Oxytocin is often called the “love hormone” or “cuddle hormone,” famous for its role in feelings of closeness during sex, childbirth, breastfeeding, and affectionate touch.
It’s also released during positive social interactions, helping to build trust and attachment.
But scientists have long debated whether its effects go beyond romance and family bonds.
A new study from the University of California, Berkeley, shows that oxytocin plays a critical role in forming friendships—at least in prairie voles, small, social rodents that often serve as models for human bonding.
The research, published in Current Biology, suggests that while oxytocin isn’t absolutely required for long-term relationships, it makes them form faster and more efficiently, especially in the early stages.
Prairie voles are unusual in the animal world because they form selective, stable relationships, not only with mates but also with peers—something like human friendships.
Annaliese Beery, associate professor of integrative biology and neuroscience at UC Berkeley and senior author of the study, wanted to understand how oxytocin influences these peer bonds.
Working with graduate student Alexis Black and collaborators at UC San Francisco, the team studied voles that were genetically engineered to lack oxytocin receptors.
Normally, voles that spend a day together show clear signs of preference for each other—huddling, grooming, and choosing to be near one another over strangers.
But the receptor-deficient voles didn’t form this preference in the first 24 hours. It often took them a week to reach the same level of attachment, if at all.
“Oxytocin seems to be especially important in the early formation phase of relationships and in recognizing who’s familiar and preferred,” Beery explained.
Without it, the animals not only took longer to bond but also struggled to maintain connections when placed in new social groups. They quickly lost track of their original partners and mingled indiscriminately, unlike typical voles that stick close to friends at first before meeting new individuals.
In another test, the researchers measured how hard the voles were willing to work to see a friend or mate. Female voles with normal oxytocin signaling pressed a lever more often to be near their chosen partner than a stranger, whether it was a mate or a peer.
The receptor-deficient voles still pressed more to be with a mate, but not for a peer, suggesting that oxytocin may be more critical for the rewarding aspects of friendship than for romantic bonds.
Interestingly, the altered voles were also less aggressive toward strangers and less likely to avoid them, pointing to oxytocin’s role in both positive attachment and in-group versus out-group behavior.
To understand how the lack of oxytocin receptors affected the brain, the team collaborated with UC Berkeley professor Markita Landry and postdoctoral fellow Natsumi Komatsu, who developed nanosensors that light up when they detect oxytocin.
The results showed that receptor-deficient voles actually released less oxytocin from fewer sites in the brain’s nucleus accumbens, a key region for social reward. This finding rules out the idea that other brain systems might be compensating by increasing oxytocin release.
Beery’s broader research examines social relationships in a variety of rodent species to understand what’s unique to each and what’s shared across species.
She suspects that peer bonds may have evolved before monogamous mating in voles and possibly other mammals, meaning that friendship-like connections are deeply rooted in social biology.
This new study builds on previous work from the same team that challenged the long-standing belief that oxytocin is essential for pair bonding and parenting. In those earlier studies, voles without oxytocin receptors could still form monogamous relationships and care for young, though it took longer.
The findings may have relevance for understanding human conditions like autism or schizophrenia, which can affect the ability to form and maintain social relationships. By revealing how oxytocin influences the speed and selectivity of friendships, researchers hope to better understand the biology behind social connection—and how to support it when it’s disrupted.
As Beery puts it, “Oxytocin isn’t the whole story of relationships, but it’s an important piece, especially in deciding who we connect with and how quickly that connection forms.”
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Source: UC Berkeley.
