High oxytocin causes a mother to become familiar with the unique odor of her newborn infant, and once attracted to it, to prefer her own baby's odor above all others. Baby is similarly imprinted on mother, deriving feelings of calmness and pain reduction along with mom. When the infant is born, he is already imprinted on the odor of his amniotic fluid. This odor imprint helps him find mother's nipple, which has a similar but slightly different odor. In the days following birth, the infant can be comforted by the odor of this fluid.
Gradually over the next days, baby starts to prefer the odor of his mother's breast, but continued imprinting upon his mother is not food related. In fact, formula-fed infants are more attracted (in laboratory tests) to their mother's breast odor than to that of their formula, even two weeks after birth .
By influencing maternal behavior and stimulating milk "let down" during nursing, oxytocin helps make the first attempts at breastfeeding feel natural. Attempts at nursing during the initial hour after birth cause oxytocin to surge to exceptional levels in both mother and baby. Mothers who postpone nursing lose part of the ultimate hormone high provided for immediately after birth. Powerful initial imprinting for mother and baby is intended to occur chiefly so that mother and baby will be able to find and recognize each other in the hours and days after birth.
Yet a lifetime opportunity for bonding and love is not lost if this initial window is missed. Beyond birth, mother continues to produce elevated levels of oxytocin as a consequence of nursing and holding her infant, and the levels are based on the amount of such contact. This hormonal condition provides a sense of calm and well being. Oxytocin levels are higher in mothers who exclusively breastfeed than in those who use supplementary bottles. Under the early influence of oxytocin, nerve junctions in certain areas of mother's brain actually undergo reorganization, thereby making her maternal behaviors "hard-wired."
As long as contact with the infant remains, oxytocin causes mother to be more caring, to be more eager to please others, to become more sensitive to other's feelings, and to recognize nonverbal cues more readily. Continued nursing also enhances this effect. With high oxytocin, mother's priorities become altered and her brain no longer signals her to groom and adorn herself in order to obtain a mate, and thus a pregnancy.
Now that the child has already been created, mom's grooming habits are directed toward baby. High oxytocin in the female has also been shown to promote preference for whatever male is present during its surges (one good reason for dad to hang around during and after the birth). Prolonged high oxytocin in mother, father, or baby also promotes lower blood pressure and reduced heart rate as well as certain kinds of artery repair, actually reducing lifelong risk of heart disease .
Although baby makes her own oxytocin in response to nursing, mother also transfers it to the infant in her milk. This provision serves to promote continuous relaxation and closeness for both mother and baby. A more variable release of oxytocin is seen in bottle-fed infants, but is definitely higher in an infant who is "bottle-nursed" in the parents' arms rather than with a propped bottle.
Persistent regular body contact and other nurturing acts by parents produce a constant, elevated level of oxytocin in the infant, which in turn provides a valuable reduction in the infant's stress-hormone responses.
Multiple psychology studies have demonstrated that, depending on the practices of the parents, the resulting high or low level of oxytocin will control the permanent organization of the stress-handling portion of the baby's brain -- promoting lasting "securely attached" or "insecure" characteristics in the adolescent and adult. Such insecure characteristics include anti-social behavior, aggression, difficulty forming lasting bonds with a mate, mental illness, and poor handling of stress.