Oxytocin has long been called the love hormone, thanks to the warm and fuzzy feelings it creates in the brain. It also plays a key role in encouraging social bonding in humans and animals and it's an effective painkiller to boot, but the brain circuitry behind these effects is still being untangled. Now neuroscientists at Emory University have found the regions in brains of prairie voles responsible for pair bonding, and by stimulating those areas have been able to encourage the formation of such bonds.

Scientists often turn to prairie voles to study pair bonding because the adorable little rodents mate for life and will nest together, cuddle up, and share parenting work. Like humans, hormones like oxytocin and dopamine play a big part in forming these pair bonds, but the Emory team wanted to study what's going on in the brains of the animals in the early days of their relationships.

"Prairie voles were critical to our team's findings because studying pair bonding in humans has been traditionally difficult," says Elizabeth Amadei, co-lead author of the study. "As humans, we know the feelings we get when we view images of our romantic partners, but, until now, we haven't known how the brain's reward system works to lead to those feelings and to the voles' pair bonding."

To study that system, the team examined the brain activity of adult female prairie voles while they were socializing with a prospective mate. It turns out that the prefrontal cortex, which plays a part in decision-making, has a functional connection with the nucleus accumbens, which controls the reward system. The stronger this connection was in each animal, the faster they cuddled up with their partner, which could help scientists understand and treat social disorders in humans.

"It is remarkable there are neural signatures of a predisposition to begin huddling with the partner," says Larry Young, co-author of the study. "Similar variation in corticostriatal communication could underlie individual differences in social competencies in psychiatric disorders in humans, and enhancing that communication could improve social function in disorders such as autism."

To test whether social function could be enhanced, the researchers tried using optogenetics to stimulate these neurons with pulses of light. Sure enough, they found that they could accelerate a female vole's preference for a certain partner, even under conditions where a bond wouldn't normally form.

"Now, we want to know if oxytocin regulates functional connectivity and how circuit activity changes the way the brain processes social information about a partner," says Robert Liu, senior author of the study. "Our team's work is an example of a larger effort in neuroscience to better quantify how brain circuits function during natural social behaviors. Our goal is to promote better neural communication to boost social cognition in disorders such as autism, in which social functioning can be impaired."

The research was published in the journal Nature.

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