Kato Takayuki, Fujita Kazuhisa, Kashimori Yoshiki
Graduate School of Information Systems, Univ. of Electro-Communications, Chofu, Tokyo 182-8585 Japan.
Dept. of Engineering Science, Univ. of Electro-Communications, Chofu, Tokyo 182-8585 Japan; National Institute of Technology, Tsuyama Collage, 654-1 Numa, Tsuyama, Okayama 708-8506, Japan.
Biosystems. 2015 Aug;134:24-36. doi: 10.1016/j.biosystems.2015.05.007. Epub 2015 May 29.
The central nucleus of the inferior colliculus (ICc) is an auditory region that receives convergent inputs from a large number of lower auditory nuclei. ICc neurons phase-lock to low frequencies of sinusoidally amplitude-modulated (SAM) signals but have a different mechanism in the phase-locking from that in neurons of lower nuclei. In the mustached bat, the phase-locking ability in lower nuclei is created by the coincidence of phase-locked excitatory and inhibitory inputs that have slightly different latencies. In contrast, the phase-locking property of ICc neurons is little influenced by the blocking of inhibitory synapses. Moreover, ICc neurons exhibit different characteristics in the spike patterns and synchronicity, classified here by three types of ICc neurons, or sustained, onset, and non-onset phase-locking neurons. However it remains unclear how ICc neurons create the phase-locking ability and the different characteristics. To address this issue, we developed a model of ICc neuronal population. Using this model, we show that the phase-locking ability of ICc neurons to low SAM frequencies is created by an intrinsic membrane property of ICc neuron, limited by inhibitory ion channels. We also show that response characteristics of the three types of neurons arise from the difference in an inhibitory effect sensitive to SAM frequencies. Our model reproduces well the experimental results observed in the mustached bat. These findings provide necessary conditions of how ICc neurons can give rise to the phase-locking ability and characteristic responses to low SAM frequencies.
下丘中央核（ICc）是一个听觉区域，它接收来自大量低位听觉核团的汇聚输入。ICc神经元对正弦幅度调制（SAM）信号的低频进行锁相，但在锁相机制上与低位核团的神经元不同。在髯蝠中，低位核团的锁相能力是由潜伏期略有不同的锁相兴奋性和抑制性输入的巧合产生的。相比之下，ICc神经元的锁相特性受抑制性突触阻断的影响较小。此外，ICc神经元在放电模式和同步性方面表现出不同的特征，在此分为三种类型的ICc神经元，即持续、起始和非起始锁相神经元。然而，目前尚不清楚ICc神经元如何产生锁相能力和不同的特征。为了解决这个问题，我们构建了一个ICc神经元群体模型。利用这个模型，我们表明ICc神经元对低SAM频率的锁相能力是由ICc神经元的内在膜特性产生的，受抑制性离子通道的限制。我们还表明，三种类型神经元的反应特性源于对SAM频率敏感的抑制作用的差异。我们的模型很好地再现了在髯蝠中观察到的实验结果。这些发现为ICc神经元如何产生锁相能力和对低SAM频率的特征性反应提供了必要条件。
