Das V E, Dell'Osso L F, Leigh R J
Department of Neurology, Department of Veterans Affairs Medical Center and University Hospitals, Case Western Reserve University, Cleveland, Ohio 44106, USA.
J Neurophysiol. 1999 Jun;81(6):2884-92. doi: 10.1152/jn.1999.81.6.2884.
We investigated the effect of visually mediated eye movements made before velocity-step horizontal head rotations in eleven normal human subjects. When subjects viewed a stationary target before and during head rotation, gaze velocity was initially perturbed by approximately 20% of head velocity; gaze velocity subsequently declined to zero within approximately 300 ms of the stimulus onset. We used a curve-fitting procedure to estimate the dynamic course of the gain throughout the compensatory response to head rotation. This analysis indicated that the median initial gain of compensatory eye movements (mainly because of the vestibulo-ocular reflex, VOR) was 0. 8 and subsequently increased to 1.0 after a median interval of 320 ms. When subjects attempted to fixate the remembered location of the target in darkness, the initial perturbation of gaze was similar to during fixation of a visible target (median initial VOR gain 0.8); however, the period during which the gain increased toward 1.0 was >10 times longer than that during visual fixation. When subjects performed horizontal smooth-pursuit eye movements that ended (i.e., 0 gaze velocity) just before the head rotation, the gaze velocity perturbation at the onset of head rotation was absent or small. The initial gain of the VOR had been significantly increased by the prior pursuit movements for all subjects (P < 0.05; mean increase of 11%). In four subjects, we determined that horizontal saccades and smooth tracking of a head-fixed target (VOR cancellation with eye stationary in the orbit) also increased the initial VOR gain (by a mean of 13%) during subsequent head rotations. However, after vertical saccades or smooth pursuit, the initial gaze perturbation caused by a horizontal head rotation was similar to that which occurred after fixation of a stationary target. We conclude that the initial gain of the VOR during a sudden horizontal head rotation is increased by prior horizontal, but not vertical, visually mediated gaze shifts. We postulate that this "priming" effect of a prior gaze shift on the gain of the VOR occurs at the level of the velocity inputs to the neural integrator subserving horizontal eye movements, where gaze-shifting commands and vestibular signals converge.
我们研究了11名正常受试者在水平头部进行速度阶跃旋转之前由视觉介导的眼球运动的影响。当受试者在头部旋转之前及旋转过程中注视一个静止目标时，注视速度最初会受到约20%头部速度的干扰；刺激开始后约300毫秒内，注视速度随后降至零。我们使用曲线拟合程序来估计在对头部旋转的代偿性反应过程中增益的动态变化过程。该分析表明，代偿性眼球运动的初始增益中位数（主要由于前庭眼反射，VOR）为0.8，在中位数间隔320毫秒后随后增加到1.0。当受试者试图在黑暗中注视目标的记忆位置时，注视的初始干扰与注视可见目标时相似（初始VOR增益中位数为0.8）；然而，增益增加到1.0的时间段比视觉注视时长10倍以上。当受试者在头部旋转之前进行水平平滑跟踪眼球运动并结束（即注视速度为0）时，头部旋转开始时的注视速度干扰不存在或很小。所有受试者先前的跟踪运动均使VOR的初始增益显著增加（P<0.05；平均增加11%）。在4名受试者中，我们确定水平扫视和对头固定目标的平滑跟踪（眼球在眼眶中静止时的VOR抵消）在随后的头部旋转过程中也增加了初始VOR增益（平均增加13%）。然而，在垂直扫视或平滑跟踪之后，水平头部旋转引起的初始注视干扰与注视静止目标后出现的干扰相似。我们得出结论，在突然的水平头部旋转过程中，VOR的初始增益会因先前的水平而非垂直视觉介导的注视转移而增加。我们推测，先前注视转移对VOR增益的这种“启动”效应发生在为水平眼球运动服务的神经积分器的速度输入水平，在这里注视转移命令和前庭信号汇聚。
