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Healthy mom, healthy baby

pregnancy

One day I gave a lecture to a group of expecting couples. A woman and her husband came up to me afterward, looking anxious. “My father is a ham radio operator,” the wife said. “He told my husband that he should start tapping on my belly. Is that a good thing?” She looked puzzled. So did I. “Why tapping?” I asked. The husband said, “Not just any tapping. He wants me to learn Morse code. He wants me to start tapping messages into the kid’s brain, so the little guy will be smart. Maybe we could teach him to tap back!” The wife interjected, “Will that make him smart? My belly is really sore, and I don’t like it.”

I remember this being a funny moment; we had a good laugh. But it was also sincere. I could see the questioning look in their eyes.

Whenever I lecture on the extraordinary mental life of the developing fetus, I can almost feel a wave of panic ripple across the room. Pregnant couples in the audience become concerned, then start furiously scribbling down notes, often talking in excited whispers to their neighbors. Parents with grown children sometimes seem satisfied, sometimes regretful; a few even look guilty. There is skepticism, wonder, and, above all, lots of questions. Can a baby really learn Morse code in the latter stages of pregnancy? And if he could, would it do him any good?

Scientists have uncovered many new insights about a baby’s mental life in the womb. In this chapter, we’ll delve into the magnificent mystery of how brains develop—all starting from a handful of tiny cells. We’ll talk about what that means for Morse code, detailing the things proven to aid in utero brain development. Hint: There are only four. And we will explode a few myths along the way; for one, you can put away your Mozart CDs.

Quiet, please: Baby in progress

If I were to give a single sentence of advice based on what we know about in utero development during the first half of pregnancy, it would be this: The baby wants to be left alone.

At least at first. From the baby’s point of view, the best feature of life in the womb is its relative lack of stimulation. The uterus is dark, moist, warm, as sturdy as a bomb shelter, and much quieter than the outside world. And it needs to be. Once things get going, your little embryo’s pre-brain will pump out neurons at the astonishing rate of 500,000 cells a minute. That’s more than 8,000 cells per second, a pace it will sustain for weeks on end. This is readily observable three weeks after conception, and it continues until about the midpoint in your pregnancy. The kid has a great deal to accomplish in a very short time! A peaceful lack of interference from amateur parents is just what you’d expect the baby to need.

In fact, some evolutionary biologists believe this is why morning sickness still persists in human pregnancies. Morning sickness, which can last the entire day (and, for some women, the entire pregnancy), makes a woman stick to a bland, boring diet—if she eats much at all. This avoidance strategy would have kept our maternal ancestors away from the natural toxins in exotic or spoiled foods in the wild, unregulated menu of the Pleistocene diet. The accompanying fatigue would keep women from engaging in physical activity risky enough to harm the baby.

Researchers now think it could make the baby smarter, too. One study, yet to be replicated, looked at children whose mothers suffered from major nausea and vomiting during pregnancy. When the children reached school age, 21 percent scored 130 or more points on a standard IQ test, a level considered gifted. If their mothers had no morning sickness, only 7 percent of kids did that well. The researchers have a theory—still to be proved—about why. Two hormones that stimulate a woman to vomit may also act like neural fertilizer for the developing brain. The more vomiting, the more fertilizer; hence, the greater effect on IQ.

Whatever the reasons, the baby seems to be going to great lengths to get you to leave it alone.

How good are we at leaving baby alone—at this stage or any other in the womb? Not very. Most parents have a gnawing desire to do something to help baby, especially when it comes to baby’s brain. Fueling that drive is an enormous sector of the toy economy whose sole strategy is, I am convinced, to play off the fears of well-meaning parents. Pay close attention, for I am about to save you a ton of money.

Pregaphones and prodigies

Shopping in a toy store several years ago, I came across an ad for a DVD designed for newborns and toddlers, called Baby Prodigy. The flier stated: “Did you know that you can actually help to enhance the development of your baby’s brain? The first 30 months of life is the period when a child’s brain undergoes its most critical stages of evolution… . Together we can help to make your child the next Baby Prodigy!” It made me so angry, I crushed the flier and threw it in the garbage can.

