Microlyte

During each testing block (Figure 1), tDCS was applied to the scalp over the target using a battery-powered Soterix 1X1 tDCS device (Figure 2; Soterix Medical Inc., New York, NY, USA). This single-channel device has one stimulating and one reference electrode. The device delivers a maximum of 2 mA of direct current stimulation for no more than 20 minutes. Stimulation was applied with carbon-rubber electrodes enclosed in disposable 3 × 5 cm sponge pockets. The sponges were saturated in normal saline (0.9% NaCl) and affixed to the head with a rubber headband adjusted to fit snugly but without discomfort. To enhance the connection, standard conductive gel (Microlyte, Coulbourn Instruments, Whitehall, PA, USA) was applied between the scalp and the sponge pocket. We started tDCS seven minutes before the first experimental task for participant acclimation; this was two to three minutes longer than similar studies demonstrating tDCS-associated effects on cognitive task performance (26 ,27 ).

To target left DLPFC, the stimulating electrode was placed on the scalp at F3 per the 10-20 electroencephalography (EEG) system. The return electrode was placed over the contralateral mastoid process. Electrodes were carbon rubber and enclosed in 3 cm by 5 cm sponge pockets saturated in normal saline (0.9% NaCl) and held on the scalp with rubber headbands adjusted to be snug but comfortable. No hair was shaved. To enhance connection, conductive gel (Microlyte, Coulbourn Instruments, Whitehall, PA, USA) was applied to scalp beneath the sponge pocket. Electrodes were then connected to a battery-powered Soterix 1×1 bipolar tDCS device (Soterix Medical Inc., New York, NY, USA). Before stimulation, impedance of the electrode-to-scalp interface was checked with the device to ensure that it remained at or below a predetermined safety cutoff level. Amplitude of tDCS was ramped up to 2 mA over 30 seconds and then maintained for 20 minutes before being ramped back down to 0 mA. Current was otherwise lowered by tDCS staff only in the event of poor tolerability. We began tDCS seven minutes before the first experimental task to acclimate participants fully to stimulation; similar studies of tDCS-associated effects on cognitive task performance (38 ,39 ) used acclimation periods of four to five minutes.