tDCS
CORTEX
The left dorsolateral prefrontal cortex (left DLPFC) brain region, a key node in the top-down mood-regulating circuitry frequently implicated in depressionFor HD tDCS, a 4 × 1 setup was used with the central stimulating anode electrode placed over the stimulation target and the cathode electrodes placed 5 cm away and equidistant from the neighboring cathodes. For conventional tDCS, 5 × 7 cm-sized electrodes were employed, with the anode placed over the stimulation target and the cathode placed over [56, 30, − 1] mm MNI coordinates (~ approximately F8 in the 10–20 coordinate system). Each enrolled participant received 12 sessions of active or sham tDCS (depending on the randomization) over 12 consecutive working days. Active tDCS involved 2 mA × 20 min of tDCS, including 30 s ramp-times. Sham tDCS involved a 30 s ramp up to 2 mA followed by a 30 s ramp down to zero at the beginning of the 20 min session. Apart from this ramp up/down period, ammeter readings showed that the stimulator emitted a steady current of 65 µA during sham tDCS. This current intensity is an order of magnitude smaller than the intensity employed in active tDCS and is similar to sham-tDCS utilized byTo maintain blinding, each participant was assigned a unique code upon enrollment, and this code was used by study staff to operate the double-blind stimulator device (Soterix Model #5100D). Both participants and assessors were asked to guess the stimulation condition (active/sham) at the study endpoint to verify integrity of blinding. Data on stimulation-related discomfort was also acquired using the Generic Assessment of Side Effects (GASE) scale