On Mother's Day, Thank Mom for Following Her Hardwired Maternal Instincts

In addition to dispensing endless moral guidance and unconditional love, moms have to do a ton of tedious manual labor. Rocking a newborn means shuttling a nearly-nine-pound (sorry, mom) loaf back and forth using only your arms until it passes out; breastfeeding means letting that weight hang off of chafed nipples. If the payoff is merely the well-being of their ungrateful spawn, then it seems like moms are getting a bad deal. But according to research published in Neuron in early April, there’s another, more fundamentally satisfying reason for biological moms to do mom things.

In the study on mice, the New York University Langone researchers show that doing an extremely mom thing — chasing after wandering kids — elicits a lovely little dopamine rush in the brain. Tracking the brains of dozens of mouse mothers and their pups showed that this critical process of the brain’s reward system was triggered every time the mouse moms went collecting their wayward children and stopped once the pups were returned home. Because the biochemistry of most mammals is conserved, explained senior investigator Dayu Lin, Ph.D. in a statement, it’s reasonable to think that the same satisfaction-supplying dopamine rush occurs in the brains of human mothers doing maternal things. In other words, performing these actions is hardwired into a mom’s brain chemistry, and thank goodness it is.

“Our study shows precisely how a maternal instinct is generated in the mammalian brain,” said Lin, an assistant professor at the Neuroscience Institute at NYU Langone Health.

Lin’s team zeroed in on a part of the mouse brain previously implicated in pup retrieval called the medial preoptic area, looking for neurons that seemed especially active. The most active ones had one distinctive characteristic: They all expressed a protein called MPOA Esr1 on their surfaces. When the scientists stimulated all of these cells at once, mothers would instantly pick up their pups. Even female virgin mice would pick up random pups when this part of the brain was stimulated. Tracing these neurons to other parts of the brain, the team discovered that they were linked to the ventral tegmental area (VTA), a part of the brain associated with the reward system’s release of dopamine.

Dopamine release is broadly associated with a feeling of satisfaction (it’s implicated in sex and illicit drug use as well), so the implication here is that mothering feels good. In previous studies, when scientists blocked the dopamine-linked cells of the VTA, mouse moms stopped retrieving their pups, suggesting that when the reward part of motherhood doesn’t work, then the job becomes a lot less appealing. What that also sugests, however, is that dopamine doesn’t just give mom a rush after she chases her kids — it also helps motivate her to do it in the first place, since moms without any dopamine can’t seem to get going.

“Moreover, we believe that the findings overturn the longstanding idea that the dopamine system produces a ‘rush’ after a good behavior, and argue instead that dopamine may drive actions before any satisfaction is felt,” says Lin.

Brain chemistry is important in shaping how we behave, but it doesn’t dictate every aspect of how we act. Mothers can sometimes choose not to follow their hardwired instincts; other times, their brains are not wired as scientists might expect. One of the reasons it’s important to understand this “maternal circuit,” the team writes, is because sometimes brain chemistry goes awry, making it hard for mothers to nurse or bond with their kids. Understanding the details of the circuit better, they say, might suggest new ways to help those moms — and better explain how any mother can deal with tirelessly feeding, cuddling, and chasing after an incessantly crying kid.