Processing of Different Social Scales in the Human Brain

Abstract

For an individual to lead a healthy and fulfilling social life, it is essential to have relationships with multiple people who are at different levels of emotional closeness. Based on ethological, sociological and psychological evidence, social networks have been divided into five scales of emotional closeness, gradually increasing in size and decreasing in emotional proximity. Is this division also reflected in different brain processes? During functional MRI, participants compared their emotional closeness to different members of their social network. We examined the brain area that was differentially activated for levels of emotional closeness, and found that its vast majority (78%) showed preference for people who are closest to participants, including the temporoparietal junction, middle temporal gyrus, precuneus and dorsomedial prefrontal cortex. A different system, which includes the medial temporal lobe, retrosplenial cortex and ventromedial prefrontal cortex showed preference for all other social scales. Moreover, we found a significant correlation between brain responses to emotionally close people and smaller spaces (room, building) as well as between emotionally distant people and larger spaces (neighborhood, city). Finally, brain activity at the default mode network (DMN) was associated with social scale preference, such that its subnetwork DMN A, related to social processing, showed preference to closer social scales, while DMN C, related to spatiotemporal processing, showed preference to farther social scales. Our results show that the cognitive processing of a few intimately close people differs from the rest of the social network, emphasizing their crucial role in social life.SignificanceWe divide the people in our lives according to levels of emotional closeness, called social scales, ranging from the few people who are the closest to us, in which we invest most of our social efforts and time (support clique), to the farthest level of ∼150 acquaintances. Here, we used neuroimaging to investigate the brain processing of different social scales. We found that the area of cortex dedicated to the support clique is much larger than that of all other scales and encompasses different brain regions. Interestingly, this division is similar to the one between processing of small and larger spaces, and processed by different subregions of the default mode network. Our study emphasizes the importance of close relationships in our social lives as found in the brain.