An increasing body of recent research suggests that cognitive inconsistency, or heightened intrainidividual variability (IIV), maybe an index of cognitive and neurological vulnerability. Increasing age, cognitive impairment, and Parkinson's disease have all been associated with greater inconsistency, as indicated by individuals'greater fluctuations around their own intra-personal mean levels. Increased cognitive inconsistency has been related to lower overall performance and steeper decline of cognitive abilities. Functionally, the inability to consistently produce adequate levels of cognitive performance may yield inconsistency in daily tasks that rely on cognition, such as driving, medication adherence, and balancing checkbooks. The current proposal seeks support to conduct secondary data analyses of a study of physical fitness promotion for older adults in which participants received 18 weekly assessments of multiple cognitive tasks (e.g., reasoning, speed, attention) as well as measures of affect and self-efficacy, daily assessments of physical activity participation, and sleep diaries. The current study seeks to investigate whether concurrent variations in sleep and physical activity were lawfully related to variations in cognition, and whether such associations differed by domain of cognition. Several studies have examined the positive effect of increased physical activity and more sleep in late-life, and the positive relationship between sleep and exercise, but no research has examined the effects of physical activity and sleep on cognitive inconsistency, nor has any research examined sleep as a possible mediator through which physical activity may be associated with cognitive functioning. The specific aims of this NRSA are: (1) to describe elders'magnitude of cognitive inconsistency at two different temporal resolutions (weekly, momentary), (2) to explore how level of performance and inconsistency in sleep and physical activity are related to cognitive inconsistency, and (3) to explore the extent to which weekly fluctuations in cognition co-occur with concurrent fluctuations in physical activity and sleep;moreover, various dynamic associations (i.e., lagged, reciprical associations overtime) will be explored. Furthermore, sleep will be examined as a mediator of the relationship between activity and cognition over time. PUBLIC HEALTH RELEVANCE: The findings from this research will aid public health by identifying (potentially modifiable) factors that are associated with cognitive inconsistency in older adults. This research will also provide information regarding normative levels of cognitive inconsistency.