PROJECT SUMMARY/ABSTRACT Dementia is the fifth most common cause of death in the United States. Personality traits, specifically Neuroticism and Extraversion, are implicated in cognitive decline and forms of dementia such as Alzheimer’s disease and related disorders (ADRD). The long-term goal is to better understand why personality is such a strong predictor of cognitive decline and dementia. The overall objective in this R01 is to disentangle the role of personality change as an indicator of dementia from personality as a risk factor that precedes cognitive decline. This R01 proposes to augment a funded prospective longitudinal study of cognitive decline and dementia by assessing markers of personality in the form of emotion, negative thought, and social interaction patterns in daily life rather than relying solely on broad surveys of personality traits. The central hypothesis is that this novel approach will allow us to disambiguate the role of personality change as an indicator from personality differences as risk factors. The rationale for the proposed research is that current approaches measure to infrequently, are delayed in detecting personality change, and are too broad to identify the specific, potentially modifiable behavioral, thought, and emotional patterns that pose risks for decline and dementia. Guided by preliminary measurement work, we will test everyday markers of Neuroticism and Extraversion alongside commonly used trait measures. Specific aims extended from this hypothesis include: 1) Test the prediction that everyday emotions, thoughts, and behaviors map onto trait Neuroticism and Extraversion, 2) Test the prediction that everyday markers of Neuroticism and Extraversion are more sensitive than trait measures in detecting personality change, and 3) Test the prediction that both trait and everyday measures of personality will predict subsequent cognitive decline but that everyday markers will identify specific emotional, thought, and behavioral patterns which may be amenable to intervention. The approach is innovative, in the applicant’s opinion, because it tests theory-based predictions related to personality and cognitive decline and dementia, leverages a large prospective longitudinal sample, and tests a novel measurement approach against standard methods. The proposed research is significant because it is expected to advance and expand understanding of personality is related to cognitive decline and ADRD. Such knowledge has the potential to direct interventions to specific targets most associated with risk and identify everyday indicators of cognitive impairment.