Tsuchitani C
Medical School, University of Texas Health Sciences Center at Houston 77030-2901, USA.
Hear Res. 1997 Mar;105(1-2):211-24. doi: 10.1016/s0378-5955(96)00212-2.
The medial nucleus of the trapezoid body (MNTB) contains components of a neural network that functions as an interaural level difference (ILD) detector. In the cat, lateral superior olivary (LSO) neurons compare the contralateral inhibitory input from the MNTB with an excitatory input form the ipsilateral anteroventral cochlear nucleus to extract information about binaural stimuli. To better specify the inhibitory inputs to the LSO and gain a better understanding of the inhibitory component of the LSO network, the response characteristics of MNTB neurons were examined in cats under stimulus conditions similar to those used to study LSO inhibitory responses. The inhibitory tuning curves of LSO units were wider than the tuning curves of MNTB units. Hence, MNTB neurons with similar, but not identical, characteristic frequencies converge to provide inhibitory input to single LSO neurons. Variations in the number of converging MNTB inputs produced a range of LSO excitatory-inhibitory threshold differences, thus creating a coding mechanism for representing the ILD. Convergence of MNTB inputs also increased the dynamic range over which contralateral stimulus level effects LSO binaural responses beyond the dynamic ranges of individual MNTB units, thus expanding the ILD range encoded by the LSO network. The differences between the first-spike latencies of MNTB and LSO tone burst responses were small and the precision of the LSO first-spike discharges was significantly greater than that of MNTB units. As tone bursts delivered simultaneously to the two ears can consistently inhibit LSO first-spike discharges, the inhibitory input must match the LSO precision by converging a number of the more variably timed MNTB discharges. Because of their precision LSO first-spike discharges may be used to encode interaural time-of-arrival differences of mid- to high-frequency transients. These findings add to the foundation for a comprehensive network model that describes the inputs to the LSO as point processes, delimits the biophysical mechanisms underlying excitatory and inhibitory interactions at the single neuron level, and reveals how these inputs determine the response to different binaural stimulus conditions.
梯形体内侧核（MNTB）包含神经网络的组成部分，该神经网络起着耳间声级差（ILD）检测器的作用。在猫中，外侧上橄榄核（LSO）神经元将来自MNTB的对侧抑制性输入与来自同侧前腹侧耳蜗核的兴奋性输入进行比较，以提取有关双耳刺激的信息。为了更明确地确定输入到LSO的抑制性输入，并更好地理解LSO网络的抑制性成分，在与用于研究LSO抑制性反应相似的刺激条件下，对猫的MNTB神经元的反应特性进行了研究。LSO单位的抑制性调谐曲线比MNTB单位的调谐曲线更宽。因此，具有相似但不相同特征频率的MNTB神经元汇聚在一起，为单个LSO神经元提供抑制性输入。汇聚的MNTB输入数量的变化产生了一系列LSO兴奋-抑制阈值差异，从而创建了一种用于表示ILD的编码机制。MNTB输入的汇聚还增加了动态范围，在该动态范围内，对侧刺激水平影响LSO双耳反应的范围超出了单个MNTB单位的动态范围，从而扩大了LSO网络编码的ILD范围。MNTB和LSO短纯音反应的首次放电潜伏期之间的差异很小，并且LSO首次放电的精度明显高于MNTB单位。由于同时传递到双耳的短纯音可以持续抑制LSO的首次放电，抑制性输入必须通过汇聚一些时间变化更大的MNTB放电来匹配LSO的精度。由于LSO首次放电具有精确性，它们可用于编码中高频瞬态的耳间到达时间差异。这些发现为一个全面的网络模型奠定了基础，该模型将输入到LSO的信号描述为点过程，界定了单个神经元水平上兴奋和抑制相互作用的生物物理机制，并揭示了这些输入如何决定对不同双耳刺激条件的反应。
