Nature: The secret of crying? Babies cry → mothers release oxytocin | World Breastfeeding Week

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Introduction: A baby's cry is more than just noise

We may have had this experience: in the dark night, the cry of a baby suddenly breaks the silence of the night! For many people, this may be a worrying sound. But for mothers, this sound means more. It can wake up the sleeping mother, trigger a series of physiological reactions in the mother, and even change her brain activity. But how does this happen? A groundbreaking study recently published in the journal Nature reveals the scientific secrets behind this magical process.

The research team explored an observation that has existed in humans and other mammals for centuries: when a baby starts to feed, the cry alone can prompt the mother to secrete breast milk. Studies from decades ago showed that this call for food, rather than nursing itself, prompts a surge in oxytocin. However, until now, the mechanism and purpose behind this pipeline from crying to milk production have remained unclear. This study found that the cry of a newborn can trigger the release of oxytocin. Stimulated by the cry of a baby, the mother's oxytocin secretion will increase and last for about 5 minutes before gradually decreasing. This period of time allows the mother to continue feeding the child until it is full or starts crying again.

Ⅰ. Oxytocin: The Chemical Messenger of Love

Before we get into the details, let's first understand an important player: oxytocin. This neuropeptide, affectionately known as the "love hormone" or "cuddle hormone," plays multiple roles in our bodies.

Oxytocin is not only involved in the process of childbirth, but also plays a key role in breastfeeding, parent-child bonding and social interaction.

But one of the most amazing properties of oxytocin is that it can be triggered by the sound of a baby crying. Yes, you heard it right! Oxytocin here is a brain chemical that controls the release of breast milk from a mother. The sound of a baby crying can trigger the release of oxytocin in the mother's brain. This discovery excited the researchers because it suggested that there is some mysterious connection between the sound of a baby crying and the oxytocin neurons in the mother's brain.

Ⅱ. Decoding the "maternal love circuit" in the brain

Determined to unravel this mystery, the research team conducted a series of sophisticated experiments on awake mother mice and recorded the responses of oxytocin neurons to the cries of their pups.

The results were surprising: the oxytocin neurons did respond to the cries of the pups, but not to ordinary sounds, suggesting that the baby's cry carries some special information that can "talk" directly to the oxytocin system in the mother's brain.

But how is the sound information transmitted to the oxytocin neurons? The researchers used a "reverse engineering" method to trace the transmission path of sound information in the brain. They found that when the baby mice began to cry, the sound information was first transmitted to an area in the mother's brain called the posterior intralaminar nucleus of the thalamus (PIL). This sensory center then sends signals to oxytocin neurons located in the hypothalamus, triggering the release of oxytocin. The hypothalamus is the control center for hormone activity.

III. The magic of crying: how to open the floodgates of oxytocin

One of the study's lead authors explains it this way: "Most of the time, these hypothalamic neurons are 'locked down' by proteins that act as gatekeepers, preventing false alarms and the release of breast milk. However, after 30 seconds of continuous crying, signals from the nucleus posterior thalamus build up and overwhelm these inhibitory proteins, triggering the release of oxytocin."

Think of it like a sophisticated safety system. A short cry might be a false alarm, but a persistent cry means the baby has a real need. This system ensures that the mother does not respond to every little sound, but only activates maternal behavior when it is truly needed.

IV. Baby crying - Selectivity of maternal behavior: Not all sounds can trigger

The research team revealed the amazing selectivity of this system. The increase in oxytocin seemed to occur only in lactating mother mice, but not in female mice that had never given birth. Even more interestingly, the brain circuits of the mother mice were only responsive to the real cries of pups, but not to computer-simulated sounds. This precise selectivity seems to ensure that mothers only respond to their own offspring, reflecting a kind of wisdom of nature.

V. Beyond Breastfeeding: Oxytocin and Enduring Maternal Behavior

The research team further explored the impact of this neural circuit on maternal behavior. They found that when the communication between the nucleus posterior thalamus and oxytocin neurons was blocked, mother mice became tired faster when caring for their pups. Once the system was restarted, mother mice seemed to be able to recover from fatigue immediately to complete breastfeeding and care needs.

"These results suggest that the brain circuits triggered by crying are important not only for nursing behavior, but also for keeping a mother focused and encouraged to care for her child effectively, even when she is exhausted," said Robert Froemke, PhD, senior author of the study.

Lessons from mice to humans

Although the study was conducted in mice, it provides valuable insight into the bond between human mothers and their babies. Dr. Froemke says that understanding how the oxytocin system works in humans (and what can go wrong) could lead to new ways to help mothers who want to breastfeed but have trouble doing so.

This study not only reveals the amazing connection between baby crying, mother's brain and oxytocin, but also gives us a deeper understanding of maternal love, a seemingly simple but extremely complex emotion. It reminds us that behind every baby's cry, there is a sophisticated biological mechanism at work to ensure that the new life receives the best care and love.

So, next time, when you hear a baby crying, maybe we will think: this is not just a signal for help, but also a wonderful mechanism designed by nature to activate the "love hormone" in the mother's body to help us establish that unique and precious mother-child connection.

Breastfeeding is a gift from nature, but it is not the only choice at certain times. What is more important is love and care. We should work together to support all mothers and jointly nurture the growth of life. Because every mother is a hero, and every choice should be respected!