New research on prairie voles reveals that the ‘cuddle hormone’ isn’t just for romance—it’s a critical catalyst for building and maintaining our closest platonic bonds.
Oxytocin. For decades, it’s been hailed as the “love hormone” or the “cuddle chemical,” the magical molecule released during childbirth, sex, and intimate moments that forges powerful feelings of attachment and trust. We’re often told to boost our oxytocin for better well-being through hugs and social connection. But what if this simple narrative misses a crucial part of the story? Recent scientific investigations are revealing a far more nuanced and fascinating role for oxytocin, one that extends beyond romantic partners and parents to the very core of our social lives: our friendships. A groundbreaking new study from the University of California, Berkeley, dives deep into the neurobiology of friendship, using a unique animal model to uncover how oxytocin truly shapes who we choose to keep close.
The stars of this study are not humans, but small, unassuming rodents called prairie voles. Why them? Because, like humans, prairie voles are social creatures that form selective, stable, and long-lasting relationships. While most research has focused on their famously monogamous mating bonds, Dr. Annaliese Beery and her lab at UC Berkeley are interested in something equally important but less studied: their peer relationships, or what we would call friendships. “Prairie voles are special because they allow us to get at the neurobiology of friendship and how it’s similar to and different from other types of relationships,” explains Beery. By understanding the mechanisms in these animals, we can gain invaluable insights into our own social wiring and even shed light on psychiatric conditions like autism and schizophrenia, which can profoundly affect a person’s ability to form and maintain social bonds.
To isolate the role of oxytocin, the research team, in collaboration with Dr. Devanand Manoli’s lab at UCSF, studied prairie voles that had been genetically engineered to lack oxytocin receptors. In simple terms, even if their brains produced oxytocin, their cells had no way to “hear” its message. This created a perfect opportunity to ask a fundamental question: What happens to friendship when the so-called cuddle hormone is taken out of the equation? The results were not what the conventional wisdom might predict. The voles didn’t become antisocial loners. Instead, something much more subtle and significant occurred.
The first major finding was about speed. In the wild, forming a quick bond can be a matter of survival. The researchers found that normal, or “wild-type,” prairie voles form a robust preference for a new friend after just 24 hours of co-housing. They huddle, groom, and clearly choose their new companion over a stranger. The voles without oxytocin receptors, however, were a different story. After 24 hours, they showed no preference at all. It took them up to a full week to finally establish a similar peer bond. “Oxytocin isn’t required to have a relationship,” Beery clarifies, “but it’s really important in those early phases of a relationship to facilitate it happening quickly and efficiently.” Oxytocin, it seems, acts as a social catalyst, dramatically accelerating the chemical reaction that turns an acquaintance into a friend.
But speed was only part of it. The researchers then tested the stability of these bonds in a more complex, party-like environment. They placed long-term bonded pairs into a large enclosure with multiple rooms and other voles. Normal voles did what many of us would do at a party with a friend: they stuck close to their known partner at first before gradually mingling. They kept track of who they knew. The voles lacking oxytocin receptors, however, behaved as if they were at the party alone. “They just mixed,” Beery notes. “It was as if they didn’t even have a partner in there with them.” This points to oxytocin’s critical role in what scientists call social selectivity. It’s not just about being social; it’s about being social with specific individuals. As Beery puts it, “oxytocin is playing a crucial role not so much in how social they are, but more in who they are social with.”
This selectivity has a flip side. The hormone doesn’t just foster affiliation with trusted companions; it also helps reinforce boundaries with outsiders. The voles lacking oxytocin signaling were not only less attached to their friends, but they were also less avoidant of and less aggressive toward strangers. This suggests that oxytocin helps create the “in-group/out-group” dynamic that is fundamental to social structures. It sharpens the line between “friend” and “stranger,” promoting prosocial behavior toward the former and cautious or defensive behavior toward the latter. Without it, the social landscape becomes blurry and indiscriminate.
The team also explored the motivational aspect of friendship. Using an experiment where voles could press a lever to gain access to another vole, they found that normal female voles would work harder to get to their friend or mate than to a stranger. The receptor-deficient voles still worked hard to access their mating partner, but they showed no such preference for their peer partners. This implies that without oxytocin signaling, the intrinsic “reward” of a platonic friendship is significantly diminished. The motivation to seek out a friend’s company simply wasn’t as strong.
To ensure their findings were robust, the scientists used a cutting-edge tool: a novel oxytocin nanosensor developed in Dr. Markita Landry’s lab at UC Berkeley. This allowed them to measure oxytocin release in the brain in real-time. They found that in the modified voles, oxytocin release was actually lower in the nucleus accumbens, a key brain region for social reward. This ruled out the possibility that the brain was trying to compensate for the lack of receptors by flooding the system with more oxytocin.
This elegant study reshapes our understanding of oxytocin. It’s not a simple “love drug” that magically creates bonds. Instead, it’s a sophisticated neuromodulator that acts as a social accelerator and a selectivity filter. It fast-tracks the formation of friendships, helps us distinguish friend from foe, and imbues our platonic relationships with a rewarding quality that makes us seek them out. While a life without oxytocin signaling doesn’t mean a life of solitude, it suggests a world where friendships are slower to form, less stable, and less distinct from interactions with strangers. By untangling the complex chemistry of the prairie vole’s social life, these researchers have given us a profound new appreciation for the invisible biological forces that help build, maintain, and define our own most cherished friendships.
References
Beery, A. K., Black, A., Komatsu, N., Manoli, D. S., Landry, M. P., Zhao, J., Taskey, S., Serrano, N., & Sharma, R. (2024). Oxytocin receptors mediate social selectivity in prairie vole peer relationships. Current Biology.
