Examining the effects of theta-tACS over left DLPFC on reward-based learning across the adult lifespan

Aging is associated with dopaminergic decline, which may disrupt the balance between exploiting known rewards and exploring alternative options during learning. This exploration-exploitation tradeoff is central to adaptive decision-making, and its disruption may contribute to maladaptive learning patterns that increase susceptibility to poor financial decisions. This study investigates whether transcranial alternating current stimulation (tACS) can modulate reward-based learning by enhancing prefrontal theta oscillations, and whether age moderates stimulation efficacy. Adults aged 20-80+ years will complete a probabilistic two-armed bandit task under both active theta-tACS (6 Hz) and sham conditions. We predict that individuals with poorer cognitive function and/or lower sensitivity to reward and punishment feedback will show more rigid exploration-exploitation patterns, characterized by elevated win-stay and reduced lose-shift behavior. We further predict that theta-tACS will normalize these asymmetries, with effects moderated by age.