By adulthood the brain is crisscrossed with more than 100 billion neurons, each reaching out to thousands of others so that, all told, the brain has more than 100 trillion connections. It is those connections – more than the number of galaxies in the known universe – that give the brain its unrivaled powers.
Yet, once wired, there are limits to the brain’s ability to create itself. Time limits, called “critical periods,” which are windows of opportunity that nature flings open, starting before birth, and then slams shut, one by one, with every additional candle on the child’s birthday cake. In the experiments that gave birth to this paradigm in the 1970s, Torsten Wiesel and David Hubel found that sewing shut one eye of a newborn kitten rewired its brain: so few neurons connected from the shut eye to the visual cortex that the animal was blind even after its eye was reopened. Such rewiring did not occur in adult cats whose eyes were shut. Conclusion: there is a short, early period when circuits connect the retina to the visual cortex.
But, does the same thing happen to humans? Yes it does! For example, if an adult has a vision-impairing cataract removed from his eye, chances are his sight will be restored. However, a child born with a cataract that isn’t removed promptly will retain forever sightless in that eye, because the necessary connections between the eye and the brain’s visual centers were never made. And there’s a large emotional component to brain development: Children who are rarely played with or touched as infants develop brains 20 to 30 percent smaller than normal for their age, according to researchers at Baylor College of Medicine in Houston.
Hence, when brain regions mature dictates how long they stay malleable. Sensory areas mature in early childhood; the emotional limbic system is wired by puberty; the frontal lobes – seat of understanding – develop at least through the age of 16. The implications of this new understanding are at once promising and disturbing. They suggest that, with the right input at the right time, almost anything is possible. But they imply, too, that if you miss the window you’re playing with a handicap.
These findings suggest that “the brain develops on a ‘use it or lose it’ principle,” explains Harry Chugani, M.D., a pediatric neurologist at Children’s Hospital of Wayne State University in Detroit and a leading expert on infant brain development. “There are critical periods when the brain must be used in order for certain kinds of development to tale place” – like sight, language, emotion, and movement.
Consequently, the best time to master a skill associated with a system is just when a system is coming on line in your brain. Language is a good example. It’s very easy for a 2- or 3-year old to learn any language. But if that person waits until 18 or 30, learning a new language will be more difficult because the systems governing this have been used for something else. This explains why the gains a toddler makes in head start are so often evanescent: this intensive instruction begins too late to fundamentally rewire the brain. And this makes clear the mistake of postponing instruction in a second language. As Chugani asks, “What idiot decreed that foreign-language instruction not begin until high school?”
What’s more, the latest research has revealed that, between birth and age 3, more brain activity occurs than anyone – proud parent or scientist – ever previously imagined. For example, babies as young as 5 months already have a basic understanding of quantity. Between birth and 4 months, babies appear to have an innate sense of the rudimentary laws of physics – the way in which physical objects interact.
As for those parents whose children have passed through the critical years from birth to age 3 and who are wondering if they did all they should have to get those brain synapses Dr. Chugani says it’s never too late to stimulate a child’s intellect. “Although the tremendous growth of a child’s brain begins to slow at age 3, the brain remains amazingly plastic and adaptable into adolescence,” he says.