Ohtsuka K, Enoki T
Department of Ophthalmology, Sapporo Medical University, School of Medicine, Japan.
Brain. 1998 Mar;121 ( Pt 3):429-35. doi: 10.1093/brain/121.3.429.
Recent neurophysiological experiments in the monkey have demonstrated that the flocculus and the posterior vermis, lobules VIc-VII (oculomotor vermis), are involved in the generation of pursuit eye movements. Whereas the functions of the flocculus in the control of smooth pursuit have been intensively investigated, sufficient data are not available for a profitable discussion of the functions of the oculomotor vermis in the control of smooth pursuit. We previously indicated that the posterior vermis can be electrically stimulated by a focal transcranial magnetic stimulation (TMS) device through the skull in man, and that focal TMS of the posterior vermis can modulate saccadic eye movements. In this study we investigated the effects of cerebellar stimulation on smooth pursuit metrics in man using a focal TMS device. Focal TMS was applied over the posterior cerebellum in an area approximately 7 mm lateral and caudal to the inion, where saccadic eye movements are modulated by TMS, during horizontal smooth pursuit elicited by a step-ramp target with a constant velocity of 15 degrees/s in four normal subjects. The TMS device was triggered after the onset of smooth pursuit during the initial acceleration phase (latency range = 40-80 ms) or the steady-state tracking phase (latency range = 300-340 ms). We investigated the effect of TMS on the velocity and acceleration of smooth pursuit. For smooth pursuit directed ipsilateral to the stimulation side (ipsiversive), focal TMS of the posterior cerebellum produced abrupt acceleration of pursuit in both initial acceleration and steady-state tracking phases. On the other hand, TMS produced abrupt deceleration of contraversive pursuit in both initial acceleration and steady-state tracking phases. These findings suggest that the posterior vermis controls smooth pursuit velocity in a direction-selective manner in both initial acceleration and steady-state tracking phases.
最近在猴子身上进行的神经生理学实验表明，绒球和后蚓部，即小叶VIc - VII（动眼蚓部），参与了追踪性眼球运动的产生。虽然已经对绒球在控制平稳追踪中的功能进行了深入研究，但关于动眼蚓部在控制平稳追踪中的功能，尚无足够数据进行有益的讨论。我们之前指出，在人类中，后蚓部可通过颅骨被局灶性经颅磁刺激（TMS）设备电刺激，并且后蚓部的局灶性TMS可调节眼球的扫视运动。在本研究中，我们使用局灶性TMS设备研究了小脑刺激对人类平稳追踪指标的影响。在四名正常受试者中，当以15度/秒的恒定速度的阶梯斜坡目标引发水平平稳追踪时，将局灶性TMS施加于枕外隆凸外侧和尾侧约7毫米处的小脑后部区域，在此处，TMS可调节眼球的扫视运动。TMS设备在平稳追踪开始后的初始加速阶段（潜伏期范围 = 40 - 80毫秒）或稳态追踪阶段（潜伏期范围 = 300 - 340毫秒）触发。我们研究了TMS对平稳追踪速度和加速度的影响。对于指向刺激侧同侧（同向）的平稳追踪，小脑后部的局灶性TMS在初始加速阶段和稳态追踪阶段均使追踪突然加速。另一方面，TMS在初始加速阶段和稳态追踪阶段均使反向追踪突然减速。这些发现表明，后蚓部在初始加速阶段和稳态追踪阶段均以方向选择性方式控制平稳追踪速度。
