School of Mathematical Sciences, University of Nottingham, Nottingham, United Kingdom.
J Neurophysiol. 2010 Mar;103(3):1226-37. doi: 10.1152/jn.00070.2009. Epub 2009 Dec 30.
We report evidence of mode-locking to the envelope of a periodic stimulus in chopper units of the ventral cochlear nucleus (VCN). Mode-locking is a generalized description of how responses in periodically forced nonlinear systems can be closely linked to the input envelope, while showing temporal patterns of higher order than seen during pure phase-locking. Re-analyzing a previously unpublished dataset in response to amplitude modulated tones, we find that of 55% of cells (6/11) demonstrated stochastic mode-locking in response to sinusoidally amplitude modulated (SAM) pure tones at 50% modulation depth. At 100% modulation depth SAM, most units (3/4) showed mode-locking. We use interspike interval (ISI) scattergrams to unravel the temporal structure present in chopper mode-locked responses. These responses compared well to a leaky integrate-and-fire model (LIF) model of chopper units. Thus the timing of spikes in chopper unit responses to periodic stimuli can be understood in terms of the complex dynamics of periodically forced nonlinear systems. A larger set of onset (33) and chopper units (24) of the VCN also shows mode-locked responses to steady-state vowels and cosine-phase harmonic complexes. However, while 80% of chopper responses to complex stimuli meet our criterion for the presence of mode-locking, only 40% of onset cells show similar complex-modes of spike patterns. We found a correlation between a unit's regularity and its tendency to display mode-locked spike trains as well as a correlation in the number of spikes per cycle and the presence of complex-modes of spike patterns. These spiking patterns are sensitive to the envelope as well as the fundamental frequency of complex sounds, suggesting that complex cell dynamics may play a role in encoding periodic stimuli and envelopes in the VCN.
我们报告了在耳蜗腹核（VCN）的斩波器单元中，周期性刺激包络的锁模现象的证据。锁模是对周期性强制非线性系统中响应如何与输入包络紧密相关的广义描述，同时显示出比纯相位锁定期间更高阶的时间模式。重新分析以前未发表的数据，我们发现，在对调幅（AM）纯音的响应中，有 55%的细胞（6/11）表现出随机锁模，调制深度为 50%。在 100%调制深度的 SAM 下，大多数单元（3/4）显示出锁模。我们使用脉冲间隔（ISI）散点图来揭示斩波器锁模响应中的时间结构。这些响应与斩波器单元的泄漏积分和点火（LIF）模型非常吻合。因此，周期性刺激下斩波器单元响应的脉冲时间可以根据周期性强制非线性系统的复杂动力学来理解。VCN 的更大的起始（33）和斩波器单元（24）集合也对稳态元音和余弦相位谐波复合物表现出锁模响应。然而，虽然复杂刺激下 80%的斩波器反应符合我们存在锁模的标准，但只有 40%的起始细胞显示出类似的复杂脉冲模式。我们发现单元的规律性与其显示锁模脉冲序列的倾向之间存在相关性，以及每个周期的脉冲数与复杂脉冲模式的存在之间存在相关性。这些脉冲模式对复杂声音的包络和基频都很敏感，这表明复杂细胞动力学可能在 VCN 中对周期性刺激和包络的编码中起作用。
