Brain Rules for Baby (6 page)

The same thing is true of smells. Just five weeks after fertilization, you can see the brain’s complex wiring for smell. But, as with the other senses, the perception is not available simply because the machinery is there. Between the second and sixth month of life in the womb, babies suffer from an acutely stuffy nose. The nasal cavities are filled with a giant plug of tissues, probably preventing smell perception of any kind. All of that changes during the third trimester. The tissue plug is replaced with snot (mucous membranes)—and lots of neurons hooked directly into the perceptual areas of the brain. Mom’s placenta also becomes less picky, granting permission for more and more smell-mediating molecules (called odorants) to enter the womb. Because of these biological changes, the olfactory world of
your baby becomes richer and more complex after the sixth month of gestational life. Your baby can smell the perfume you wear, and she can detect the garlic on the pizza you just ate.

As a newborn, your baby will actually prefer these smells. The preference is called “olfactory labeling”. This is the basis for an odd piece of advice: Immediately after your baby is born, rub her with her own amniotic fluid before washing her with soap and water. It will calm her down, studies show. Why? As with sounds, smells remind babies of the comfortable home they were inhabiting for the past nine months. That’s because smell and certain types of memory form powerful neural linkages in the human brain. (Indeed, many mothers can identify their own newborns based on smell alone.)

Here’s something you can try at home if you are eight months pregnant or if you have a baby younger than 5 months old. If the infant has already arrived, place him on his back. Then gently lift up both legs, or both arms, and let them drop back to the bed of their own weight. His arms will usually fling out from the sides of his body, thumbs flexed, palms up, with a startled look on his face. This is called the Moro Reflex.

At eight months of pregnancy, you can usually observe the Moro Reflex internally. If you are reading this in your soft bed, go ahead and roll over; if you are seated, stand up. Feel anything dramatic? A fetus is capable of executing a full Moro while still in the womb. These actions often incite it.

The Moro Reflex is normal and usually occurs if an infant is startled, especially if he senses he is falling. It is believed to be the only unlearned fear response humans possess. It’s important that an infant has these reflexes. The absence of a good solid Moro can be a sign of a neurological disorder. Infants need to be able to do it within five months of birth. It is time-limited, though; its persistence beyond five months is also a sign of a neurological disorder.

The Moro demonstrates that a great deal of motor (movement) and vestibular (balance) abilities have already been laid down by eight months. Vestibular abilities allow muscles to be in constant communication with the ears, all coordinated by the brain. You need a fairly sophisticated form of this communication in order to do a Moro.

Babies don’t start off capable of doing full-tilt gymnastics, of course. But they are capable of “quickening,” which is a flutter of embryonic limbs, about six weeks post-conception (though the mother usually can’t feel anything for another five weeks). This movement is also important. It must occur, or your baby’s joints will not develop properly. By the middle of the third trimester, your baby is fully capable of deliberately commanding her body to perform a coordinated series of movements.

The tissues that mediate taste (“gustatorial sensations”) don’t emerge from your embryo’s tiny tongue until about eight weeks post-conception. That doesn’t mean your baby simultaneously acquires the ability to taste something, of course. That doesn’t happen until the third trimester. Once again we see the reception-before-perception pattern of sensory development.

At that point, you can observe some behaviors familiar to all of us. Third-trimester babies change their swallowing patterns when mom eats something sweet: They gulp more. Flavorful compounds from a mother’s diet cross the placenta into the amniotic fluid, which babies in the third trimester swallow at the rate of a quart a day. The effect is so powerful that what you eat during the last stages of pregnancy can influence the food preferences of your baby.

In one study, scientists injected apple juice into the wombs of pregnant rats. When the rat pups were born, they showed a dramatic preference for drinking apple juice. A similar taste preference happens with humans. Mothers who drank lots of carrot juice in the later
stages of pregnancy had babies who preferred carrot juice after birth. This is called flavor programming, and you can do it soon after your baby is born, too. Lactating mothers who eat green beans and peaches while nursing produce weaned toddlers with the same preferences.

It’s possible that anything that can cross the placenta can incite a preference.

From touch and smell to hearing and vision, babies have an increasingly active mental life in the womb. What does this mean for parents eager to aid that development? If motor skills are so important, shouldn’t moms-to-be do cartwheels every 10 minutes to induce the Moro Reflex in their in utero partners? If food preferences are established in the womb, shouldn’t moms-to-be become vegetarians in the last half of pregnancy if they want their kids to eat fruits and vegetables? And is there an effect, beyond creating potential preferences, of pumping Mozart or Dr. Seuss into your unborn baby’s brain?

It is easy to start making assumptions. So, a word of caution. These studies represent the edge of what is known, and it is very easy to over-interpret what the data mean. These are all interesting research questions. But today’s data are not strong enough to solve the mystery of early mental life. They are just enough to reveal it.

 

The biology of infant brain development reminds me of “Goldilocks and the Three Bears. The classic version of the story describes a young girl with blond hair breaking into and essentially vandalizing a bear family’s vacant hut. She samples and renders judgments over their bowls of porridge, chairs, and beds. Goldilocks doesn’t like Papa Bear’s or Mama Bear’s materials; the physical characteristics are just too extreme. But Baby Bear’s stuff is “just right”,
from temperature to sturdiness to the bed’s cozy comfort. Like so many legendary children’s stories, there are many renditions of this odd little tale. The first published version, by 19th-century poet Robert Southey, had an angry old woman breaking into the bears hut and sampling the wares of three male bears. Some literary historians suggest Southey borrowed from the story of Snow White, who breaks into the dwarves house, tastes their food, sits on their stools, and then falls asleep on one of their beds. In one early version of “Goldilocks”, the intruder was a fox, not a woman; later she became a girl variously called Silver Hair, Silver-Locks, and Golden Hair. But the “just right” principle is preserved throughout.

