Wearne S, Raphan T, Cohen B
Department of Neurology, Mount Sinai School of Medicine, New York 10029, USA.
J Neurophysiol. 1998 May;79(5):2690-715. doi: 10.1152/jn.1998.79.5.2690.
Spatial orientation of the angular vestibuloocular reflex (aVOR) was studied in rhesus monkeys after complete and partial ablation of the nodulus and ventral uvula. Horizontal, vertical, and torsional components of slow phases of nystagmus were analyzed to determine the axes of eye rotation, the time constants (Tcs) of velocity storage, and its orientation vectors. The gravito-inertial acceleration vector (GIA) was tilted relative to the head during optokinetic afternystagmus (OKAN), centrifugation, and reorientation of the head during postrotatory nystagmus. When the GIA was tilted relative to the head in normal animals, horizontal Tcs decreased, vertical and/or roll time constants (Tc(vert/roll)) lengthened according to the orientation of the GIA, and vertical and/or roll eye velocity components appeared (cross-coupling). This shifted the axis of eye rotation toward alignment with the tilted GIA. Horizontal and vertical/roll Tcs varied inversely, with T(chor) being longest and T(cvert/roll) shortest when monkeys were upright, and the reverse when stimuli were around the vertical or roll axes. Vertical or roll Tcs were longest when the axes of eye rotation were aligned with the spatial vertical, respectively. After complete nodulo-uvulectomy, T(chor) became longer, and periodic alternating nystagmus (PAN) developed in darkness. T(chor) could not be shortened in any of paradigms tested. In addition, yaw-to-vertical/roll cross-coupling was lost, and the axes of eye rotation remained fixed during nystagmus, regardless of the tilt of the GIA with respect to the head. After central portions of the nodulus and uvula were ablated, leaving lateral portions of the nodulus intact, yaw-to-vertical/roll cross-coupling and control of Tc(vert/roll) was lost or greatly reduced. However, control of Tchor was maintained, and T(chor) continued to vary as a function of the tilted GIA. Despite this, the eye velocity vector remained aligned with the head during yaw axis stimulation after partial nodulo-uvulectomy, regardless of GIA orientation to the head. The data were related to a three-dimensional model of the aVOR, which simulated the experimental results. The model provides a basis for understanding how the nodulus and uvula control processing within the vestibular nuclei responsible for spatial orientation of the aVOR. We conclude that the three-dimensional dynamics of the velocity storage system are determined in the nodulus and ventral uvula. We propose that the horizontal and vertical/roll Tcs are separately controlled in the nodulus and uvula with the dynamic characteristics of vertical/roll components modulated in central portions and the horizontal components laterally, presumably in a semicircular canal-based coordinate frame.
在恒河猴的小结和腹侧蚓垂完全或部分切除后，研究了角向前庭眼反射（aVOR）的空间定向。分析了眼震慢相的水平、垂直和扭转分量，以确定眼球旋转轴、速度存储的时间常数（Tcs）及其定向矢量。在视动性眼震后效（OKAN）、离心以及旋转后眼震期间头部重新定向过程中，重力惯性加速度矢量（GIA）相对于头部发生倾斜。在正常动物中，当GIA相对于头部倾斜时，水平Tcs减小，垂直和/或翻滚时间常数（Tc(vert/roll)）根据GIA的方向延长，并且出现垂直和/或翻滚眼球速度分量（交叉耦合）。这使眼球旋转轴朝着与倾斜的GIA对齐的方向移动。水平和垂直/翻滚Tcs呈反比变化，当猴子直立时，T(chor)最长而T(cvert/roll)最短，当刺激围绕垂直或翻滚轴时则相反。当眼球旋转轴分别与空间垂直方向对齐时，垂直或翻滚Tcs最长。在小结和蚓垂完全切除后，T(chor)变长，并且在黑暗中出现周期性交替眼震（PAN）。在任何测试范式中，T(chor)都无法缩短。此外，偏航到垂直/翻滚交叉耦合消失，并且在眼震期间眼球旋转轴保持固定，无论GIA相对于头部的倾斜情况如何。在切除小结和蚓垂的中央部分而保留小结的外侧部分后，偏航到垂直/翻滚交叉耦合以及对Tc(vert/roll)的控制丧失或大大减弱。然而，对Tchor的控制得以维持，并且T(chor)继续随倾斜的GIA而变化。尽管如此，在部分小结和蚓垂切除后，在偏航轴刺激期间眼球速度矢量仍与头部对齐，无论GIA相对于头部的方向如何。这些数据与aVOR的三维模型相关，该模型模拟了实验结果。该模型为理解小结和蚓垂如何控制前庭核内负责aVOR空间定向的处理提供了基础。我们得出结论，速度存储系统的三维动力学由小结和腹侧蚓垂决定。我们提出，水平和垂直/翻滚Tcs在小结和蚓垂中分别受到控制，垂直/翻滚分量的动态特性在中央部分受到调制，而水平分量在外侧受到调制，大概是在基于半规管的坐标系中。
