Transcranial direct current stimulation combined with cognitive training for working memory in healthy adults: a...

Transcranial direct current stimulation (tDCS) has been proposed as a potential tool for enhancing the benefits of cognitive training, but its added value for working memory in healthy adults remains unclear. This systematic review and robust variance estimation meta-analysis examined whether active tDCS combined with cognitive training improves post-training working memory performance compared with sham tDCS combined with the same training, and whether the effect varies by outcome type, assessment time point, and training characteristics.

PubMed, Scopus, and Web of Science were searched from database inception to January 2026. Eligible studies were randomized controlled trials involving healthy adults, comparing active tDCS plus structured cognitive training with sham tDCS plus otherwise identical training, and reporting at least one post-training working memory outcome. Multiple correlated effect sizes within studies were synthesized using robust variance estimation. Outcomes were classified as trained-task outcomes or untrained working-memory outcomes, and both immediate post-test and follow-up assessments were included.

A total of 23 studies contributing 135 effect sizes were included. Active tDCS combined with cognitive training produced a small but statistically significant improvement in post-training working memory performance, Hedges' g = 0.191, 95% CI [0.062, 0.320], p = 0.006. Effects were significant for trained-task outcomes, whereas effects on untrained working-memory outcomes were smaller and not statistically significant; however, the direct difference between the two outcome categories was not significant. Immediate post-test effects were significant, whereas follow-up effects remained positive and similar in magnitude but lay at the conventional alpha threshold, with no significant difference between time points. Stimulation timing, age group, and training type did not significantly moderate the effect. Sensitivity analyses confirmed the stability of the overall estimate, and no clear evidence of small-study effects was detected.

These findings suggest that tDCS may provide a small adjunctive benefit when combined with cognitive training in healthy adults, with the most consistent benefits observed for trained-task performance and more limited evidence for transfer to untrained working-memory outcomes.