Corticospinal excitability related to reciprocal muscles during the motor preparation period: effect of movement repetition

Objectives Voluntary movements require a preparatory phase before action initiation to elaborate optimal motor commands. This study investigated the time course of change in corticospinal excitability related to each agonist or antagonist muscle during the motor preparation period and the influence of movement repetition on time course change in corticospinal excitability. Methods The participants were instructed to perform wrist flexion as quickly as possible in response to the appearance of a red circle. One hundred fifty milliseconds after the presentation of the red circle cue, we delivered transcranial magnetic stimulation at the primary motor cortex related to the agonist flexor and the antagonist extensor carpi radialis muscles. Results The motor evoked potential amplitudes for both the flexor and extensor carpi radialis during the motor preparation period which were regressed on the logarithm of time, and there were no significant differences in the slope of the logarithmic curves in the early half trials of movement repetition. However, the slope of the logarithmic curve of the flexor carpi radialis was steeper than that of the extensor carpi radialis in the late half trials of movement repetition. Conclusion These results implied that corticospinal excitability for agonist muscles during the motor preparation period is consistently modulated by movement repetition, whereas that for antagonist muscles is weakened by movement repetition. Copyright (C) 2019 Wolters Kluwer Health, Inc. All rights reserved.