Beta tACS over rIFG and preSMA Improves Stopping Ability for Younger but not Older Adults

A growing body of research suggests that changes in both structural and functional connectivity in the aging brain contribute to cognitive declines observed in later life. 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 the response inhibition performance of healthy older (n =15, aged 61-79 years) and healthy younger (n = 18, aged 18-34 years) adults. Two tACS conditions were administered in separate sessions: in-phase tACS, where electrical currents delivered to rIFG and preSMA have a 0° phase difference, and anti-phase tACS, where the currents have a 180° phase difference. In-phase tACS was found to significantly improve response inhibition of only younger individuals, with better inhibitory performance associated with stronger rIFG-preSMA functional connectivity. Despite no significant changes in response inhibition performance of the older adults, their task-related EEG data suggest potential increases in proactive inhibition resulting from in-phase tACS. Anti-phase tACS did not result in any significant changes in response inhibition or functional connectivity for either age group. The current study sheds light on the complex nature of responses to non-invasive brain stimulation, which potentially contributes to the development of novel neuromodulation-based therapeutic interventions for the maintenance of cognitive function in older adults.