How the brain represents a romantic partner: Dissociable roles of the nucleus accumbens and anterior insula.

Humans form selective and enduring pair bonds with romantic partners, a principal feature of human sociality. Neuroimaging studies have shown that romantic partners are differentially represented from other individuals in the nucleus accumbens (NAcc) and anterior insula (aINS) and that the specificity of partner representations in the NAcc diminishes as relationships mature. However, it remains unclear whether such differentiation reflects partner-specific coding or mere differences in familiarity with others and whether these regions play different roles in romantic bonding. To address these questions, we applied multiple regression representational similarity analysis to fMRI data from 51 heterosexual male participants in early romantic relationships. The data were acquired during a social incentive delay task, in which participants anticipated social approval from their female romantic partner, a female friend, or an unfamiliar female individual. This approach allowed us to dissociate partner-specific representations from familiarity-related effects in the NAcc and aINS. We found that both regions exhibited partner-specific representations that could not be explained by familiarity. Consistent with previous findings, partner specificity in the NAcc was negatively associated with relationship duration, indicating that partner-specific coding in this region is established early in romantic relationships and diminishes as relationships progress. Moreover, greater partner specificity in the aINS was associated with more frequent intrusive thoughts about the partner. Together, these findings demonstrate that romantic partners are represented in the NAcc and aINS in a qualitatively distinct manner from other individuals, and that these regions support dissociable aspects of romantic bonding.