Motor training strengthens corticospinal suppression during movement preparation

Training can improve motor skills and modify neural activity at rest and during movement execution. Learning-related modulations may also concern motor preparation but the neural correlates and the potential behavioral relevance of such adjustments remain unclear. In humans, preparatory processes have been largely investigated using transcranial magnetic stimulation (TMS) with several studies reporting decreased corticospinal excitability (CSE) relative to a baseline measure; a phenomenon called preparatory suppression. Here, we investigated the effect of motor training on preparatory suppression of CSE in humans, as compared to modulatory changes at rest. We trained participants to initiate quick movements in an instructed-delay reaction time (RT) task and used TMS to investigate changes in CSE over the practice blocks. Training on the task speeded up RTs, with no repercussion on error rates. Training also increased baseline CSE at rest. Most interestingly, we found that motor activity during action preparation did not mirror the training-related rise in resting CSE. Rather, the degree of preparatory suppression from the rising baseline strengthened with practice. This training-related change in preparatory suppression predicted RT gains (but not the changes in baseline CSE): subjects showing a stronger expansion of preparatory suppression were also those exhibiting larger gains in RTs. Finally, such relationship between RTs and preparatory suppression was also evident at the single-trial level: RTs were generally faster in trials where preparatory suppression was deeper. These findings suggest that training induces changes in motor preparatory processes that are linked to an enhanced ability to initiate fast movements. New and Noteworthy Any movement is preceded by a period of preparation, which involves a broad suppression of the corticospinal pathway, a phenomenon called preparatory suppression. Here, we show that motor training strengthens preparatory suppression and that this strengthening is associated with an acceleration of movement initiation. Our findings yield an extension of former work, highlighting a key role of preparatory suppression in training-driven behavioral improvements.