The brain circuit that causes the sound of a newborn crying to trigger the release of breast milk in mothers has been uncovered by scientists.
The study, in mice, gives fresh insights into sophisticated changes that occur in the brain during pregnancy and parenthood. It found that 30 seconds of continuous crying by mouse pups triggered the release of oxytocin, the brain chemical that controls the breast-milk release response in mothers.
“Our findings uncover how a crying infant primes its mother’s brain to ready her body for nursing,” said Habon Issa, a graduate student at NYU Langone Health and co-author of the study. “Without such preparation, there can be a delay of several minutes between suckling and milk flow, potentially leading to a frustrated baby and stressed parent.”
The study showed that once prompted, the surge of hormones continued for roughly five minutes before tapering off, enabling mouse mothers to feed their young until they were sated or began crying again.
The observation that a mother’s breasts can leak milk when they hear a crying baby is not new. But the latest research is the first to identify the brain mechanisms behind what the scientists described as the “wail-to-milk pipeline”, and could pave the way for a better understanding of the challenges of breastfeeding for many women.
The findings, published in Nature, showed that when a mouse pup starts crying, sound information travels to an area of its mother’s brain called the posterior intralaminar nucleus of the thalamus (PIL). This sensory hub then sends signals to oxytocin-releasing brain cells (neurons) in another region called the hypothalamus.
Most of the time these hypothalamus neurons are “locked down” to prevent false alarms and wasted milk. However, after 30 seconds of continuous crying, signals from the PIL built up and overpowered the in-built inhibitory mechanism, setting off oxytocin release.
“It’s like the brain wants to make sure the infant is really there, that there is really a need to feed, not just a random bird cry,” said Prof Robert Froemke, of NYU Langone and co-author. “There’s specific brain circuitry that has a brake on this process. Once it’s convinced there’s really a baby there, the brake is released.”
Froemke said the findings give scientists a roadmap for how the process might work in humans. “A mouse mom is different from a human mom, but in broad strokes we’d expect it to be similar,” he said. “It’s baffling. We can put a robot on mars and don’t understand the basics of how we feed our children and breastfeed.”