Lai E J, Hodgson A J, Milner T E
Department of Mechanical Engineering, University of British Columbia, 2324 Main Mall, Vancouver, BC, V6T 1Z4, Canada.
Exp Brain Res. 2003 Nov;153(1):76-83. doi: 10.1007/s00221-003-1584-4. Epub 2003 Aug 29.
Studies have shown that the point-to-point reaching movements of subjects seated in a dark, rotating room demonstrate errors in movement trajectories and endpoints, consistent with the direction of the Coriolis force perturbations created by room rotation. Adaptation of successive reaches and the presence of postrotation aftereffects have indicated that subjects form internal models of the Coriolis field dynamics in order to make appropriate movement corrections. It has been argued that these findings are inconsistent with predictions of peripheral stabilization assumed in equilibrium-point models of motor control. A possibility that has been raised, however, is that the Coriolis field findings may in fact stem from changes in control commands elicited due to the magnitude and destabilizing nature of the Coriolis perturbations. That is, it has been suggested that a perturbation threshold exists, below which central reactions are not necessary in order to maintain movement stability. We tested the existence of a perturbation threshold in normal-speed reaching movements. Twelve normal human subjects performed non-visually guided reaching movements while grasping a robotic manipulandum. The endpoints and trajectory deviations of their movements were measured before, during, and after a position-dependent force field (similar to a Coriolis field in terms of the time history of applied forces) was applied to their movements. We examined the responses to a range of perturbation field strengths from small to considerable. Our experimental results demonstrated a substantial adaptation response over the entire range of perturbation field magnitudes examined. Neither the amount of adaptation after 5 trials nor after 25 trials was found to change as disturbance magnitudes decreased. These findings indicate that there is an adaptive response even for small perturbations; i.e., threshold behavior was not found. This result contradicts the assertion that peripheral stabilization mechanisms enable the central controller to ignore small details of peripheral or environmental dynamics. Our findings instead point to a central dynamic modeler that is both highly sensitive and continually active. The results of our study also showed that subjects were able to maintain baseline pointing accuracies despite exposure to perturbation forces of sizeable magnitude (more than 7 N).
研究表明，坐在黑暗、旋转房间里的受试者进行的点对点伸手动作，在运动轨迹和终点上表现出误差，这与房间旋转产生的科里奥利力扰动方向一致。连续伸手动作的适应性以及旋转后效应的存在表明，受试者会形成科里奥利场动力学的内部模型，以便进行适当的运动校正。有人认为，这些发现与运动控制平衡点模型中假设的外周稳定预测不一致。然而，有人提出的一种可能性是，科里奥利场的发现实际上可能源于由于科里奥利扰动的大小和破坏稳定性的性质而引起的控制命令变化。也就是说，有人认为存在一个扰动阈值，低于该阈值，为了保持运动稳定性，中枢反应是不必要的。我们测试了正常速度伸手动作中扰动阈值的存在情况。12名正常人类受试者在握住机器人操作器时进行非视觉引导的伸手动作。在对他们的动作施加位置相关力场（就施加力的时间历程而言类似于科里奥利场）之前、期间和之后，测量他们动作的终点和轨迹偏差。我们研究了对从小到相当大的一系列扰动场强度的反应。我们的实验结果表明，在所研究的整个扰动场大小范围内都有显著的适应性反应。未发现随着干扰幅度减小，5次试验后或25次试验后的适应量发生变化。这些发现表明，即使对于小扰动也存在适应性反应；即未发现阈值行为。这一结果与外周稳定机制使中枢控制器能够忽略外周或环境动力学小细节的断言相矛盾。我们的发现反而指向一个高度敏感且持续活跃的中枢动态建模器。我们的研究结果还表明，尽管受到相当大的扰动力（超过7牛）作用，受试者仍能够保持基线指向精度。
