Motor training modulates intracortical inhibitory dynamics in motor cortex during movement preparation

Abstract

Background: The primary motor cortex (M1) has a vital role to play in the learning of novel motor skills. However, the physiological changes underpinning this learning, particularly in terms of dynamic changes during movement preparation, are incompletely understood. In particular, a substantial decrease in resting gamma-amino butyric acid (GABA) activity, i.e. a release of resting inhibition, is seen within M1 as a subject prepares to move. Although there is evidence that a decrease in resting inhibition occurs within M1 during motor learning it is not known whether the pre-movement "release" of GABAergic inhibition is modulated during skill acquisition. Objective: Here, we investigated changes in pre-movement GABAergic inhibitory "release" during training on a motor skill task. Methods: We studied GABAA activity using paired-pulse TMS (Short-Interval Intracortical Inhibition (SICI)) during training on a ballistic thumb abduction task, both at rest and at two time-points during movement preparation. Results: Improvement in task performance was related to a later, steeper, release of inhibition during the movement preparation phase. Specifically, subjects who showed greater improvement in the task in the early stages of training showed a reduced level of GABAergic release immediately prior to movement compared with those who improved less. Later in training, subjects who performed better showed a reduction in GABAergic release early in movement preparation. Conclusions: These findings suggest that motor training is associated with maintained inhibition in motor cortex during movement preparation.

Increasing motor skill acquisition by driving theta-gamma coupling

“…104 healthy participants performed a M1-dependent ballistic thumb abduction task with their left hand [32][33][34] while tACS was applied over the right M1. Volunteers trained to increase thumb abduction acceleration in their left, non-dominant, thumb over 5 blocks of 70 trials each (figure 1).…”

“…Participants performed a ballistic thumb abduction training task requiring abduction of their left (nondominant) thumb with maximal acceleration [32][33][34] . Participants were seated with their left arm slightly abducted, with the elbow flexed to 45° (where 0° is full extension) and the forearm semi-pronated with the palm facing inwards.…”

“…Data were analysed via Matlab (Mathworks). The maximal acceleration was calculated for each trial, and any trials with a maximum acceleration less than 4.9ms 2 were rejected 32 . Additionally, if movements were made too early or too late, i.e.…”

“…Additionally, if movements were made too early or too late, i.e. the onset of acceleration of the movement lay more than 300 ms before or after the expected movement time, they were also rejected 32…”

“…We therefore wished to test the hypothesis that θ-γ PAC is a conserved mechanism for learning across the brain. To investigate the functional role of θ-γ PAC in learning outside the hippocampus, we modulated local theta-gamma activity via externally applied alternating current stimulation (tACS) over M1 during learning of an M1-dependent skill 32 , which shows robust behavioural improvements over a relatively short period of time.…”