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Throughout the course of their lives, people typically encounter numerous other individuals with different interests, values and backgrounds. However, not all these individuals will become their good friends, life partners, or meaningful people in their lives.

Many past psychology and behavioral science studies investigated the relationships between different people and what contributes to their perceived affinity to others. While some of these studies linked friendship to physical proximity, interpersonal similarities and other factors, the neural patterns associated with social connections between people have not yet been fully elucidated.

Researchers at University of California Los Angeles (UCLA) and Dartmouth College recently carried out a study exploring the possibility that people who end up becoming friends exhibit similar neural activity patterns. Their findings, in Nature Human Behavior, suggest that people are in fact drawn to others who exhibit similar emotional and mental responses to their surroundings.

"We were inspired by a long-standing puzzle: why do some people 'click' or connect right away, while others don't?" Carolyn Parkinson, senior author of the paper, told Â鶹ÒùÔº.

"Earlier research showed that friends tend to process the world similarly, but most of that work looked at people after friendships had already formed or examined relatively coarse variables, like demographics.

"We wanted to test if similarity in how people process the world around them, captured by neural responses to naturalistic stimuli (such as video clips), actually precede friendship and predict who will connect and grow closer to one another in the future."

As part of their study, Parkinson and her colleagues carried out a series of experiments involving a group of young people who were about to move to a new town and start their undergraduate studies at the same university. Their goal was to determine whether these incoming students' patterns of brain activity could be used to forecast the friendships that they would form during their first year at university.

"For all our participants, within days of their arrival in their new town (so before they had a chance to get to know and befriend each other), we scanned their brains using fMRI while they watched a set of video clips," explained Parkinson.

"Next, we followed these people over the next academic year to track who became friends with whom, and how close each pair of participants ended up relating to each other in the friendship network of their program."

The researchers subsequently compared the brain imaging data collected at the beginning of their experiment with information that participants had provided months later in a friendship-related survey. This allowed them to determine the extent to which the participants' neural responses when watching videos resembled those of other students who they did not yet know, but with whom they later became friends.

"The most striking finding of our study is that brain-to-brain similarity can predict future friendship," said Parkinson.

"Even before two people met or spoke with each other, if their brains responded in similar ways to the same videos, they were more likely to become friends months later and more likely to grow closer over time. This suggests that friendships aren't just built from chance encounters. Rather, friendships seem to be shaped in part by shared ways of seeing and interpreting the world."

The results of this recent study could have interesting implications for the study of social relationships, as they suggest that pre-existing similarities in people's interpretation of the world increases the likelihood that they will become friends. Other researchers could soon draw inspiration from these findings when investigating the neural underpinnings of human social connections.

Meanwhile, Parkinson and her colleagues are looking at the other side of the coin, or in other words, how friendships and shared experiences might shape the brains of individuals who have become socially close. Specifically, they are exploring the possibility that friends progressively develop similar patterns of brain activity as their bond grows over time.

"We're also interested in digging deeper into the mental processes that drive these neural similarities," added Parkinson.

"For example, are they tied to shared values, similar senses of humor, or common attention patterns? We are expanding our investigations to cover more diverse groups, as this will allow us to see how general these effects are outside of the specific population and context that we looked at in this particular study.

"In addition, we'd like to understand not just how friendships form, but also how interpersonal alignment might support cooperation, trust, and social bonding in larger groups."

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