Kushiro Keisuke, Dai Mingjia, Kunin Mikhail, Yakushin Sergei B, Cohen Bernard, Raphan Theodore
Department of Neurology, Mount Sinai School of Medicine, New York City 10029, Brooklyn, New York 11210, USA.
J Neurophysiol. 2002 Nov;88(5):2445-62. doi: 10.1152/jn.00197.222.
Nystagmus induced by off-vertical axis rotation (OVAR) about a head yaw axis is composed of a yaw bias velocity and modulations in eye position and velocity as the head changes orientation relative to gravity. The bias velocity is dependent on the tilt of the rotational axis relative to gravity and angular head velocity. For axis tilts <15 degrees, bias velocities increased monotonically with increases in the magnitude of the projected gravity vector onto the horizontal plane of the head. For tilts of 15-90 degrees, bias velocity was independent of tilt angle, increasing linearly as a function of head velocity with gains of 0.7-0.8, up to the saturation level of velocity storage. Asymmetries in OVAR bias velocity and asymmetries in the dominant time constant of the angular vestibuloocular reflex (aVOR) covaried and both were reduced by administration of baclofen, a GABA(B) agonist. Modulations in pitch and roll eye positions were in phase with nose-down and side-down head positions, respectively. Changes in roll eye position were produced mainly by slow movements, whereas vertical eye position changes were characterized by slow eye movements and saccades. Oscillations in vertical and roll eye velocities led their respective position changes by approximately 90 degrees, close to an ideal differentiation, suggesting that these modulations were due to activation of the orienting component of the linear vestibuloocular reflex (lVOR). The beating field of the horizontal nystagmus shifted the eyes 6.3 degrees /g toward gravity in side down position, similar to the deviations observed during static roll tilt (7.0 degrees /g). This demonstrates that the eyes also orient to gravity in yaw. Phases of horizontal eye velocity clustered ~180 degrees relative to the modulation in beating field and were not simply differentiations of changes in eye position. Contributions of orientating and compensatory components of the lVOR to the modulation of eye position and velocity were modeled using three components: a novel direct otolith-oculomotor orientation, orientation-based velocity modulation, and changes in velocity storage time constants with head position re gravity. Time constants were obtained from optokinetic after-nystagmus, a direct representation of velocity storage. When the orienting lVOR was combined with models of the compensatory lVOR and velocity estimator from sequential otolith activation to generate the bias component, the model accurately predicted eye position and velocity in three dimensions. These data support the postulates that OVAR generates compensatory eye velocity through activation of velocity storage and that oscillatory components arise predominantly through lVOR orientation mechanisms.
绕头部偏航轴进行的非垂直轴旋转（OVAR）所诱发的眼球震颤由偏航偏置速度以及随着头部相对于重力改变方向而产生的眼位和眼速度调制组成。偏置速度取决于旋转轴相对于重力的倾斜度以及头部角速度。对于小于15度的轴倾斜，偏置速度随着投影到头部水平面上的重力矢量大小的增加而单调增加。对于15 - 90度的倾斜，偏置速度与倾斜角度无关，随头部速度线性增加，增益为0.7 - 0.8，直至速度存储的饱和水平。OVAR偏置速度的不对称性以及角前庭眼反射（aVOR）的主导时间常数的不对称性是共变的，并且通过给予GABA(B)激动剂巴氯芬两者均降低。俯仰和横滚眼位调制分别与头向下和头侧向下位置同相。横滚眼位变化主要由缓慢运动产生，而垂直眼位变化的特征是缓慢眼动和扫视。垂直和横滚眼速度的振荡比各自的位置变化超前约90度，接近理想的微分，表明这些调制是由于线性前庭眼反射（lVOR）的定向成分激活所致。水平眼球震颤的摆动场在头侧向下位置使眼睛向重力方向偏移6.3度/g，类似于在静态横滚倾斜期间观察到的偏差（7.0度/g）。这表明眼睛在偏航时也会定向于重力。水平眼速度的相位相对于摆动场调制聚集在约180度，并非简单地是眼位变化的微分。使用三个成分对lVOR的定向和补偿成分对眼位和眼速度调制的贡献进行建模：一种新的直接耳石 - 动眼神经定向、基于定向的速度调制以及速度存储时间常数随头部相对于重力的位置变化。时间常数从视动性眼震后眼震获得，这是速度存储的直接表现。当将定向lVOR与补偿性lVOR模型以及来自连续耳石激活的速度估计器相结合以生成偏置成分时，该模型准确地预测了三维空间中的眼位和眼速度。这些数据支持以下假设：OVAR通过激活速度存储产生补偿性眼速度，并且振荡成分主要通过lVOR定向机制产生。
