When it comes to romance, Zoe Donaldson has seen it all: arranged marriage, unrequited love, long distance, breaking up. The CU Boulder professor matches up couples and looks at their brains in love, and once she’s done, she sends them to get fed to the raptors.
For more than 20 years, Donaldson has studied the brains of prairie voles for insights into the neuroscience of committed relationships. These rodents are in the 3%-10% of mammals that practice monogamy, which makes them a top contender for lab research on human romance. They’ve helped Donaldson understand how love and grief shape the vole brain, in hopes of understanding human ones.
“I immediately fell in love with them,” Donaldson said. “They’re really cute, right? They’re furry little tennis balls with short ears and short tails. They smell way better than laboratory mice.”
But what makes them most compelling to people are their parallels with human relationships, she said. A more classic lab animal, like a mouse, is likely to mate with several different males and raise her children either alone or with a group of other females. In comparison, a prairie vole romance is a little more fairytale, with dating (for at least six hours), moving in together and often raising multiple litters together over their lifetimes.
In Donaldson’s lab, researchers play matchmaker for male and female voles, leaving them together in their cage until they get attached, then separating the happy couple to see how their brains react. In January they published findings on the role of dopamine in pair bonds. Their work suggests biological evidence of humans’ high motivation to get close to a partner, as well as our ability to get over that partner if we break up.
Researchers first tested the voles with distance, placing pairs on opposite sides of a transparent barrier. In some cases, one vole had to press a lever to join its partner. In the others, it would scamper over a wall three times its height to reach the other side. The vole’s nucleus accumbens, part of the brain’s reward system, released much more dopamine when going to its partner rather than to an unfamiliar vole.
“When they get to the top of the barrier, they could just hop out of the cage entirely, but instead they just always drop down,” Donaldson said. “I think it’s fascinating, because their drive to escape is overcome by their drive to go hang out with their partner for 30 seconds.”
Once those 30 seconds pass, it’s back to the other side of the barrier, until the vole scrambles back to its mate. And on it goes for 15 minutes, until the trial ends and researchers leave the couple in peace.
They’ve done it enough times to know it won’t be long until they’re reunited, Donaldson said. Yet they spend every moment apart trying to get back together.
Compare that to spending hundreds on plane tickets just to spend the weekend with your beloved. “We show incredible levels of motivation for these relationships,” Donaldson said.
But like many long-distance couples, even those not subject to experimentation, the dedicated voles had to break up. Researchers kept them in separate cages for four weeks, long enough for a vole to successfully find a new mate. When the original couples finally saw each other again, they recognized each other, but the dopamine levels were no higher than for a stranger. The motivation to get back to each other was no longer there.
The next step is determining whether these mechanisms also occur in the human brain, Donaldson said. But for now, there’s something for everyone to fantasize about: couples can swoon over the brain-altering power of their love, and everyone else can rest assured that their last heartbreak doesn’t actually spell the end of the world.
Every vole researcher has their own favorite stories about the charismatic creatures, Donaldson said. Just walking into the lab, she’s met with a flurry of activity: voles running around their cages, voles making nests and even voles doing pull-ups.
While it’s important not to ascribe too much humanity to the rodents, they provide a simplified model for complex human emotions.
“If you look at history, if you look at literature, there’s so many stories that revolve around pair bonding. We’re trying to understand something that’s a fundamentally human experience,” Donaldson said. “I’m constantly fascinated by how rewarding and strong and important these relationships are, and how profoundly we feel.”