Marti Sarah, Palla Antonella, Straumann Dominik
Neurology Department, Zürich University Hospital, CH-8091 Zürich, Switzerland.
Ann Neurol. 2002 Dec;52(6):712-21. doi: 10.1002/ana.10370.
Downbeat nystagmus is a frequent ocular motor sign in patients with lesions of the vestibulocerebellum. The upward drift in downbeat nystagmus is a combination of a gaze-evoked drift, due to an impaired vertical neural integrator, and a velocity bias. Using a three-dimensional turntable, we analyzed the influence of gravity on these two mechanisms. Patients with cerebellar downbeat nystagmus (n = 6) and healthy subjects (n = 12) were placed in various whole-body positions along the roll, pitch, and oblique vertical planes of the head. Ocular drift was monitored with scleral search coils. Although there was no gravity dependence of the vertical gaze-evoked drift, the vertical velocity bias consisted of two components: a gravity-dependent component that sinusoidally modulated as a function of body position along the pitch plane, and a gravity-independent component that was directed upward. The combination of the two components led to an overall drift that was minimal in supine and maximal in prone position. In healthy subjects, only the gravity-dependent component was present, but in a scaled-down manner. Our results suggest that the intact vestibulocerebellum minimizes an overacting otolith-ocular reflex elicited by pitch tilt and cancels an inherent upward ocular drift that is independent of gravity-modulated otolith signals.
下跳性眼球震颤是前庭小脑病变患者常见的眼球运动体征。下跳性眼球震颤中的向上漂移是由垂直神经整合器受损导致的视诱发漂移和速度偏差的组合。我们使用三维转台分析了重力对这两种机制的影响。将患有小脑性下跳性眼球震颤的患者(n = 6)和健康受试者(n = 12)置于沿头部的横滚、俯仰和倾斜垂直平面的各种全身位置。用巩膜搜索线圈监测眼球漂移。虽然垂直视诱发漂移不存在重力依赖性,但垂直速度偏差由两个分量组成:一个重力依赖性分量,其随身体沿俯仰平面的位置呈正弦调制;一个与重力无关的向上分量。这两个分量的组合导致了一个总体漂移,在仰卧位时最小,在俯卧位时最大。在健康受试者中,仅存在重力依赖性分量,但程度较小。我们的结果表明,完整的前庭小脑可使由俯仰倾斜引起的过度活跃的耳石 - 眼反射最小化,并消除与重力调制耳石信号无关的固有向上眼球漂移。