tDCS was applied via water-soaked pair of surface sponge electrodes (35 cm2) and delivered through battery-driven power supply. The constant current stimulator had a maximum output of 10 mA (Soterixmedical, Model 1224-B, New York, USA). The stimulation site over the left M1, located based on the international electroencephalography (EEG) 10/20 electrode placement system. The reference electrode was placed over the right shoulder area. The tDCS device was designed to allow sham stimulation by placing the control switch in front of the instrument which was easily covered by an opaque adhesive during stimulation. Therefore the participants or their gradients could not know whether active or sham stimulation. The power lit up indicator was also on the front of the machine during the time of intervention both in active and sham stimulations. However, in sham stimulation, the current was discontinued after 30 seconds while the power indicator remained on [18].