Collaborative Research: encoding and learning of internal models by the Purkinje cells of the cerebellum

大脑不需要小脑来做运动。相反，它需要小脑来做出准确的运动。小脑赋予机体内部监控和纠正正在进行的运动指令的能力。这种监测需要小脑能够预测即将发生的错误，并在错误发生之前进行纠正。也就是说，大脑依靠小脑建立准确的内部模型，学习预测运动命令的感觉后果。然而，很难破译小脑如何代表许多行为形式的内部模型，包括跳眼运动。通过检查浦肯野细胞（p细胞）的简单尖峰与行为之间的关系，该项目将推进我们对小脑计算的理解。这些研究结果为小脑损伤患者的康复治疗提供了新的途径。这一提议的新观点是，小脑中计算的基本单位可能不是单个p细胞或随机选择的p细胞群，而是一组特定的p细胞，其中所有的p细胞都具有相同的预测误差偏好。利用这个想法，来自约翰霍普金斯大学和华盛顿大学的合作研究小组发现，在眼跳过程中，p细胞的简单尖峰非常准确地预测了眼睛未来的行为。这个项目的目的是了解小脑如何学会做出如此准确的预测。研究人员提出了一个新的范例，其中感觉误差垂直于眼睛的运动方向。这个范例很有趣，因为行为表现出相当丰富的内容：在运动中较早到达的运动命令在错误发生后似乎变化不大，但那些较晚到达的运动命令表现出较高的学习能力和快速的遗忘能力。通过实验和计算模型的结合，研究人员将验证行为变化是由于p细胞的神经变化引起的观点：不喜欢错误的微集群在运动的加速阶段表达他们的学习，而那些喜欢错误的微集群在运动的减速阶段表达他们的学习。

The brain does not need the cerebellum to make movements. Rather, it needs the cerebellum to make accurate movements. The cerebellum endows the organism with the ability to internally monitor and correct ongoing motor commands. This monitoring requires the cerebellum to be able to predict errors that are about to happen, and correct for them before they occur. That is, the brain relies on the cerebellum to have accurate internal models that learn to predict sensory consequences of motor commands. However, it has been difficult to decipher how the cerebellum represents internal models: for many forms of behavior, including saccadic eye movements. By examining the relationship between simple spikes of Purkinje cells (P-cells) and behavior, this project will advance our understanding of computations in the cerebellum. Results of these studies could provide new avenues of rehabilitation for patients with cerebellar damage.The new idea in this proposal is that the basic unit of computation in the cerebellum may not be a single P-cell or a randomly selected population of P-cells, but rather a specific group of P-cells wherein all the P-cells share the same preference for prediction error. Using this idea, the collaborative team of investigators from Johns Hopkins University and University of Washington has found that during saccades, the simple spikes of P-cells predict with exquisite accuracy future behavior of the eyes. The aim of this project is to understand how the cerebellum learns to make such accurate predictions. The investigators present a new paradigm, one in which sensory errors are perpendicular to the direction of motion of the eyes. This paradigm is interesting because behavior shows considerable richness: motor commands that arrive early in the movement appear to change little following error, but those that come late show both high learning and rapid forgetting. Using a combination of experiments and computational modelling, the investigators will test ideas that behavioral changes are due to the neural changes in the P-cells: micro-clusters that do not prefer the error express their learning in the acceleration phase of the movement, whereas those that prefer the error express their learning in the deceleration phase.