Chen Yi-Ching, Lin Yen-Ting, Chang Gwo-Ching, Hwang Ing-Shiou
School of Physical Therapy, Chung Shan Medical UniversityTaichung, Taiwan; Physical Therapy Room, Chung Shan Medical University HospitalTaichung, Taiwan.
Physical Education Room, Asian University Taichung, Taiwan.
Front Physiol. 2017 Mar 13;8:140. doi: 10.3389/fphys.2017.00140. eCollection 2017.
The detection of error information is an essential prerequisite of a feedback-based movement. This study investigated the differential behavior and neurophysiological mechanisms of a cyclic force-tracking task using error-reducing and error-enhancing feedback. The discharge patterns of a relatively large number of motor units (MUs) were assessed with custom-designed multi-channel surface electromyography following mathematical decomposition of the experimentally-measured signals. Force characteristics, force-discharge relation, and phase-locking cortical activities in the contralateral motor cortex to individual MUs were contrasted among the low (LSF), normal (NSF), and high scaling factor (HSF) conditions, in which the sizes of online execution errors were displayed with various amplification ratios. Along with a spectral shift of the force output toward a lower band, force output with a more phase-lead became less irregular, and tracking accuracy was worse in the LSF condition than in the HSF condition. The coherent discharge of high phasic (HP) MUs with the target signal was greater, and inter-spike intervals were larger, in the LSF condition than in the HSF condition. Force-tracking in the LSF condition manifested with stronger phase-locked EEG activity in the contralateral motor cortex to discharge of the (HP) MUs (LSF > NSF, HSF). The coherent discharge of the (HP) MUs during the cyclic force-tracking predominated the force-discharge relation, which increased inversely to the error scaling factor. In conclusion, the size of visualized error gates motor unit discharge, force-discharge relation, and the relative influences of the feedback and feedforward processes on force control. A smaller visualized error size favors voluntary force control using a feedforward process, in relation to a selective central modulation that enhance the coherent discharge of (HP) MUs.
错误信息的检测是基于反馈的运动的一个基本前提。本研究调查了使用减少误差和增强误差反馈的周期性力跟踪任务的差异行为和神经生理机制。在对实验测量信号进行数学分解后，采用定制设计的多通道表面肌电图评估了相对大量运动单位（MU）的放电模式。在低（LSF）、正常（NSF）和高比例因子（HSF）条件下，对比了对单个MU的对侧运动皮层中的力特性、力-放电关系和锁相皮层活动，其中在线执行误差的大小以不同放大率显示。随着力输出频谱向较低频段的偏移，具有更多相位超前的力输出变得不那么不规则，并且LSF条件下的跟踪精度比HSF条件下更差。与HSF条件相比，LSF条件下高相位（HP）MU与目标信号的相干放电更大，且峰间期更大。LSF条件下的力跟踪在对侧运动皮层中表现为与（HP）MU放电更强的锁相脑电图活动（LSF>NSF，HSF）。周期性力跟踪期间（HP）MU的相干放电主导了力-放电关系，其与误差比例因子成反比增加。总之，可视化误差的大小控制着运动单位放电、力-放电关系以及反馈和前馈过程对力控制的相对影响。较小的可视化误差大小有利于使用前馈过程进行自主力控制，这与增强（HP）MU相干放电的选择性中枢调制有关。
