Transcranial electric stimulation and neurocognitive training in clinically depressed patients: a pilot study of the effects on rumination.

Rumination is a cognitive-affective thinking style that plays a key role in the onset and maintenance of depression. Recently, it was shown that clinically depressed patients who received a neurocognitive training - involving two weeks of repetitive cognitive control exercises that necessitate prefrontal engagement - are more able to control over ruminative negative thoughts than patients who only received treatment as usual. Transcranial Direct Current Stimulation (tDCS) is a biological technique that can directly modulate prefrontal excitability via the manipulation of neural membrane potentials. In this randomized double-blind trial, we investigated whether bifrontal tDCS (anode over the left/cathode over the right dorsolateral prefrontal cortex (DLPFC)) would enhance the influence of a neurocognitive training on depressive brooding, the maladaptive form of rumination. Major depressed patients were trained using a procedure based on the Paced Auditory Serial Addition Task (PASAT), a task that relies heavily on working memory and is found to engage the DLPFC. One group (n=19) completed the PASAT training together with active tDCS and another group (n=14) completed the same training together with sham (placebo) tDCS. In both groups, depressive brooding was reduced following the PASAT training. Moreover, we observed that improvement in working memory over the course of the training was associated with a greater reduction in depressive brooding post- versus pre-intervention. However, tDCS did not moderate this association between changes in working memory and changes in depressive brooding. Possible explanations for this absent moderation of tDCS, as well as avenues for future research to influence ruminative thinking in depression, are discussed.