How Children Learn To Read [Archive.org URL]

Why is it easy for some people to learn to read, and difficult for others? It’s a tough question with a long history. We know that it’s not just about raw intelligence, nor is it wholly about repetition and dogged persistence. We also know that there are some conditions that, effort aside, can hold a child back. Socioeconomic status, for instance, has been reliably linked to reading achievement. And, regardless of background, children with lower general verbal ability and those who have difficulty with phonetic processing seem to struggle. But what underlies those differences? How do we learn to translate abstract symbols into meaningful sounds in the first place, and why are some children better at it than others?

This is the mystery that has animated the work of Fumiko Hoeft, a cognitive neuroscientist and psychiatrist currently at the University of California, San Francisco. […] When Hoeft took into account all of the explanatory factors that had been linked to reading difficulty in the past—genetic risk, environmental factors, pre-literate language ability, and overall cognitive capacity—she found that only one thing consistently predicted how well a child would learn to read. That was the growth of white matter in one specific area of the brain, the left temporoparietal region. The amount of white matter that a child arrived with in kindergarten didn’t make a difference. But the change in volume between kindergarten and third grade did.

What is white matter? You can think of it as a sort of neural highway in the brain—roads that connect the various parts of the cortex and the brain surface. Information, in the form of electrical signals, runs across the white matter, allowing for communication between the different parts of the brain: you see something, you give it meaning, you interpret that meaning.

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Hoeft’s discovery builds on previous research that she conducted on dyslexia. In 2011, she found that, while no behavioral measure could predict which dyslexic children would improve their reading skills, greater neural activation in the right prefrontal cortex along with the distribution of white matter in the brain could, with seventy-two-per-cent accuracy, offer such a prediction. If she looked at overall brain activation while the children performed an initial phonological task, the predictive power rose to more than ninety per cent. Overall intelligence and I.Q. didn’t matter; what was key was a very specific organizational pattern within your brain.

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And the white-matter development, Hoeft believes, is surely a function of both nature and nurture. “Our findings could be interpreted as meaning that there’s still genetic influence,” Hoeft says, noting that preexisting structural differences in the brain may indeed influence future white-matter development. But, she adds, “it’s also likely that the dorsal white-matter development is representing the environment the kids are exposed to between kindergarten and third grade. The home environment, the school environment, the kind of reading instruction they’re getting.”