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动作。小脑赋予生物体内部监控和纠正正在进行的运动命令的能力。这种监测要求小脑能够预测即将发生的错误，并在错误发生前进行纠正。也就是说，大脑依赖小脑拥有准确的内部模型，这些模型学习预测运动指令的感觉后果。然而，很难破译小脑如何代表内部模型：对于许多形式的行为，包括眼跳运动。通过研究浦肯野细胞(P细胞)的简单尖峰和行为之间的关系，这个项目将促进我们对小脑计算的理解。这些研究的结果可能为小脑损伤患者提供新的康复途径。这一建议的新想法是，小脑的基本计算单位可能不是单个P细胞或随机选择的一组P细胞，而是一组特定的P细胞，其中所有P细胞都有相同的预测误差偏好。约翰斯·霍普金斯大学和华盛顿大学的合作研究团队利用这一想法发现，在眼跳过程中，简单的P细胞尖峰信号可以非常准确地预测眼睛未来的行为。这个项目的目的是了解小脑是如何学会做出如此准确的预测的。研究人员提出了一种新的范式，在这种范式中，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：运动中较早到达的运动指令似乎不会改变后续错误，但较晚到达的运动指令显示出高度学习和快速遗忘。通过实验和计算模型的结合，研究人员将测试行为变化是由于P细胞的神经变化的想法：不喜欢错误的微簇在运动的加速阶段表达他们的学习，而那些喜欢错误的微簇表达他们的学习在减速阶段。

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.