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Given the evolutionary importance of social ties for survival, humans are thought to have evolved psychobiological mechanisms to monitor and safeguard the status of their social bonds. At the psychological level, self-esteem is proposed to function as a gauge—‘sociometer’—reflecting one’s social belongingness status. At the biological level, endogenous opioids appear to be an important substrate for the hedonic signalling needed to regulate social behaviour. We investigated whether endogenous opioids may serve as the biological correlate of the sociometer. We administered 50 mg naltrexone (an opioid receptor antagonist) and placebo in a counterbalanced order to 26 male and female participants on two occasions ∼1 week apart. Participants reported lower levels of self-esteem—particularly self-liking—on the naltrexone (vs placebo) day. We also explored a potential behavioural consequence of naltrexone administration: attentional bias to accepting (smiling) faces—an early-stage perceptual process thought to maximize opportunities to restore social connection. Participants exhibited heightened attentional bias towards accepting faces on the naltrexone (vs placebo) day, which we interpret as an indicator of heightened social need under opioid receptor blockade. We discuss implications of these findings for understanding the neurobiological underpinnings of sociality as well as the relationship between adverse social conditions, low self-esteem and psychopathology.

We investigated the effects of intranasal oxytocin (OXT) on trust and cooperation in borderline personality disorder (BPD), a disorder marked by interpersonal instability and difficulties with cooperation. Although studies in healthy adults show that intranasal OXT increases trust, individuals with BPD may show an altered response to exogenous OXT because the effects of OXT on trust and pro-social behavior may vary depending on the relationship representations and expectations people possess and/or altered OXT system functioning in BPD. BPD and control participants received intranasal OXT and played a social dilemma game with a partner. Results showed that OXT produced divergent effects in BPD participants, decreasing trust and the likelihood of cooperative responses. Additional analyses focusing on individual differences in attachment anxiety and avoidance across BPD and control participants indicate that these divergent effects were driven by the anxiously attached, rejection-sensitive participants. These data suggest that OXT does not uniformly facilitate trust and pro-social behavior in humans; indeed, OXT may impede trust and pro-social behavior depending on chronic interpersonal insecurities, and/or possible neurochemical differences in the OXT system. Although popularly dubbed the ‘hormone of love’, these data suggest a more circumspect answer to the question of who will benefit from OXT.