PROJECT SUMMARY Social and lifestyle interventions are a promising innovation for delaying the onset of Alzheimer’s disease (AD) and related dementias. Extensive work has shown that maintaining social connectedness through personal social networks (the group of family members, friends, and other acquaintances in which individuals are socially embedded) confers resilience to cognitive decline and AD. The current proposal uses an interdisciplinary and multi-method approach to elucidate the mechanism by which this occurs. To date, existing research has focused on the implications of social networks for one neurocognitive pathway – general cognitive ability. The current proposal tests the novel prediction that a different pathway – social cognitive function – is a key component underlying the linkages between social networks, general cognitive function, and AD resilience. Social cognitive function – the process by which people understand, store, and apply information about others – is essential for successfully navigating social interactions, and declines over the lifespan. The proposed work explores the prediction that exercising social cognitive abilities through complex social interactions within their personal social networks stimulates older adults’ general cognitive function, thereby improving their resilience. In Aim 1, we examine the relationship between older adults’ social networks and their social cognitive function, as well as the possibility that having better social cognitive function may be protective for general cognitive function. Aim 2 uses a novel neuroimaging approach to identify the neurobiological mechanisms that give rise to the relationship between social networks and social cognitive function. Finally, Aim 3 uses a longitudinal design to gain insight into the causal relationship between social network dynamics, social cognitive decline, and general cognitive decline. The proposed study is interdisciplinary, combining cutting-edge methods from the social and biomedical sciences, and leveraging the resources of funded centers for AD, neuroimaging, and network science. The long-term goal of this project is to improve the clinical course of AD, and reduce the prevalence and public health impact of dementia. By increasing our understanding of the links between biological and social processes, this project may help identify novel targets for intervention to reduce the burden of AD on individuals, families, and the health care system.