Broussard Dianne M, Priesol Adrian J, Tan Yao-Fang
Division of Neurology, Department of Medicine, University of Toronto, Toronto, ON, Canada M5T 2S8.
Brain Res. 2004 Apr 16;1005(1-2):137-53. doi: 10.1016/j.brainres.2004.01.042.
The horizontal rotatory vestibulo-ocular reflex (VOR) stabilizes gaze by moving the eyes at an angular velocity proportional to head velocity, and can accomplish this for a broad range of frequencies and amplitudes of head motion. Rotation at 5 Hz and above may be processed differently than lower frequencies by the VOR network. We recorded discharges and calculated spike densities of a small sample of vestibular neurons in alert cats during low-velocity rotation at frequencies up to 8 Hz. At high frequencies, we found both vestibular-only (V-only) and eye-movement-sensitive (EM) cells that generated asymmetric output signals. Asymmetry was primarily of the cutoff type, i.e., changes in spike density were smallest for rotation in the inhibitory direction. Most cells were identified as secondary neurons. The mean spike density was 23 sp/s, which was lower than previously reported in vestibular neurons of monkeys. A few neurons had very high sensitivities, associated with phase-locking, to rotation at high frequencies. In general, vestibular neurons carried a high-pass-filtered version of rotational signals. When synaptic inputs from the vestibular commissure were quantified, we found that the immediate change in probability of firing due to commissural vestibular input was inversely correlated with the degree of high-pass filtering. At high frequencies, increased asymmetry and phase-locking occurred in some neurons. A small number of neurons responded with increased probability of firing to both directions of rotation. Together, these observations suggest that high frequencies of rotation may be encoded differently than low frequencies by central vestibular neurons in alert animals.
水平旋转性前庭眼反射（VOR）通过以与头部速度成比例的角速度移动眼睛来稳定注视，并且能够在很宽的头部运动频率和幅度范围内做到这一点。VOR网络对5Hz及以上的旋转处理方式可能与较低频率不同。我们记录了清醒猫在频率高达8Hz的低速旋转过程中一小部分前庭神经元的放电情况，并计算了其放电密度。在高频时，我们发现了仅前庭（V-only）细胞和对眼动敏感（EM）的细胞，它们产生不对称的输出信号。不对称主要是截止型的，即抑制方向旋转时放电密度变化最小。大多数细胞被鉴定为次级神经元。平均放电密度为23个脉冲/秒，低于先前报道的猴子前庭神经元的放电密度。少数神经元对高频旋转具有非常高的敏感性，并伴有锁相现象。一般来说，前庭神经元携带旋转信号的高通滤波版本。当对来自前庭连合的突触输入进行量化时，我们发现由于连合前庭输入导致的放电概率的即时变化与高通滤波程度呈负相关。在高频时，一些神经元出现了不对称增加和锁相现象。少数神经元对两个旋转方向的放电概率都增加。总之，这些观察结果表明，在清醒动物中，中央前庭神经元对高频旋转的编码方式可能与低频不同。