These outlandish claims have a long history. The late 1970s saw the creation of Prenatal University, a for-purchase curriculum that claimed to boost a baby’s attention span, cognitive performance, and vocabulary, all before labor. The kid actually received a degree declaring him or her “Baby Superior” after birth. The late ’80s introduced the Pregaphone, a glorified funnel-and-speaker system designed to pump into a pregnant woman’s belly the mother’s voice or classical music or whatever other IQ-boosting noise du jour. More products soon followed, complete with some extraordinary advertising hype: “Teach your baby to spell in the womb!” “Teach your child a second language before birth!” “Improve your baby’s math scores by playing classical music!” Mozart was a particular favorite, culminating in something you may have heard before: the Mozart Effect. Things did not get better in the 1990s. Books published in that decade outlined short, daily activities for pregnant couples claiming to “raise your baby’s IQ as much as 27 to 30 points” and increase your baby’s attention span “as much as 10 to 45 minutes.”

No commercial product has ever been shown to do anything to improve the brain performance of a developing fetus.

If you walk into any toy store today, you are bound to find products making similar claims. Almost none of their assertions are backed up by in-house testing, let alone backed up by independent, peer-reviewed research.

Crinkle. Toss.

Believe it or not, no commercial product has ever been shown in a scientifically responsible manner (or even in an irresponsible non-scientific manner) to do anything to improve the brain performance of a developing fetus. There have been no double-blind, randomized experiments whose independent variable was the presence or absence of the gadget. No rigorous studies showing that an in utero education curriculum produced long-term academic benefits when the child entered high school. No twins-separated-at-birth studies attempting to tease out nature and nurture components of a given product’s effects. That includes the in utero university. And the in utero Mozart.

Sadly, myths rush in when facts are few, and they have a way of snaring people. Even after all these years, many of these products are still out there, functioning like untethered gill nets, trapping unsuspecting parents into parting with their hard-earned dollars.

The rush to create marketable products is appalling to us in the research community. Their spuriousness is also counter-productive. These products generate so much attention, they can obscure the reporting of some truly meaningful findings. There are activities that expecting parents can do to aid the cognitive development of their baby-under-construction. They’ve been tested and evaluated, with the results hashed out in refereed scientific literature. To understand their value, you need to know a few facts about the developing infant brain. Once you get a peek at what’s really going on in there, it will be easy to see why so many products are just hype.

Let’s get it on

The opening cast members of the baby-making play are simply a sperm and an egg and a saucy Marvin Gaye song. Once these two cells are joined, they begin producing lots of cells in a small space. The human embryo soon looks like a tiny mulberry. (Indeed, one early development stage is called the morula, Latin for mulberry.) Your mulberry’s first decision is practical: It has to decide what part becomes baby’s body and what part becomes baby’s shelter. This happens quickly. Certain cells are assigned to housing construction, creating the placenta and the water balloon in which the embryo will float, the amniotic sac. Certain cells are assigned the duties of constructing the embryo, creating a knot of internal tissues termed the inner cell mass.

We need to stop right here and contemplate something: The inner cell mass at this stage possesses a cell whose entire offspring will form the human brain. The most complex information-processing device ever constructed is on its way. And it starts out a fraction of the size of the period at the end of this sentence.

I have been studying this stuff for more than 20 years, and I still find it amazing. As scientist Lewis Thomas put it in The Medusa and the Snail: “The mere existence of such a cell should be one of the great astonishments of the earth. People ought to be walking around all day, all through their waking hours, calling to each other in endless wonderment, talking of nothing except that cell.” Go ahead, call your neighbor; I’ll wait.

The miracle continues. If you could see it in action, this embryo floating in seawater, you would notice that the inner cell mass is actually swarming with cells, scurrying around like busy short-order cooks at the county fair. The cells arrange themselves into three living layers, looking for all the world like a cheeseburger. The bottom bun, called the endoderm, will form most of the cell systems that line your baby’s organs and vessels. The burger layer, the mesoderm, forms your baby’s bones, muscles, blood, and various connective tissues, amongst other systems. The top bun is the ectoderm. It will create your baby’s skin, hair, nails, and nervous systems. It is within the ectoderm that the miraculous little pre-brain cell resides.

