PROJECT SUMMARY A crucial question in the brain and cognitive aging literature is why some older adults exhibit relatively little cognitive decline, despite neurodegeneration and/or Alzheimer’s disease pathologies. Various forms of real- world experience that remain largely intact or improve over the lifespan may contribute to and may help support a broad range of cognitive capacities and resist against neurodegeneration. However, the literature has substantially focused on relatively static “cognitive reserve” factors (e.g., education, occupation, etc.), overlooking factors that evolve with aging. We propose to examine a novel, experience-based factor – positive affective experience – as a mechanism for explaining why some older adults exhibit relatively intact cognitive function despite neurodegeneration. Positive affective experience emphasizes an individual’s disposition to maintain overall positive valence and/or stable arousal across various, repeated everyday experiences via adaptive affective regulation. The overarching objective is to elucidate the relationships between positive affective experience, domains of cognitive function, and neurodegeneration in older adults. In Aim 1, we will characterize positive affective experience in older adults to understand how positive affective experience relates to quality of life, severity of affective symptoms, and resting-state functional connectivity. In Aim 2, we will examine relationships between positive affective experience, neurodegeneration, and cognition to determine whether positive affective experience moderates the impact of baseline neurodegeneration on cognition over time. We will use an intervention study design to test mechanistic hypotheses over a condensed period. The differential response to the intervention will serve as an indirect longitudinal proxy, with the underlying assumption that individuals who respond better, cognitively, to the intervention, despite the influence of baseline neurodegeneration, would be expected to show slower cognitive decline over time, if followed prospectively. Therefore, mechanisms underlying receptiveness to cognitive improvement after an intervention may inform mechanisms of cognitive reserve. Overall, the application has the potential to contribute a novel mechanism for cognitive reserve. Relevance to parent U24: Research thus far has largely focused on understanding the impact of brain aging on affect and emotional well-being. The proposed study will contribute to the parent U24’s premise of understanding the directionality of the relationships between emotional well-being and aging by adding a novel, understudied component: addressing how positive emotional factors may influence brain aging (i.e., emotional well-being brain and cognition) in a relevant aging population.