Becoming a mother is a life-changing event, bringing out hormones and natural tendencies in a woman that help prepare her during the nine months until the child is born. Nature has ensured that women are ready when the baby finally arrives, kicking and screaming, through a progression of hormones that flow through her body and her brain during gestation.

But what about the men?
“Parenthood is exactly the kind of event that you might expect to harness the brain’s natural neuroplasticity to help prepare individuals for the adventure that awaits,” says Kayt Sukel, author of Dirty Minds: How Our Brains Influence Love, Sex and Relationships (Free Press, 2012). “Given the sheer number of physical changes that a woman goes through, you’d expect that some major rewiring might be happening in the brain. But work in animal models suggests that dad’s brains are getting a bit of a reorg, too.”

Changes in Daddy’s Brain
Recent studies show that indeed, a few days after birth, changes occur in the brains of both daddy and baby, depending on whether daddy sticks around. According to research, not only do men get better at hearing a baby’s cry as the due date of their child approaches, but a baby’s smile activates the same circuits in the brain that are involved with falling in love.

“In a sense, you can place the changes on a continuum or curve, with the virgin male on the far left and the mother on the far right,” says Dr. Craig Kinsley, professor of psychology and coordinator of neuroscience at the University of Richmond. “The father would shift his place on the curve several portions to the right, never quite catching up to the maternal female, however.” Kinsley says it’s helpful to think in terms of parental requirements. In the mammal, the female gets pregnant and bears the primary burden of internal fertilization, pregnancy, lactation and, eventually and for a long time, infant care. The male’s role, for all intents and purposes, ends at fertilization, if he so desires.

“A father who remains to care for his young increases the likelihood of successful reproduction and a maximization of his reproductive fitness. Behaviors change in good, investing fathers. In mice, which are bi-parental—that is, both parents caring for young—the males show some changes, in brain and behavior, similar to the mothers, shifting that curve to the right. So in species where fathers do more than have sex and then abandon their young to the mother, marked changes are apparent.”
In a recent study, male mice were observed after the birth of their newborn pups. It was found that in the days that followed, a neurogenesis—spontaneous formation of additional neurons—occurred, but only if the mouse father stayed with his pups. If he was removed from his offspring the day of the birth, nothing happened. The study showed these new brain cells to be formed in the olfactory bulb—to be specifically tuned to the smell of his pups—and in the hippocampus, the brain’s memory center.
But it isn’t just after the birth of the baby that daddy’s brain starts changing. “During his partner’s pregnancy, the male brain begins to release more of the hormone prolactin and to gradually suppress the hormone testosterone,” says Professor Louann Brizendine, MD, neuropsychiatrist and author of The Female Brain and The Male Brain (Three Rivers Press, 2007 and 2011, respectively). “Evolutionary biologists believe this happens because it is critical to the survival of human infants that the male parent be prepared to protect and nurture the helpless offspring and support the new mother, instead of chasing new females to mate with as in most other mammals.”
Prolactin is the same hormone that is responsible for milk production in the breasts of new mothers. “There have been a few studies over the past five years that suggest prolactin has a role in the paternal brain, too,” says Sukel, quoting Professor Ruth Feldman from Bar Ilan University’s research, which looked at a number of different neurochemicals that may change in response to fatherhood. Feldman found that higher prolactin levels are linked to exploratory play. The higher the prolactin, the more dads will help their babies explore and play.

Another important hormone is oxytocin, which is released in the brain in response to social and skin-to-skin contact. The higher it is, the more emotionally a father appeared to be bonding with the baby.

Finally, there’s vasopressin, which is possibly the only hormone that plays a bigger part in dad than it does in mom, promoting paternal behaviors and bringing out the protective instinct in a father.

“The hypothesis is that the brain is readying itself for the challenges and rewards of offspring,” Sukel says. “By increasing these connections and receptors, dad is primed not only to help care for kids, but also to better bond with them.”

The Father-Child Bond
Once a child is conceived, the role of a father, medically speaking, is finished. The dad doesn’t need to be around to give birth or to feed the baby. Yet, increasingly, research proves that a father’s role is crucial in a child’s life and that children raised solely by mothers tend to have behavioral problems as they grow up. “Many babies and children raised without a father in our modern world can grow up to be just fine; however, having an involved, committed father has been shown to increase the chances of a child’s educational success,” says Dr. Brizendine.
A father’s love, as it happens, not only helps his child’s brain develop better, but also affects his own. A recent study was done on degus, ratlike rodents who, like human beings, are biparental, with degu fathers behaving like human fathers in taking care of their young by warming, grooming and helping with their basic care. Researchers found that when they separated the degu fathers from their pups, the offsprings’ brains started to work differently than those pups who had access to their dads. Specifically, the degu pups who didn’t have fathers had fewer synapses in both the orbitofront cortex and the somatosensory cortex—regions of the brain responsible for decision-making, rewards and emotion. Researchers say this could explain why some children brought up without fathers or father figures find it hard to fit into society.

“We don’t know the exact neurobiology behind the formation of a [father-child] bond,” says Sukel. “Chemicals like vasopressin, oxytocin and prolactin appear to be important in mediating that bond, and are known to work directly on brain regions that are involved in both emotion and reward process—but how exactly they are working that voodoo, both together and apart, has yet to be determined.”

Nature vs. Nurture
Babies not only make their own oxytocin but also get it from their mother’s milk, a harmonious relationship that allows the mother-child bond to form. Research has shown that there is decreased release of oxytocin for babies who are not nursing; however, it is higher in infants who are bottle-fed in the arms of their parents.
Regular touch from either or both parents is essential in creating this oxytocin.

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