When joining a group, we may initially like some individuals more than others. Likewise, certain group members may be particularly drawn to us. Over months of interaction, these attractions inevitably change and typically become reciprocated. This study uses fMRI to predict such changes in liking. Specifically, we measure newly acquainted group members’ reward system responses to images of one another’s faces. We find that T1 neural responses predict whom one will like in the future. More strikingly, we find that others’ T1 neural responses to us predict whom we will like months later, at T2. This brain-based mechanism helps explain how group members’ initially unreciprocated liking sentiments become mutually reciprocated. This study reveals how our brains interdependently shape interpersonal relationships.Abstract
Why do certain group members end up liking each other more than others? How does affective reciprocity arise in human groups? The prediction of interpersonal sentiment has been a long-standing pursuit in the social sciences. We combined fMRI and longitudinal social network data to test whether newly acquainted group members’ reward-related neural responses to images of one another’s faces predict their future interpersonal sentiment, even many months later. Specifically, we analyze associations between relationship-specific valuation activity and relationship-specific future liking. We found that one’s own future (T2) liking of a particular group member is predicted jointly by actor’s initial (T1) neural valuation of partner and by that partner’s initial (T1) neural valuation of actor. These actor and partner effects exhibited equivalent predictive strength and were robust when statistically controlling for each other, both individuals’ initial liking, and other potential drivers of liking. Behavioral findings indicated that liking was initially unreciprocated at T1 yet became strongly reciprocated by T2. The emergence of affective reciprocity was partly explained by the reciprocal pathways linking dyad members’ T1 neural data both to their own and to each other’s T2 liking outcomes. These findings elucidate interpersonal brain mechanisms that define how we ultimately end up liking particular interaction partners, how group members’ initially idiosyncratic sentiments become reciprocated, and more broadly, how dyads evolve. This study advances a flexible framework for researching the neural foundations of interpersonal sentiments and social relations that—conceptually, methodologically, and statistically—emphasizes group members’ neural interdependence.