Adaptive control of saccades via internal feedback
Adaptive control of saccades via internal feedback
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DOI：
10.1523/jneurosci.5300-07.2008
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发表时间：
2008-03-12
影响因子：
5.3
通讯作者：
Shadmehr, Reza
中科院分区：
文献类型：
--
作者：
Chen-Harris, Haiyin;Joiner, Wilsaan M.;Shadmehr, Reza
像扫视这样的弹道运动需要大脑在没有感觉反馈的情况下产生运动指令。尽管如此，扫视是非常准确的。理论表明，这种准确性的出现是因为大脑依赖于一个内部的前向模型，该模型监测运动命令，预测其感官后果，并在飞行中纠正眼球轨迹。如果扫视的控制依赖于前向模型，则前向模型应该在其预测与运动结束时的感觉反馈不匹配时进行调整。使用最优反馈控制理论，我们预测这种适应应该如何改变眼跳轨迹。我们训练受试者的一个范例中，水平的目标垂直跳眼跳。通过训练，扫视的最终位置移向第二个目标。然而，扫视变得越来越弯曲，即，次优的，因为在线校正眼动命令以将眼睛转向第二目标。适应性反应有两个组成部分：（1）启动眼跳的运动指令变化缓慢，使眼跳更接近跳跃的目标。这些最早的运动指令的适应在休息期间表现出很少的遗忘。(2)在眼跳轨迹的后期，另一种适应性反应使它更接近跳跃的目标，产生曲率。在休息期间，这些晚期运动指令的适应表现出近乎完全的遗忘。这两种成分在不同的时间尺度上适应，迟效成分显示出更快的速度。看来，在控制扫视，大脑依赖于内部反馈，具有快速适应的前向模型的特点。
Ballistic movements like saccades require the brain to generate motor commands without the benefit of sensory feedback. Despite this, saccades are remarkably accurate. Theory suggests that this accuracy arises because the brain relies on an internal forward model that monitors the motor commands, predicts their sensory consequences, and corrects eye trajectory midflight. If control of saccades relies on a forward model, then the forward model should adapt whenever its predictions fail to match sensory feedback at the end of the movement. Using optimal feedback control theory, we predicted how this adaptation should alter saccade trajectories. We trained subjects on a paradigm in which the horizontal target jumped vertically during the saccade. With training, the final position of the saccade moved toward the second target. However, saccades became increasingly curved, i.e., suboptimal, as oculomotor commands were corrected on-line to steer the eye toward the second target. The adaptive response had two components: (1) the motor commands that initiated the saccades changed slowly, aiming the saccade closer to the jumped target. The adaptation of these earliest motor commands displayed little forgetting during the rest periods. (2) Late in saccade trajectory, another adaptive response steered it still closer to the jumped target, producing curvature. Adaptation of these late motor commands showed near-complete forgetting during the rest periods. The two components adapted at different timescales, with the late-acting component displaying much faster rates. It appears that in controlling saccades, the brain relies on an internal feedback that has the characteristics of a fast-adapting forward model.