Researchers found close similarity in brain patterns between individuals and their friends

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If you ever wondered what’s going on in your friends’ brains when they think about you, new research may provide a clue.

It turns out that the brain activity patterns found in your friends’ brains when they consider your personality traits may be remarkably similar to what is found in your brain when you think of yourself, the study suggests.

Those same friends will have a different brain activity pattern when they think of someone else in your group – and more in alignment with that person’s pattern, findings indicate.

It was somewhat surprising to see the close similarity in brain patterns between individuals and their friends, said Dylan Wagner, co-author of the study and assistant professor of psychology at The Ohio State University.

“It didn’t have to be that way.

We thought it was equally possible that you would think of me in the same way as I think of myself, but the way your brain encodes that information could be totally different,” Wagner said.

The study was led by Robert Chavez, an assistant professor of psychology at the University of Oregon, who did the work as a postdoctoral researcher at Ohio State.

Their research was published online recently in the Journal of Personality and Social Psychology: Attitudes and Social Cognition.

Chavez and Wagner made this finding using a research design that had rarely been used in functional neuroimaging experiments before. They recruited 11 people who were all friends with each other to varying degrees.

(“They were a pretty tight-knit group from the same academic program who all spent time together at the university as well as outside of it,” Wagner said.)

The novel part is that the researchers used a round-robin design in which everyone evaluated each other – and evaluated themselves – on a variety of personality traits, Wagner said.

In one session, each participant rated each of the other 10 and themselves on a variety of personality traits in a written questionnaire.

In a separate session, the 11 participants conducted similar evaluations while in a functional magnetic resonance imaging (fMRI) scanner.

The fMRI took images of each person’s brain while they completed a task similar to the one they did earlier.

They rated each of their friends and themselves on 48 traits, including lonely, sad, cold, lazy, overcritical, trustworthy, enthusiastic, clumsy, fashionable, helpful, smart, punctual and nice.

As they expected from previous research, the researchers saw activity in the medial prefrontal cortex, a part of the brain implicated in thinking about the self and close others, as the participants thought about the personality traits of themselves and their friends.

The study found that for each participant, the combined brain activity of their friends evaluating them looked a lot like their own brain activity.

This suggests that order to accurately perceive another person, your neural representation of that person – your patterns of brain activity for their identity – has to essentially match the pattern in that persons’ brain when they are thinking about themselves, Wagner said.

Those same friends will have a different brain activity pattern when they think of someone else in your group – and more in alignment with that person’s pattern, findings indicate.

The researchers note, however, that their data only suggest this in aggregate, as the analysis focused on taking the brain patterns of all a person’s friends and averaging them together, an approach commonly taken in non-fMRI personality research when comparing friends’ consensus judgments of each other.

In some ways, that is not surprising, Chavez said.

“Each one of your friends gets to see a slightly different side of you. When you put them all together, it is a better approximation of how you seen yourself than any one person individually,” Chavez said.

The researchers plan to follow up this initial study with a larger version of this round-robin design focusing on different groups of people (i.e., work friends vs. personal friends)


The notion that people tend to resemble their friends is an enduring intuition, as evidenced by the centuries-old adage, “birds of a feather flock together”1.

Research has borne out this intuition: social ties are forged at a higher-than-expected rate between individuals of the same age, gender, ethnicity, and other demographic categories2.

This assortativity in friendship networks is referred to as homophily and has been demonstrated across diverse contexts and geographic locations, including online social networks25.

Indeed, consistent evidence suggests that homophily is an ancient organizing principle and perhaps the most robust empirical regularity of human sociality.

Despite pressures to divide labor and otherwise organize complementary needs and roles in the kinds of social groups in which humans evolved, social ties in small hunter-gatherer bands reflect similarities, rather than differences, across a range of attributes, including age, weight, body fat, handgrip strength, and cooperative behavioral tendencies4.

Significant examples of heterophily, which refers to the tendency to associate with others who are dissimilar from oneself, are markedly rarer in such groups.

Consistent with its ancient history, homophily also characterizes the social networks of our close primate relatives6 and has been suggested to confer advantages for cohesion, collective action, and empathy4,6.

