The New Science of Dyslexia — page 2

The stakes have never been higher. Right now in the U.S. there are almost 3 million students in special-education classes specifically because they can't read. Most of them are probably dyslexic. But there are other slow readers who are simply overlooked—ignored in crowded classrooms or dismissed as discipline problems. Unless corrective action is taken, their self-confidence often crumbles as they see other students progressing. Even worse, their peers might taunt or ostracize them—a situation that Sean Slattery's mother, Judy, remembers all too well. "Sean cried for four hours every day after kindergarten," she says. "He was so unhappy."

In Asia, research on dyslexia suggests its incidence might be significantly lower than in the West due to the differences in how Asian scripts are processed by the brain (see following story). The bad news is that Asians with dyslexia are far more likely than Westerners to go undiagnosed, unaided and branded as lifetime losers. Growing up in Malaysia, Ahmad Fitri Isahak was taunted by friends and felt cold-shouldered by teachers because he failed most of his tests. It was only at the age of 25, while studying computer and software engineering at university in England, that a professor told him he was probably dyslexic. "I was devastated and failed that year," he recalls. But he got back in the saddle, finished his degree, and Fitri is now an IT consultant in Kuala Lumpur—a happy ending that he admits is unusual for dyslexics in his homeland. "For now, they are a lost lot," he says.

To be sure, researchers still don't understand everything there is to know about learning disabilities. Dyslexia, for one, might consist of several subtypes. "It would be very dangerous to assume that every child with reading problems is uniform and has the same kinds of breakdowns preventing him from learning to read," says Dr. Mel Levine, a pediatrician and author of several influential books about learning disabilities and dyslexia, including A Mind at a Time. But whatever the exact nature of the deficit, the search for answers begins with the written word.

When you think about it, that anyone can read at all is something of a miracle. Reading requires your brain to rejigger its visual and speech processors in such a way that artificial markings, such as the letters on a piece of paper, become linked to the sounds they represent. It's not enough simply to hear and understand different words. Your brain has to pull them apart into their constituent sounds, or phonemes. When you see the written word cat, your brain must hear the sounds /k/ ... /a/ ... /t/ and associate the result with an animal that purrs.

Unlike speech, which any developmentally intact child will eventually pick up by imitating others who speak, reading must be actively taught. That makes sense from an evolutionary point of view. Linguists believe that the spoken word is 50,000 to 100,000 years old. But the written word—and therefore the possibility of reading—has probably been around for no more than 5,000 years. "That's not long enough for our brains to evolve certain regions for just that purpose," says Guinevere Eden, a professor of pediatrics at Georgetown University in Washington, D.C., who also uses brain scans to study reading. "We're probably using a whole network of areas in the brain that were originally designed to do something slightly different." As Eden puts it, the brain is moonlighting—and some of the resulting glitches have yet to be ironed out.

	Boys and girls are equally likely to suffer from dyslexia

To understand what sorts of glitches we're talking about, it helps to know a little about how the brain works. Researchers have long been aware that the two halves, or hemispheres, of the brain tend to specialize in different tasks. Although the division of labor is not absolute, the left side is particularly adept at processing language and the right is more attuned to analyzing spatial cues. The specialization doesn't stop there. Within each hemisphere, different regions of the brain break down various tasks even further. So reading a sonnet, catching a ball or recognizing a face requires the complex interaction of a number of different regions of the brain.

Most of what neuroscientists know about the brain has come from studying people who were undergoing brain surgery or had suffered brain damage. Clearly, this is not the most convenient way to learn about the brain, especially if you want to know more about what passes for normal. Even highly detailed pictures from the most advanced computer-enhanced X-ray imaging machines could reveal only the organ's basic anatomy, not how the various parts worked together. What researchers needed was a scanner that didn't subject patients to radiation and that showed which parts of the brain are most active in healthy subjects as they perform various intellectual tasks. What was needed was a breakthrough in technology.

That breakthrough came in the 1990s, with the development of a technique called functional magnetic resonance imaging (fMRI). Basically, fMRI enables researchers to see which parts of the brain are getting the most blood—and hence are the most active—at any given point in time.

Neuroscientists have used fMRI to identify three areas of the left side of the brain that play key roles in reading. Scientifically, these are known as the left inferior frontal gyrus, the left parieto-temporal area and the left occipito-temporal area. But for our purposes, it's more helpful to think of them as the "phoneme producer," the "word analyzer" and the "automatic detector." We'll describe these regions in the order in which they are activated, but you'll get closer to the truth if you think of them as working simultaneously, like the sections of an orchestra playing a symphony.

Using fMRI, scientists have determined that beginning readers rely most heavily on the phoneme producer and the word analyzer. The first of these helps a person say things—silently or out loud—and does some analysis of the phonemes found in words. The second analyzes words more thoroughly, pulling them apart into their constituent syllables and phonemes and linking the letters to their sounds.

As readers become skilled, something interesting happens: the third section—the automatic detector—becomes more active. Its function is to build a permanent repertoire that enables readers to recognize familiar words on sight. As readers progress, the balance of the orchestra shifts and the automatic detector begins to dominate. If all goes well, reading eventually becomes effortless.

In addition to the proper neurological wiring, reading requires good instruction. In a recent study published in Biological Psychiatry, neuroscientist Shaywitz and her colleagues identified a group of poor readers who were not classically dyslexic, as their phoneme producers, word analyzers and automatic detectors were all active. But the three regions were linked more strongly to the brain's memory processors than to its language centers, as if the children had spent more time memorizing words than understanding them.

The situation is different for children with dyslexia. Brain scans suggest that a glitch in their brains prevents them from easily gaining access to the word analyzer and the automatic detector. In the past year, several fMRI studies have shown that dyslexics tend to compensate for the problem by overactivating the phoneme producer.

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