Project Summary/Abstract Mobility, defined as an individual?s ability to move about effectively in his or her surroundings, is vital for the independence and quality of life of older adults. Despite the severe burden of mobility limitations on both the individual and the public health system, effective strategies to promote mobility are sparse. Environmental factors and brain aging are both associated with age-related mobility limitations. However, mobility research often occurs in disciplinary silos, such that research on brain aging rarely accounts for the environmental context in which seniors walk and research on environmental determinants rarely considers the cognitive challenges that complex community environments pose. This proposal addresses this issue by assessing interactions of physical environment characteristics and cognitive function on walking behavior and mobility disability in a longitudinal cohort of older adults with state-of-the art characterization of the systems involved in mobility control. The aims of this proposal are to 1) obtain and test reliability of new measures of the physical environment for participants in the Health, Aging, and Body Composition study using archived Google Street View images; 2) characterize the associations between physical environment, cognitive decline, and mobility; and 3) explore the associations between physical environment, speed of processing, structural integrity of the neural circuitry, and mobility in a subsample with brain magnetic resonance imaging. These aims will be accomplished by creating an environmental walkability score for participants based on factors such as sidewalk presence and safety. This measure will then be used to test associations with reported walking in the past week and reported mobility disability, or the inability to walk mile. Interactions of the walkability measure with cognitive decline will be assessed to determine whether those individuals with greater cognitive decline have stronger associations between environmental walkability and mobility outcomes. The mechanisms of these associations will then be explored using neuroimaging measures of the integrity of specific networks in the brain. This research is innovative in that it aims to break down disciplinary boundaries for the study of two important determinants of mobility performance: brain aging and the physical environment. It will also retrospectively incorporate measures of street-scale physical environment into an existing cohort of community dwelling older adults. The addition of environmental measures to the Health ABC cohort will provide a rich data resource for the aims of this proposal and for future studies by our team and other investigators. A greater understanding of the interactions between brain aging and environmental complexities could inform future intervention strategies to make community environments more accessible to the most vulnerable.