Dow E R, Anastasio T J
Research Technologies and Discovery (Bioinfomatics), Lilly Corporate Center, Indianapolis, IN 46285, USA.
J Comput Neurosci. 1999 Jul-Aug;7(1):55-70. doi: 10.1023/a:1008967511172.
Modification of the vestibulo-ocular reflex (VOR) by vestibular habituation is an important paradigm in the study of neural plasticity. The VOR is responsible for rotating the eyes to maintain the direction of gaze during head rotation. The response of the VOR to sinusoidal rotation is quantified by its gain (eye rotational velocity/head rotational velocity) and phase difference (eye velocity phase--inverted head velocity phase). The frequency response of the VOR in naïve animals has been previously modeled as a high-pass filter (HPF). A HPF passes signals above its corner frequency with gain 1 and phase 0 but decreases gain and increases phase lead (positive phase difference) as signal frequency decreases below its corner frequency. Modification of the VOR by habituation occurs after prolonged low-frequency rotation in the dark. Habituation causes a reduction in low-frequency VOR gain and has been simulated by increasing the corner frequency of the HPF model. This decreases gain not only at the habituating frequency but further decreases gain at all frequencies below the new corner frequency. It also causes phase lead to increase at all frequencies below the new corner frequency (up to some asymptotic value). We show that habituation of the goldfish VOR is not a broad frequency phenomena but is frequency specific. A decrease in VOR gain is produced primarily at the habituating frequency, and there is an increase in phase lead at nearby higher frequencies and a decrease in phase lead at nearby lower frequencies (phase crossover). Both the phase crossover and the frequency specific gain decrease make it impossible to simulate habituation of the VOR simply by increasing the corner frequency of the HPF model. The simplest way to simulate our data is to subtract the output of a band-pass filter (BPF) from the output of the HPF model of the naïve VOR. A BPF passes signals over a limited frequency range only. A BPF decreases gain and imparts a phase lag and lead, respectively, as frequency increases and decreases outside this range. Our model produces both the specific decrease in gain at the habituating frequency, and the phase crossover centered on the frequency of habituation. Our results suggest that VOR habituation may be similar to VOR adaptation (in which VOR modification is produced by visual-vestibular mismatch) in that both are frequency-specific phenomena.
通过前庭习服对前庭眼反射（VOR）进行调节是神经可塑性研究中的一个重要范例。VOR负责在头部旋转时转动眼睛以维持注视方向。VOR对正弦旋转的反应通过其增益（眼旋转速度/头旋转速度）和相位差（眼速度相位 - 反转的头速度相位）来量化。在未受过训练的动物中，VOR的频率响应先前被建模为高通滤波器（HPF）。高通滤波器通过其截止频率以上的信号，增益为1且相位为0，但当信号频率降低到其截止频率以下时，增益降低且相位超前增加（正相位差）。在黑暗中长时间低频旋转后会发生通过习服对VOR的调节。习服会导致低频VOR增益降低，并且已通过增加HPF模型的截止频率进行模拟。这不仅会在习服频率处降低增益，还会在新截止频率以下的所有频率处进一步降低增益。它还会导致在新截止频率以下的所有频率处相位超前增加（达到某个渐近值）。我们表明金鱼VOR的习服不是一种广泛的频率现象，而是频率特异性的。VOR增益的降低主要在习服频率处产生，并且在附近较高频率处相位超前增加，在附近较低频率处相位超前降低（相位交叉）。相位交叉和频率特异性增益降低都使得仅通过增加HPF模型的截止频率来模拟VOR的习服变得不可能。模拟我们数据的最简单方法是从未受过训练的VOR的HPF模型的输出中减去带通滤波器（BPF）的输出。带通滤波器仅通过有限频率范围内的信号。当频率在该范围之外增加和降低时，带通滤波器分别降低增益并赋予相位滞后和超前。我们的模型既产生了习服频率处增益的特异性降低，也产生了以习服频率为中心的相位交叉。我们的结果表明，VOR习服可能与VOR适应（其中VOR调节由视觉 - 前庭不匹配产生）类似，因为两者都是频率特异性现象。
