Does Non-Invasive Brain Stimulation Improve Cognition in Major Depressive Disorder? A Systematic Review

Abstract

Non-invasive brain stimulation (NIBS) techniques, such as repeated transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS), have been increasingly used in different contexts to improve cognitive performance and ameliorate depression symptoms. Considering that major depression is usually accompanied by cognitive deficits, NIBS technique could be also helpful to improve cognition in depressed patients. In this systematic review, we researched for articles published in PubMed/MEDLINE from the first date available to June 2014 that assessed cognitive performance in patients with depression before and after NIBS. Out of 191 references, 25 (16 for rTMS and 9 for tDCS) studies matched our eligibility criteria. Non-invasive brain stimulation interventions, such as rTMS and tDCS seem to be a promising tool for cognitive enhancement in MDD, although several issues and biases (e.g., blinding issues, tests without correction for multiple comparisons, placebo effects and exploratory analyses, practice effects) hinder us to conclude that NIBS technique improve cognition in patients with depression. We discussed possible shortcomings of the included studies, such as the use of different depression treatment protocols, the possibility that some findings were false-positive results of the employed cognitive tasks and whether cognition improvement could have been an epiphenomenon secondary to depression improvement. To conclude, whereas these non-pharmacological, non-invasive techniques are particularly appealing for cognitive improvement in depression, further studies are still warranted to disentangle whether NIBS technique induce positive effects on cognition beyond their antidepressant effects.

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

“…Previous studies suggested that tDCS has pro-cognitive effects in MDD, although they were hindered by different methodological issues such as the absence of a control group, concomitant antidepressant use and a lack of sensitivity to detect cognitive changes due to task choice [24]. Therefore, our findings of acute working memory improvement after a single tDCS session confirm and expand the evidence regarding the potential benefits of tDCS on cognitive amelioration in MDD.…”

“…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].…”

Transcranial direct current stimulation in psychiatric disorders

“…In many studies, researchers have noticed improvement in cognitive aspects of patients, such as working memory, attention, executive functions and processing speed [122] . Furthermore, reports have demonstrated its utility in the facilitation of several cognitive domains, such as implicit motor learning and visuo-motor learning [123,124] , indicating its potential effectiveness on the modulation of behavior through the modulation of neurotransmitterdependent plasticity on the network level.…”

Application of transcranial direct current stimulation to psychiatric disorders: trends and perspectives

“…several types of memory, executive function, attention, and fluency (Mondino et al 2014;DemirtasTatlidede et al 2013) (Table 3). This has promoted recent tDCS research targeting cognitive enhancement in other psychiatric conditions, although a recent systematic review is reluctant to conclude that tDCS improves cognition in depressive patients due to methodological issues and risk of biases (Tortella et al 2014).…”