However, further investigation is needed to understand how brain stimulation can consolidate motor improvement after mental training. It is highly unlikely that the observed effect of the present study is due to an effect of anodal tDCS alone on the M1. Studies point out that a single tDCS Pexidartinib session might not be sufficient to

modify sensorimotor learning of a highly skilled task (Boggio et al., 2006; Buttkus et al., 2011). Thus, it is probable that the association between MP and tDCS was, in fact, responsible for reducing the writing time with the non-dominant hand. At first sight, compared with baseline, anodal tDCS on the SMA and PMA also seems to decrease the time of the handwriting task after MP. However, these results were not statistically significant. This negative finding was not expected, as SMA and PMA activation during MP is well documented (Stephan et al., 1995; Lotze et al., 1999). It is possible this website that the MP type (externally guided motor imagery) used in our study was not

effective enough to activate the SMA. Electrophysiological studies in monkeys point out that the SMA exhibits preferential activity during internally-guided movements and PMA neurons are more active during externally guided tasks (Mushiake et al., 1991; Tanji & Shima, 1994). In line with our result, another study, which used an externally guided task, nearly also failed to show after-effects of repetitive transcranial magnetic stimulation over the SMA on the performance of a tapping task (Del Olmo et al., 2007). However, excitability elevation of the PMA induced by anodal tDCS did not also improve the non-dominant handwriting skill. We cannot exclude the possibility that, because medial and lateral area 6 is located further from the surface of the scalp than the M1, our tDCS protocol was unable to activate neurons in the SMA and PMA. In a former study, anodal tDCS on the premotor cortex, in contrast to on

the M1, also resulted in no effect on motor learning (Nitsche et al., 2003b), which suggests that the pattern of tDCS-induced plasticity changes might be slightly different in distinct cortical areas. Anodal tDCS on the left DLPFC applied during mental training clearly decreased the writing time not only relative to baseline, but also compared with the sham condition. Knowledge about the cognitive processes (such as working memory) responsible for generating the motor actions needed for producing written words (Purcell et al., 2011) can help to understand these results. Motor plans for producing the writing, such as letter forms, the size and ordering of the strokes, and subsequently, effector-specific motor programming compiles instructions for the specific limb to be used in carrying out the motor actions, held in memory working (Ellis & Young, 1988).