By Emma Young

How well do you know your best friend? New research led by Robert Chavez at the University of Oregon suggests that scans of both your brains might provide the answer. The study, published in the Journal of Personality and Social Psychology: Attitudes and Social Cognition, reveals that the brain activity patterns of people asked to think about what a mutual friend is like can be remarkably similar to those observed in that friend when they think about themselves.

For the round-robin study, the researchers recruited 11 students aged 24-29 who were all friends and spent a lot of time together. Each of the students first rated themselves, as well as each of their friends, on a variety of personality measures, including Big Five personality traits, and self-esteem.

Next came the brain-scanning. While their brains were imaged using fMRI, the participants were given tasks that would later allow the researchers to identify which region of their medial prefrontal cortex (mPFC) was most active when they thought about themselves. Then, while still in the scanner, the participants completed the main task, which was similar to the initial one: they had to indicate whether 48 trait adjectives (including sad, lonely, cold, lazy, trustworthy, fashionable, helpful, punctual and nice) applied to themselves and also to each of their friends.

Using all this data, Chavez and co-author, Dylan Wagner at Ohio State University identified, for each participant, a pattern of mPFC activity that occurred when they rated themselves on these traits. They also averaged out the friends’ mPFC patterns when they thought about a specific individual. This gave them one aggregated pattern that they could compare to the individual’s own.

The pair found distinct similarities. When the participants were thinking about one particular friend in the group — let’s call him ‘Person A’ — their aggregated activity pattern was closer to that seen in ‘Person A’ when he thought about himself than to anybody else’s “self” pattern.

The similarity between an individual’s activity pattern and that of their friends related to the initial judgement ratings: the more closely the friends’ initial ratings matched an individual’s self-judgements, the more similar the self/friends brain activity patterns. This may be because participants with particularly close self/friend judgement ratings are better at conveying their personalities to others, the researchers suggest.

The study does have some limitations. Notably, the sample size of 11 is small, although the researchers are at pains in the paper to explain why this was the case. Partly it related to task timing — because of the round robin design, every extra individual included in the study would have extended the time taken to test everybody else. Also, the participants were all young students in a tight-knit social group. The results may or may not extend to other age groups and types of relationships — such as groups of co-workers. It’s also worth bearing in mind that thinking about the personalities of similar friends can influence a person’s judgments of their own personality, which may perhaps have affected the results.

Still, showing that there are these self/friend similarities in mFPC activity does point to all kinds of potentially interesting future studies. For example, one way to explore discrepancies between how a person with anxiety or depression sees themselves versus how others see them could be to look at mPFC activity. Overall, as the researches note, the results “point to a neural mechanism underlying accuracy in interpersonal perception.”

– The neural representation of self is recapitulated in the brains of friends: A round-robin fMRI study

Emma Young (@EmmaELYoung) is a staff writer at BPS Research Digest