Cerebellar contributions to adaptive control of saccades in humans.
Cerebellar contributions to adaptive control of saccades in humans.
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DOI：
10.1523/jneurosci.3115-09.2009
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发表时间：
2009-10-14
期刊：
影响因子：
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通讯作者：
Shadmehr R
中科院分区：
文献类型：
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作者：
Xu-Wilson M;Chen-Harris H;Zee DS;Shadmehr R
小脑可以监控运动指令，并通过内部反馈纠正预期的错误。扫视是对这一观点的一种测试，因为这些动作完成得太快，感官反馈无法发挥作用。早些时候，我们报道了加速眼睛走向恒定振幅目标的运动指令表现出可变性。在这里，我们证明了这种可变性不是随机噪声，而是由于主体的认知状态。健康的人在扫视期内会用在同一扫视期较晚到达的指令来补偿这种可变性。然而，在患有小脑损伤的人群中，同样的变异性导致了测量障碍。这种纠正引发扫视的运动指令的可变性的能力可以预测每个受试者从端点错误中学习的能力。在水平子午线上的目标在扫视过程中垂直跳跃（导致端点误差）的范式中，自适应反应表现出两个时间尺度：快速时间尺度，从端点误差中学习快，但保留率差；慢时间尺度，学习慢，但保留率强。小脑皮质损伤后，快速适应时间标度缺失，慢速适应时间标度受损程度较轻。因此，小脑通过一种适应性反应来纠正在同一运动中启动扫视的运动命令的可变性，这种反应不仅对先前的端点错误表现出强烈的敏感性，而且还表现出快速遗忘。
The cerebellum may monitor motor commands and through internal feedback corrects for anticipated errors. Saccades provide a test of this idea because these movements are completed too quickly for sensory feedback to be useful. Earlier we reported that motor commands that accelerate the eyes toward a constant amplitude target showed variability. Here, we demonstrate that this variability is not random noise, but is due to the cognitive state of the subject. Healthy people showed within saccade compensation for this variability with commands that arrived later in the same saccade. However, in people with cerebellar damage, the same variability resulted in dysmetria. This ability to correct for variability in the motor commands that initiated a saccade was a predictor of each subject’s ability to learn from endpoint errors. In a paradigm in which a target on the horizontal meridian jumped vertically during the saccade (resulting in an endpoint error), the adaptive response exhibited two timescales: a fast timescale that learned quickly from endpoint error but had poor retention, and a slow timescale that learned slowly but had strong retention. With cortical cerebellar damage, the fast timescale of adaptation was effectively absent, but the slow timescale was less impaired. Therefore the cerebellum corrects for variability in the motor commands that initiate saccades within the same movement via an adaptive response that not only exhibits strong sensitivity to previous endpoint errors, but also rapid forgetting.