Corticomuscular coherence reflects somatosensory feedback gains during motor adaptation.

Beta-band corticomuscular coherence (CMC) observed between the sensorimotor cortex activity and contracting muscle is declaratively described as a neurophysiological reflection of sensorimotor binding. However, much remains unknown about the functional meaning of 'sensorimotor binding.' The efficacy of information binding in the sensorimotor system is assumed to be influenced by the gain of the feedback controller, which is regulated through a process that may in part be implemented in the primary sensorimotor cortex (SM1). Thus, we predicted that CMC is modulated together with feedback gains during motor learning. We examined this hypothesis using a hand-reaching adaptation task under a novel dynamical environment. CMC modulation was assessed before and after adaptation, and feedback gains were probed by long latency triggered muscle reactions. Overall, we found that CMC significantly decreased during the adaptation period, and such CMC decrease was associated with the decreased long latency reflexes. These results suggest that CMC has a related function to modulation of feedback gains. Our findings provided an electrophysiological hallmark of the sensorimotor binding process, which was stated as a function of CMC but poorly understood.

Difference in the electromyographic onset of the deep and superficial multifidus during shoulder movement while standing.

Based on the current literature, it remains unclear whether electromyographic onset of the deep fibers of the multifidus (DM) is dependent on the direction of shoulder movement and the position of the center of foot pressure (CFP). In the present study, we re-examined the electromyographic onset of the DM during shoulder flexion and extension and investigated the influence of the CFP position before arm movement. Intramuscular and surface electrodes recorded the electromyographic onset of the DM, superficial fibers of the multifidus (SM), rectus abdominis, and anterior and posterior deltoid. Eleven healthy participants performed rapid, unilateral shoulder flexion and extension in response to audio stimuli at three CFP positions: quiet standing, extreme forward leaning, and extreme backward leaning. It was found that the electromyographic onset of the DM and SM relative to the deltoid was dependent on the direction of arm movement. Additionally, of all electromyographic onsets recorded, only that of the DM occurred earlier in the extreme forward leaning position than in the extreme backward leaning position during shoulder flexion. These results suggest that the electromyographic onset of DM was influenced by the biomechanical disturbance such as shoulder movement and CFP position.