Acute working memory improvement after tDCS in antidepressant-free patients with major depressive disorder

Abstract

Based on previous studies showing that transcranial direct current stimulation (tDCS), a non-invasive brain stimulation technique that employs weak, direct currents to induce cortical-excitability changes, might be useful for working memory (WM) enhancement in healthy subjects and also in treating depressive symptoms, our aim was to evaluate whether tDCS could acutely enhance WM in depressed patients. Twenty-eight age- and gender-matched, antidepressant-free depressed subjects received a single-session of active/sham tDCS in a randomized, double-blind, parallel design. The anode was positioned over the left and the cathode over the right dorsolateral prefrontal cortex. The n-back task was used for assessing WM and it was performed immediately before and 15min after tDCS onset. We found that active vs. sham tDCS led to an increase in the rate of correct responses. We also used signal detection theory analyses to show that active tDCS increased both discriminability, i.e., the ability to discriminate signal (correct responses) from noise (false alarms), and response criterion, indicating a lower threshold to yield responses. All effect sizes were large. In other words, one session of tDCS acutely enhanced WM in depressed subjects, suggesting that tDCS can improve "cold" (non affective-loaded) working memory processes in MDD. Based on these findings, we discuss the effects of tDCS on WM enhancement in depression. We also suggest that the n-back task could be used as a biomarker in future tDCS studies investigating prefrontal activity in healthy and depressed samples.

Effects of acute transcranial direct current stimulation in hot and cold working memory tasks in healthy and depressed subjects

“…Our findings in MDD patients are in accordance to previous literature showing that tDCS increased performance in the n-back task [16], ameliorated emotional inhibitory control [28], enhanced performance in the Emotional Stroop Task [8] and in the affective go/no-go task [2]. Thus, tDCS effects in depression might not be limited to the DLPFC, but also extends to the broader cortico-subcortical network associated with cognitive dysfunction in MDD and regulation of emotionally loaded information processing.…”

“…TDCS is a non-invasive neuromodulatory technique that employs weak direct currents (0.5-2 mA) to modulate brain activity [4] by regulating the frequency of action potentials triggered in the neuronal network [3]. Previous reports demonstrated that anodal tDCS over the DLPFC exerts beneficial effects in cognitive tasks [5], although most of them were methodologically limited [7,16,24,28].…”

“…The bifrontal tDCS montage that was already demonstrated to be an effective montage for the treatment of the acute depressive episode [15] was used, besides positive effects in emotional and non-emotional cognition in depressed patients after tDCS [2,16,24] For the non-emotional working memory task, we used the n-back task that assesses the short-term storage, selective and sustained attention, online manipulation of information in a mental workspace and is robustly associated with prefrontal cortex activation.N-back have been studied for several authors that related impairment of performance in MDD patients [5][17] (Diamond,2013). For the emotional working memory task we used the IST that evaluates the ability to update and shift between emotional representations in working memory [11].…”

Working memory improvement with non-invasive brain stimulation of the dorsolateral prefrontal cortex: A systematic review and meta-analysis

“…Regarding sham procedures, sham tDCS was performed using a procedure in which the electric current was turned off shortly after stimulation onset, although this short period ranged from 5 to 60 (Oliveira et al, 2013)seconds.…”

“…Regarding blinding, half of the studies were double-blinded (Barr et al, 2013;Gaudeau-Bosma et al, 2012;Guse et al, 2013;Keeser et al, 2013;Oliveira et al, 2013;Teo et al, 2011) and the other half were double single-blinded, i.e., the subject and the evaluator were blinded to the allocation group, but not the person applying the stimulation. The time period between stimulation conditions ranged from at least one hour to more than one week (Mulquiney, Hoy, Daskalakis, & Fitzgerald, 2011).…”