HD-tDCS Over the dACC in High Trait Impulsivity

TDCS is a non-invasive neuromodulation technique that modulates membrane potentials by means of small electrical currents. Electrical currents induced by tDCS electrodes produce an electrical field that modulates the excitability of brain areas. In the present HD-tDCS montage, one anodal electrode and four return electrodes are applied. Hereby, the anodal electrode modulates the excitability of the targeted area, whereas the other 4 electrodes return electrical currents that flow away from that area. Direct currents will be transmitted through 5 circular PiStim electrodes of 3.14cm2 (Neuroelectrics, Barcelona, Spain; current density=0.32 mA/cm2) with a current intensity of 1.5 mA. The HD-tDCS session will last for 20 minutes in total, with a 60 sec ramp at the beginning and end of the session. The electrodes will be filled with conductive gel and plugged into an EEG cap, with the anode placed over Fz and the four return electrodes over Fp1, Fp2, F7, and F8 (10-20 system).

For the sham-condition, the placement of the electrodes was identical to active HD-tDCS stimulation with the anode placed over Fz and the four return electrodes over Fp1, Fp2, F7, and F8 (10-20 system). The direct current, also transmitted through 5 circular PiStim electrodes of 3.14cm2 (Neuroelectrics, Barcelona, Spain; current density=0.32 mA/cm2), was increased in a ramp-like fashion over 60 seconds until it reached 1.5 mA. Directly after ramp-up, the current intensity was gradually switched off over 60 seconds, followed by 20 minutes without active stimulation. Sham procedures for tDCS mimic the transient skin sensation at the beginning of active HD-tDCS, without producing any conditioning effects on the brain. Consequently, participants are reliably blinded for sham tDCS.