Prefrontal oscillatory stimulation modulates access to cognitive control references in retrospective metacognitive commentary

Objective: We intended to examine how theta-rhythm transcranial alternating current stimulation (tACS) (versus sham non-active stimulation) modulated associations between working memory accuracy and later retrospective self-evaluation scores. Methods: Healthy participants were required to complete a verbal working memory task while receiving tACS bilaterally over the dorsolateral prefrontal cortex (DLPFC) versus sham DLPFC stimulation. After completion of the online and post-stimulation working memory tasks, participants were asked to rate the level of success-confidence on the two preceding working memory tasks. Results: As expected, online working memory accuracy was improved in the active bilateral DLPFC condition versus sham stimulation. Importantly, this working memory enhancement was related to post-stimulation self-evaluation scores. Conclusions: Theoretically, our findings indicated that cognitive-control representations (e.g., working memory accuracy) could serve as the optimal frame of reference for later retrospective metacognitive judgments. Significance: Noninvasive application of bi-frontal oscillatory currents might enhance functional connectivity between prefrontal regulatory components of working memory and retrospective monitoring in humans. Importantly, along with recent electrophysiological finding indicating interaction of tACS with ongoing oscillatory activity, our preliminary findings support the feasibility of utilizing tACS to treat theta-rhythm functional disconnectivity and related cognitive impairments in schizophrenia.