The social brain hypothesis originally developed by evolutionary psychologists has focused on the neural foundation of one of the most unique human characteristics: complex social interactions involving social networks. Although there is evidence to suggest that the capacity of the social brain contributes significantly to the size and position of one’s social network, it is also possible that social networking influences the structure and function of the individual’s brain. By using the unique features of the Korean Social Life, Health, and Aging Project (KSHAP), a dataset equipped with both neuroimaging data and comprehensive tracking of the social networks of the residents of two villages, this chapter explores the possible mechanisms through which brain and social networks interact with each other to form and change the social brain. It examines this relationship with studies utilizing mostly volumetry and resting-state activation of the brain. The studies show how social brain volume and connectivity are related to not only social network size but also to a variety of social network indices. By employing these indices, studies have been able to link the complex social world to human beings’ social brain in recent years. Furthermore, the chapter discusses causality issues in the relationship between the social brain and social networks.

A growing body of evidence suggests a strong link between how individuals maintain an enriched social network and their brain health. Both the quantity and quality of social networks provide abundant social connections. Through persistent social interactions, individuals’ neurocognitive health appears to benefit from cognitively stimulating activity as well as social support. By utilizing various neuroimaging methods, researchers have found that maintaining an enriched social network is likely to lead to better neural functioning that could delay or counter the effects of neuropathological progression in late life. This chapter reviews studies examining the relationship between social network characteristics and neurocognitive health. The studies highlight that social connectedness and brain functioning have reciprocal effects. It also discusses whether larger and cohesively connected social networks lead to a healthier brain and better cognitive function, as well as the moderators of this association.