Brain Rules for Baby (Updated and Expanded). John Medina
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experienced the storm. Their verbal IQs and language development appeared stunted, even when the parents’ education, occupation, and income were taken into account. Was the mother’s stress the culprit? The answer turned out to be yes.
Maternal stress can profoundly influence prenatal development. We didn’t always think so. For a while, we weren’t even sure if mom’s stress hormones could reach her baby. But they do, and that has long-lasting behavioral consequences, especially if the woman is severely or chronically stressed in those hypersensitive last months of pregnancy. What kind of consequences?
If you are severely stressed during pregnancy, it can:
• change the temperament of your child. Infants become more irritable, less consolable.
• lower your baby’s IQ. The average decline is about 8 points in certain mental and motor inventories measured in a baby’s first year of life. Using David Wechsler’s 1944 schema, that spread can be the difference between “average IQ” and “bright normal.”
• inhibit your baby’s future motor skills, attentional states, and ability to concentrate—differences still observable at age 6.
• damage your baby’s stress-response system.
• shrink the size of your baby’s brain.
A review of more than 100 studies in various economically developed countries confirm that these powerful, negative effects on prenatal brain development are cross-cultural. David Laplante, lead author of the ice-storm study, said in a somewhat understated fashion: “We suspect that exposure to high levels of [stress] may have altered fetal neurodevelopment, thereby influencing the expression of the children’s neurobehavioral abilities in early childhood.”
Moderate vs. toxic stress
Is this stressing you out? Luckily, not all stresses are created equal. Moderate stress in small amounts, the type most women feel in a typical pregnancy, actually appears to be good for infants. Stress tends to get people moving, and we think that enriches the baby’s environment. The womb is a surprisingly hearty structure, and both it and its tiny passenger are well equipped to ride out the typical stressors of pregnancy. It is just not prepared for a sustained assault. How can you tell the brain-damaging stress from the typical, benign, even mildly positive stress?
Most toxic stresses have one common characteristic: you feel out of control over the bad stuff coming at you. As stress moves from moderate to severe, and from acute to chronic, this loss of control turns catastrophic. That can affect baby. Bad types of stress seem obvious once you know where to look. They include major life events such as a divorce, death of spouse (or other loved one), job termination, or being a victim of a crime. Income is a big factor too, especially around the poverty line. Other factors may not seem so obvious: a lack of friends (social isolation), sustained dissatisfaction at work, or a long-term illness.
Of course, the story of stress reactivity isn’t simple. Some people appear to weather stressful events better than others. Some are stress resistant; others are stress sensitive. There is increasing evidence that this sensitivity has a genetic component. Women under such a biological dictatorship need to keep stress to a minimum during pregnancy. The key issue, regardless of your background, is a loss of control.
Bull’s-eye: Baby’s stress-response system
Lots of research has gone into trying to understand how maternal stress affects brain development. And we have begun to answer this question at the most intimate level possible: that of cell and molecule. The important stress hormone is cortisol. It’s the star player in a team of nasty molecules called glucocorticoids. These hormones control many of our most familiar stress responses, from making our hearts race like NASCAR autos to a sudden urge to pee and poop. Glucocorticoids are so powerful, the brain has developed a natural “braking” system to turn them off as soon as the stress has passed. A pea-sized piece of neural real estate in the middle of the brain, called the hypothalamus, controls the release and braking of these hormones.
A woman’s stress hormones affect her baby by slipping through the placenta and entering the baby’s brain, like cruise missiles programmed to hit two targets. The first target is the baby’s limbic system, an area profoundly involved in emotional regulation and memory. This region develops more slowly in the presence of excess hormone, one of the reasons we think baby cognition is damaged if mom is severely or chronically stressed.
The second target is that braking system I mentioned, the one that’s supposed to rein in glucocorticoid levels after the stress has passed. Excess hormone from mom can mean baby has a difficult time turning off her own stress hormone system. Her brain becomes marinated in glucocorticoids whose concentrations are no longer easily controllable. The baby can carry this damaged stress-response system into adulthood. The child may have a difficult time putting on the brakes whenever she gets stressed out; elevated levels of glucocorticoids thus become a regular part of her life. If she eventually gets pregnant, she bathes her developing infant with the excess toxic stuff. The fetus develops a partially confused hypothalamus, pumping out more glucocorticoids, and the next-generation brain shrinks further. The vicious cycle continues. Excessive stress is contagious: You can get it from your kids, and you can give it to them, too.
Take back control
Clearly, too much stress is not good for pregnant women or their babies. For optimal development of your baby’s brain, you will want to exist in a less-stressed environment, especially in the last few months of pregnancy. You can’t completely upend your life, of course, which could be stressful on its own. But you can reduce your stress, with your spouse’s tender loving care. We’ll say much more about that in the next chapter. You can also begin identifying the areas in your life where you feel out of control, then deliberately form strategies that will allow you to take back control. In some cases, that means exiting the situation that is causing the stress. A temporary helping of courage will translate to a lifetime of benefit for your baby’s brain.
There are plenty of ways to actively practice general stress relief, too. At www.brainrules.net, we’ve listed a number of techniques known from the research literature to reduce stress. A big one is exercise, which has so many benefits that it is the subject of our fourth and final balancing act.
4. Exercise just the right amount
I am always amazed at the life cycle of wildebeests. They are best known for their spectacular annual migrations in the plains and open woodlands of Tanzania and Kenya, thousands upon thousands of them in hypnotic, constant motion. They move for two reasons. First and foremost, they are looking for new pastures. But wildebeests are also 600-pound steaks on legs; they have to keep moving because they are very popular with predators.
Given this urgency, the most interesting part of their life cycle is their pregnancy and birth. The gestation is nearly as long as a human’s, about 260 days, but the similarities end as soon as labor begins. The mother gives birth quickly. Unless there are complications, she also recovers quickly. So do the calves, typically rising to their feet—well, hooves—an hour after they’re born. They have to. Calves represent the herd’s future, but they are also the herd’s most vulnerable population, liable to become leopard food.
We, too, spent our evolutionary adolescence on these same savannahs, and we share many of the wildebeests’ same predator/prey problems. There are, you might imagine, major differences in birthing and parenting between wildebeests and humans. Women take a long time to recover from birth (it’s that big, overweight brain again, evolution’s secret weapon, forcing itself through a narrow birth canal), and their kids won’t be walking for almost a year. Nonetheless, evolutionary echoes imply that exercise was very much a part of our lives, including during pregnancy. Anthropologists think we walked as many as 12 miles per day.
Fit women have to push less
Does that mean exercise should be a part of human pregnancies? Evidence suggests the answer is yes. There are many reasons to stay fit during pregnancy, but the first benefit is a practical one having to do with labor. Many women report that giving birth is both the most exhilarating experience of their lives and the most painful. Pushing, as you know, is