Neural Responses Predict Friendships

Megan Zhou ‘21

An example of a social network diagram. (Source: Wikimedia Commons)

The proverb that “birds of a feather flock together” is based on the concept of homophily—the tendency of individuals to associate and bond with similar others. Throughout history, this trend has created evolutionary advantages in cohesion, collective action, and empathy (1). Previous studies have shown that homophily does organize human social networks, but the question of how homophily arises and functions in those networks remained. As a result, a research group from Dartmouth College recently completed a study that measured the association between humans who view the world similarly, as this had not been previously analyzed to confirm the similarity in cognitive processes.

The researchers hypothesized that neural responses to what people see and hear would be more similar among friends than those who are farther removed in a real-world social network, which was determined as people three degrees removed (friends-of-friends-of-friends) (2). This was tested by analyzing the social network of an entire group of 279 graduate students and first establishing the mutually reported social ties from a survey. A subset of 42 students then participated in an fMRI study, where each subject watched a series of videos. These videos were chosen such that they were variable in their topics in a way that was likely unfamiliar to the students to minimize mind wandering and were presented to the participants in the same order with the same instructions. A dyad-level regression model was used to test the relationship between fMRI response similarity and social distance (1). Additionally, the neural responses were then used to predict the social distance between members in the social network.

The findings show that there clearly is a strong relationship between neural responses and the degree of closeness of participants. Even when controlled for variables such as age, gender, and ethnicity, this connection was still evident (1). This research expanded upon the group’s earlier work that found that people’s brains highlight the importance of others as soon as one sees them (2).  However, despite the fact that the results show extreme similarity in neural responses to audio and visual stimuli, this study alone cannot determine whether the neural response similarity is the cause or effect of friendship.

Ultimately, the aim is to use this information and develop future longitudinal experimental designs to truly determine if these results reflect homophily, social influence processes, or a combination of these. Further investigations should also examine more behavioral measures and more constrained experimental patterns (1). The team behind the present study is currently attempting to analyze the impact of shared experiences on neural responses and if homophily and social influence processes dynamics reinforce each other.

(1) Carolyn Parkinson, Adam M. Kleinbaum, Thalia Wheatley. Similar neural responses predict friendship. Nature Communications, 2018; 9 (1) DOI: 10.1038/s41467-017-02722-7

(2) Dartmouth College. (2018, January 30). Your brain reveals who your friends are: Study illustrates how similar neural responses predict friendships. ScienceDaily. Retrieved February 3, 2018 from