In this placebo-controlled study patients with a diagnosis of MDD receive a single treatment with prefrontal tDCS (anode over electrode position F3, cathode over F4, 20 min, 2mA intensity) or sham tDCS (frequency and duration correspondent active tDCS, ramp in and ramp out periods only without intermittent stimulation). Before, during, and after the treatment resting-state measurements in the fMRI scanner are conducted. Subsequently, participants perform the cognitive control task (in dependence of Plewnia, C., Schroeder, P. A., & Wolkenstein, L. (2015)) in the scanner. The patients are assigned to either the real or sham tDCS condition according to a randomised, double-blind parallel design.