Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota 55455, USA.
J Neurosci. 2012 Oct 31;32(44):15345-58. doi: 10.1523/JNEUROSCI.2151-12.2012.
The cerebellum has been implicated in processing motor errors required for on-line control of movement and motor learning. The dominant view is that Purkinje cell complex spike discharge signals motor errors. This study investigated whether errors are encoded in the simple spike discharge of Purkinje cells in monkeys trained to manually track a pseudorandomly moving target. Four task error signals were evaluated based on cursor movement relative to target movement. Linear regression analyses based on firing residuals ensured that the modulation with a specific error parameter was independent of the other error parameters and kinematics. The results demonstrate that simple spike firing in lobules IV-VI is significantly correlated with position, distance, and directional errors. Independent of the error signals, the same Purkinje cells encode kinematics. The strongest error modulation occurs at feedback timing. However, in 72% of cells at least one of the R(2) temporal profiles resulting from regressing firing with individual errors exhibit two peak R(2) values. For these bimodal profiles, the first peak is at a negative τ (lead) and a second peak at a positive τ (lag), implying that Purkinje cells encode both prediction and feedback about an error. For the majority of the bimodal profiles, the signs of the regression coefficients or preferred directions reverse at the times of the peaks. The sign reversal results in opposing simple spike modulation for the predictive and feedback components. Dual error representations may provide the signals needed to generate sensory prediction errors used to update a forward internal model.
小脑被认为参与了运动在线控制和运动学习所需的运动误差处理。主流观点认为，浦肯野细胞复合锋电位放电信号表示运动误差。本研究探讨了在猴子中，当它们被训练手动跟踪随机运动目标时，浦肯野细胞的简单锋电位放电是否编码了误差。根据光标相对于目标运动的位置，评估了四个任务误差信号。基于放电残差的线性回归分析确保了与特定误差参数的调制与其他误差参数和运动学无关。结果表明，在 lobules IV-VI 中的简单锋电位放电与位置、距离和方向误差显著相关。与误差信号无关，相同的浦肯野细胞编码运动学。最强的误差调制发生在反馈时间。然而，在 72%的细胞中，至少有一个细胞的 R(2)时间分布，该分布是通过将放电与单个误差进行回归得到的，表现出两个峰值 R(2)值。对于这些双峰分布，第一个峰值的 τ 为负（领先），第二个峰值的 τ 为正（滞后），这意味着浦肯野细胞编码了对错误的预测和反馈。对于大多数双峰分布，回归系数或优选方向的符号在峰值时反转。符号反转导致预测和反馈成分的简单锋电位调制相反。双误差表示可能提供了生成用于更新前向内部模型的感觉预测误差所需的信号。