Looking closer, you would see the tiniest line of cells forming atop the bun’s center. Below, a log-shaped cylinder begins to form and elongate itself, using the overhead line as a guide. This cylinder is the neural tube. It will give rise to the spinal column—the far end of the log becoming your baby’s butt, the near end becoming baby’s brain.

When something goes wrong

It’s vital that this neural tube develop properly. If it doesn’t, the baby could have a protruding spinal cord or a tumor near his lower back, a condition known as spina bifida. Or the baby could grow without a complete head, a rare condition known as anencephaly. This is why every pregnancy book strongly recommends taking the B-complex vitamin folic acid: It helps shape the proper neural tube—both the near and far ends. Women who take folic acid around conception and during the first few weeks of pregnancy are 76 percent less likely to create a fetus with neural tube defects than those who don’t take the supplement. It is the first thing you can do to aid brain development.

Parents-to-be throughout history have worried about whether their babies are developing properly. In 1573, French surgeon Ambroise Paré catalogued the events to which prudent young pregnant couples should be alerted to avoid a child with birth defects. “There are several things that cause monsters,” he wrote in On Monsters and Marvels. “The first is the glory of God. The second, His wrath. The third, too great a quantity of seed [sperm]. The fourth, too little a quantity.” Paré hypothesized that a birth defect could be caused by indecent posturing of mom (she sat too long with her legs crossed). Or it could be due to the narrowness of the uterus, demons and devils, or the wicked spittle of beggars.

We can perhaps forgive Paré’s pre-scientific misunderstanding of in utero brain development. Even to the modern mind, it is scary, hopelessly complex, and mostly mysterious. Researchers today are at a complete loss to explain nearly two-thirds of all birth defects. Indeed, only a quarter of all known birth defects have been tied to an isolable DNA problem. One of the reasons we know so little is that mom’s body appears to have a fail-safe mechanism. If something goes wrong during development, her body often senses trouble and deliberately induces a miscarriage. About 20 percent of pregnancies end in spontaneous abortion. Known environmental toxins, things you can actually monitor, account for only 10 percent of the birth defects observed in the lab.

A delicate web of cells, crackling with electricity

Fortunately, most babies’ brains form just fine. The brain end of the neural tube continues its construction project by creating bulges of cells that look like complex coral formations. These eventually form the large structures of the brain. Before the first month, the baby’s tiny pre-brain cell has grown into a hefty army, millions of cells strong.

The brain does not develop in isolation, of course. The early embryo temporarily displays gill arches around the fourth week, for example, much like the ones fish have. These soon convert into face muscles and the throat structures that will allow your baby to speak. Your embryo next gets the stub of a tail but soon reverses course and resorbs the structure. There are strong evolutionary roots to our development, and we share this miracle with every other mammal on the planet. Except for one thing.

Those bulges at the end of your embryo’s neural tube will turn into a great big, fat, super-smart brain—about the heaviest brain-per-body mass that exists on the planet. This massive structure is composed of a delicate spider web of cells, crackling with tiny bolts of electricity. Two types of cells are important here. The first type, glial cells, make up 90 percent of the brain cells inside your child’s head. They give the brain its structure and help the neurons correctly process information. It’s a good name; glial is a Greek word for glue. The second type of cell is the familiar neuron. Though they do a lot of your child’s thinking, neurons make up only about 10 percent of the total number of brain cells. That’s probably where we get the myth that you use only 10 percent of your brain.

One neuron, 15,000 connections

So how do cells turn into brains? Embryonic cells are manufactured into neurons in a process called neurogenesis. This is when the baby would like to be left alone, in the first half of pregnancy. Then, in the second half of pregnancy, the neurons migrate to the region they eventually will call home and start wiring together. This is called synaptogenesis.

Cell migration reminds me of when tracking bloodhounds are suddenly loosed from the sheriff’s truck to pick up the scent of a criminal. Neurons bolt out of their ectodermal cages, crawling over one another, sniffing out molecular cues, pausing, trying out different pathways, slithering helter-skelter throughout the developing brain. Eventually they stop, having arrived at a destination that may be pre-programmed into their cellular heads. They look around their new cellular digs and try to hook up with the neighbors. When they do, tiny, lively gaps between neural cells are created, called synapses (hence, the term synaptogenesis). Electrical signals jump between the naked spaces to allow neural communication. This final step is the real business of brain development.

