We have identified a visually driven output from the flocculus of the monkey by studying the simple-spike responses of Purkinje cells (P-cells) during the initiation of smooth-pursuit eye movements. We report on two groups of P-cells that appear to be the horizontal and vertical gaze-velocity P-cells (GVP-cells) studied previously during periodic target and head motion. 2. During pursuit of periodic target motion, one group of P-cells prefers downward motion (down GVP-cells), and the other prefers motion toward the side of recording (ipsi GVP-cells). The two groups have mean directional preferences that are nearly orthogonal, but their responses during pursuit of sinusoidal target motion and sinusoidal vestibular stimulation are in other respects quantitatively similar. 3. During the initiation of pursuit to step-ramp target motion, GVP-cells show a large transient change in simple-spike firing rate followed by a sustained change in firing that persists during steady-state pursuit. 4. The transient response is directionally selective, so that GVP-cells show a pulse of simple spikes for pursuit in the ON-direction and a dip in simple-spike firing for pursuit in the OFF-direction. The amplitude of the transient response is too large to be explained by the sensitivity of GVP-cells to eye velocity measured during pursuit of sinusoidal target motion. 5. To test whether the transient change in simple-spike firing was related to a visual input or to an eye-acceleration input to the flocculus, we recorded the firing of ipsi GVP-cells during a rapid eye acceleration caused by a transient vestibular stimulus in darkness. Most GVP-cells showed little or no transient response under these conditions, even though eye acceleration was greater than during the initiation of pursuit. We conclude that the transient response at the initiation of pursuit is probably caused by visual mossy-fiber inputs to the flocculus. 6. The sustained change in simple-spike firing is also directionally selective, with large increases in simple-spike firing for pursuit in the ON-direction and smaller decreases for pursuit in the OFF-direction. For pursuit in the ON-direction, the amplitude of the sustained response is well predicted by the sensitivity of GVP-cells to eye velocity measured during pursuit of sinusoidal target motion. 7. To determine whether the sustained response was driven by visual inputs, we recorded simple-spike firing when image motion was prevented by electronically stabilizing the target image on the fovea during steady-state pursuit.(ABSTRACT TRUNCATED AT 400 WORDS)
摘要
通过研究平稳跟踪眼球运动起始阶段浦肯野细胞（P 细胞）的简单锋电位反应，我们已确定了猴子小脑绒球由视觉驱动的输出。我们报告了两组 P 细胞，它们似乎是先前在周期性目标和头部运动期间所研究的水平和垂直注视速度 P 细胞（GVP 细胞）。2. 在跟踪周期性目标运动期间，一组 P 细胞偏好向下运动（向下 GVP 细胞），另一组偏好朝向记录侧的运动（同侧 GVP 细胞）。这两组细胞的平均方向偏好几乎相互垂直，但它们在跟踪正弦目标运动和正弦前庭刺激期间的反应在其他方面在数量上相似。3. 在开始跟踪阶跃斜坡目标运动时，GVP 细胞的简单锋电位发放率会出现大幅瞬态变化，随后在稳定跟踪期间发放持续变化。4. 瞬态反应具有方向选择性，因此 GVP 细胞在 ON 方向跟踪时会出现简单锋电位脉冲，而在 OFF 方向跟踪时简单锋电位发放会减少。瞬态反应的幅度太大，无法用在跟踪正弦目标运动期间测量的 GVP 细胞对眼球速度的敏感性来解释。5. 为了测试简单锋电位发放的瞬态变化是与视觉输入还是与小脑绒球的眼球加速度输入有关，我们在黑暗中由瞬态前庭刺激引起的快速眼球加速度期间记录了同侧 GVP 细胞的发放。在这些条件下，即使眼球加速度大于跟踪起始阶段，大多数 GVP 细胞几乎没有或没有瞬态反应。我们得出结论，跟踪起始时的瞬态反应可能是由小脑绒球的视觉苔藓纤维输入引起的。6. 简单锋电位发放的持续变化也具有方向选择性，在 ON 方向跟踪时简单锋电位发放大幅增加，在 OFF 方向跟踪时减少幅度较小。对于 ON 方向的跟踪，持续反应的幅度可以通过在跟踪正弦目标运动期间测量的 GVP 细胞对眼球速度的敏感性很好地预测。7. 为了确定持续反应是否由视觉输入驱动，我们在稳定跟踪期间通过电子方式稳定中央凹上的目标图像来防止图像运动时记录了简单锋电位发放。（摘要截断于 400 字）
