Dyslexic people show an abnormal pattern of brain function when reading - under-activity in some regions, over-activity in another - that accounts for the difficulty they have in extracting meaning from the printed word, researchers say.
The findings provide dramatic evidence that people with dyslexia are not poorly taught, lazy, or stupid, but have an inborn brain abnormality that has nothing to do with intelligence, say the scientists from Yale School of Medicine.
"I feel really very gratified that these individuals can now say there us good evidence that this is a neurobiological disorder," said Dr. Sally Shaywitz, a Yale pediatrician who headed the study. The evidence has been accumulating for a number of years in research on dyslexia, which is believed to afflict 10 percent or more of all children.
Dyslexia is defined as a significant reading disability in people with normal intelligence.
The new picture, literally, of brain abnormalities was obtained by placing normal and reading impaired volunteers inside computerized MRI scanners while they were presented with successively harder tasks.
Shaywitz said the study "means we've identified a system in the brain that allows us to go from looking at printed words to connecting it to the sound structure of words," and that dyslexics have "glitches" in the system.
Shaywitz said the poorly performing brain centers are the ones that are crucial to what is called phonological processing. This processing is the ability to crack the "code" that underlies written language, that is, the relationship between letters and letter groups with the spoken sounds they represent.