Synaptogenesis is a prolonged process, for an easily understood reason: It is ridiculously complex. A single neuron has to make an average of 15,000 connections with the locals before its wiring job is done. Some neurons have to make more than 100,000 connections. That means your baby’s brain has to lash together an astonishing 1.8 million new connections per second to make a complete brain. Many of the neurons never complete the process. Like post-sex salmon, they simply die off.

Even given this incredible speed, baby brains never make the birth deadline. About 83 percent of synaptogenesis continues after birth. Surprisingly, your baby girl’s brain will not completely finish its wiring until she is in her early 20s. Boys’ brains may take even longer. In humans, the brain is the last organ to finish developing.

When can baby hear you, smell you?

The purpose of that furiously fast (then frustratingly slow) production is to build a functioning brain, one that can receive and respond to inputs. So the questions for prying parents become: What do fetuses know, and when do they know it? When is your baby capable of sensing, say, taps on your belly?

The developmental principle to remember is this: The brain spends the first half of pregnancy setting up its neuroanatomical shop, blissfully ignoring most parental involvement. (I am referring to well-intentioned interference. Drugs, including alcohol and nicotine, clearly can damage a baby’s brain during pregnancy.) The second half of pregnancy is a different story. As brain development moves from mostly neurogenesis to mostly synaptogenesis, the fetus begins to exhibit much greater sensitivity to the outer world. The wiring of cells is much more subject to outside influences—including you—than the act of creating them in the first place.

The senses develop strategically

What is baby’s approach to constructing the brain’s sensory systems? Ask paratroop commanders. They will tell you that successfully fighting a war involves three steps: parachuting into enemy territory, securing hostile real estate, and communicating back to home base. This process gives central command both knowledge about progress and “situational awareness” of what to do next. Something similar happens to sensory systems in the brain as they develop in utero.

Like parachutists securing enemy territory, neurons invade a given region of the brain and establish various sensory bases. Neurons that hook up to the eyes will eventually be used for vision, ears for hearing, nose for smelling. Once their areas are secured, these cells will establish linkages that help them reach out to the perceptual command-and-control structures also growing up within the brain. (In the real world of the brain, there are many central commands.) These CEO-like structures, which give us perceptual abilities, are busily capturing territory just like the paratroopers. And they are some of the last areas in utero to wire up properly. This means neurons hooked up to the eyes or ears or nose might receive a busy signal when they try to report back to their home base. Because of this odd timing, parts of a baby’s brain can respond to sensory stimulation before a baby can actually perceive being stimulated.

But once babies can perceive inputs like sounds and smells, starting around the second half of the pregnancy, they become precisely attuned to them. And they subconsciously remember. Sometimes it’s spooky, as legendary conductor Boris Brott discovered one day.

Babies remember

“It just jumped out at me!” Brott exclaimed to his mother. Brott had been at the podium of a symphony orchestra, conducting a piece of music for the first time, when the cellist began to play. He instantly knew he’d heard this piece before. This was no casual reminder of some similar but forgotten work: Brott could predict exactly what musical phrase was coming next. He could anticipate the flow of the entire work during the course of the rehearsal; he knew how to conduct it even when he lost his place in the score.

Freaking out, he called his mother, a professional cellist. She asked for the name of the piece of music, then burst out laughing. It was the piece she had been rehearsing when she was pregnant with him. The cello was up against her late-pregnancy mid-abdomen, a structure filled with sound-conducting fluids, fully capable of relaying musical information to her unborn son. His developing brain was sensitive enough to record the musical memories. “All the scores I knew by sight were the ones she had played while she was pregnant with me,” Brott later said in an interview. Incredible stuff for an organ not even 0 years old.

This is but one of many examples of how babies in the womb can pick up information from the outer world. As we’ll see, what you eat and smell can influence your infant’s perceptions, too. For a newborn, these things are the familiar comforts of home.

