Raghavan Ramanujan T, Lisberger Stephen G
Department of Neurobiology, Duke University School of Medicine Durham, North Carolina.
Department of Neurobiology, Duke University School of Medicine Durham, North Carolina
J Neurophysiol. 2017 Aug 1;118(2):986-1001. doi: 10.1152/jn.00209.2017. Epub 2017 May 17.
We recorded the responses of Purkinje cells in the oculomotor vermis during smooth pursuit and saccadic eye movements. Our goal was to characterize the responses in the vermis using approaches that would allow direct comparisons with responses of Purkinje cells in another cerebellar area for pursuit, the floccular complex. Simple-spike firing of vermis Purkinje cells is direction selective during both pursuit and saccades, but the preferred directions are sufficiently independent so that downstream circuits could decode signals to drive pursuit and saccades separately. Complex spikes also were direction selective during pursuit, and almost all Purkinje cells showed a peak in the probability of complex spikes during the initiation of pursuit in at least one direction. Unlike the floccular complex, the preferred directions for simple spikes and complex spikes were not opposite. The kinematics of smooth eye movement described the simple-spike responses of vermis Purkinje cells well. Sensitivities were similar to those in the floccular complex for eye position and considerably lower for eye velocity and acceleration. The kinematic relations were quite different for saccades vs. pursuit, supporting the idea that the contributions from the vermis to each kind of movement could contribute independently in downstream areas. Finally, neither the complex-spike nor the simple-spike responses of vermis Purkinje cells were appropriate to support direction learning in pursuit. Complex spikes were not triggered reliably by an instructive change in target direction; simple-spike responses showed very small amounts of learning. We conclude that the vermis plays a different role in pursuit eye movements compared with the floccular complex. The midline oculomotor cerebellum plays a different role in smooth pursuit eye movements compared with the lateral, floccular complex and appears to be much less involved in direction learning in pursuit. The output from the oculomotor vermis during pursuit lies along a null-axis for saccades and vice versa. Thus the vermis can play independent roles in the two kinds of eye movement.
我们记录了在平稳跟踪和扫视眼动过程中动眼蚓部浦肯野细胞的反应。我们的目标是使用能够直接与小脑另一用于跟踪的区域——绒球复合体中浦肯野细胞的反应进行比较的方法，来描述蚓部的反应。在跟踪和扫视过程中，蚓部浦肯野细胞的简单锋发放具有方向选择性，但偏好方向足够独立，以便下游回路能够解码信号，分别驱动跟踪和扫视。在跟踪过程中，复合锋电位也具有方向选择性，并且几乎所有浦肯野细胞在至少一个方向的跟踪起始阶段，复合锋电位的概率都出现峰值。与绒球复合体不同，简单锋电位和复合锋电位的偏好方向并非相反。平稳眼动的运动学很好地描述了蚓部浦肯野细胞的简单锋电位反应。对于眼位，敏感性与绒球复合体中的相似；对于眼速度和加速度，敏感性则低得多。扫视与跟踪的运动学关系有很大不同，这支持了蚓部对每种运动的贡献可在下游区域独立发挥作用的观点。最后，蚓部浦肯野细胞的复合锋电位和简单锋电位反应都不适于支持跟踪中的方向学习。目标方向的指导性变化并不能可靠地触发复合锋电位；简单锋电位反应显示出非常少量的学习。我们得出结论，与绒球复合体相比，蚓部在跟踪眼动中发挥着不同的作用。与外侧的绒球复合体相比，中线动眼小脑在平稳跟踪眼动中发挥着不同的作用，并且似乎在跟踪的方向学习中参与程度要低得多。跟踪过程中动眼蚓部的输出沿扫视的零轴，反之亦然。因此，蚓部可在两种眼动中发挥独立作用。
