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Biological “Signature of Desire” That Binds Couples Identified

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When separated from the person they love, humans will go to extreme lengths to get back to their side. A new study suggests that such bonding behavior is motivated by a torrent of the rewarding brain chemical dopamine. The same study also highlights why we are less relentless in our desire to be reunited with occasional acquaintances.

You’re my heart, you’re my vole

The study, published in Current Biology, didn’t actually separate humans from their loved ones in some kind of Squid Game-adjacent test, but instead investigated a fellow monogamous mammal: the prairie vole.

Only about 1 in 30 mammal species form long-term monogamous bonds. The polycule-shunning prairie vole builds a home and family with a single partner, and the animals appear to mourn when their other half dies.

The new research, led by Zoe Donaldson, an associate professor of behavioral neuroscience at the University of Colorado Boulder, wanted to test the strength of these bonds when the animals were separated.

“What we have found, essentially, is a biological signature of desire that helps us explain why we want to be with some people more than other people,” said Donaldson. “This research suggests that certain people leave a unique chemical imprint on our brain that drives us to maintain these bonds over time.”

Ain’t no mountain high enough

The researchers presented the voles with various obstacles that blocked their path to their partner; some voles were tasked with pulling a lever to open the room their partner was trapped in, while others had to climb a fence blocking their path. While they surmounted these obstacles, the research team tracked activity in the animals’ brains using a minuscule fiber optic sensor. This device could track shifts in brain chemicals, like dopamine, over millisecond time periods.

What is dopamine?

Dopamine, a neurotransmitter synthesized in the brain, acts as a chemical messenger, enabling interaction between nerve cells within the brain and throughout the body. Dopamine is most strongly associated with reward signaling in the brain. It also plays a crucial role in various functions including movement, thinking, and learning processes.  

The team homed in on the nucleus accumbens, a brain area central to reward processing and motivation. This region lights up when humans are presented with desired items like food, water or drugs. It also activates when humans see their partner smiling at them.

The sensor’s glow flared as soon as the love-hungry voles climbed the dividing wall or flicked the lever that separated them from their partner. The sensor’s light stayed dim, however, when the vole on the other side of the wall was revealed to be the vole equivalent of Dave from accounts. Previous work  also suggests that voles don’t try as hard to reach unrelated voles.

“This suggests that not only is dopamine really important for motivating us to seek out our partner, but there’s actually more dopamine coursing through our reward center when we are with our partner than when we are with a stranger,” said Anne Pierce, who contributed to the work as a graduate student in Donaldson’s group.

Don’t you (forget about me)

Prairie voles have a short lifespan, rarely living longer than a year in the wild. To test the endurance of the voles’ bonds, the team separated the animals from their partners for four weeks before conducting similar pair-bond tests again. Wild prairie voles would be expected to find another mate after a similar period.

Indeed, after this lengthy separation, the reunited voles had lost their spark of love. While the animals appeared to remember each other, their brain activity no longer had a partner-specific boost.  

Donaldson suggested that this diminished activity could represent a neural reset that allows the animals to find new bonds after a separation. While the team said more work is needed to assess how well their findings translate to humans, they hope that their study could help people who struggle with life-limiting and damaging long-term responses after loss – or those who have trouble getting into close relationships in the first place.

“The hope is that by understanding what healthy bonds look like within the brain, we can begin to identify new therapies to help the many people with mental illnesses that affect their social world,” concluded Donaldson.

Reference: Pierce AF, Protter DSW, Watanabe YL, Chapel GD, Cameron RT, Donaldson ZR. Nucleus accumbens dopamine release reflects the selective nature of pair bonds. Current Biology. 2024;0(0). doi:10.1016/j.cub.2023.12.041

This article is a rework of a press release issued by CU Boulder. Material has been edited for length and content.