tDCS improves global cognition in Alzheimer's and MCI

BackgroundTranscranial direct current stimulation (tDCS) has shown promise in improving the cognitive function of patients with Alzheimer’s disease (AD) and mild cognitive impairment (MCI). However, data from clinical trials or meta-analyses involving tDCS have produced conflicting results.ObjectiveThis systematic review and meta-analysis aimed to evaluate the efficacy of tDCS in improving global cognition and specific cognitive domains in patients with AD and MCI.MethodsThe review and analysis were conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Four electronic databases—PubMed, Web of Science, the Cochrane Library and Embase—were searched up to 20 August 2025. Cochrane’s risk of bias assessment tools were used to evaluate the risk of bias and the methodological quality of the included studies. Statistical analyses were performed using Review Manager 5.3.ResultsThis meta-analysis of 13 studies (n = 616) showed that tDCS significantly improved global cognition as measured by MMSE and MoCA (SMD = 0.49). For other cognitive domains, evidence was limited: visuospatial ability (4 studies, Clock Drawing Test) showed a significant but preliminary effect (SMD = −0.75); attention (2 studies, Digit Span Test) showed a small effect (SMD = −0.33); executive function (4 studies, Trail Making Test) showed no significant effect (SMD = 0.09).ConclusiontDCS significantly improves global cognition in patients with AD and MCI. Preliminary evidence suggests possible benefits for visuospatial ability, but findings for attention and executive function remain inconclusive. Future studies should employ multi-test, domain-specific neuropsychological batteries in adequately powered trials.