 A crossover trial to establish an optimized tDCS protocol will be accomplished. Anodal and cathodal tDCS will be applied over the primary motor cortex C3 - active and contralateral supra-orbital region - reference and visual cortex Oz - active and Cz - reference. Dual tDCS anodal and cathodal - optimized protocol will be applied on C3 - active and Oz - active. 