In the present study, the motor learning was studied by observing and measuring handwriting performance components. Considering the hypothesis that handwriting movements become faster with motor learning (Overvelde & Hulstijn, 2011), our results suggest that the M1 and left dorsolateral prefrontal cortex are the brain structures
mainly associated with MP effects on motor skill performance. In contrast to previous studies, where motor imagery alone sufficed to induce motor improvement (Blair et al., 1993; Roure et al., 1999; Gentili et al., 2006, 2010), in our study, although there was a slight trend for a reduction of writing time after MP (sham tDCS group), the motor imagery alone did not significantly alter motor learning. One reason for this discrepancy Torin 1 cell line might be that one session of MP would not CDK inhibitor be able to induce motor skill improvement. Indeed, most studies with no evidence of the effectiveness of mental imagery
on motor improvement conducted evaluation of MP outcomes on the same day, usually after only one session (Epstein, 1980; Wilkes & Summers, 1984; Woolfolk et al., 1985). For optimal results, Warner & McNeill (1988) recommend a minimum of five mental training sessions on separate days. Another alternative explanation for the MP used in our study not being effective enough to improve the motor skill might be due to the fact that, in the present study, we used audiotape with directed instruction of MP (externally guided task). An active mental process in contrast to passiveness seems to be more effective in producing neural modulation after motor imagery (Jones, 1965). In the passive
mental process, using directed instructions during the mental activity, subjects may tend Non-specific serine/threonine protein kinase to follow the mechanically taped instruction rather than create their own mental image similar to when MP is self-directed (Warner & McNeill, 1988). The observed trend of reduced time of the handwriting task with the non-dominant hand after MP was confirmed when it was associated with anodal tDCS on the M1. In line with this result, as mental and physical motor practice share common neural substrates (Ehrsson et al., 2003; Bakker et al., 2007), improvements in motor function as measured by clinical scores have been described for combined tDCS with motor practice in both healthy (Dockery et al., 2009) and stroke (Fregni et al., 2005a; Hummel & Cohen, 2005; Hesse et al., 2007; Celnik et al., 2008) patients. The mechanisms of action underlying motor practice (mental or physical)-induced and/or tDCS-induced performance enhancement are not well understood. However, as the learning facilitation seems to be a process dependent on increasing the cortical excitability (Nitsche et al.