Dual‐Site Beta <scp>tACS</scp> Over the <scp>rIFG</scp> and <scp>preSMA</scp>‐Induced Phase‐Specific Changes in Functional Connectivity but not Response Inhibition Performance in Older Adults

Research suggests that changes in functional connectivity contribute to age-related declines in response inhibition. Through a double-blind crossover study, we investigated the effects of dual-site beta transcranial alternating current stimulation (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) in 15 older (aged 61-79 years) and 18 young (aged 18-34 years) adults. Two tACS conditions were administered in separate sessions: in-phase tACS, where electrical currents delivered to rIFG and preSMA had a 0° phase difference, and anti-phase tACS, where currents had a 180° phase difference. Resting-state beta band rIFG-preSMA connectivity significantly increased after in-phase tACS for older and young adults and decreased after anti-phase tACS for older adults. Response inhibition significantly improved after both in- and anti-phase tACS for young and older adults. These findings suggest that tACS can potentially modulate rIFG-preSMA connectivity in a phase-specific manner in the aging brain, and that inhibitory performance might not be directly regulated by resting-state rIFG-preSMA phase connectivity. Due to the lack of sham control, placebo effects cannot be ruled out. However, the differing neurophysiological effects from in- and anti-phase tACS suggest that rIFG-preSMA resting-state phase connectivity is unlikely to underpin the changes in inhibitory performance. Future studies incorporating a sham control are required to verify these findings.