To clarify whether dyslexia, a fairly-common disorder characterised by an unexpected low reading ability, involves the brain's defective processing of visual information, US-based National Center for Research Resources-funded experts studied brain activity in a visual pathway. Using a method known as functional magnetic resonance imaging, that non-invasively measures changes in the flow of oxygen-rich blood in the brain, they evaluated brain activity in five dyslexic and five nondyslexic students while they were reading. Compared to the nondyslexic students, those with the disorder had diminished activity in the brain's visual cortex and in a secondary visual area known as MT+, found in the back of the brain. MT+ activation is believed to indicate activity in the brain's magnocellular (M) pathway, a region long suspected to be impaired in dyslexics. Lower MT+ responses also strongly correlated with slower reading speed. These results not only implicate the M pathway as a marker for dyslexia, but also suggests that this pathway is deficient in dyslexics ( NCCR Reporter , Vol 22, No 1).
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