Effects of transcranial electrical stimulation (tES) in visual search, vigilance, and working memory/inhibition tasks: Meta-analysis of findings from healthy populations

Introduction: Transcranial electrical stimulation (tES) techniques have shown promise in both research and applied settings. However, a comprehensive review of tES and its applications is needed to understand efficacy and safety. We completed a meta-analysis in several domains: visual search, vigilance, and a sample of studies that covered both working memory and inhibition Method: Several databases were searched: PsycINFO (Ovid), Pubmed, Web of Science Core Collection (Web of Knowledge), tDCS Database, and CINAHL, covering the period until October 2020. Inclusion criteria were: healthy adults; single or multi-session tES protocol (tDCS, tACS, tRNS, HD-TDCS, HD-TACS). Only sham-controlled designs with primary outcome measures of reaction time or accuracy were included. Risk of bias was assessed using the RevMan Cochrane tool. Results: We selected 72 papers with 247 effect sizes. Overall, we report a small effect of tES (Hedges’ g=0.112, p<0.001). We found significant effects for online stimulation that ends before task completion (Hedges’ g=0.243, p<0.005), between-subject design (Hedges’ g=0.159, p<0.005), and frontal stimulation (Hedges’ g=0.410, p<0.005). tES combined with a training task trends to larger effect sizes (Hedges’ g=.417 for training task and Hedges’ g=.024 for non-training tasks). We also found significant effects of anodal stimulation for working memory (Hedges’ g=0.325, p<0.05) and visual search tasks (Hedges’ g=0.244, p<0.05). tRNS and tACS did not yield significant effects, because only few studies used these protocols in our selection of studies. Risk of bias was most prominent in blinding of outcome assessment, blinding of personnel, and selective data reporting. Conclusion: There are clear differences in effectiveness of tES between domains, with larger effects in visual search and working memory. Multiple tES sessions in combination with cognitive training show promise. This work also highlights the need for replication, more systematicity in outcome reporting, and the necessity for large, well-powered studies prior to application of tES. Research Category and Technology and Methods Basic Research: 9. Transcranial Direct Current Stimulation (tDCS) Keywords: meta-analysis, visual search, vigilance, training

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