Background: We recently showed that repetitive transcranial magnetic stimulation (rTMS) of the dorsolateral prefrontal cortex (DLPFC) can affect the performance in an affective go-no-go (AGN) task. We aimed to extend this previous investigation testing whether one session of anodal transcranial direct current stimulation (tDCS) of the left DLPFC, as compared with anodal occipital and sham tDCS, affects this AGN task performance.
Methods: Twenty-six patients with major depression were randomized to receive anodal tDCS of the left DLPFC, occipital cortex or sham tDCS (the cathode electrode was placed over the frontopolar area for the three conditions). An AGN task was performed immediately before and after treatment. Performance changes (pre and post-treatment) were compared across groups of treatment and correlated with Hamilton Depression Rating Scale (HDRS) score changes.
Results: The results show that anodal stimulation of the left DLPFC was the only condition that induced a significant improvement in task performance as shown by the increase in the number of correct responses. In addition, this effect was specific for figures with positive emotional content. This performance enhancement was not correlated with mood changes after 10 days of tDCS treatment.
Limitations: Although the effects of tDCS are less focal than rTMS, it can induce a longer and stronger modulation of cortical excitability.
Conclusions: Our findings suggest that left DLPFC activity is associated with positive emotional processing, confirming and extending results of previous studies that associated right DLPFC and orbito-frontal cortex activity with emotional processing. Furthermore the effects of tDCS on mood and cognition seem to be independent in major depression. These lines of evidence together shed light on the neural circuitry involved with emotional processing in major depression.