Efficacy of non-invasive brain stimulation on cognitive functioning in brain disorders: a meta-analysis.

Marieke J Begemann,André Aleman,Branislava Ćurčić-Blake,Iris E Sommer,Bodyl A Brand

doi:10.1017/s0033291720003670

Abstract

Cognition is commonly affected in brain disorders. Non-invasive brain stimulation (NIBS) may have procognitive effects, with high tolerability. This meta-analysis evaluates the efficacy of transcranial magnetic stimulation (TMS) and transcranial Direct Current Stimulation (tDCS) in improving cognition, in schizophrenia, depression, dementia, Parkinson's disease, stroke, traumatic brain injury, and multiple sclerosis. A PRISMA systematic search was conducted for randomized controlled trials. Hedges' g was used to quantify effect sizes (ES) for changes in cognition after TMS/tDCS v. sham. As different cognitive functions may have unequal susceptibility to TMS/tDCS, we separately evaluated the effects on: attention/vigilance, working memory, executive functioning, processing speed, verbal fluency, verbal learning, and social cognition. We included 82 studies (n = 2784). For working memory, both TMS (ES = 0.17, p = 0.015) and tDCS (ES = 0.17, p = 0.021) showed small but significant effects. Age positively moderated the effect of TMS. TDCS was superior to sham for attention/vigilance (ES = 0.20, p = 0.020). These significant effects did not differ across the type of brain disorder. Results were not significant for the other five cognitive domains. Our results revealed that both TMS and tDCS elicit a small trans-diagnostic effect on working memory, tDCS also improved attention/vigilance across diagnoses. Effects on the other domains were not significant. Observed ES were small, yet even slight cognitive improvements may facilitate daily functioning. While NIBS can be a well-tolerated treatment, its effects appear domain specific and should be applied only for realistic indications (i.e. to induce a small improvement in working memory or attention).

Highlights

Cognitive functioning is affected in many brain disorders (Robbins, 2011)
Following the Preferred Reporting for Systematic Reviews and Meta-analysis (PRISMA) Statement (Moher, Liberati, Tetzlaff, & Altman, 2009), a systematic search was performed in PubMed (Medline), EMBASE, Web of Science, and Cochrane Database of Systematic Reviews, using the following search terms: [‘cognition’ OR ‘cognitive functioning’] AND [‘transcranial magnetic stimulation’, ‘pulsed electromagnetic field therapy’, ‘low field magnetic stimulation’, ‘transcranial electrical stimulation’ OR ‘transcranial direct current stimulation’] AND [‘randomized controlled trial’, ‘randomized controlled trials (RCTs)’ OR ‘randomized controlled study’], for each brain disorder
Study inclusion (1) RCTs investigating the effects of transcranial magnetic stimulation (TMS) or transcranial Direct Current Stimulation (tDCS) treatment on cognition measured with a neuropsychological test; (2) Studying patients affected by one of our conditions of interest; (3) Single/double-blind studies comparing the treatment to a patient control group receiving sham stimulation

Summary

Introduction

Cognitive functioning is affected in many brain disorders (Robbins, 2011). The observed impairment can be profound, as in Alzheimer’s disease or Parkinson’s disease (PD), or relatively mild, as in depression (Brown & Marsden, 1990; Caviness et al, 2007; Douglas et al, 2018; Petersen et al, 2001). Impairments may affect multiple cognitive domains, including information processing, working memory, executive functioning and attention (Caviness et al, 2007; Higuchi et al, 2017; Maloni, 2018). These disturbances can profoundly impact daily functioning and quality of life (Papakostas et al, 2004; Schrag, Jahanshahi, & Quinn, 2000). TDCS was superior to sham for attention/vigilance (ES = 0.20, p = 0.020) These significant effects did not differ across the type of brain disorder. While NIBS can be a well-tolerated treatment, its effects appear domain specific and should be applied only for realistic indications (i.e. to induce a small improvement in working memory or attention)

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