粗糙的单元准确地指定一个值。在处理退化和模糊的声刺激时，粗糙的编码策略可能需要在听觉皮层中大量招募神经元，这可能是CI使用者颞叶皮层强烈言语激活的基础。在这种情况下，布洛卡区和辅助运动区（SMA）表现出强烈的言语激活。SMA是一个高阶运动区域，已知它是由运动序列的纯粹内部排练激活的。该区域与布洛卡区通过长束连接，通常在建立包括语言和日常技能在内的运动序列程序时被激活。布洛卡区通过弓形神经束与听觉关联区相连。假设有一个由SMA、Broca区和听觉关联区组成的微电路，用来建立语言解码和编码的工作记忆，使大脑能够保持原始听觉信息的内部副本。这种内部回放机制可能会被更多地激活，以完成对不完整语音信号的准确分类感知，识别受损内耳或CI编码的音素或单词通常是困难的，并且需要将听到的信息与存储的类似单词版本进行多次比较。为了验证这一假设，有必要对每个区域的功能解剖进行更多的研究。少

Based on PET (positron emission tomography) findings on central mechanisms for spoken language processing in normal hearing subjects, those with inner ear hearing loss and in profoundly deaf cochlear implant (CI) users, it has been suggested that the neuronal networks for categorical perception in the auditory cortex may be located in the mid portion of the superior and middle temporal cortex. Perception of distorted and incomplete speech signals coded by cochlear implant may require excessive activity of speech processing networks, and the mid portion of the middle temporal gyrus, that is strongly activated under such condition, may play an important role in categorical perception. It was reported that the excitatory responses of neurons in the middle temporal gyrus had no close links to certain phonemic or prosodic features, and the degraded and incomplete speech signals may be recognized as speech on the basis of coarse coding, in which a profile of responses from a population of co … More arsely tuned units accurately specify a value. A coarse coding strategy may require extensive recruitment of neurons in the auditory cortex during processing degraded and ambiguous acoustic stimuli, which possibly underlie strong speech activation of the temporal cortex in CI users. Under such condition, the Broca's area and the supplementary motor area (SMA) exhibited strong speech activation. The SMA is a higher-order motor area and is known to be activated by pure internal rehearsal of motor sequences. This area is connected by long tracts with Broca's area, and is commonly activated when establishing programs for motor sequences including speech and daily skills. Broca's area has connections with the auditory association area via the arcuate fascicles. A hypothetical microcircuit consisting of the SMA, Broca's area and the auditory association area is supposed to establish working memory for language decoding and encoding, enabling the brain to maintain an internal copy of the original auditory message. Such an internal playback mechanism might be activated more to accomplish accurate categorical perception of incomplete speech signals, recognizing phonemes or words coded by damaged inner ear or by CI is often difficult, and requires comparison of the heard message several times with the stored versions of similar words. More studies focused on the functional anatomy of each area are necessary to verify this hypothesis. Less