tDCS over left M1 or DLPFC does not improve learning of a bimanual coordination task

Abstract

Previously, transcranial direct current stimulation (tDCS) over the primary motor cortex (M1) hasresulted in improved performance in simple motor tasks. For a complex bimanual movement, studiesusing functional magnetic resonance imaging and transcranial magnetic stimulation indicated theinvolvement of the left dorsolateral prefrontal cortex (DLPFC) as well as left M1. Here we investigatedthe relative effect of up-regulating the cortical function in left DLPFC and left M1 with tDCS.Participants practised a complex bimanual task over four days while receiving either of five stimulationprotocols: anodal tDCS applied over M1, anodal tDCS over DLPFC, sham tDCS over M1, sham tDCSover DLPFC, or no stimulation. Performance was measured at the start and end of each training day tomake a distinction between acquisition and consolidation. Although task performance improved overdays, no significant difference between stimulation protocols was observed, suggesting that anodaltDCS had little effect on learning the bimanual task regardless of the stimulation sites and learningphase (acquisition or consolidation). Interestingly, cognitive performance as well as corticomotorexcitability did not change following stimulation. Accordingly, we found no evidence for behavioural orneurophysiological changes following tDCS over left M1 or left DLPFC in learning a complex bimanualtask.