The Effects of Dual-Site Beta tACS over the rIFG and preSMA on Response Inhibition in Young and Older Adults

A growing body of research suggests that changes in both structural and functional connectivity in the aging brain contribute to declines in cognitive functions such as response inhibition. In recent years, transcranial alternating current stimulation (tACS) has garnered substantial research interest as a potential tool for the modulation of functional connectivity. Here, we report the findings from a double-blind crossover study that investigated the effects of dual-site beta tACS over the right inferior frontal gyrus (rIFG) and pre-supplementary motor area (preSMA) on functional connectivity measured with electroencephalography and response inhibition (stop-signal task performance) of healthy young ( n = 18, aged 18-34 years) and older ( n =15, aged 61-79 years) adults. Two tACS conditions were administered in separate sessions: in-phase tACS, where electrical currents delivered to the rIFG and preSMA had a 0° phase difference, and anti-phase tACS, where currents had a 180° phase difference. Stop-signal task performance was assessed before and after tACS. We found significant improvements in response inhibition that were not due to the phase of the tACS applied. There were also no significant changes in rIFG-preSMA phase connectivity in either age group from in- or anti-phase tACS. Furthermore, we did not observe significant differences in rIFG-preSMA phase connectivity between successful and unsuccessful inhibition, which suggests that rIFG-preSMA phase-coupling might not underlie effective response inhibition. The results offer insight into the neurophysiology of response inhibition and contribute to the future development of non-pharmacological interventions aimed at alleviating age-related declines in cognitive function.