Let’s look at when your baby’s senses—touch, sight, hearing, smell, balance, taste—start to function as you transit through pregnancy.

Touch

One of the earliest senses to come on line is touch. Embryos about 1 month old can sense touch to their noses and lips. The ability spreads quickly, and nearly the entire surface of the skin is sensitive to touch by 12 weeks of age.

I swear I could detect this by the time my wife was in the middle of her third trimester with our youngest son. He was quite a mover, and at times I could see what looked like a bulging shark’s fin move across my wife’s belly, swelling, then submerging. Creepy. And cool. Thinking it might be the little guy’s foot, I tried touching the bulge when it appeared one morning. The bulge immediately “kicked” back (!), causing us both to yelp with excitement.

If you try this in the first half of pregnancy, you won’t get any results. Not until about the fifth month after conception can babies truly experience touch in the way you and I might perceive it. That’s when your baby’s brain develops “body maps”—tiny neurological representations of his entire body.

By the beginning of the third trimester, a fetus readily displays avoidance behaviors (trying to swim away, for example, when a needle comes near for biopsy). From this we conclude that babies can feel pain, though it is impossible to measure this directly.

The fetus appears to possess sensitivity to temperature by this time, too. But it’s possible that the wiring diagrams for temperature sensation aren’t fully completed at birth and that they require experience with the outside world to fully develop. In two unrelated child-abuse cases, a French boy and an American girl were kept in isolation for years. Both children had an eerie inability to distinguish between hot and cold. The little girl never dressed appropriately for the weather, even when it was freezing outdoors. The little boy regularly pulled potatoes out of a roaring fire with his bare hands, oblivious to the temperature difference. We don’t know exactly why. We do know that touch remains very important for a baby’s development after birth.

Sight

Can babies see in the womb? That’s a tough question to answer, mostly because vision is our most complex sense.

Vision begins developing about four weeks after conception, the fetus forming little eye-dots on either side of her tiny head. Cup-shaped structures within these dots soon emerge, which will form, in part, the lens of the eye. Retinal nerves then snake out from behind these primitive eyes, trying to reach the back of the head and connect to regions that will eventually form the visual cortex. The cells in this cortex have themselves been busy, getting ready to greet these neural travelers and form partnerships. The second and third trimesters are filled with massive neural meet and greets in these regions, a fair bit of cell death, and lots of chattering connectivity. At this point, the brain is forming about 10 billion new synapses per day. You’d think a baby would get a migraine!

One result of all this activity is that the neural circuitry necessary to control blinking, dilation of pupils, or tracking moving objects is present before birth. Experiments show that infants just entering the third trimester will move or alter their heart rate, or both, in response to a strong light beamed at the womb. But it takes so long to build adequately functioning circuits that the baby needs more than nine months to finish the job. The brain will continue forming 10 billion synapses a day for almost a year after birth. During that interval, the brain uses external visual experiences to help it finish its internal construction projects.

Hearing

If you were to tell me that an important scientific fact was going to be discovered using a combination of mouth sucking and reading The Cat in the Hat, I would have suggested you change your brand of beer. But in the early 1980s, that’s exactly what happened. During the final six weeks of pregnancy, women in a study were asked to read the Dr. Seuss book out loud twice a day. That’s a lot: Total infant exposure was about five hours. When the babies were born, they were given a pacifier hooked up to a machine that could measure the strength and frequency of their sucking. Rates of strength and frequency can be used to assess whether an infant recognizes something (a form of pattern matching). The babies then heard tapes of their mothers reading The Cat in the Hat or a different story. Sucking rates and patterns were measured at all points.

What the researchers found was astonishing. The babies who had heard Dr. Seuss while in the womb appeared to recognize, and prefer, a tape of their mother reading The Cat in the Hat. They sucked their pacifiers in a pattern triggered by her reading that book, but not a different book. The babies recognized their previous in-womb auditory experience.

We now know that auditory perception begins at a much earlier age than that of the babies tested in this amazing result. Tissues involved in hearing can be observed just four weeks after conception. Hearing begins with the emergence of two structures that look like miniature saguaro cacti sprouting from either side of your baby’s head. They are called primordial otocysts, and they will form a great deal of your child’s hearing apparatus. Once this territory is established, the next weeks are devoted to setting up house, from internal hairs that look like tiny whiskers to the canals they line, which look just like snail shells.

