What Can Rodents Tell Us About Why Humans Love?

A relative of the mouse may hold the key to understanding why human beings are one of the few mammals that seek lifelong mates

(Joel Sartore / National Geographic Creative / Photo Illustration By Erik Washam, SI)
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Voles, and by extension oxytocin, have begun to capture imaginations more widely, though the outcome is sometimes silly. There’s the self-help book Make Love Like a Prairie Vole: Six Steps to Passionate, Plentiful and Monogamous Sex, as well as a fragrance called “Liquid Trust,” a synthetic oxytocin spray marketed to “singles” and “salespeople” alike. Of course, Young points out, even if the spray works (and he is not saying it does), the wearer would inhale much more of the hormone than any potential target: “Who’s going to end up trusting who?” he laughs.

But some human uses are quite serious. One of Young’s primary interests is autism therapies. “Autism is a disorder where social cues are not as salient, kids are not motivated to interact with others and have difficulty reading emotions,” he points out. “All of these social things, oxytocin seems to stimulate.” Already synthetic oxytocin, administered through the nose, is being used in experimental treatments related to autism.

There’s good reason to be cautious about the curative powers of oxytocin, though. “In my own opinion, there hasn’t been enough preliminary data from animals,” says Karen Bales, who studies social bonding at the University of California, Davis, and worries about the consequences of exposing developing brains to the molecule. Bales and her colleagues have found that oxytocin exposure may inhibit later-life pair-bonding, particularly in male voles. And though some work, including in human beings, shows that the molecule may help sociality, others find that the effect depends on the individual and the situation.

“You have to beware of premature extrapolation,” says Insel, of the National Institute of Mental Health. “You want to be very careful and not assume that we are very, very large prairie voles.”

Less controversial, for the moment, is Young’s work in grief therapy. He and a German colleague recently studied what happens when voles and their life partners become separated. In rigorous stress tests, including ones that dropped rodents in a beaker of water, those that had just lost a partner struggled far less than the others. Instead, they passively floated, not seeming to care if they lived or died. In some ways, their symptoms resembled depression. “When animals form this pair-bond they become addicted to that partner, and when they lose the partner it is almost like withdrawal from a drug,” Young explains. “It’s a maladaptive consequence of an evolutionarily helpful thing. It’s love sickness.”

When researchers dissected the bereaved animals’ brains, they found elevated levels of a chemical called corticotropin-releasing factor, or CRF. If the bereaved animals’ chemical receptors were blocked, the voles behaved normally, struggling fiercely for life. “It helps us understand the neurocircuitry that may be involved in depression in general,” Young says.

He knows firsthand the pain of separation. About a decade ago, his first wife, his partner since high school, left him, taking their three children with her. For months he floated in a metaphorical beaker. “I lived in a house with no furniture,” he says. “I slept on a little kid’s mattress. I realized the consequences that happen when you lose someone you love, because I went through it. In the moment, when you’re going through it, you don’t think about experiments and things—these urges and drives are just happening.”

Young has since recovered his momentum. He recently founded the Center for Translational Social Neuro­science at Emory, which focuses on how basic animal research can inform new treatments for human social disorders, and convened an international meeting for vole researchers. A world map on the wall of his office highlights just how far he has traveled from his Sylvester “dirt road.” On one madcap journey to Madagascar, he and other researchers collected brain samples of two closely related species of plover, another animal with “love” in its name. One species is monogamous and the other isn’t. Young hopes to compare their neural wiring with that of the voles.

Perhaps most significantly, he also pair-bonded again, this time with another neuroscientist. Over dinner he and his partner discuss the finer points of his hormone work and how it relates to the human condition. Genetics and brain chemistry may shape every relationship, but they don’t make magic last on their own. “I still gotta remember the anniversary,” he says. “I still gotta buy the flowers.”


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