Torte M P, Clément G, Courjon J H, Magenes G
Laboratoire Vision et Motricité, INSERM U94, Bron, France.
Exp Brain Res. 1997 Aug;116(1):73-82. doi: 10.1007/pl00005746.
The effect of exposure to repeated angular velocity steps about the earth-vertical axis on the vertical vestibulo-ocular reflex (VOR) during onside pitch rotation was investigated in normal cats. By contrast with the VOR in the horizontal plane, the amplitude and duration of the vertical VOR did not progressively decrease throughout the repetition of velocity steps alternated in both directions. Instead, the amplitude of VOR decreased by about 40% during the very first trials in naive cats and then stayed unchanged with repeated stimuli. Habituation of the amplitude of the vertical VOR was observed when the velocity steps were always directed in the same direction. However, the duration of the vertical VOR did not show any signs of habituation. The habituation of the amplitude of the vertical VOR during unidirectional training was due to the progressive development of an initial inhibition of the VOR. This initial inhibition appeared much earlier during the bidirectional protocol, and was presumably responsible for the larger reduction in VOR amplitude observed during the very first session. These results support the model of two distinct mechanisms for VOR habituation, one producing an increasing inhibition of nystagmus, and the other depressing the response duration, and suggest that only the first mechanism is generated during repeated stimulation in the vertical plane. The low-frequency information provided by the velocity storage mechanism during onside pitch rotation, when the otoliths are positioned so they do not signal head tilt relative to gravity, could prevent a decrease in the overall response by the second mechanism.
在正常猫中研究了在同侧俯仰旋转期间，反复暴露于绕地球垂直轴的角速度阶跃对垂直前庭眼反射（VOR）的影响。与水平面上的VOR相比，在两个方向交替的速度阶跃重复过程中，垂直VOR的幅度和持续时间并未逐渐减小。相反，在初次试验中，未接触过实验的猫的VOR幅度下降了约40%，然后在重复刺激时保持不变。当速度阶跃始终指向同一方向时，观察到垂直VOR幅度的习惯化。然而，垂直VOR的持续时间没有表现出任何习惯化的迹象。单向训练期间垂直VOR幅度的习惯化是由于VOR初始抑制的逐渐发展。这种初始抑制在双向实验中出现得更早，可能是导致在第一次实验中观察到的VOR幅度更大降低的原因。这些结果支持了VOR习惯化的两种不同机制的模型，一种机制会增加对眼球震颤的抑制，另一种机制会缩短反应持续时间，并表明在垂直平面的重复刺激过程中仅产生第一种机制。在同侧俯仰旋转期间，当耳石的位置使其不会发出相对于重力的头部倾斜信号时，速度存储机制提供的低频信息可以防止第二种机制导致整体反应降低。
