Assessment of efficacy of tDCS polarity (anodal, cathodal), dosage (1mA, 2mA) and laterality (left and right dlPFC) on working memory (adaptive n-back(6)) in patients (n=2x2x2x16=128). In a two-session cross-over design, stimulation (tDCS and sham) will be applied to the dlPFC (left or right) for 20min (during task performance).