Transcranial electrical stimulation for memory enhancement: A systematic review and meta-analysis

BackgroundNon-invasive brain stimulation techniques have received increasing interest for their potential to enhance memory function, a fundamental cognitive aspect of daily life. MethodsThis systematic review and meta-analysis investigated the efficacy of transcranial electrical stimulation (tES) in enhancing memory function in healthy adults, following the pre-registered strategy at PROSPERO (CRD42022353630). ResultsA total of 66 articles (119 trials, 3,786 participants) focusing on transcranial direct current stimulation and transcranial alternating current stimulation were identified. Meta-analysis revealed a significant overall effect of tES on memory function compared with sham stimulation (standardized mean difference [95% confidence interval] = 0.19 [0.12-0.27]), with anodal transcranial direct current stimulation showing the most consistent enhancement. In particular, stimulation of the frontal regions effectively improved working and declarative memories. While the effects remained significant within hours post-stimulation, they diminished after one day or longer. Regarding adverse events, tingling and itching sensations on the scalp occurred more frequently in the active group than in the sham group, but no severe adverse events were reported. Challenges, including publication bias, heterogeneity, and bias toward specific aspects of memory were noted, emphasizing the need for improved experimental rigor and diversification of memory tasks. ConclusionThese findings highlight the potential of tES as a safe and effective tool for memory enhancement while emphasizing areas for future research to develop its applications.