Further insights into the efficacy and moderators of transcranial alternating current stimulation for working memory

This letter offers a critical appraisal of the systematic review and meta-analysis by Hou et al, which examined the effect of theta-band transcranial alternating current stimulation (theta-tACS) on working memory in healthy adults. The authors initially reported a moderate, statistically significant enhancement of working memory performance (Hedges' g = 0.405), although this effect became non-significant following adjustment for publication bias. This commentary highlights key strengths of the meta-analysis, including its targeted focus on a frequency band theoretically relevant to working memory, comprehensive moderator analyses, and task-specific subgroup comparisons (N-back vs delayed match-to-sample). At the same time, it emphasizes the substantial impact of publication bias, the considerable heterogeneity among included studies, and the unexpected finding that fixed-frequency stimulation protocols outperformed individualized approaches. While uncertainty remains regarding the overall efficacy of theta-tACS, the observed task-specific improvements in N-back performance and the identification of critical stimulation parameters (such as frequency, duration, and stimulation timing relative to task performance) offer valuable direction for protocol refinement. Taken together, this meta-analysis provides an important and cautionary synthesis that reinforces the need for pre-registered, methodologically rigorous studies to establish the cognitive and potential clinical benefits of theta-tACS with greater confidence.