Transcranial direct current stimulation enhances offline consolidation of implicit sequential learning in individuals with insomnia

BACKGROUND: Insomnia not only compromises sleep quality but may also impair learning and memory processes within cognitive function. OBJECTIVE: This study aims to investigate the effects of transcranial direct current stimulation (tDCS) on offline consolidation of implicit sequence learning and sleep quality in individuals with insomnia. METHODS: We employed a randomized, double-blind, controlled trial, assigning individuals with insomnia to either an active stimulation group or a sham stimulation group for consecutive 7-day interventions. Sleep quality (PSQI) and implicit sequence learning performance were assessed before and after the intervention. RESULTS: Forty-two participants with insomnia were randomly assigned to the active stimulation group (n = 21) or sham stimulation group (n = 21). Repeated-measures ANOVA revealed significant Group × Time interactions for both sleep quality (PSQI: F(1, 40) = 31.375, p < 0.001, ηp2 = 0.440) and offline consolidation of implicit sequence learning (F(1, 40) = 7.913, p = 0.008, ηp2 = 0.165). Post hoc analyses showed that, following the 7-day intervention, the active stimulation group exhibited significantly lower PSQI scores and greater offline consolidation effects compared with the sham stimulation group (both p < 0.01), whereas no significant improvements were observed in the sham stimulation group. CONCLUSIONS: The 7-day tDCS intervention not only effectively improved sleep quality in individuals with insomnia but also enhanced offline consolidation effects in implicit sequence learning, providing new evidence for non-pharmacological interventions for insomnia.