Transcranial direct current stimulation
In the current study, tDCS device (ActivaDose® II, ActivaTeKTM Inc., Gilroy, CA, USA) was used to apply direct current intensities of 1 and 2 mA for 20 min concurrent with SRTT training. The current intensity was controlled by the ammeter of the device. The size of the stimulation electrodes was 5×7 cm. The electrodes were carbon rubber electrodes. The current ramp-up and down during a period of 10 seconds of the beginning and the end of stimulation.
In two M1 a-tDCS groups, the active anode electrode was placed over the left M1 (C3, International 10–20 system) and the cathode return electrode was placed over the right side of the contralateral supraorbital area, respectively. In the two c-tDCS groups, the active cathode electrode was located over the left M1 (C3, International 10–20 system) and the return anode electrode was located over the right side of the contralateral supraorbital area. The electrodes were placed transversely over left M1 area and right supraorbital region. Electrical stimulation was administered to either the M1 a-tDCS or M1 c-tDCS groups at an intensity of 1 mA, while the remaining groups received stimulation at an intensity of 2 mA.
In the Sham tDCS group, electrodes labeled as anode and cathode, along with a stimulation intensity of 1 mA or 2 mA, were randomly chosen and placed over the designated areas for a duration of 20 minutes. The stimulation was gradually deactivated after 30 seconds, following the Fade-in Short Stimulation Fade-out (FiSsFo) approach. Nonetheless, the electrode montage mirrored that of the active M1 tDCS groups.