Angelaki D E
Department of Surgery (Otolaryngology), University of Mississippi Medical Center, Jackson, Mississippi 39216-4505, USA.
J Neurophysiol. 1998 Aug;80(2):680-95. doi: 10.1152/jn.1998.80.2.680.
The three-dimensional (3-D) properties of the translational vestibulo-ocular reflexes (translational VORs) during lateral and fore-aft oscillations in complete darkness were studied in rhesus monkeys at frequencies between 0.16 and 25 Hz. In addition, constant velocity off-vertical axis rotations extended the frequency range to 0.02 Hz. During lateral motion, horizontal responses were in phase with linear velocity in the frequency range of 2-10 Hz. At both lower and higher frequencies, phase lags were introduced. Torsional response phase changed more than 180 degrees in the tested frequency range such that torsional eye movements, which could be regarded as compensatory to "an apparent roll tilt" at the lowest frequencies, became anticompensatory at all frequencies above approximately 1 Hz. These results suggest two functionally different frequency bandwidths for the translational VORs. In the low-frequency spectrum (<<0.5 Hz), horizontal responses compensatory to translation are small and high-pass-filtered whereas torsional response sensitivity is relatively frequency independent. At higher frequencies however, both horizontal and torsional response sensitivity and phase exhibit a similar frequency dependence, suggesting a common role during head translation. During up-down motion, vertical responses were in phase with translational velocity at 3-5 Hz but phase leads progressively increased for lower frequencies (>90 degrees at frequencies <0.2 Hz). No consistent dependence on static head orientation was observed for the vertical response components during up-down motion and the horizontal and torsional response components during lateral translation. The frequency response characteristics of the translational VORs were fitted by "periphery/brain stem" functions that related the linear acceleration input, transduced by primary otolith afferents, to the velocity signals providing the input to the velocity-to-position neural integrator and the oculomotor plant. The lowest-order, best-fit periphery/brain stem model that approximated the frequency dependence of the data consisted of a second order transfer function with two alternating poles (at 0.4 and 7.2 Hz) and zeros (at 0.035 and 3.4 Hz). In addition to clearly differentiator dynamics at low frequencies (less than approximately 0.5 Hz), there was no frequency bandwidth where the periphery/brain stem function could be approximated by an integrator, as previously suggested. In this scheme, the oculomotor plant dynamics are assumed to perform the necessary high-frequency integration as required by the reflex. The detailed frequency dependence of the data could only be precisely described by higher order functions with nonminimum phase characteristics that preclude simple filtering of afferent inputs and might be suggestive of distributed spatiotemporal processing of otolith signals in the translational VORs.
在完全黑暗的环境中，研究了恒河猴在0.16至25Hz频率范围内进行横向和前后振荡时平移前庭眼反射（translational VORs）的三维（3-D）特性。此外，恒速离垂直轴旋转将频率范围扩展到0.02Hz。在横向运动期间，水平响应在2-10Hz频率范围内与线速度同相。在较低和较高频率时，都会引入相位滞后。在测试频率范围内，扭转响应相位变化超过180度，使得在最低频率下可被视为对“明显滚动倾斜”进行补偿的扭转眼动，在高于约1Hz的所有频率下都变为反补偿。这些结果表明平移VORs存在两种功能不同的频率带宽。在低频谱（<<0.5Hz）中，对平移进行补偿的水平响应较小且经过高通滤波，而扭转响应灵敏度相对与频率无关。然而，在较高频率下，水平和扭转响应灵敏度及相位都表现出相似的频率依赖性，表明在头部平移过程中具有共同作用。在上下运动期间，垂直响应在3-5Hz时与平移速度同相，但在较低频率（<0.2Hz时>90度）时相位超前逐渐增加。在上下运动期间垂直响应分量以及横向平移期间水平和扭转响应分量均未观察到对静态头部方向的一致依赖性。平移VORs的频率响应特性由“外周/脑干”函数拟合，该函数将由初级耳石传入纤维转导的线性加速度输入与为速度到位置神经积分器和动眼神经装置提供输入的速度信号相关联。近似数据频率依赖性的最低阶、最佳拟合外周/脑干模型由具有两个交替极点（分别在0.4和7.2Hz）和零点（分别在0.035和3.4Hz）的二阶传递函数组成。除了在低频（小于约0.5Hz）时有明显的微分器动态特性外，没有如先前所建议的频率带宽，其外周/脑干函数可以由积分器近似。在该方案中，假设动眼神经装置动力学执行反射所需的必要高频积分。数据的详细频率依赖性只能由具有非最小相位特性的高阶函数精确描述，这排除了对传入输入的简单滤波，并且可能暗示了平移VORs中耳石信号的分布式时空处理。
