Keywords: oxytocin, prolactin, child abuse, child raising, breast milk, breastfeeding, mother-infant interaction, mother, Noboru Kobayashi
"Mother-infant interaction" is a concept that pediatricians in the US began to talk about in the late 1960s, and in Japan, from the late 1970s. Amid the postwar affluence of the US, the field of neonatal medicine quickly grew, and even tiny premature babies came to be able to survive with medical care. In tandem with this, another phenomenon appeared: cases of child abuse also increased. As for the reason, this was attributed to poor bonding between the mother and child. In other words, in the case of premature babies, placing the baby in an incubator drastically restricts the mother's ability to hold her child, hindering mother-infant bonding and thereby contributing to child abuse. In actuality, statistics also indicate that a large percentage of children who are abused by their mothers were premature babies. Such findings led to the concept of mother-infant interaction.
This mother-infant interaction is clearly a psychological one. In other words, by holding her child, the mother's affection for the child deepens, and the child who is held by the mother experiences a deepening of affection toward the mother. The mother and child deepen their bond through information mediated by the sense organs - the eyes, ears, nose and skin. The sensory information exchanged is diverse: visual information from their respective smiles and eye-to-eye contact; auditory information including the content of the mother's speech and affective information, such as rhythm, pitch, and intonation, the child's happy voice and babbling; tactile information based on direct touching; and olfactory information from their smells. This exchange is thought to create emotional bonds between the mother and child.
Mother-infant interaction is not only psychological or sensory bonding, but also plays an important role in the physical relationship between mother and child. Breastfeeding is the typical example of this, and it has been established that in breastfeeding this mutual interaction is important in a number of ways.
When the infant suckles at the mother's breast, sensory stimulation due to the suckling action is relayed from the nipple to the mother's brain via the spinal cord. The pituitary gland is stimulated and the hormones prolactin and oxytocin are excreted from the anterior and posterior lobes, respectively. It is believed that prolactin stimulates the mammary tissue to produce breast milk and the brain to promote mothering. On the other hand, oxytocin works to contract cells around the mammary tissue, increasing pressure in the mammary ducts for the letdown of breast milk into the infant's mouth. If this pressure is too strong, a milk ejection reflex will cause the breast milk to gush from the nipple. In the act of breastfeeding, the excretion of breast milk is dependent upon the sucking action of the infant, which makes it a superb example of mother-infant interaction through tactile sensation and hormones.
Moreover, the mother-infant interaction that takes place during breastfeeding is hardly simple for we now know that the composition of the excreted breast milk changes in response to the health of the breastfed infant. Recent research shows that when an infant has an infectious disease, the immunological components of breast milk will change in order to improve the health of the infant. In other words, the composition of the breast milk changes to reduce disease-causing bacteria and increase immunity.
Unfortunately, research has not yet established how the mother is able to detect the cause of the infant's infectious disease and then produce the components within her breast milk to fight it. It has long been said that when the bacteria causing the infant's infectious disease or some component of it enters the mother's digestive tract, it comes into contact with the lymphoid tissue associated with immunity in the digestive tract, and the lymphocytes acquire immunity. The lymphocytes circulate and move into breast tissue where it appears that they produce the immunological components that the infant needs. In this sense, the lymphoid tissue of the intestines plays a central role in immunity, with the lymphoid tissue in the intestines and the breast working together as one system.
Another substance in breast milk that varies with breastfeeding is fat. Breast milk fat concentration follows a curve, increasing gradually when the infant begins to suckle and then leveling off. As such, milk at the end of the feeding will have a high fat concentration and taste creamy. In this sense, breastfeeding is also an occasion for food education, that is, the infant learns that eating has a beginning and end. It is known that obesity is higher in infants raised on baby formula than those who are breastfed, which seems to point to another effect of breastfeeding.
It is also possible that breastfeeding teaches infants about the food of their culture. Cuisines are associated with different flavors, Korea with kimchi, India with curry, and Japan with soy sauce and miso, and these substances appear in trace amounts in the mother's breast milk, which may then be passed on to the infant. While this theory has not been substantiated, it does seem quite plausible.
With "mother-infant interaction" as a keyword, we have considered child raising from a broad perspective with the main focus on breastfeeding. In our affluent society, artificial foods are convenient, but when it comes to raising children, they should be avoided to the extent possible. In particular, this is important considering that breastfeeding is a time when children are in their most formative stage of life and lasts only for a short time. It is an issue that concerns not just the health of children, but the transmission of culture.