When humans do forge ties with individuals who are dissimilar from themselves, these relationships tend to be instrumental, task-oriented (e.g., professional collaborations involving people with complementary skill sets7), and short-lived, often dissolving after the individuals involved have achieved their shared goal8.

Thus, human social networks tend to be overwhelmingly homophilous8.

Despite robust evidence that homophily organizes human social networks, significant lacunae remain in our understanding of how homophily arises and functions in these networks3,6.

Prior studies of homophily have been concerned largely with physical traits and demographic variables, such as age, gender, and class. Importantly, additional research has demonstrated that homophily extends beyond overt, demographic cues, to at least some aspects of behavior and personality.

For example, behavioral tendencies (e.g., donations in public goods games) associated with altruistic behavior are more similar among individuals who are friends compared with those who are not4, consistent with suggestions from evolutionary game theory that altruistic behavior only benefits individuals if their interaction partners also behave altruistically9,10.

Remarkably, social network proximity is as important as genetic relatedness and more important than geographic proximity in predicting the similarity of two individuals’ cooperative behavioral tendencies4.

Thus, although prior research on homophily focused largely on relatively coarse variables, such as demographic categories, a growing body of evidence has begun to move beyond externally evident demographic attributes, and suggests that social network proximity can be a powerful predictor of behavioral similarity.

In addition to the cooperative behavioral tendencies described above, some personality traits may also exhibit social assortativity.

Two of the “Big Five” personality traits—extraversion11,12 and openness to experience12—appear to be more similar among friends than among individuals who are not friends with one another.

However, the remaining Big Five traits do not predict friendship formation well13. Similarities in conscientiousness and neuroticism are not associated with friendship formation12, and evidence for more similar levels of trait agreeableness among friends has been found in some studies12, but not in others11.

Thus, the extant research on homophily has recently begun to examine personality but has focused predominantly on demographic variables.

It is possible that people cluster along these dimensions because they reflect commonalities in perceiving, thinking about, and reacting to the world. Similarity in how individuals interpret and respond to their environment increases the predictability of one another’s thoughts and actions during social interactions14, since knowledge about oneself is a more valid source of information about similar others than about dissimilar others.

This increased predictability during social interactions, in turn, allows for less effortful and more confident communication, thus fostering more enjoyable social interactions, and increasing the likelihood of developing friendships14.

In the same vein, interacting with individuals who share similar values, opinions, and interests may be rewarding because it reinforces one’s own values, opinions, and interests, thus producing an implicit positive affective response, promoting attraction to similar others, and increasing the likelihood of developing friendships with individuals who see the world similarly to ourselves15.

If friends are indeed exceptionally similar to one another in terms of how they perceive, interpret, and react to their environment, then social network proximity should be associated with similarity of cognitive processes as they unfold in real time. Whether or not humans tend to associate with others who see the world similarly has yet to be tested directly.

Here we tested the proposition that neural responses to naturalistic audiovisual stimuli are more similar among friends than among individuals who are farther removed from one another in a real-world social network.

Measuring neural activity while people view naturalistic stimuli, such as movie clips, offers an unobtrusive window into individuals’ unconstrained thought processes as they unfold16.

Inter-subject correlations of neural response time series during natural viewing of complex, dynamic stimuli are associated with similarities in subjects’ interpretation and understanding of those stimuli1619.

Thus, inter-subject similarities of neural response time series data afford insight into the similarity of individuals’ thought processes as they experience the world around them.

The current results suggest that neural response similarity decreases with increasing distance between individuals in their shared social network, such that friends have exceptionally similar neural responses.

Social network proximity appears to be significantly associated with neural response similarity in brain regions involved in attentional allocation, narrative interpretation, and affective responding, suggesting that friends may be exceptionally similar in how they attend to, interpret, and emotionally react to their surroundings.


Source:
Ohio State University
Media Contacts:
Dylan Wagner – Ohio State University
Image Source:
The image is in the public domain.

Original Research: Closed access
“The neural representation of self is recapitulated in the brains of friends: A round-robin fMRI study”. Dylan Wagner et al.
Journal of Personality and Social Psychology doi:10.1037/pspa0000178.

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