Comparative efficacy of tDCS and tACS in the context of enhancing executive function under acute stress: A randomized, sham-controlled study

Background: Acute stress impairs executive function and prefrontal cortex (PFC) activity. Transcranial electrical stimulation (tES) is a promising approach to the task of mitigating these deficits. This study directly compared the efficacy of two tES techniques-transcranial direct (tDCS) and alternating current (tACS) stimulation-targeting the left dorsolateral PFC (DLPFC) in terms of protecting executive functions under stress and potential neural mechanisms. Methods: In a randomized, participant-blinded, sham-controlled study, 110 healthy male undergraduates (18-25 years) received active tDCS, tACS, or sham stimulation before stress induction via the Trier Social Stress Test for Groups. Executive function was assessed using 3-back, Go/no-go, Stroop, and task-switching paradigms, and prefrontal hemodynamics were recorded with functional near-infrared spectroscopy (fNIRS). Results: Stress induction was successfully maintained throughout the testing period. Compared with both the tACS and sham groups, the tDCS group exhibited greater working memory (3-back) accuracy. Compared with the sham group, both tES groups exhibited enhanced response inhibition (Go/no-go). Neuroimaging revealed lower left DLPFC activation during the 3-back, Go/no-go, and Stroop tasks in the tES groups, in which context tDCS was characterized by the lowest activation during cognitive inhibition. During task switching, both tES groups exhibited elevated activation in the right pre-supplementary motor area. Conclusions: Both tDCS and tACS enhance performance in specific executive domains (working memory and response inhibition) under acute stress and demonstrate a pattern of lower prefrontal activation, consistent with the concept of improved neural efficiency. Among them, tDCS offers superior benefits. These findings establish a foundation for efforts to optimize tES-based interventions to support cognitive resilience in real-world acute-stress settings.