Abstract
Proactive motor control refers to endogenous preparatory mechanisms facilitating the selection of a specific motor effector and it can be affected by implicit statistical learning. In this study, we aimed to investigate whether transcranial random noise stimulation (tRNS) over frontoparietal regions, areas involved in attentional functions, may affect proactive motor inhibition driven by implicit statistical learning. 40 healthy participants were asked to discriminate a horizontally oriented target (high-contrast Gabor) presented simultaneously with a vertically oriented one. Stimuli were preceded by two different color cues each one always associated with one of the two hands, across all conditions. Crucially, color cues also indicated the location where the stimuli would be presented. Subjects responded by key press, using the hand assigned to the preceding colored cue. We measured performance at baseline, and immediately after training on the task that could be coupled either with active tRNS or sham. During training, and unbeknownst to the subjects, target position relative to the distractor could either be balanced (Group1), with equal probability that the target appeared to the left or right of the distractor, or unbalanced (Group2), with a higher probability (75%) for the target to appear to the right of the distractor. Results showed that response times in the post-test were biased by the training type, and this pattern was enhanced by the left frontoparietal stimulation, compared to sham. Specifically, in the balanced condition subjects were faster at responding to the stimuli with the right hand after active tRNS. However, in the unbalanced condition subjects responded faster to targets presented to the right of the distractor, irrespective of the responding hand. These results indicate that tRNS likely boosted the effect of implicit visual statistical learning over proactive motor control.