Comparing effects of 1 mA M1 a-tDCS and c-tDCS
It was hypothesized in the current study that 1 mA M1 a-tDCS compared to 1 mA M1 c-tDCS had more effects on online and offline motor learning. The findings of the current study were consisting with this hypothesis and even indicated disturbing effects of 1 mA c-tDCS as compared to 1 mA a-tDCS on motor learning. In this regard, there is evidence that applying M1 a-tDCS leads to an increase in excitability of the region through modulation of NMDA receptors, GABA receptors, BDNF, and calcium-dependent mechanisms (Liebetanz et al. , 2002; Nitscheet al. , 2003; Stagg et al. , 2009). It appears that anodal stimulation leads to a reduction in the activation threshold and ultimately increases the opening of voltage-dependent ion channels (Pellicciari et al. , 2013). By depolarizing the postsynaptic membrane and increasing the presynaptic firing frequency, it strengthens synaptic connections and improves learning (Pellicciari et al. , 2013). On the other hand, cathodal stimulation at 1 mA leads to decreased neuronal excitability due to an increase in the activation threshold (Pellicciari et al. , 2013). Additionally, reducing presynaptic activity and hyperpolarization in the postsynaptic membrane weaken synaptic connections (Pellicciari et al. , 2013). The results of the current study also indicated that M1 1 mA a-tDCs as compared to M1 1 mA c-tDCS induces more online and offline motor learning.