title: Working memory improvement with non-invasive brain stimulation of the dorsolateral prefrontal cortex: a systematic review and meta-analysis.
abstract: Recent studies have used non-invasive brain stimulation (NIBS) techniques, such as repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS), to increase dorsolateral prefrontal cortex (DLPFC) activity and, consequently, working memory (WM) performance. However, such experiments have yielded mixed results, possibly due to small sample sizes and heterogeneity of outcomes. Therefore, our aim was to perform a systematic review and meta-analyses on NIBS studies assessing the n-back task, which is a reliable index for WM. From the first data available to February 2013, we looked for sham-controlled, randomized studies that used NIBS over the DLPFC using the n-back task in PubMed/MEDLINE and other databases. Twelve studies (describing 33 experiments) matched our eligibility criteria. Active vs. sham NIBS was significantly associated with faster response times (RTs), higher percentage of correct responses and lower percentage of error responses. However, meta-regressions showed that tDCS (vs. rTMS) presented only an improvement in RT, and not in accuracy. This could have occurred in part because almost all tDCS studies employed a crossover design, possibly due to the reliable tDCS blinding. Study design was also associated with no improvement in correct responses in the active vs. sham groups. To conclude, rTMS of the DLPFC significantly improved all measures of WM performance whereas tDCS significantly improved RT, but not the percentage of correct and error responses. Mechanistic insights on the role of DLPFC in WM are further discussed, as well as how NIBS techniques could be used in neuropsychiatric samples presenting WM deficits, such as major depression, dementia and schizophrenia.
authors: Interdisciplinary Center for Applied Neuromodulation & Clinical (CINA) and Epidemiological Research Centre, University Hospital, University of São Paulo, São Paulo, Brazil; Service of Interdisciplinary Neuromodulation (SIN), Department and Institute of Psychiatry, Faculty of Medicine of University of São Paulo, São Paulo, Brazil. Electronic address: Brunoni@usp.br.
authors: André Russowsky
authors: AR
authors: Brunoni
authors: Psychopathology and Affective Neuroscience Laboratory, Department of Experimental Clinical and Health Psychology, Faculty of Psychology, Ghent University, Ghent, Belgium. Electronic address: MarieAnne.Vanderhasselt@UGent.be.
authors: Marie-Anne
authors: MA
authors: Vanderhasselt
mesh_terms: D004558:Electric Stimulation; D005260:Female; D006801:Humans; D008297:Male; D008570:Memory, Short-Term / Q000502:physiology*; D017397:Prefrontal Cortex / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation
keywords: N-back task; Non-invasive brain stimulation; Prefrontal cortex; Repetitive transcranial magnetic stimulation; Transcranial direct current stimulation; Working memory