Brain Activity Predicts How Much Individuals Like Each Other

What's the science?

Within a group, people tend to like each other over time as they get to know one another. When considering interpersonal factors, if Person A likes Person B, this can lead Person B to like Person A over time (reciprocal liking). Interpersonal reward might affect this process; if a person experiences something rewarding during a social encounter, this can further influence reciprocal liking (a positive feedback loop). Two brain regions, the ventromedial prefrontal cortex and the ventral striatum are known to be involved in processing reward. In some cases, activity in these brain regions can predict an individual’s preferences, and therefore may also be able to predict how much an individual will like someone else. This week in PNAS, Zerubavel and colleagues tested whether interpersonal liking and brain activity in reward-related regions could predict how much people liked each other after a period of time.

How did they do it?

Sixteen healthy young adults, most of whom did not previously know each other, were recruited for the study while volunteering for a summer program that took place over nine weeks. At two timepoints, once at the beginning of the summer program and again 9 weeks later, participants rated how much they liked each other ‘not very’ to ‘very’, 0-100 scale, and also viewed pictures of each other's faces while undergoing functional magnetic resonance imaging (fMRI) scans. The authors employed structural equation modelling (which can account for multiple interrelated variables) to assess liking cross all possible pairs of participants. Each participant was in turn referred to as the ‘actor’ and other participants were referred to as ‘partners.’ The authors assessed: a) the effects of both the actor and the partner’s liking of each other at timepoint 1 on the actor’s liking of the partner at timepoint 2 and b) the effects of both the actor’s and the partner’s neural responses in the ventromedial prefrontal cortex and ventral striatum at timepoint 1 on how much the actor liked the partner at timepoint 2 (i.e. whether either person’s brain activity at timepoint 1 predicted how much the actor liked the partner, controlling for how much they reported liking each other).

What did they find?

The authors found that how much the actor liked the partner, and how much the partner liked the actor at time point 1 predicted how much the actor liked the partner at timepoint 2. Next, after accounting for how much the partner and actor liked each other at timepoint 1 (and other known predictors of future liking) the authors found that neural responses in the ventromedial prefrontal cortex and ventral striatum in both the actor and the partner (brain activity in response to viewing each other's face) at timepoint 1 predicted how much the actor liked the partner at timepoint 2. This indicates that neural processes leading to future liking could be occurring subconsciously.

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What's the impact?

This is the first study to demonstrate that fMRI responses (measuring brain activity) in reward-related regions of the brain can predict how much one individual will like another individual months in the future. Specifically, neural responses in both people can affect how much one person likes the other person at a later timepoint. The study furthers our understanding of the neural basis for interpersonal relationships.

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N. Zerubavel et al., Neural precursors of future liking and affective reciprocity. PNAS (2018). Access the original scientific publication here.