Highstein Stephen M, Porrill John, Dean Paul
Department of Otolaryngology, Washington University School of Medicine, St Louis, Missouri, USA.
Cerebellum. 2005;4(2):140-50. doi: 10.1080/14734220510007987.
A one-day meeting on the cerebellum and motor learning was held in St Louis (October 2004), to address issues arising from a previous larger meeting (Tuebingen, June 2004). The learning tasks considered were VOR adaptation, saccadic adaptation and eyeblink conditioning. A theoretical development was reported that indicated how the cerebellum could use sensory error signals for adaptive control, by decorrelating them from an efferent copy of motor commands. The main topics for discussion were the nature of the error signals actually used by the cerebellum, and the evidence for multiple sites of synaptic plasticity. Reports of studies on VOR adaptation confirmed the presence of error signals in addition to retinal slip, in particular the eye-movement related simple-spike firing of floccular PCs. This firing appears to drive synaptic plasticity in the vestibular nuclei. From a theoretical perspective, a second site of plasticity in the brainstem has two advantages: it improves the high-frequency performance of the VOR given a delayed slip signal, and it allows VOR adaptation when smooth pursuit effectively removes the retinal slip signal. In contrast, some of the physiological data reported on saccadic adaptation seemed incompatible with current theoretical ideas about error signals. However, since other reported data were broadly consistent with those ideas, an important area of experimental disagreement was identified. Furthermore, behavioural studies indicated the presence of multiple sites of plasticity, consistent with earlier lesion studies that suggested one such site within cerebellar cortex and another outside it. Data from eyeblink conditioning suggested that the predictability of the error signal was important. Related ideas have previously emerged from studies of skeletal movement, but their theoretical implications for the cerebellar algorithm have yet to be fully explored. Finally, the long-standing controversy concerning sites of plasticity in eyeblink conditioning illustrated the technical difficulties involved in tracking down such sites.
2004年10月，一场关于小脑与运动学习的为期一天的会议在圣路易斯召开，旨在探讨此前一场规模更大的会议（2004年6月于图宾根召开）所引发的问题。会议所讨论的学习任务包括前庭眼反射（VOR）适应性、扫视适应性以及眨眼条件反射。会上报告了一项理论进展，该进展表明小脑如何通过将感觉误差信号与运动指令的传出副本去相关，从而利用这些信号进行适应性控制。讨论的主要话题包括小脑实际使用的误差信号的性质，以及突触可塑性多个位点的证据。关于VOR适应性的研究报告证实，除了视网膜滑动外还存在误差信号，特别是绒球浦肯野细胞（PC）与眼动相关的单峰放电。这种放电似乎驱动了前庭核中的突触可塑性。从理论角度来看，脑干中可塑性的第二个位点有两个优点：在存在延迟滑动信号的情况下，它能改善VOR的高频性能，并且当平稳跟踪有效地消除视网膜滑动信号时，它能使VOR产生适应性变化。相比之下，所报告的一些关于扫视适应性的生理数据似乎与当前关于误差信号的理论观点不相符。然而，由于其他报告的数据与这些观点大致一致，因此确定了一个重要的实验分歧领域。此外，行为学研究表明存在多个可塑性位点，这与早期的损伤研究一致，早期研究表明一个位点在小脑皮质内，另一个在小脑皮质外。眨眼条件反射的数据表明误差信号的可预测性很重要。相关观点此前已在骨骼肌运动研究中出现，但其对小脑算法的理论影响尚未得到充分探索。最后，关于眨眼条件反射中可塑性位点的长期争议说明了追踪这些位点所涉及的技术困难。
