PROJECT SUMMARY/ABSTRACT Confirmation bias refers to the tendency to interpret new information in a way that conforms to one's pre-existing beliefs. It is associated with deficits in cognitive functions like working memory and error detection, both commonly associated with the prefrontal cortex (PFC). As such, age-related changes to the PFC may leave older adults vulnerable to this bias and its negative outcomes, including financial exploitation. Older adults are disproportionately impacted by financial exploitation, and as cognitive decline progresses to mild cognitive impairment (MCI) and Alzheimer's disease and related dementias, risk for fraud increases. Given these connections, confirmation bias may serve as an indicator of cognitive decline and vulnerability to fraud; however, progress towards understanding these relationships has been hampered by three main issues. First, little is known about the latent processes shaping confirmation bias in older adults. Second, much of the work to date has relied on correlations between brain responses and behavior, leaving the causal mechanisms unclear. Third, behavioral changes over time in this population are underexplored. To address these concerns, this project has two specific aims. The first is to characterize how age-related differences in cognitive function contribute to susceptibility to confirmation bias. In an online study, participants will play an investment game involving the opportunity to update an initial judgment after receiving feedback from a partner (Aim 1). We hypothesize that older adults showing cognitive decline will exhibit confirmation bias at higher rates than younger adults, characterized by greater bias towards initial judgments and decreased engagement with conflicting feedback from the partner. Our second aim is to assess the causal relationship between confirmation bias and the PFC in older adults using transcranial alternating current stimulation (tACS; Aim 2). By applying tACS to the PFC, we will entrain individualized theta rhythms to enhance function across the region. Using the investment task from Aim 1 concurrent with tACS, it is hypothesized that confirmation bias will be diminished in older adults, particularly among those with MCI. Finally, to fully characterize the predictive role of confirmation bias, we will follow up with participants after two years to assess the progression of cognitive decline. It is predicted that higher rates of confirmation bias at visit one will be associated with greater cognitive decline at follow-up. The funding from this grant will provide the applicant with the opportunity to learn essential new skills in computational modeling (Aims 1 & 2) and noninvasive brain stimulation (Aim 2). These objectives will be accomplished through a combination of workshops, expert mentorship, and institutional training. Overall, this project will leverage training in well- established and cutting-edge techniques to help expand the understanding o...