Right frontal gamma transcranial alternating current stimulation modulates optimism biases

Background When forecasting the future, people often underestimate the likelihood of adverse life events, a phenomenon known as optimism bias. While transcranial alternating current stimulation (tACS) over frontal regions has been employed to modulate various cognitive and emotional functions, its potential impact on optimism bias remains unexplored. Results Using a single-blind, sham-controlled, between-subjects design, we investigated the effects of alpha- and gamma-tACS on optimism bias. Three groups of participants received 15-min of either individualized alpha frequency (IAF)-tACS, 40 Hz-tACS, or sham stimulation over the right frontal cortex during rest. To assess how tACS impacted the optimism bias, participants completed a belief update task before and immediately after the tACS. To assess potential delayed effect of the tACS, participants completed a delay estimation task 24 hours later. We found that across all three groups, participants showed the classic optimism bias, such that they were more likely to update their beliefs toward desirable than undesirable feedback. Notably, compared to the sham and IAF-tACS groups, 40 Hz-tACS further enhanced optimism biases after 24 hours. Conclusion These findings suggest that right frontal gamma- but not alpha-tACS could effectively modulate the long-term optimistic belief updating. Our study highlights the potential of non-invasive brain stimulation as a promising tool for altering optimism biases, which may benefit individuals with pessimistic outlooks.