The human brain processes a romantic partner differently from close friends, but over time this distinction becomes less pronounced. This conclusion was reached by an international team of scientists. The study was published in the journal Social Cognitive and Affective Neuroscience (SCAN).

The research showed that in the early stages of a relationship, a special “neural signature” of a partner forms in the brain’s reward system. However, as the bond becomes more stable, this signature gradually loses its uniqueness. According to the authors, this reflects a shift from passionate love to a calmer, companionate form of attachment.

Psychologists focused on the activity of the nucleus accumbens — a brain region closely linked to dopamine and responsible for motivation and the experience of reward. Previous animal studies have shown that this area plays a key role in the formation of pair bonds.

The study involved 47 men aged 20 to 29 who had been in romantic relationships for an average of about one and a half years. Participants provided video recordings of their partners and close friends. During functional MRI scanning, the men completed a task in which they anticipated receiving a positive reaction from one of these individuals.

“Romantic relationships are characterized by exclusivity, strong involvement, and passionate love, which distinguishes them from friendship,” explained the study’s author, Kenji Fujisaki. According to him, the researchers were interested in “how the brain distinguishes between a partner and friends, and whether this distinction changes over time.”

The analysis showed that the brain indeed encodes a partner as a distinct, unique category: activity patterns in the nucleus accumbens reliably differentiated responses to a partner from responses to a female or male friend. At the same time, the brain’s representation of a female friend was closer to that of a male friend than to that of a romantic partner.

However, the duration of the relationship proved to be a key factor. The scientists found that the longer a couple had been together, the less pronounced the neural difference between the partner and a close friend became. This effect persisted even after accounting for subjective ratings of closeness, passion, and attachment.

“Early stages of relationships are marked by passionate love, which requires high specificity in the functioning of the reward system,” Fujisaki noted. “As the relationship develops, this neural specificity decreases, which may reflect a transition to a more stable, companionate love that in many ways resembles deep friendship.”

The authors emphasized that the reduction in neural “uniqueness” does not mean the relationship is deteriorating. On the contrary, it may indicate a shift in the biological mechanisms that sustain it. In future studies, the researchers plan to examine which other brain systems help maintain long-term bonds and how they are influenced by milestones such as cohabitation or marriage.