When a new mother looks at her baby and feels a rush of warmth and love, that feeling comes from somewhere specific in her brain — and scientists in New Zealand have just found the key to it.
Researchers at the University of Otago in Dunedin discovered that a hormone called prolactin — the same hormone that helps women make breast milk — switches on a special brain pathway that makes caring for a newborn feel rewarding, not just like a job that has to be done.
"The brain is undergoing remarkable change during pregnancy that really shapes the way we think and feel," said Associate Professor Rosie Brown, one of the study's senior authors. "It's not surprising that sometimes these changes can be difficult."
The team, working in the university's R. Brown Lab, found that in mice, this pathway runs from a part of the brain that senses hormones into the brain's reward center, which releases a chemical called dopamine. Dopamine is what makes us feel good when we do something enjoyable — like eating chocolate or hearing your favorite song.
Co-lead author Dr. Michael Perkinson said the findings help explain why new mothers often feel so intensely connected to their babies.
"We know the brain's reward system gets rewired after birth to prioritize offspring," Perkinson said. "Our findings help explain how that rewiring might happen, showing that prolactin acting through this specific pathway tips the balance and makes time with a newborn feel rewarding rather than just necessary."
The researchers tested this by doing two experiments. First, they artificially turned on this brain pathway in female mice that had never had babies. Those mice suddenly started acting like devoted new mothers, showing strong interest in pups they had never seen before. Then, when they blocked this pathway in actual mother mice, the normal surge of interest in their babies didn't happen at all.
The study, published in the journal Science Advances, could have real-world impact. In New Zealand, about one in five new mothers experience peripartum mood disorders — a term for depression, anxiety, or emotional struggles during pregnancy or after giving birth. Yet there are very few treatments designed specifically for pregnant or breastfeeding mothers.
Perkinson hopes the research will help take some of the blame away from parents who struggle to bond with their baby.
"It points to a brain pathway that isn't switching on as expected, not a personal failing," he said.
The researchers say understanding exactly how mood and behavior are regulated in new mothers could help scientists develop better treatments — ones that actually target the root cause of what goes wrong, not just the symptoms.
"We are trying to understand how the brain is critically changing during pregnancy to bring about healthy changes in mood in mothers that enable them to thrive during this stage of life," Brown said.