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The trick to fatherhood has a lot to do with the brain — and how close a dad gets to his kids. At least that's the message from a mounting pile of research into the neurological and hormonal cues that translate into fatherly nurturing. And what better time to keep that message in mind than on Father's Day?
"Mothers have an advantage, in that the hormones of pregnancy give them a head start and get them primed to be nurturing," said James Rilling, an anthropologist at Emory University who specializes in studying the neurological basis of social behavior. "In particular, when women give birth, there's a big surge of oxytocin, and oxytocin is also released during breastfeeding. Fathers don't have that."
Oxytocin has been called the "love hormone," even though its effect isn't always that lovely. It's thought to deepen the bond that a mom has with her newborn. But what about the dads, who don't get pregnant or breastfeed? It turns out that a father's interactions with his children produce a similar rise in oxytocin levels.
Researchers have found that emotionally involved fathers feel other hormonal effects: reduced levels of aggression-promoting testosterone; higher levels of prolactin, a lust-squelching hormone that shows up in women during breastfeeding and in men after sexual climax; and higher levels of vasopressin, a hormone linked to bonding as well as the maternal stress response.
It turns out that fathers get many of the same rushes that mothers do from parenthood — but the payoff depends on proximity and interaction. For example, researchers see the effect if the child sleeps with the parents, if the father recognizes and responds to the baby's cries, if Dad plays with the kids. When that proximity isn't present, the fatherhood effect isn't as strong.
"There seems to be some kind of fundamental social-neurobiological framework that comes into play when fathers interact with their kids," said Lee Gettler, an anthropologist at Notre Dame who worked on the prolactin study.
Why is it that the mothers and fathers come to the same hormonal response through different paths? "It may be that the most parsimonious way to engineer a paternal brain would be to take the circuitry that was already in place for maternal care, and maybe tweak that," Rilling said. "That might be the reason why there's some overlap there."
Or it may merely be that when it comes to parenting, familiarity breeds fatherhood. University of Michigan psychiatrist James Swain has been analyzing a huge data set of MRI snapshots to see how maternal and paternal brains respond to the cries of their own babies and the children of strangers. He and his colleagues have found that brain activity patterns don't change as quickly for fathers as they do for mothers.
"I joke that this may be the physiological basis for why a father can roll over in bed when the baby's crying at 3 weeks," Swain told NBC News.
However, by the 4-month mark, "the fathers seem to catch up," Swain said. And there's some indication that the brain patterns for stay-at-home dads are more similar to the changes that moms go through. Swain and his colleagues are still trying to figure out exactly how the parenthood effect works on the neurological level — and how moms and dads get to the same place by different hormonal paths.
Rilling said the study of the fatherhood effect is a "wide open frontier."
"Humans are an alloparental species, which means mothers get help," he said. "In some cultures it's the father, but in other cultures it's the grandmother, the aunts, the older children. Fathers seem to be particularly important in modern developed Western nations like the U.S., because there are so many people who are living in isolated nuclear families, largely separated from their extended family. That limits the number of potential helpers out there. ... It's really important that fathers step up."
More about science and fatherhood:
- How fatherhood made us human
- Mice get less violent when they're dads
- Scientists see why fathers matter
Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the NBC News Science Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with NBCNews.com's stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.