Dopamine—the same chemical signal that drives us to seek out everything from water to intimacy to cocaine, leaves a lasting imprint on the brains of monogamous animals, a new study reveals.

While the role of oxytocin, also known as the ‘love hormone' has been well studied in the context of human and animal pair bonding, it's the reward hormone, or dopamine, that's responsible for why we desire to be with some people more than others.

Hormones are endogenous chemical signals that drive behavior and organ function, and dopamine is sent into the brain's nucleus accumbens region as both the metaphorical carrot on a stick and pat on the back for accomplishing a task, whether that's climbing Mount Everest, or going into the kitchen to get a snack.

In a study that looked at prairie voles, a small rodent that mates for life, scientists at the University of Colorado in Boulder, found that dopamine is also responsible for driving these little animals to want to be with their pair-bonded partners.

"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 senior author Zoe Donaldson, associate professor of behavioral neuroscience. "This research suggests that certain people leave a unique chemical imprint on our brain that drives us to maintain these bonds over time."

Only 3 to 5% of mammals mate for life, and these little high-plains furballs share a home, raise offspring together, and experience something akin to grief when they lose their partner.

In the study, a tiny fiber-optic sensor neuroimaged the voles' nuclei accumbens during a series of tests to see what they would be willing to do in order to physically get back to their pair-bonded partner.

In one experiment, a vole and her partner were separated by a gate, which the vole could get through if she pulled a level. In another experiment, they were separated by a fence which she decided to scale just to return to her partner's side.

The imaging fiber "lit up like a rave" when she decided to scale the fence, and it continued "like a glowstick" as she snuggled up to her vole.

When it was a stranger on the other side of the fence, the dopamine image was dim, and the vole didn't work nearly as hard to reach the stranger.

In another trial, pair-bonded voles were separated for 4 weeks, which while difficult for human lovers, is an eternity in vole-time. The chemical signaling of dopamine after such a timespan had reset to the same profile as when seeing a mere acquaintance, suggesting that vole brains have a mechanism to protect their reproductive potential from endless loss or unrequited love.

"We think of this as sort of a reset within the brain that allows the animal to now go on and potentially form a new bond," Donaldson said.

While a vole is no human, the research shows that humans may also have such as reset; meaning that when we tell our friends who are going through a tough separation that time heals all wounds, chemically speaking, it could be true; that eventually the chemical imprint as Donaldson calls it will fade away, and we won't feel so drawn to be near to a previous love.

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