Brain Rules for Baby (Updated and Expanded). John Medina
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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