Feeling left out or just surprised? Neural correlates of social exclusion and expectancy violations in adolescence

Social belonging and affiliation are important human drives that impact decision-making and health outcomes. While neural responses to social exclusion are increasingly well-characterized, studies rarely identify whether these responses reflect the affective distress or expectancy violation associated with exclusion. The present study compares neural responses to exclusion and over-inclusion, a similarly unexpected social occurrence that violates fair play expectations, but does not involve rejection, with a focus on implications for models of dorsal anterior cingulate cortex (dACC) function. In an fMRI adaptation of the Cyberball paradigm with human adolescents 11.1-17.7 years of age (N=69), we employed parametric modulators to examine scaling of neural signal with cumulative exclusion and inclusion events. The use of parametric modulators overcomes arbitrary definitions of condition onsets and offsets imposed on fluid, continuous gameplay. In support of the notion that the dACC plays a role in processing affective distress, this region exhibited greater signal with cumulative exclusion than cumulative inclusion events. However, this difference was partly driven by diminished signal accompanying cumulative inclusion, a finding that does not conform to either affective distress or expectancy violation model predictions. Additionally, we found that signal in the insula and dorsomedial prefrontal cortex scaled uniquely with social exclusion and over-inclusion, respectively, while conjunction analyses revealed that the rostromedial prefrontal cortex and left intraparietal sulcus responded similarly to both conditions. These findings shed light on which neural regions may exhibit patterns of differential sensitivity to exclusion or over-inclusion, as well as those that are more broadly engaged by both types of social interaction.