Having a baby, so the cooing commercials say, changes everything.
While perhaps not changing everything, parenthood does set in motion an array of hormonal and even structural changes in the brains of Mom and Dad, in ways that researchers continue to try to understand.
Recent studies have made it clear that, contrary to the ditzy moments once dismissed as "mommy brain," mothers of newborns -- whether or not they already have kids -- tend to experience growth in key brain structures that influence motivation and maternal behavior.
In a small study, neuroscientists compared the brain images of 19 Connecticut women taken a few weeks before and several months after they gave birth. They found a small but significant increase in the amount of gray matter in several areas: the hypothalamus, which supports maternal motivation; the substantia nigra and amygdala, which process emotions and rewards; the parietal lobe, source of sensory integration; and the prefrontal cortex, which makes judgments. None of these regions otherwise grow in adults, the researchers noted in the journal Behavioral Neuroscience in October 2010.
The researchers suggest that the surge in hormones, prolactin, estrogen and oxytocin, during and after birth may make mothers' brains more susceptible to such reshaping.
Many more maternal brain studies have involved animals. One reported in October from the Hebrew University of Jerusalem showed that mouse moms undergo neural changes integrating odors and sounds from their pups, particularly in a region called the primary auditory cortex.
The changes were particularly strong in mice that were nursing their pups.
Another recent review of links between changes to the maternal brain done by Chapman University psychologist Laura Glynnn suggests that the restructuring actually begins early-on in pregnancy, through not only hormones, but also physical signals such as fetal movement that raise heart rate and skin conductivity, and even the movement of fetal cells from the womb into the mother's brain.
There is no evidence yet of such direct tweaking, but "it's exciting to think about whether those cells are attracted to certain regions of the brain" that may be involved in optimizing maternal behavior, Glynn and collegue Curt Sandman wrote in the December issue of Current Directions in Pyschological Science.
So what's going on with the daddy brain?
First, most guys make some hormonal adjustments, beginning with exposure to pregnancy hormones through their partners' sweat glands.
Men produce less testosterone after entering stable relationships and becoming fathers. Those who are most involved in taking care of their kids have the lowest levels, according to a report published last fall based on a long-term health survey of 600 men in the Philippines.
Another study published last fall in the Journal of Marriage and Family tracked 200 high-risk males ages 12 to 31. It found that, aside from all other factors, fatherhood made them less likely to commit crime, drink alcohol or use tobacco.
Other recent studies of animals and men have shown that exposure to infants gives males higher motivation and they become more skilled at problem solving, even when the babies are not biologically related.
Many men also experience heightened senses of sound and smell with fatherhood, and actually holding their baby particularly perks up prolactin levels and bonding behaviors.