"Parents and other caregivers who are able to form close, nurturing relationships with their children can foster resilience in them that protects them from many of the worst effects of a harsh early environment. This message can sound a bit warm and fuzzy, but it is rooted in cold, hard science. The effect of good parenting is not just emotional or psychological, the neuroscientists say; it is biochemical.
The researcher who has done the most to expand our understanding of the relationship between parenting and stress is a neuroscientist at McGill University named Michael Meaney. Like many in the field, Meaney does much of his research with rats, as rats and humans have similar brain architecture. At any given time, the Meaney lab houses hundreds of rats. They live in Plexiglas cages, and usually each cage holds a mother rat, called a dam, and her small brood of baby rats, called pups.
Scientists in rat labs are always picking up baby rats to examine them or weigh them, and one day about ten years ago, researchers in Meaney’s lab noticed a curious thing: When they put the pups back in the cages after handling them, some dams would scurry over and spend a few minutes licking and grooming their pups. Others would just ignore them. When the researchers examined the rat pups, they discovered that this seemingly insignificant practice had a distinct physiological effect. When a lab assistant handled a rat pup, researchers found, it produced anxiety, a flood of stress hormones, in the pup. The dam’s licking and grooming counteracted that anxiety and calmed down that surge of hormones.
Meaney and his researchers were intrigued, and they wanted to learn more about how licking and grooming worked and what kind of effect it had on the pups. So they kept watching the rats, spending long days and nights with their faces pressed up against the Plexiglas, and after many weeks of careful observation, they made an additional discovery: different mother rats had different patterns of licking and grooming, even in the absence of their pups' being handled. So Meaney’s team undertook a new experiment, with a new set of dams, to try to quantify these patterns. This time, they didn’t handle any of the pups. They just closely observed each cage, an hour at a time, eight sessions a day, for the first ten days of the pups' lives. Researchers counted every instance of maternal licking and grooming. And after ten days, they divided the dams into two categories: the ones that licked and groomed a lot, which they labeled high LG, and the ones that licked and groomed a little, which they labeled low LG.
...
The researchers ran test after test, and on each one, the high-LG offspring excelled: They were better at mazes. They were more social. They were more curious. They were less aggressive. They had more self-control. They were healthier. They lived longer. Meaney and his researchers were astounded. What seemed like a tiny variation in early mothering style, so small that decades of researchers hadn’t noticed it, created huge behavioral differences in mature rats, months after the licking and grooming had taken place. And the effect wasn't just behavioral; it was biological too. When Meaney’s researchers examined the brains of the adult rats, they found significant differences in the stress-response systems of the high—LG and low-LG rats, including big variations in the size and shape and complexity of the parts of the brain that regulated stress."
[1] http://www.amazon.com/How-Children-Succeed-Curiosity-Charact...