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

Non-invasive brain stimulation techniques have received increasing interest for their potential to enhance memory function, a fundamental cognitive aspect of daily life. This systematic review and meta-analysis aimed to investigate the efficacy of transcranial electrical stimulation (tES) in enhancing memory function in healthy adults, following the pre-registered strategy at PROSPERO (CRD42022353630). A total of 113 articles (193 trials, 7,299 participants) examining tES were identified. Meta- analysis revealed a significant overall effect of tES on memory function compared with sham stimulation (standardised mean difference [95% confidence interval] = 0.19 [0.12, 0.25]). A positive pooled effect was also observed in the subgroup receiving frontal transcranial direct current stimulation (tDCS). Stimulation was associated with positive pooled effects for working- and declarative-memory task performance. Significant pooled effects were observed within 1 day after stimulation; longer-term estimates were imprecise. Regarding adverse events, tingling and itching sensations on the scalp occurred more frequently in the active group than in the sham group, but no serious adverse events were reported. Limitations, including small- study effects, heterogeneity, and uneven coverage of memory domains, were noted, emphasising the need for improved experimental rigour and diversification of memory tasks. These findings suggest that tES is associated with small improvements in memory-task performance and was generally well tolerated under the studied protocols. Heterogeneity, small- study effects, and limited adverse-event reporting constrain conclusions about efficacy, durability, and safety