How To Build A Baby's Brain

Research on language has shown how "neuroplastic" an infant's brain is, and how that plasticity lessens with age. Patricia Kuhl of the University of Washington studies the "auditory maps" that infants' brains construct out of phonemes (the smallest units of sound in a language, such as "ee" or 'T'). At first, neurons in the auditory cortex are like laborers to whom jobs have not yet been assigned. But as a newborn hears, say, the patter of English, a different cluster of neurons in the auditory cortex is recruited to respond to each phoneme. Each cluster then fires only when a nerve from the ear carries that particular sound, such as "pa" or "ma." If one sound is clearly distinct from another, as "ra" and "la" are in English, then the neurons whose job it is to hear one will lie far from those whose job it is to hear the other. (Kuhl makes noninvasive electrical measurements, through the babies' scalps, to identify which neurons fire in response to a particular sound.) But if the sounds are nearly identical, as "ra" and "la" are in Japanese, then the two sets of neurons are so close that the baby will have trouble distinguishing the two phonemes. By 12 months, an infant's auditory map is formed. He will be unable to pick out phonemes he has not heard thousands of times for the simple reason that no cluster of neurons has been assigned the job of responding to that sound. And the older he gets, the more he will struggle to learn a new language: fewer unassigned neurons are available for the job of hearing new phonemes.

Experience counts in building vocabulary, too, and at a very young age. The size of a toddler's vocabulary is strongly correlated with how much a mother talks to the child, reports Janellen Huttenlocher of the University of Chicago. At 20 months, children of chatty mothers averaged 131 more words than children of less talkative mothers; at 2 years, the gap had more than doubled, to 295 words. "The critical factor is the number of times the child hears different words," says Huttenlocher. The effect holds for the complexity of sentence structure, too, she finds. Mothers who used complex sentences (those with dependent clauses, such as "when..." or "because...") 40 percent of the time had toddlers who did so 35 percent of the time; mothers who used such sentences in only 10 percent of their utterances had children who did so only 5 percent of the time.

ONLY "LIVE" LANGUAGE, not television, produced these vocabulary- and syntax-boosting effects. Why doesn't all the gabbing on TV stimulate language development? Huttenlocher suspects that "language has to be used in relation to ongoing events, or it's just noise." That may hold for other sorts of cognition, too. Information embedded in an emotional context seems to stimulate neural circuitry more powerfully than information alone. A child will more readily learn the concept of "more" if it refers to the happy prospect of more cookies, and "later" if it is attached to a frustrating wait for a trip to the playground, than if the word is presented in isolation from things the baby cares about. There is nothing mysterious about this: adults form a memory much more readily if it has emotional content (how did you hear that the space shuttle had exploded?) than if it doesn't (what's the difference between a sine and a cosine?). Causality, a key component of logic, is also best learned through emotion: if I smile, Mommy smiles back. A sense that one thing causes another forms synapses that will eventually support more abstruse concepts of causality. Feelings, concepts and language begin to be linked in this way in the months from 7 through 12.

Another route to brain wiring seems to be tapping into its natural harmonies. In the last year, new studies have nailed down how music affects spatial-temporal reasoning--the ability to see a disassembled picture of, say, a rabbit and mentally piece it back together. Such reasoning underlies math, engineering and chess. In a study published in February in the journal Neurological Research, scientists report how spatial-temporal reasoning in 3- and 4-year-olds was affected by weekly piano lessons. After six months, the budding Horowitzes--all of whom scored at the national average on tests of spatial recognition-scored 34 percent above average on this reasoning skill. None of the other children (who had received computer keyboard and mouse lessons, singing lessons or nothing at all) had improved. What explains the effect? Physicist Gordon Shaw of the University of California, Irvine, suspects that in playing the piano, "you are seeing how patterns work in space and time." When sequential finger and key patterns make melodies, neural circuits that connect positions (keys) to sounds in space and time (the melody) are strengthened. "Music training produces long-term modifications in neural circuitry," says Shaw. What scientists do not know is whether the effects of early music training endure-whether the preschoolers will be math wizards in high school.

The downside of the brain's great plasticity is that it is acutely vulnerable to trauma. "Experience may alter the behavior of an adult," says Dr. Bruce Perry of Baylor College of Medicine, but it "literally provides the organizing framework" for the brain of a child. If the brain's organization reflects its experience, and the experience of the traumatized child is fear and stress, then the neurochemical responses to fear and stress become the most powerful architects of the brain. "If you have experiences that are overwhelming, and have them again and again, it changes the structure of the brain," says Dr. Linda Mayes of the Yale Child Study Center. Here's how:

Trauma elevates stress hormones, such as cortisol, that wash over the tender brain like acid. As a result, regions in the cortex and in the limbic system (responsible for emotions, including attachment) are 20 to 30 percent smaller in abused children than in normal kids, finds Perry; these regions also have fewer synapses.