Effects of horizontal-vertical eye positions on the 3D on-direction of extraocular muscles and extraocular motoneurons.

1.三只头部稳定的猴（Macaca fuscata）参与了本研究。双巩膜探测线圈法用于三维眼球运动记录。用细胞外单单位记录法鉴定滋养神经纤维。此后，我们在自发性眼球运动期间每2秒刺激一次位于滑车交叉点附近的滑车神经纤维，同时将每只猴子保持在不同的静态滚动位置（直立，右耳向下40 °，左耳向下40 °）。刺激序列由0.25 ms负矩形脉冲组成。刺激频率为500 Hz，电流强度和训练持续时间在10 - 50 μ A和25- 200毫秒的范围内变化。电刺激在刺激期间将眼睛从Listing的平面移开。之后，在刺激结束点之后6-8 ms开始漂移回到Listing平面，这与在刺激开始和眼运动开始之间观察到的潜伏期相同。诱发眼球运动由大的非扭转分量、大的向下分量和小的外展分量组成。诱发方向与解剖学报道的恒河猴上级斜肌牵拉方向相似。诱发眼球运动的旋转轴与电刺激强度和持续时间无关。平均而言，在冠状面（扭转-垂直）诱发眼球运动的旋转轴与初始眼球位置的水平分量无关.结论：在警觉状态下，电刺激滑车神经引起的眼球旋转轴稳定在冠状面内的轨道上，该轨道与上级斜肌路径和眼球假想中心所形成的平面几乎平行。据报道，上级、下、内侧和外侧直肌中的软滑轮在上级斜肌中不能有效工作。

1. Three head-stabilized monkeys (Macaca fuscata) were engaged in this study. A dual scleral search coil method was used for three-dimensional eye movement recordings. Trochlear nerve fibers were identified with extracellular single unit recordings. Thereafter, we stimulated the trochlear nerve fibers at the sites near to the trochlear decussation every 2 seconds during spontaneous eye movements while holding each monkey in different static roll positions (upright, 40ﾟ right ear down and 40ﾟ left ear down).2. Stimulation trains consisted of 0.25 ms negative rectangular pulses. Stimulus frequency was 500 Hz and current strength, and train duration were varied over the ranges of 10 -50 muA and 25-200msec.3. Electrical stimulation moved the eye away from Listing's plane during stimulation periods. Afterwards, drifts back to Listing's plane started 6-8 ms after stimulus end points, which was the same latency observed between stimulus onset and eye movement onset. Evoked eye movements were consisted of large intorsional and large downward components and small abduction components. The evoked direction was similar to the anatomically reported pulling direction of the superior oblique muscle in rhesus monkeys. The axis of rotation of evoked eye movements was independent of the electrical stimulation intensity and duration. On average, the axis of rotation of evoked eye movements in the coronal (torsional-vertical) plane was independent of the horizontal component of initial eye positions.4. We conclude that, in the alert monkeys, the axis of eye rotation evoked by electrical stimulation of the trochlear nerve is stabilized to the orbit in coronal plane which is almost in parallel with the plane formed by the superior oblique muscle path and the imaginary center of eye ball. Soft pulley that is reported in the superior, inferior, medial and lateral rectus muscles does not work effectively in the superior oblique muscle.