Non-Invasive Brain Stimulation Does Not Improve Working Memory in Schizophrenia: A Meta-Analysis of Randomised Controlled Trials.

ABSTRACT

Poor working memory functioning is commonly found in schizophrenia. A number of studies have now tested whether non-invasive brain stimulation can improve this aspect of cognitive functioning. This report used meta-analysis to synthesise the results of these studies to examine whether transcranial electrical stimulation (tES) or repetitive transcranial magnetic stimulation (rTMS) can improve working memory in schizophrenia. The studies included in this meta-analysis were sham-controlled, randomised controlled trials that utilised either tES or rTMS to treat working memory problems in schizophrenia. A total of 22 studies were included in the review. Nine studies administered rTMS and 13 administered tES. Meta-analysis revealed that compared to sham/placebo stimulation, neither TMS nor tES significantly improved working memory. This was found when working memory was measured with respect to the accuracy on working memory tasks (TMS studies Hedges' g = 0.112, CI95 -0.082, 0.305, p = .257; tES studies Hedges' g = 0.080, CI95 -0.117, 0.277, p = .427) or the speed working memory tasks were completed (rTMS studies Hedges' g = 0.233, CI95 -0.212, 0.678, p = .305; tES studies Hedges' g = -0.016, CI95 -0.204, 0.173, p = .871). For tES studies, meta-regression analysis found that studies with a larger number of stimulation sessions were associated with larger treatment effects. This association was not found for TMS studies. At present, rTMS and tES is not associated with a reliable improvement in working memory for individuals with schizophrenia.