Center for Neurology, Hertie Institute for Clinical Brain Research, Department of Cognitive Neurology, University of Tübingen, Hoppe-Seyler-Str. 3, 72076, Tübingen, Germany.
Exp Brain Res. 2010 Aug;205(1):41-55. doi: 10.1007/s00221-010-2331-2. Epub 2010 Jun 24.
Contemporary theories of the cerebellum hold that the complex spike (CS) fired by cerebellar Purkinje cells (PCs) reports the error signal essential for motor adaptation, i.e., the CS serves as a teacher reducing the performance error. This hypothesis suggests a monotonic relationship between CS modulation and performance error: the modulation of CS responses should be maximal at adaptation onset and turn back to its pre-adaptation state when the error is nulled. An alternative viewpoint based on studies of saccades suggests that the modulation of the CS discharge builds up as performance error decreases, and maximum and stable CS modulation is found after adaptation has been completed (Catz et al. 2005). We wanted to know whether this pattern can be generalized to other forms of motor adaptation. We resorted to smooth-pursuit adaptation (SPA) as an example of cerebellar-dependent adaptation. SPA is induced by increasing or decreasing target velocity during pursuit initiation that leads to a gradual increase or decrease in eye velocity. We trained 2 rhesus monkeys and recorded CS from PC in vermal lobuli VI and VII during SPA. We find that SPA is accompanied by a pattern of CS firing, which at the onset of adaptation, i.e., when the error is large, is not modulated significantly. On the other hand, when initial eye velocity is stably increased or decreased by adaptation, the probability of CS occurrence during pursuit initiation decreases or increases, respectively. Overall, our results deviate from the predictions made by the classical error-coding concept.
当代小脑理论认为，小脑浦肯野细胞（PC）发出的复杂峰电位（CS）报告了运动适应所必需的误差信号，即 CS 作为教师可以降低表现误差。这一假说表明 CS 调制与表现误差之间存在单调关系：CS 反应的调制应该在适应开始时达到最大值，并在误差为零时恢复到适应前的状态。基于扫视研究的另一种观点表明，CS 放电的调制随着表现误差的减小而增加，并且在适应完成后会发现最大和稳定的 CS 调制（Catz 等人，2005 年）。我们想知道这种模式是否可以推广到其他形式的运动适应。我们以平滑追踪适应（SPA）为例，研究小脑依赖的适应。SPA 是通过在追踪开始时增加或减少目标速度来诱导的，这会导致眼速度逐渐增加或减少。我们训练了 2 只恒河猴，并在 SPA 期间记录了 VI 和 VII 蚓部的 CS。我们发现 SPA 伴随着 CS 放电模式，在适应开始时，即误差较大时，CS 放电模式没有明显调制。另一方面，当初始眼速度通过适应稳定增加或减小时，在追踪开始时 CS 发生的概率分别降低或增加。总的来说，我们的结果与经典的误差编码概念的预测不符。
