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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, 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.
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 while 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 allows 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.