Neuroscientists studying prairie voles have identified circuits in the brain’s reward center that may be a key part of forming social connections. They published their study today in the journal Nature.
Monogamous relationships, or pair bonds, are a lot less common than you’d think, arising in fewer than 5 percent of mammal species, including us and prairie voles (Microtus ochrogaster). What makes us so dang determined to stick with just one other person (or vole)? And what prompts us to latch onto them in the first place?
It’s kind of hard to tell. Human pair bonding is notoriously difficult to study, says co-lead author Elizabeth Amadei of Emory University’s Silvio O. Conte Center for Oxytocin and Social Cognition. “As humans, we know the feelings we get when we view images of our romantic partners,” she said in a statement, "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."
Scientists love prairie voles. They especially love prairie vole love—or at least the behaviors and brain chemistry that look like love to us. The voles are touchingly tender with one another, grooming, mating, and snuggling their partners until death does them part.
Previous studies have suggested that these intense connections may begin with hormones like oxytocin and dopamine swirling around the brain’s reward system. To learn more, the authors of the current study installed tiny probes in female prairie voles’ brains—the rodent neural version of a wiretap. They then paired the lady voles with males and left the couples alone to get to know each other a little better.
The neural wiretaps told a story of complex interactions between different regions of the female voles’ brains. As the ladies began to bond with their assigned dudes, a flurry of information was exchanged between their prefrontal cortices and nucleus accumbens, areas associated with decision-making and rewards, respectively.
The strength of these circuits varied by vole and seemed to influence her relationship. The stronger a vole’s connections were, the faster she started huddling with her partner. The reverse was also true: The more the two voles bonded, the stronger the neural connections became.
To further test their hypothesis, the researchers plopped lady voles down with new males, but only for a short period of time—not long enough to get attached and mate. During the voles’ brief date, the scientists sent a tiny pulse of light to the brain circuit in question, giving it a little boost. The next day, despite barely knowing the males they met the day prior, the light-pulsed ladies were significantly more likely to choose them over voles they’d never met. Just a little zap had been enough to kick off their courtship.
"It is amazing to think we could influence social bonding by stimulating this brain circuit with a remotely controlled light implanted into the brain," co-lead author Zack Johnson said in a statement.
Some caveats, of course: This study was on prairie voles, who are decidedly not people, and it only included female subjects. We couldn’t tell you what’s going on in those vole boys’ brains.