not-yet-known not-yet-known not-yet-known unknown The effects of 1 or 2 mA M1 c-tDCS compared to sham tDCS on motor learning According to the second hypothesis of the current study, c-tDCS with an intensity of 1 mA led to an inhibitory effect on online and offline motor learning. The findings of the current study supported this hypothesis. Similarly, Stagg et al. (2011) demonstrated that applying 1 mA c-tDCS decreased motor learning (Stagg et al. , 2011). Additionally, Pellicciari et al. (2013) showed that c-tDCS with an intensity of 1 mA led to a decrease in excitability and a reduced cortical response (Pellicciari et al. , 2013). On the other hand, Ciechanski et al. (2017) found that applying c-tDCS with a current intensity of 1 mA on the left M1 of right-handed children improved left-hand motor learning (Ciechanski & Kirton, 2017). It seems that the duration of c-tDCS application, the number of treatment sessions and the specific population under study may be the reasons of this controversy in the finding of the studies (Stagg et al. , 2011; Pellicciari et al. , 2013; Ciechanski & Kirton, 2017). However, the results of the current study indicate that c-tDCS with 1 mA current intensity not only doesn’t lead to enhance online and offline motor learning, but also induces inhibitory effects on online and offline motor learning. We also hypothesized that applying M1 c-tDCS with a current intensity of 2 mA deteriorate online and offline motor learning. The findings of the current study did not support this hypothesis and indicated that 2 mA c-tDCS improved the motor learning with reducing RT during online learning and decreasing the ER during offline learning. These results are consistent with the findings of the study conducted by Greeley et al. (2020). In line with the study by Greeley et al. (2020), the group receiving 2 mA M1 c-tDCS demonstrated a faster reduction in RT compared to the sham group (Greeley et al. , 2020). Additionally, the findings of the study by Ciechanski et al. (2017) indicated that applying M1 c-tDCS with a current intensity of 2 mA area enhances motor learning in children compared to the sham group (Ciechanski & Kirton, 2017).