So many creatures have this just-right characteristic embedded in their biology that scientists have given the phenomenon its own rather unscientific name: the Goldilocks Effect. It is so common because biological survival in this hostile world often calls for a balancing act between opposing forces. Too much or too little of something, such as heat or water, often hurts biological systems, most of which are obsessed with homeostasis. A full description of many biological processes involves this “just right” idea.

The behaviors proven to aid and abet brain development in the womb—especially important in the second half of pregnancy—all follow the Goldilocks principle. We will look at four of these balancing acts:

And there’s not a pregaphone in sight.

You’re pregnant, so you need to eat more food. And if you don’t overdo it, you will grow a smarter baby. Why? Your baby’s IQ is a function of her brain volume. Brain size predicts about 20 percent of the variance in her IQ scores (her prefrontal cortex, just behind her forehead, is particularly prescient). Brain volume is related to birth weight, which means that, to a point, larger babies are smarter babies.

The fuel of food helps grow a larger baby. Between four months and birth, the fetus becomes almost ridiculously sensitive to both the amount and the type of food you consume. We know this from malnutrition studies. Babies experiencing a critical lack of nutriment have fewer neurons, fewer and shorter connections between the neurons that exist, and less insulation all around in the second trimester. When they grow up, the kids carrying these brains exhibit more behavioral problems, show slower language growth, have lower IQs, get worse grades, and generally make poor athletes.

 

How big should baby grow? Here’s another balancing act. A baby’s IQ rises steadily with birth weight, up to about 8 pounds. The job is mostly done prior to this benchmark: There is only 1 IQ point difference between a 6.5-pounder and a 7.5-pounder. Above 9 pounds, IQ actually drifts down a bit, about 1 point on average. This loss probably occurs because larger babies are more likely to experience hypoxia—a restriction of oxygen—or other injuries during birth.

How much do you need to eat? That depends upon how fit you are going into the pregnancy. The bad news is that 55 percent of women of childbearing age in the United States are already too fat. Their Body Mass Index, or BMI, which is a kind of a “gross domestic product” of how fat you are, is between 25 and 29.9. If that’s you, then you need to gain only about 15 to 25 pounds to create a healthy baby, according to the Institute of Medicine. You want to add about half a pound a week in the critical second and third trimesters of pregnancy. If you
are underweight, with a typical BMI of less than 18.5, you need to gain between 28 and 40 pounds to optimize your baby’s brain development. That’s about a pound a week in the critical last half of pregnancy. This is true for women of normal weight, too.

So, the amount of fuel is important. There is increasing evidence that the type of fuel you eat during the critical period is important, too. The next balance comes between foods that a pregnant mom
wants
to eat and foods that are optimal for a baby’s brain development. Unfortunately, they are not always the same thing.

Women have strange experiences with food preferences during pregnancy, suddenly loving foods they used to loathe and loathing foods they used to crave. It’s not just pickles and ice cream, as any pregnant woman can tell you. One woman developed a craving for lemon juice on a burrito—a need that lasted for three months. Another wanted pickled okra. A surprising number crave crushed ice. Women can even desire things that aren’t food. An item that regularly makes the Top Ten List of Weird Pregnancy Cravings is baby talcum powder. So is coal. One woman wanted to lick dust. Pica is a common disorder: a craving lasting longer than a month for eating things that aren’t food, like dirt and clay.

Is there any evidence you should pay attention to these cravings? Is the baby telegraphing its nutritional needs? The answer is no. There is some evidence that iron deficiencies can be consciously detected, but the data are thin. Mostly it’s a matter of how a person uses food in her daily life. An anxious person who is comforted by the chemicals in chocolate might grow to crave chocolate whenever she feels stressed. And a woman will feel stressed a lot during pregnancy. (This craving for chocolate reflects a learned response, not a biological need, though I think my wife would probably disagree.) We actually don’t know why a pregnant woman’s crazy cravings occur.

That doesn’t mean the body doesn’t have nutritional needs, of course. The pregnant mom is a ship with two passengers but only one galley. And we’re looking to stock this kitchen with the right ingredients for brain growth. Of the 45 nutrients known to be necessary for growth of the body, 38 have been shown to be essential for neurological development. You can look on the back of most pregnancy-formulated vitamin supplements to see the list. We can look to our evolutionary history for some guidance on what to eat to get these nutrients. Since we know something of the climate through which we developed for millions of years—one that supported ever-increasing brain girth—we can speculate about the type of foods that helped it along.

 

An old movie called
Quest for Fire
opens with our ancestors seated by a fire, munching on a variety of foods. Large insects buzz about the flames. All of a sudden, one of our relatives shoots out his arm, clumsily grabbing an insect out of thin air. He stuffs it into his mouth, munches heartily, and continues staring into the fire. His colleagues dig around the soil for tuberous vegetables and scrounge for fruit in nearby trees later in the movie. Welcome to the world of Pleistocene haute cuisine. Researchers believe that for hundreds of thousands of years, our daily diet consisted mostly of grasses, fruits, vegetables, small mammals, and insects. Occasionally we might fell a mammoth, so we would gorge on red meat for two or three consecutive days before the kill spoiled. Once or twice a year we might get sugar, running into a beehive, but even then only as unlinked glucose and fructose. Some biologists believe we are susceptible to cavities now because sugar was not a regular part of our evolutionary experience, and we never developed a defense against it. Eating this way today (well, except for the insects) is called in some circles the paleo diet.