Hadjidimitrakis K, Moschovakis A K, Dalezios Y, Grantyn A
Department of Basic Sciences, Faculty of Medicine, University of Crete, P.O. Box 2208, Heraklion, 71003, Crete, Greece.
Exp Brain Res. 2007 May;179(1):1-16. doi: 10.1007/s00221-006-0765-3. Epub 2006 Nov 8.
Rapid gaze shifts are often accomplished with coordinated movements of the eyes and head, the relative amplitude of which depends on the starting position of the eyes. The size of gaze shifts is determined by the superior colliculus (SC) but additional processing in the lower brain stem is needed to determine the relative contributions of eye and head components. Models of eye-head coordination often assume that the strength of the command sent to the head controllers is modified by a signal indicative of the eye position. Evidence in favor of this hypothesis has been recently obtained in a study of phasic electromyographic (EMG) responses to stimulation of the SC in head-restrained monkeys (Corneil et al. in J Neurophysiol 88:2000-2018, 2002b). Bearing in mind that the patterns of eye-head coordination are not the same in all species and because the eye position sensitivity of phasic EMG responses has not been systematically investigated in cats, in the present study we used cats to address this issue. We stimulated electrically the intermediate and deep layers of the caudal SC in alert cats and recorded the EMG responses of neck muscles with horizontal and vertical pulling directions. Our data demonstrate that phasic, short latency EMG responses can be modulated by the eye position such that they increase as the eye occupies more and more eccentric positions in the pulling direction of the muscle tested. However, the influence of the eye position is rather modest, typically accounting for only 10-50% of the variance of EMG response amplitude. Responses evoked from several SC sites were not modulated by the eye position.
快速的注视转移通常是通过眼睛和头部的协调运动来完成的，其相对幅度取决于眼睛的起始位置。注视转移的大小由上丘（SC）决定，但需要在脑桥下部进行额外的处理来确定眼睛和头部运动成分的相对贡献。眼-头协调模型通常假设，发送到头部控制器的指令强度会被一个指示眼睛位置的信号所修正。最近在一项对头部受限的猴子进行上丘刺激的相位肌电图（EMG）反应研究中获得了支持这一假设的证据（Corneil等人，《神经生理学杂志》88:2000 - 2018，2002b）。鉴于眼-头协调模式在所有物种中并不相同，并且由于尚未在猫身上系统地研究相位EMG反应的眼位敏感性，在本研究中我们使用猫来解决这个问题。我们对清醒猫的尾侧上丘的中层和深层进行电刺激，并记录具有水平和垂直牵拉方向的颈部肌肉的EMG反应。我们的数据表明，相位性的、潜伏期短的EMG反应可以被眼睛位置调制，使得它们随着眼睛在测试肌肉的牵拉方向上占据越来越偏心的位置而增加。然而，眼睛位置的影响相当小，通常仅占EMG反应幅度方差变异的10% - 50%。从几个上丘部位诱发的反应不受眼睛位置的调制。
