Enhancement of affective processing induced by bi-frontal transcranial direct current stimulation in patients with major depression Running title: Emotional Stroop and tDCS

Objective: Our aim was to evaluate whether one single section of transcranial direct current stimulation (tDCS), a neuromodulatory technique that non-invasively modifies cortical excitability, could induce acute changes in affective processing in patients with major depression. enrolling 24 age-, gender-matched, drug-free, depressed subjects. Anode and cathode were placed over the left and right dorsolateral prefrontal cortex. We performed a word Emotional Stroop Task collecting the response times (RTs) for positive-, negative-and neutral-related words. Three analyses of covariance were used to evaluate changes in the RT difference between positive, negative and emotional vs. neutral words before and during tDCS. Results: At baseline, RTs were similar for emotion-and neutral-related words. We found a large, significant group effect for the positive Emotional Stroop, i.e., subjects during active tDCS responded faster to positive vs. neutral words, whereas the opposite was observed for sham tDCS. The same effect was observed for emotional (positive and negative) vs. neutral words, but not for negative only vs. neutral words. Conclusion: Active tDCS induced faster RTs for non-neutral vs. neutral and positive-vs. neutral-words, contrary to sham tDCS and inverting the pattern observed at baseline. These findings add evidence that a single tDCS session transiently induces potent 4 changes in affective processing, which might be a mechanism of tDCS functioning in ameliorating depression.