Blazquez Pablo M, Hirata Yutaka, Highstein Stephen M
Department of Otolaryngology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Cerebellum. 2004;3(3):188-92. doi: 10.1080/14734220410018120.
Motor systems are under a continuous adaptive process to maintain behavior throughout developmental changes and disease, a process called motor learning. Simple behaviors with easily measurable inputs and outputs are best suited to understand the neuronal signals that contribute to the required motor learning. Considering simple behaviors, the vestibulo-ocular reflex (VOR) allows quantification of its input and motor output and its neural circuitry is among the best documented. The main candidates for plastic change are the cerebellum and its target neurons in the brainstem. This review focuses on recent data regarding the involvement of the cerebellum in VOR motor learning. Learning can be divided into that acutely acquired over a period of hours and that chronically acquired over longer periods. Both acute and chronic learning have three phases named acquisition, consolidation, and retention. The cerebellar role in retention is disputed, but there is a consensus on the need of an intact cerebellum for acquisition. Data from neuronal recording, lesion studies and transgenic mouse experiments is complex but suggests that the signal representation in the cerebellum contains aspects of both motor output and sensory input. The cerebellum apparently uses different mechanisms for acute and chronic learning as well as for increases and decreases in VOR gain. Recent studies also suggest that the signal content in the cerebellum changes following learning and that the mechanisms used for chronic adaptation involve not only changes in a head velocity component but also in the efference copy of an eye movement command signal reaching Purkinje cells. This data leads to a new conceptual framework having implications for developing theories on the role of the cerebellum in motor learning and in the search for plastic elements within the VOR circuitry. For chronic learning we hypothesize that changes in the head velocity information traveling through the circuitry occur in parallel with changes in the integrator pathway and the efference copy pathway. We further propose that these changes are necessary to maintain the broadband characteristics of the learned behavior.
运动系统处于持续的适应性过程中，以在整个发育变化和疾病过程中维持行为，这个过程称为运动学习。具有易于测量的输入和输出的简单行为最适合用于理解促成所需运动学习的神经元信号。考虑到简单行为，前庭眼反射（VOR）能够对其输入和运动输出进行量化，并且其神经回路是记录最完备的之一。可塑性变化的主要候选者是小脑及其在脑干中的靶神经元。本综述聚焦于有关小脑参与VOR运动学习的最新数据。学习可分为在数小时内急性获得的和在较长时期内慢性获得的。急性和慢性学习都有三个阶段，即获得、巩固和保持。小脑在保持阶段的作用存在争议，但对于获得阶段需要完整的小脑这一点已达成共识。来自神经元记录、损伤研究和转基因小鼠实验的数据很复杂，但表明小脑中的信号表征包含运动输出和感觉输入两方面的内容。小脑显然对急性和慢性学习以及VOR增益的增加和减少使用不同的机制。最近的研究还表明，学习后小脑中的信号内容会发生变化，并且用于慢性适应的机制不仅涉及头部速度成分的变化，还涉及到达浦肯野细胞的眼动指令信号的传出副本的变化。这些数据导致了一个新的概念框架，对发展关于小脑在运动学习中的作用的理论以及在VOR神经回路中寻找可塑性元件具有启示意义。对于慢性学习，我们假设通过神经回路传播的头部速度信息的变化与积分器通路和传出副本通路的变化同时发生。我们进一步提出，这些变化对于维持所学行为的宽带特性是必要的。
