It’s no secret that people tend to be friends with others who are like them, but that reality goes deeper than we can readily see.

A newly published study found that an individual’s brain patterns can predict who they are friends with, indicating that it’s not just what you have in common that makes friendship likely, but also how you think and how you perceive the world.

To determine whether friends have a deeper connection than meets the eye, researchers presented volunteers with videos and monitored their neural responses as they watched the content.

This differs from many past studies into homophily among humans — that is, the tendency to associated with others who are similar to ourselves — which looked at things like demographics and physical traits.

Homophily, the Nature study explains, “is an ancient organizing principle and perhaps the most robust empirical regularity of human sociality.” While humans do commonly form relationships of some sort with people different than them, that is often for practical purposes, such as professional collaborations, and the researchers say such associations are often short-lived.

In looking at neural responses to the videos, the researchers found that friends share similar responses compared to other individuals who are further removed from them in their IRL social network (not to be confused with social media friends).

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