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Two prairie voles are interacting with one another. The vole on the left sniffs the cheek of the vole on the right.
New research in prairie voles showed that maintaining social pair bonds and recovering from lost bonds is controlled by dopamine in the brain’s reward center, the nucleus accumbens.
CU Boulder, Zoe Donaldson

Some of the best romance movies include a scene where the couple is separated and yearns to return to each other, longing to share an embrace once again. When they finally reunite, they declare their love, the music swells along with the hearts of the audience, and they live happily ever after. The stories of Harry and Sally, Noah and Allie, and even Romeo and Juliet tell tales of doing anything to be with your love. But, why do people connect with this type of storyline so strongly? And, what happens if that “happily ever after” does not occur? Scientists at the University of Colorado Boulder aimed to answer these questions, showing the chemical way brains react to love and loss in a study recently published in Current Biology.1

Personal relationships have two simple options as time passes: be maintained or lost. Zoe Donaldson, a neuroscientist at the University of Colorado Boulder, and her team set out to explore social bonds in the brains of prairie voles, one of only a small portion of mammals that bond in monogamous pairs.2 “A lot of people have looked at what is needed for two voles to form that initial bond. We were looking at what happens after bonds are already established,” said Anne Pierce, a former graduate student in the Donaldson laboratory and the study’s lead author.

I think it’s beautiful that there are innate systems in our brain that help us adapt to really salient events.
– Anne Pierce, University of Washington

The team designed a unique experiment that required motivation for separated voles to return to their partners. Motivational control is guided by the neurotransmitter dopamine.3 Utilizing a cutting-edge technology called fiber photometry, which uses light to measure neurotransmitter changes in the brain while animals exhibit a certain behavior,4 the group recorded changes in dopamine levels in the nucleus accumbens, a brain area associated with social motivation and reward.1,5 “In this context, where the voles actually have to work, dopamine is crucial,” Pierce said. When voles climbed over a barrier or pressed a lever that opened a door to where their partner was, dopamine flooded into the nucleus accumbens and continued to do so as the voles cuddled, enjoying their reunion. 

The researchers next considered broken bonds. They separated the bonded voles from each other for four weeks, long enough that the animals could form a new bond with different partners.6 When the previously-bonded couples were reintroduced to each other, the original dopamine rush was absent. Time erased the desire and the voles’ brains adapted after the loss, causing dopamine levels to be the same for their previous partner as for a stranger.

Uncovering the brain’s ability to change like this, a property known as neuroplasticity, creates exciting research questions. “When I was a student, the brain was thought to be rather fixed … Realizing that we can make changes to our system … changes the very nature about how we approach [solving] brain related issues,” said Brandon Aragona, a neuroscientist at the University of Michigan, who was not involved in this study. Aragona also highlighted the need to consider how the brain can change. “I would like to see more people apply this knowledge to their own lives, and for us to focus on making sure our brain gets what it needs.”

Losing a loved one is a stressful and traumatic event, but this research demonstrates the brain’s incredible resiliency. “I think it’s beautiful that there are innate systems in our brain that help us adapt to really salient events,” Pierce said. “I’d like people to hold on to that hope. Our brain is trying to help us get over these events and move forward.” Donaldson’s team hopes this research leads to future clinical studies in humans, investigating maladaptive forms of grieving. 

References

  1. Pierce AF, et al. Nucleus accumbens dopamine release reflects the selective nature of pair bonds. Curr Biol. 2024;34(3):519-530. 
  2. Schuiling GA. The benefit and the doubt: why monogamy?. J Psychosom Obstet Gynaecol. 2003;24(1):55-61.
  3. Bromberg-Martin ES, et al. Dopamine in motivational control: rewarding, aversive, and alerting. Neuron. 2010;68(5):815-834.
  4. Simpson EH, et al. Lights, fiber, action! A primer on in vivo fiber photometry. Neuron. 2024;112(5):718-739.
  5. Dai B, et al. Responses and functions of dopamine in nucleus accumbens core during social behaviors. Cell Rep. 2022;40(8):111246. 
  6. Harbert KJ, et al. How prior pair-bonding experience affects future bonding behavior in monogamous prairie voles. Horm Behav. 2020;126:104847.