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While researchers and educators have come a long way in recent decades in identifying and treating the reading disability dyslexia, its origins remain murky. Now, brain scientists are one step closer to understanding just how it may unfold - and when.

Using brain scans of 13 dyslexic and 13 non-dyslexic adults taken while they read and listened to matching and non-matching sets of letters and sounds, researchers in the Netherlands have found that dyslexic readers process printed symbols and their corresponding sounds differently than non-dyslexic readers.

The findings suggest that in those with dyslexia, there may be a breakdown in brain function occurring as they acquire spoken language as children, long before they start trying to read and write.

When asked to match letters and their sounds, the dyslexic readers performed well, but took longer than the others, says Vera Blau, a PhD student in cognitive neuroscience at Maastricht University.

When processing matching letters and sounds, the non-impaired readers showed stronger brain activity in the superior temporal cortex - a region of the brain associated with much of our hearing abilities - than when they were processing letters and sounds that did not match.

Dyslexic readers processed both matching and non-matching pairs at the same, slower pace. Ms. Blau also found that even when a dyslexic reader was exposed to sound only, there was less activity in the superior temporal cortex.

"This suggests that dyslexic readers learn these connections but their brains process them less automatically, which is one reason why they might experience difficulties in becoming sufficiently fluent in reading," says Ms. Blau, who conducted the research with a team led by her professor, Leo Blomert. The study was published online yesterday in the journal Current Biology.

Fellow dyslexia researcher Nadine Gaab, an assistant professor of pediatrics at Children's Hospital Boston who did not work on this study, says Ms. Blau's work builds on her own and others' work trying to locate the mechanisms in the brain that explain dyslexia.

"It shows the missing link between reading and sound processing," she says. Over the last 20 years, she says, this potential link has been ignored by even well-meaning doctors and educators, in favour of remedial reading lessons. "But if you think about it, when you learn to read, the four years of preparation are all coming through the ears."

All the study participants were matched for educational level, age, handedness and IQ. They were also tested on a battery of measures for reading status.

With this new information about how the dyslexic brain is different, Ms. Blau says the next step will be to conduct similar studies on children to zero in on how the brain learns to make the connections between letters and sounds. Future findings might validate some treatments currently being used that are already based on sound processing, and might help researchers understand whether the dyslexic brain can truly be rewired.

Dr. Gaab says the current study also adds to the ongoing evolution of the functional magnetic resonance imaging (fMRI) brain-scanning technology she, Ms. Blau and others rely on. One day, she says, it may be useful as a diagnostic tool parents might ask their doctors to use on children they suspect are at a high risk of dyslexia.

"I think we're getting there. We can scan children as young as 4," she says. "It's very child-friendly - kids love it. They get pictures of their brain ... the mock scanners that we use for training look like big playgrounds."

What's more, if scans can one day predict which children are at risk of dyslexia, they might also be applicable to the identification of other learning disabilities and disorders, Dr. Gaab says, including children who may face multiple problems. Dyslexia and attention deficit hyperactivity disorder often show up in the same child, for instance.

"If you can predict whether an ADHD kid will develop dyslexia later, maybe you can start to train them and see whether you can reduce the burden."