When an infant does not receive regular oxytocin-producing responsive care, the resultant stress responses cause elevated levels of the stress hormone cortisol. Chronic cortisol elevations in infants and the hormonal and functional adjustments that go along with it are shown in biochemical studies to be associated with permanent brain changes that lead to elevated responses to stress throughout life, such as higher blood pressure and heart rate. Mothers can also benefit from the stress-reducing effects of oxytocin-women who breastfeed produce significantly less stress hormone than those who bottle-feed.
Although present and active during bonding in the mother and infant, vasopressin plays a much bigger role in the father. This hormone promotes brain reorganization toward paternal behaviors when the male is cohabiting with the pregnant mother. The father becomes more dedicated to his mate and expresses behaviors of protection.
Released in response to nearness and touch, vasopressin promotes bonding between the father and the mother, helps the father recognize and bond to his baby, and makes him want to be part of the family, rather than alone. It has gained a reputation as the "monogamy hormone." Dr. Theresa Crenshaw, author of The Alchemy of Love and Lust, says, "Testosterone wants to prowl, vasopressin wants to stay home." She also describes vasopressin as tempering the man's sexual drive.
Vasopressin reinforces the father's testosterone-promoted protective inclination regarding his mate and child, but tempers his aggression, making him more reasonable and less extreme. By promoting more rational and less capricious thinking, this hormone induces a sensible paternal role, providing stability as well as vigilance.
Prolactin is released in all healthy people during sleep, helping to maintain reproductive organs and immune function. In the mother, prolactin is released in response to suckling, promoting milk production as well as maternal behaviors. Prolactin relaxes mother, and in the early months, creates a bit of fatigue during a nursing session so she has no strong desire to hop up and do other things.
Prolactin promotes caregiving behaviors and, over time, directs brain reorganization to favor these behaviors. Father's prolactin levels begin to elevate during mother's pregnancy, but most of the rise in the male occurs after many days of cohabitation with the infant.
As a result of hormonally orchestrated brain reorganization during parenthood, prolactin release patterns are altered. It has been shown that fathers release prolactin in response to intruder threats, whereas childless males do not.
On the other hand, nursing mothers do not release prolactin in response to loud noise, whereas childless females do. In children and non-parents, prolactin surges are related to stress levels, so it is generally considered a stress hormone. In parents, it serves as a parenting hormone.
Opioids (pleasure hormones) are natural morphine-like chemicals created in our bodies. They reduce pain awareness and create feelings of elation. Social contacts, particularly touch-especially between parent and child -- induce opioid release, creating good feelings that will enhance bonding. Odor, taste, activity, and even place preferences can develop as the result of opioid release during pleasant contacts, and eventually the sight of a loved one's face stimulates surges. Opioid released in a child's brain as a conditioned response to a parent's warm hugs and kisses can be effective for helping reduce the pain from a tumble or a disappointment.
Parents "learn" to enjoy beneficial activities such as breastfeeding and holding, and infants "learn" to enjoy contact such as being held, carried, and rocked, all as a response to opioid release.
Babies need milk, and opioids are nature's reward to them for obtaining it, especially during the initial attempts. The first few episodes of sucking organize nerve pathways in the newborn's brain, conditioning her to continue this activity. This is the reason that breastfed babies sometimes have trouble if they are given bottles in the newborn nursery-early exposure to bottles creates a confusing association of pleasure with both bottle nipples and the mother's breast.