When do these structures hook up to the rest of the brain, allowing babies to hear? The answer should be familiar by now: not until the beginning of the third trimester. At six months, you can supply a sound to a fetus in the womb (mostly clicks) and listen in astonishment as the brain weakly fires back electrical responses! In another month, this crackling call-and-response increases not only in intensity but in speed of reaction. Give it another month or so, and everything has changed. Now you have a preterm infant who can not only hear and respond but can discriminate between various speech sounds like “ah” and “ee,” or “ba” and “bi.” We once again see this paratrooper pattern of establishing the territory first, then hooking things up to central command.

Babies can hear mom’s voice in the womb by the end of the second trimester, and they prefer it to other voices at birth. They respond especially strongly after birth if mom’s voice is muffled, re-creating the sonic environment of the womb. Babies even respond to television shows their mothers watched while they were pregnant. One funny test exposed preterm infants to the opening jingle of a particular soap opera. When these babies were born, they would stop crying the moment they heard that jingle! Controls had no such distinguishing response.

Newborns have a powerful memory for sounds they encountered while still in the womb.

The point is not to panic over your reading or viewing habits. The point is simply that newborns have a powerful memory for sounds they encountered while still in the womb in the last part of gestation.

Smell

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. At first, babies suffer from an acutely stuffy nose. The nasal cavity is filled with material that probably works like protective shrink-wrap, shielding the nose’s delicate interior tissues until they are ready to become operational. Smelling, at least as we know it, is probably impossible.

All of that changes during the third trimester. The protective 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. Smells don’t have to be right under baby’s nose. Your baby can detect the perfume you wear and even the garlic you ate.

As a newborn, your baby will actually prefer these smells. The preference is called “olfactory labeling.” This is the basis for a piece of advice by neuroscientist Lise Eliot, in her book What’s Going On in There?: Don’t wash baby with soap and water immediately after she’s born. The smell of amniotic fluid calms her down, studies show. Why? As with sounds, smells remind babies of the comfortable home they were inhabiting for the past nine months.

Balance

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 of his legs, or both of his 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, at 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.

Taste

The tissues that mediate “gustatorial sensations” don’t emerge from your embryo’s tiny tongue until about eight weeks after 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 infants who preferred carrot-flavored cereal. 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.

Getting it just right

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 Goldilocks Effect

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 belongings; 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.

Four things proven to help baby’s brain

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:

• weight

• nutrition

• stress

• exercise

And there’s not a pregaphone in sight.

1. Gain just the right weight

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 increase slows as baby reaches 6.5 pounds: There is only 1 IQ point difference between a 6.5-pounder and a 7.5-pounder.

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 much do you need to eat? That depends upon how fit you are going into the pregnancy. Unfortunately, 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 healthy weight, too.

So the amount of fuel is important. There is increasing evidence that the type of fuel you eat during the critical period also is important. 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.

2. Eat just the right foods

Women have strange experiences with food preferences during pregnancy, suddenly loathing foods they used to love and craving foods they used to loathe. 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 to eat things that aren’t food. Items that regularly make the Top 10 List of Weird Pregnancy Cravings include baby talcum powder and 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 disagree.) We actually don’t know why a pregnant woman’s random cravings occur.

That doesn’t mean the body doesn’t have nutritional needs, of course. The pregnant woman 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. An infant’s body needs 45 different nutrients for healthy growth. A whopping 38 of these are critically involved in the development of the nervous system. 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 in 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.

Caveman cuisine

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 later dig around the soil for tuberous vegetables and scrounge for fruit in nearby trees. 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 run into a beehive and get sugar, but even then only as unlinked glucose and fructose. Some biologists think 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.

So it’s a bit boring. And familiar. Eating a balanced meal, with a heavy emphasis on fruits and vegetables, is probably still the best advice for pregnant women. For the non-vegetarians in the crowd, a source of iron in the form of red meat is appropriate. Iron is necessary for proper brain development and normal functioning even in adults, vegetarian or not.

