小脳虫部の眼位制御に果す役割 第1報 ネコ小脳虫部の微小電気刺激により誘発される眼球運動の特性
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概要
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The properties of eye movements evoked by cerebellar microstimulation were investigated in alert, encephale isole cats. Repetitive stimuli (20-500 Hz, 20-500 μA) were applied to the vermis, lobules V-VII with tungsten microelectrodes. Horizontal and vertical DC-EOGs were recorded with a rectigraph. In many cases, the evoked eye movements were also recorded two-dimensionally with an XY-recorder. We analyzed the dependence of the evoked eye movements on the stimulus parameter, stimulus sites and initial eye positions. 1) Two types of eye movements, saccades and smooth eye movements were evoked. The sites for the lowest stimulus threshold (about 20 μA) were both in the Purkinje cell layer and the deep layer of the white matter. The types of the evoked eye movements were not dependent upon the stimulus sites. Directions of the evoked eye movements were contingent on the stimulus sites. Horizontal eye movements were evoked by the stimulation of the lobule VI. The eye movements evoked by the stimulation of the lobule V and VII contained predominantly upward and downward components respectively. Straight upward and downward eye movements were induced by the stimulation of the midline vermis. 2) The velocity and amplitude of the evoked eye movements were not dependent on the stimulus parameters. The peak velocities of saccades increased in proportion to the amplitude of the evoked eye movements. The amplitude of the evoked eye movements depended upon the initial positions of the eye in the orbit, and the evoked eye movements tended to reach the same final goal in the orbit regardless of initial eye positions. 3) Such goal-directed eye movements were evoked in 80% of all the stimulus sites. In 70% of those sites the movements were goal-directed both horizontally and vertically. In the remaining 30% the movements were goal-directed either horizontally or vertically. The eccentricities of the goal positions increased with stimulus intensity and frequency. The goal positions of the movements evoked by the simultaneous stimuli of the two different sites were obtained by vectorial addition of the two eye movements evoked by the stimulation of each site. These results may indicate that the vermis, lobules V-VII play an important role in the control of eye position in the orbit.
- 1986-02-01