Effects of Anodal Transcranial Direct Current Stimulation on Working Memory: A Systematic Review and Meta-Analysis of Findings
From Healthy and Neuropsychiatric Populations. [Review]
Hill AT; Fitzgerald PB; Hoy KE.
Brain Stimulation. 9(2):197-208, 2016 Mar-Apr.
[Journal Article. Meta-Analysis. Research Support, Non-U.S. Gov't. Review]
BACKGROUND: Several studies have trialled anodal transcranial direct current stimulation (a-tDCS) for the enhancement of working
memory (WM) in both healthy and neuropsychiatric populations. However, the efficacy of this technique remains to be clearly
OBJECTIVE: This review provides a quantitative synthesis of the published literature investigating the effects of a-tDCS, compared to
sham, on WM, as assessed using the n-back, Sternberg and digit-span tasks. We also separated results from tasks performed
'online' (during stimulation) and 'offline' (following stimulation). The secondary aim was to assess for any additional effects of current
density and stimulation duration.
METHODS: Comprehensive literature searches were performed usingMEDLINE, Embase, PsychINFO, CENTRAL and Scopus from
July 1998 to June 2014.
RESULTS: In healthy cohorts, a-tDCS produced a trend towards improvement for offline WM accuracy (p = 0.05) and a small, but
significant improvement in reaction time (p = 0.04); however, no significant effects were observed for online tasks (accuracy [p = 0.29],
reaction time [p = 0.42]). In the neuropsychiatric cohort, a-tDCS significantly improved accuracy for online (p = 0.003), but not offline (p
= 0.87) tasks, and no effect was seen for either online (p = 0.20) or offline (p = 0.49) reaction times. Secondary analyses controlling for
current density and stimulation duration provided limited support for the role of these factors in influencing a-tDCS efficacy.
CONCLUSIONS: This review provides some evidence of a beneficial effect of a-tDCS on WM performance. However, the small effect
sizes obtained, coupled with non-significant effects on several analyses require cautious interpretation and highlight the need for future
research aimed at investigating more optimised stimulation approaches.
Copyright © 2016 Elsevier Inc. All rights reserved.
Hill, Aron T. Monash Alfred Psychiatry Research Centre, Central Clinical School, The Alfred and Monash University, Melbourne, Victoria, Australia.
Electronic address: email@example.com. Fitzgerald, Paul B. Monash Alfred Psychiatry Research Centre, Central Clinical School, The Alfred and Monash University, Melbourne, Victoria, Australia.
Hoy, Kate E. Monash Alfred Psychiatry Research Centre, Central Clinical School, The Alfred and Monash University, Melbourne, Victoria, Australia.