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CU scientist probes neurobiology of love and loss

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Love Doctor

By Roni Dengler

Zoe Donaldson is the ultimate love expert. A neuroscientist at the University of Colorado Boulder, she works to untangle the mess of hormones and neural charges that shoot off in our brains when we fall in love and make long-lasting connections with someone. This wisdom helps her grasp love’s equally universal counterpart: dying of a broken heart.

Donaldson, who has strawberry blond hair, rectangular glasses and a sincere voice, earnestly wants to help people. But, because one of her main research goals is to understand how losing a loved one stresses our health, she doesn’t study human subjects. Instead, she uses an unusual laboratory animal, the prairie vole. Unlike the promiscuous lab rat or mouse, prairie voles are monogamous. They form long-term relationships with their mates, similarly to how most humans do.

These bonds show up in prairie voles’ behavior. For example, when they’re placed in an enclosure with their significant other tethered to one side and an equally sexy stranger leashed to the opposite wall, prairie voles choose to spend more time hanging out near their partners than with the mysterious newcomer.

Puppy Love

A well-known hormone called oxytocin is partially responsible for these preferences.

Oxytocin was first used to induce labor in pregnant women who were past their due dates, but it also plays into other aspects of reproduction, like stimulating the release of breast milk and maternal nurturing. Oxytocin’s effects are so powerful, one study showed, that even cocaine-addicted rats chose to take care of pups over using cocaine. Beyond facilitating bonds between mothers and their offspring, oxytocin also fosters connections between partners.

After speaking at a scientific meeting in Abu Dhabi, Donaldson saved an afternoon to play in the desert.
(photo courtesy zoe donaldson)

In humans, oxytocin elicits the same kinds of preferences in humans as Donaldson sees in prairie voles. For example, men who are in a committed relationship stand farther from equally attractive single females than men who are not bonded to a significant other. The hormone also makes humans more trusting with each other.

Overall, oxytocin is a feel-good chemical. But, depending on the social context, it harbors a dark side, too. While oxytocin can promote already established pair bonds, it can increase isolation or even envy in those who aren’t already a part of a close relationship or friendship.

Because of this flipside, Donaldson believes oxytocin acts like a booster that amplifies the social context of a situation. In positive relationships, oxytocin reinforces trust and bonds but in negative social situations like bullying, it increases the traumatic impacts.

Social safeguard

Oxytocin isn’t the only brain feature mediating our responses to sociality. Other work in Donaldson’s lab looks at how social interactions help us deal with stressors, particularly fear. A typical mouse’s reaction to fear is to freeze and not move. Researchers may condition mice to fear a certain environment, but when the mice revisit the scary environment with a cagemate, they freeze less. Just like for us humans, sometimes doing something scary is easier when you bring a friend along.

Dr. Zoe Donaldson (second from right) with lab staff on the CU campus. (photo courtesy zoe donaldson)

Donaldson benefited from a similar social boost when she came to Colorado in 2016. Before arriving in Boulder, she had completed a five-year postdoctoral fellowship at Columbia University in New York City. She persuaded her students and some lab personnel to make the cross-country move with her when she received an offer for joint appointment in the departments of psychology and neuroscience, and molecular, cellular and developmental biology.

Now, in her recently established CU lab, Donaldson is trying to identify the specific group of cells in the brain responsible for the better-with-a-friend response. Her team has found that a set of brain cells signal to one another when a mouse interacts with a cagemate. If Donaldson artificially turns on these cells in mice in the scary environment, the mice freeze less, just as they do when an actual cagemate is with them.

Long-term social bonds help us out in many ways. They make us feel safer, more trusting and less stressed. But perhaps because of the security net, there are significant consequences to our health and well-being when we lose those bonds.

Grief, like love, is universal. We will all lose someone we love at some point in our lives. Grief is not just a sadness, but a distinct physiological and sometimes long-term response to loss. It takes on physical ramifications. People who have lost a loved one are at higher risk for heart attacks, substance abuse and suicide. Donaldson hopes that by sussing out how loving bonds are initially formed and then maintained by the chemicals in our brains, clinicians will be able to help those suffering from loss.

“That’s what’s really been driving half of our work,” she says. “How can we reverse the physiological and emotional responses upon partner loss?”


Roni Dengler is a science writer. She earned a Ph.D. from CU Boulder and wrote science news for PBS NewsHour as a AAAS Mass Media Science and Engineering Fellow. She now writes for Science Magazine in Washington, D.C., but calls Boulder home. Connect @RoniDengler.