Phase-specific alpha tACS over the dlPFC does not enhance cognitive reappraisal or autonomic responses: a sham-controlled crossover study

Background: Cognitive reappraisal (CR) relies on prefrontal top-down control over limbic systems, with the dorsolateral prefrontal cortex (dlPFC) playing a central regulatory role. Alpha frequency transcranial alternating current stimulation (α-tACS) can modulate cortical oscillations; yet, its causal contribution to emotion regulation (ER) remains unclear. Objective: In this study, we investigated whether in-phase or anti-phase alpha-tACS influenced subjective and physiological responses during cognitive reappraisal of negative emotional stimuli. Methods: Forty-two healthy young adults completed three counterbalanced sessions (in-phase, anti-phase, sham) in a single-blind, sham-controlled crossover design. During α-tACS or sham, participants applied three CR strategies (positive, fictional, distancing) while viewing negative and neutral film clips. Valence, arousal, heart rate (HR), skin conductance (SC), respiratory rate (RR), and pre/post-session affect (PANAS) were recorded. Results: The Emotional Movie Database (EMDB) emotional stimuli elicited the expected subjective and autonomic responses, confirming that the task engaged emotional-reactivity processes. Participants also showed a typical habituation pattern in physiological measures across blocks. However, neither in-phase nor anti-phase alpha-tACS was associated with measurable changes in subjective emotional ratings or autonomic responses relative to sham under the experimental conditions. Conclusion: This study provides the first evaluation of phase-specific alpha-tACS during cognitive reappraisal using film-based stimuli. Under the experimental conditions, no measurable effects of in-phase or anti-phase stimulation on subjective or autonomic measures of ER were observed.
We would like to thank all individuals who participated in the study and those who assisted in the data collection process. This research was conducted at the Psychology Research Centre (CIPsi SI/01662), School of Psychology, University of Minho, and supported by the Portuguese Foundation for Science and Technology (FCT) through national funds (UID/01662/2020). C.G.C. was supported by a doctoral scholarship from FCT (https://doi.org/10.54499/2022.14063.BD).