Shapiro Mark B, Gottlieb Gerald L, Corcos Daniel M
School of Kinesiology, University of Illinois, Chicago, Illinois 60608, USA.
J Neurophysiol. 2004 May;91(5):2135-47. doi: 10.1152/jn.00966.2003. Epub 2004 Jan 14.
When moving an object, the motor system estimates the dynamic properties of the object and then controls the movement using a combination of predictive feedforward control and proprioceptive feedback. In this study, we examined how the feedforward and proprioceptive feedback processes depend on the expected movement task. Subjects made fast elbow flexion movements from an initial position to a target. The experimental protocol included movements made over a short and a long distance against an expected light or heavy inertial load. In each task in a few randomly chosen trials, a motor applied an unexpected viscous load that produced a velocity error, defined as the difference between the expected and unexpected velocities, and electromyographic (EMG) responses. The EMG responses appeared not earlier than 170-250 ms from the agonist EMG onset. Our main finding is that the onset of the EMG responses was correlated with the expected time of peak velocity, which increased for longer distances and larger loads. An analysis of the latency of the EMG responses with respect to the velocity error suggested that the EMG responses were due to segmental reflexes. We conclude that segmental reflex gains are centrally modulated with the time course dependent on the expected movement task. According to this view, the control of fast point-to-point movement is feedforward from the agonist EMG onset until the expected time of peak velocity after which the segmental reflex feedback is briefly facilitated.
在移动物体时，运动系统会估计物体的动态特性，然后使用预测性前馈控制和本体感受反馈相结合的方式来控制运动。在本研究中，我们研究了前馈和本体感受反馈过程如何依赖于预期的运动任务。受试者从初始位置快速进行肘部屈曲运动至目标位置。实验方案包括在预期的轻或重惯性负载下进行短距离和长距离的运动。在每个任务的一些随机选择的试验中，一个电机施加意外的粘性负载，产生速度误差，定义为预期速度与意外速度之间的差异，以及肌电图（EMG）反应。EMG反应在激动剂EMG开始后不早于170 - 250毫秒出现。我们的主要发现是，EMG反应的开始与预期的峰值速度时间相关，峰值速度时间会随着距离增加和负载增大而增加。对EMG反应相对于速度误差的潜伏期分析表明，EMG反应是由于节段性反射引起的。我们得出结论，节段性反射增益在中枢受到调制，其时程取决于预期的运动任务。根据这一观点，快速点对点运动的控制从前馈开始，即从激动剂EMG开始到预期的峰值速度时间，在此之后节段性反射反馈会短暂增强。