Miracle drugs

There is a lot of mythological thinking out there about what you should and should not eat—not just during pregnancy but your whole life long. I had an honors student at the University of Washington, the thoughtful type of kid who has to sit on his hands not to answer a question. One day he came up to me after class, breathless. He was taking an entrance exam for medical school and had just found out about a “miracle” drug. “It’s a neurotonic!” he exclaimed. “It improves your memory. It’ll make you think better. Should I take it?” He thrust in front of my face an advertisement for ginkgo root. Derived from the ginkgo tree, ginkgo biloba has been advertised for decades as a brain booster, improving memory in both young and old, even treating Alzheimer’s. These claims are testable. A number of researchers began to study gingko as they would any promising pharmaceutical. Sorry, I told the student. Ginkgo biloba does not improve cognition of any kind in healthy adults—not memory, not visual-spatial construction, not language or psychomotor speed or executive function. “What about old people?” my student asked. Nope. It doesn’t prevent or slow down Alzheimer’s, dementia, or even normal age-related cognitive decline. Other botanicals, like St. John’s wort (purported to treat depression) show similar impotence. My student left, crestfallen. “The best thing you could do is get a good night’s sleep!” I hollered after him.

Why is it that these nutrition myths can fool even bright kids like my student? First, nutrition research is really, really hard to do, and it is shockingly underfunded. The types of long-term, rigorous, randomized trials needed to establish the effects of food often go undone. Second, most foods we consume are very complex at the molecular level; wines, for example, can have more than 300 ingredients. It is often tough to discern what part of a food product is actually giving the benefit or doing the harm.

The way our bodies handle food is even more complex. We don’t all metabolize food exactly the same way. Some people can suck calories out of a piece of paper; some people wouldn’t gain weight if they inhaled milkshakes. Some people use peanut butter as their primary source of protein; others will die of an allergic reaction if they smell it on an airplane. To the eternal frustration of just about every researcher in the field, no single diet is going to work the same way for all people, and that’s because of this extraordinary individuality. This is especially true if you’re pregnant.

Neurons need omega-3s

So you can see why only two supplements thus far have enough data behind them to support an influence on brain development in utero. One is the folic acid taken around conception. The other: omega-3 fatty acids. Omega-3s are a critical component of the membranes that make up a neuron; without it, neurons don’t function very well. Humans have a hard time making omega-3s, so we have to outsource the materials to get them into our nerves. Eating fish, especially oily ones, is a good way to do it. Those of us who don’t get enough omega-3s, studies show, are at much greater risk for dyslexia, attention-deficit disorders, depression, bipolar disorder, even schizophrenia. Most of us get enough of the fatty acids in our regular diet, so it’s generally not a problem. But the data underscore a central fact: The brain needs omega-3 fatty acids for its neurons to function properly. Apparently, the Three Stooges knew this decades ago! (Larry: “You know, fish is great brain food.” Moe: “You know, you should fish for a whale.”)

If a moderate amount of omega-3s keeps you from being mentally disabled, does a whale-sized helping of it increase brain power, especially for the baby? Here the evidence is decidedly mixed, but a few studies indicate the question warrants further research. One Harvard study looked at 135 infants and the eating habits of their mothers during pregnancy. The researchers determined that mothers who ate more fish starting in the second trimester had smarter babies than those who didn’t. By smarter, I mean that the babies performed better on cognitive tests that measure memory, recognition, and attention at six months post-birth. The effects weren’t large, but they existed. As a result, researchers recommend that pregnant women eat at least 12 ounces of fish per week. What about the mercury in fish, which can hurt cognition? It appears that the benefits outweigh the harm. Researchers recommend that pregnant women eat those 12 ounces from sources possessing less concentrated mercury (salmon, cod, haddock, sardines, and canned light tuna) as opposed to longer-lived predatory fish (swordfish, mackerel, and albacore tuna).

My belly is evidence that I know how tough it is to eat properly, whether you are trying to control how much to eat, what to eat, or both. There’s Goldilocks again: You need enough, but not too much, of the right types of food. And the third factor usually doesn’t help.

