New research on prairie voles reveals that oxytocin isn’t the simple ‘cuddle chemical’ we thought. It’s a crucial social accelerator, shaping who we befriend and how quickly those bonds form.
For years, oxytocin has enjoyed a reputation as the brain’s ultimate feel-good molecule. Dubbed the “love hormone” or “cuddle chemical,” it’s released during moments of connection—from childbirth and breastfeeding to a simple hug between friends. Popular science has championed it as the key to trust, attachment, and overall well-being. But as with many things in neuroscience, the real story is far more intricate and fascinating.
Recent studies have begun to chip away at this simplified narrative, suggesting oxytocin’s role in our social lives is much more nuanced. Now, a new study from UC Berkeley, focusing on the friendships of a small, unassuming rodent, adds a critical piece to the puzzle. By studying the prairie vole, an animal that, like humans, forms selective and lasting relationships, scientists are discovering that oxytocin isn’t so much the engine of our social bonds, but rather the accelerator pedal that gets them up to speed.
A More Complicated Chemical Story
The first hints that oxytocin’s role was misunderstood came from studies that seemed to defy expectations. In 2023, research showed that prairie voles genetically engineered to lack oxytocin receptors could still form monogamous pair-bonds and care for their young—behaviors long thought to be governed by the hormone. While the bonds took longer to solidify, they did eventually form, proving that oxytocin wasn’t strictly essential for the job. This left scientists with a compelling question: if it’s not required for the bond itself, what exactly is oxytocin doing?
Annaliese Beery, a UC Berkeley associate professor and senior author of the new study, has dedicated her lab to exploring these questions, with a particular focus on peer relationships, or what we would call friendships. Understanding the neurobiology of friendship in animals like prairie voles can provide invaluable insights into the human social experience and shed light on psychiatric conditions like autism and schizophrenia, where forming and maintaining social bonds can be a profound challenge.
Friendship on the Fast Track
To pinpoint oxytocin’s function in friendship, Beery and her team, including graduate student Alexis Black, designed a series of elegant experiments. They compared the behavior of normal, or wild-type, prairie voles with the genetically modified voles that lacked oxytocin receptors.
In the first test, they observed how long it took for the voles to form a preference for a specific peer. For a normal prairie vole, about 24 hours of co-housing is all it takes to form a robust bond, demonstrated by choosing to huddle with their new friend over a stranger. The results for the voles without oxytocin signaling were starkly different. After 24 hours, they showed no preference at all. It wasn’t until they had spent a full week together that a friendship began to emerge.
“Oxytocin isn’t required to have a relationship,” Beery explains, “but it’s really important in those early phases of a relationship to facilitate it happening quickly and efficiently.” It acts as a social catalyst, dramatically speeding up the initial, tentative stages of getting to know someone and deciding, on a chemical level, “I like you.”
The Brain’s Social Sorting Hat
Perhaps the most compelling discovery relates not to the speed of bonding, but to its selectivity. Oxytocin, it turns out, is critical for helping the brain answer the question: “Who do I belong with?”
The researchers tested this by placing long-term bonded voles into a complex, party-like enclosure with multiple rooms and other voles. Normal voles behaved much like a person arriving at a party with a friend: they would initially stick close to their known partner before gradually mingling with others. They always kept track of who their friend was.
The voles lacking oxytocin receptors, however, were socially adrift. They mixed randomly from the start, showing no memory or preference for the partner they had entered with. “It was as if they didn’t even have a partner in there with them,” Beery notes. This demonstrates that oxytocin is crucial for maintaining the exclusivity of a bond, helping the brain distinguish between a cherished friend and a mere acquaintance or stranger.
The Currency of Connection and Rejection
To dig deeper, the team investigated the motivational pull of these relationships. They set up a test where voles could press a lever to gain access to either their friend or a stranger. Wild-type female voles consistently worked harder to get to their partners, whether it was a peer or a mate. The modified voles, however, only put in the extra effort for their mating partners, not their friends. This suggests that without proper oxytocin signaling, the intrinsic “reward” of a peer friendship is significantly diminished.
Intriguingly, the absence of oxytocin signaling also had a flip side. The modified voles were less aggressive and less avoidant toward strangers. This finding highlights oxytocin’s dual role in our social calculus. It not only strengthens our desire to be with our “in-group” but also contributes to the wariness or rejection of the “out-group.” It sharpens the line between friend and stranger.
To ensure these effects weren’t caused by the brain trying to compensate for the missing receptors, the team deployed a novel oxytocin nanosensor developed at UC Berkeley. This high-tech tool revealed that the brains of the modified voles weren’t flooding the system with extra oxytocin. In fact, oxytocin release was lower and occurred in fewer sites within the nucleus accumbens, a brain region vital for processing social reward.
A New Understanding of Our Social Brain
This comprehensive research paints a far more sophisticated portrait of oxytocin. It is not a simple love potion that magically creates bonds. Instead, it is a master modulator of our social lives. It fine-tunes our social selectivity, accelerates the formation of friendships, and reinforces the rewarding feeling of being with those we trust.
By moving beyond the hype of the “cuddle chemical,” these findings open up new avenues for understanding the fundamental mechanics of connection. They provide a crucial framework for investigating why social relationships can be challenging for some and offer hope for developing more targeted therapies for social disorders. The humble prairie vole reminds us that the chemistry of friendship is a delicate, complex, and beautiful dance.
Reference
Black, A., Komatsu, N., Zhao, J., Taskey, S., Serrano, N., Sharma, R., Manoli, D., Landry, M., & Beery, A. (2025). [Article on the role of oxytocin in peer relationship formation]. Current Biology.
