Sakai Masashi, Chimoto Sohei, Qin Ling, Sato Yu
Department of Physiology, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Yamanashi, Japan.
BMC Neurosci. 2009 Feb 10;10:10. doi: 10.1186/1471-2202-10-10.
Primary auditory cortex (AI) neurons show qualitatively distinct response features to successive acoustic signals depending on the inter-stimulus intervals (ISI). Such ISI-dependent AI responses are believed to underlie, at least partially, categorical perception of click trains (elemental vs. fused quality) and stop consonant-vowel syllables (eg.,/da/-/ta/continuum).
Single unit recordings were conducted on 116 AI neurons in awake cats. Rectangular clicks were presented either alone (single click paradigm) or in a train fashion with variable ISI (2-480 ms) (click-train paradigm). Response features of AI neurons were quantified as a function of ISI: one measure was related to the degree of stimulus locking (temporal modulation transfer function [tMTF]) and another measure was based on firing rate (rate modulation transfer function [rMTF]). An additional modeling study was performed to gain insight into neurophysiological bases of the observed responses.
In the click-train paradigm, the majority of the AI neurons ("synchronization type"; n = 72) showed stimulus-locking responses at long ISIs. The shorter cutoff ISI for stimulus-locking responses was on average ~30 ms and was level tolerant in accordance with the perceptual boundary of click trains and of consonant-vowel syllables. The shape of tMTF of those neurons was either band-pass or low-pass. The single click paradigm revealed, at maximum, four response periods in the following order: 1st excitation, 1st suppression, 2nd excitation then 2nd suppression. The 1st excitation and 1st suppression was found exclusively in the synchronization type, implying that the temporal interplay between excitation and suppression underlies stimulus-locking responses. Among these neurons, those showing the 2nd suppression had band-pass tMTF whereas those with low-pass tMTF never showed the 2nd suppression, implying that tMTF shape is mediated through the 2nd suppression. The recovery time course of excitability suggested the involvement of short-term plasticity. The observed phenomena were well captured by a single cell model which incorporated AMPA, GABAA, NMDA and GABAB receptors as well as short-term plasticity of thalamocortical synaptic connections.
Overall, it was suggested that ISI-dependent responses of the majority of AI neurons are configured through the temporal interplay of excitation and suppression (inhibition) along with short-term plasticity.
初级听觉皮层（AI）神经元对连续听觉信号表现出性质上不同的反应特征，这取决于刺激间隔（ISI）。这种依赖ISI的AI反应被认为至少部分地构成了对点击序列（基本与融合性质）和塞音-元音音节（例如，/da/-/ta/连续体）的范畴知觉基础。
对116只清醒猫的AI神经元进行单细胞记录。矩形点击单独呈现（单点击范式）或以具有可变ISI（2 - 480毫秒）的序列形式呈现（点击序列范式）。AI神经元的反应特征被量化为ISI的函数：一种测量与刺激锁定程度相关（时间调制传递函数[tMTF]），另一种测量基于放电率（率调制传递函数[rMTF]）。进行了一项额外的建模研究，以深入了解观察到的反应的神经生理基础。
在点击序列范式中，大多数AI神经元（“同步类型”；n = 72）在长ISI时表现出刺激锁定反应。刺激锁定反应的较短截止ISI平均约为30毫秒，并且根据点击序列和辅音-元音音节的知觉边界具有水平耐受性。这些神经元的tMTF形状要么是带通要么是低通。单点击范式最多揭示了四个按以下顺序的反应期：第一次兴奋、第一次抑制、第二次兴奋然后第二次抑制。第一次兴奋和第一次抑制仅在同步类型中发现，这意味着兴奋和抑制之间的时间相互作用构成了刺激锁定反应的基础。在这些神经元中，表现出第二次抑制的神经元具有带通tMTF，而具有低通tMTF的神经元从未表现出第二次抑制，这意味着tMTF形状是通过第二次抑制介导的。兴奋性的恢复时间进程表明涉及短期可塑性。通过一个包含AMPA、GABAA、NMDA和GABAB受体以及丘脑皮质突触连接的短期可塑性的单细胞模型很好地捕捉到了观察到的现象。
总体而言，提示大多数AI神经元的ISI依赖性反应是通过兴奋和抑制（抑制）的时间相互作用以及短期可塑性来构建的。