3. Avoid too much stress

It was not a good idea to be in Quebec and pregnant around January 4, 1998. For more than 80 hours, freezing rain and drizzle fell relentlessly across eastern Canada—immediately followed by a steep drop in surface temperature. This meteorological one-two punch turned eastern Canada into ice hell. Under the weight of the freeze, more than a thousand towering metal power-line structures toppled like dominoes. Tunnels collapsed. Thirty people died. A state of emergency soon was declared; the army was called up. Even so, thousands of residents were without power for weeks, in freezing temperatures. If you were pregnant and could not get to a hospital for your regular checkups—God forbid if you went into labor—you were stressed out of your mind. And so, it turned out, was your infant. The effects of that storm could be seen on the children’s brains years later.

How do we know that? A group of researchers decided to study the effects of this natural disaster on babies in the womb—then follow the children as they grew older and entered the school system. The result was scary. By the time these “ice storm” children were 5, their behaviors differed markedly from children whose mothers hadn’t 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 usually the toughest part. Studies show that if you are not in shape, it takes you twice as long to transit through the “pushing phase” of labor than if you are fit. Not surprisingly, fit women perceive this stage as being far less painful.

Because the pushing phase is shorter, babies also are less likely to experience brain damage from oxygen deprivation. If you are afraid of labor, you owe it to yourself to become as fit as possible going into it. And the reasons are argued purely from the Serengeti.

Exercise buffers against stress

Fit mothers also tend to give birth to smarter babies than obese mothers do. There are two reasons for this. One may have to do with the direct effects of exercise—especially aerobic exercise—on a baby’s developing brain. This notion needs more research. More powerful are the data linking aerobic exercise and stress reduction.

Certain types of exercise actually buffer a pregnant woman against the negative influence of stress. Remember those toxic glucocorticoids, the ones that invade neural tissue and cause brain damage? Aerobic exercise elevates a molecule in your brain that can specifically block the toxic effects of those nasty glucocorticoids. This heroic molecule is termed brain-derived neurotrophic factor. More BDNF means less stress, which means fewer glucocorticoids in your womb, which means better baby brain development.

It may sound strange to say, but a fit mom has a much better chance of having a smart baby—or at least one best able to mobilize his or her IQ—than an unfit mom.

Too strenuous, and baby overheats

As usual, though, there’s a balance. A baby can feel and react to the mother’s motion. When her heart rate goes up, so does baby’s. When mom’s breathing rate increases, so does baby’s. But only if the exercise is moderate. During strenuous exercise, especially in the later stages of pregnancy, the baby’s heart rate and breathing begin to decline. The concern is that overdoing it might increase the temperature of the womb or restrict baby’s access to oxygen. As ever, your pediatrician can provide guidance about the amount of exercise you should be doing in these later stages. Your oxygen reserve levels are pretty low by the third trimester, so it’s a good time to wind down strenuous activities in preparation for labor. Swimming is one of the best forms of exercise in later stages; the water helps transfer excess heat away from the womb.

What is the proper balance? Four words: moderate, regular aerobic exercise. For most women, that means keeping your heart rate below 70 percent of its maximal rate (which is 220 beats per minute minus your age), then slowing things down as the due date approaches. But you should exercise. As long as you don’t have obstetric or other medical complications, the American College of Obstetricians recommends 30 minutes or more of moderate exercise per day.

Good advice, even though we are not wildebeests.

Every little bit counts

Maybe you’re not in the habit of exercising every day. Maybe you’re feeling guilty enough already for drinking that second cup of coffee while pregnant. If so, perhaps you will appreciate some reassurance from the research world: As a species, Homo sapiens have been successfully making babies for 250,000 years. We did very well without all this fancy knowledge, thank you, and with such success that we conquered the world. Your best intentions—Morse code belly tapping notwithstanding—will go a long way toward creating a great environment for your developing baby.

Key points

• In the first half of pregnancy, babies want to be left alone.

• Don’t waste your money on products claiming to improve a preborn baby’s IQ, temperament, or personality. None of them have been proved to work.

• In the second half of pregnancy, babies begin to perceive and process a great deal of sensory information. They can even smell the perfume you wear.

• Brain boosters at this stage: gaining the proper weight, eating a balanced diet, exercising moderately, and reducing stress.