The brains of friends have similar brain functional connectivities.

From Hyhon et al.: 

Significance

In what ways are we similar to our friends? Here, we characterized the social network of residents of a remote village, a subset of whom contributed personality and neuroimaging data. We demonstrate that similarity in individuals’ resting-state functional connectomes predicts individuals’ proximity in their real-world social network, even when controlling for demographic characteristics and self-reported personality traits. Our results suggest that patterns of functional brain activity during rest encode latent similarities (e.g., in terms of how people think and behave) that are associated with friendship. Taken together, integrating neuroimaging and social network analysis can offer novel insights into how the brain shapes or is shaped by the social networks that it inhabits.

Abstract

People often have the intuition that they are similar to their friends, yet evidence for homophily (being friends with similar others) based on self-reported personality is inconsistent. Functional connectomes—patterns of spontaneous synchronization across the brain—are stable within individuals and predict how people tend to think and behave. Thus, they may capture interindividual variability in latent traits that are particularly similar among friends but that might elude self-report. Here, we examined interpersonal similarity in functional connectivity at rest—that is, in the absence of external stimuli—and tested if functional connectome similarity is associated with proximity in a real-world social network. The social network of a remote village was reconstructed; a subset of residents underwent functional magnetic resonance imaging. Similarity in functional connectomes was positively related to social network proximity, particularly in the default mode network. Controlling for similarities in demographic and personality data (the Big Five personality traits) yielded similar results. Thus, functional connectomes may capture latent interpersonal similarities between friends that are not fully captured by commonly used demographic or personality measures. The localization of these results suggests how friends may be particularly similar to one another. Additionally, geographic proximity moderated the relationship between neural similarity and social network proximity, suggesting that such associations are particularly strong among people who live particularly close to one another. These findings suggest that social connectivity is reflected in signatures of brain functional connectivity, consistent with the common intuition that friends share similarities that go beyond, for example, demographic similarities.