PNAS: fMRI highlights dyslexia characteristics
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The findings could help spur earlier diagnosis of developmental dyslexia and enable early intervention. Developmental dyslexia affects 5 to 17 percent of all children; up to half of children with a family history of dyslexia will struggle with reading, experiencing poor spelling and decoding abilities and difficulties with fluent word recognition. Because of problems recognizing and manipulating the underlying sound structures of words, children with dyslexia have difficulty mapping oral sounds to written language.
Children's Hospital Boston researchers, led by Nora Raschle, PhD, of the laboratories of cognitive neuroscience, performed fMRI imaging in 36 preschool-age children (average age, 5.5 years) while they performed tasks requiring them to decide whether two words started with the same speech sound. Eighteen of the children had a family risk of dyslexia; the 18 controls were age- and IQ-matched.
During the phonological tasks, children with a family history of dyslexia had reduced metabolic activity in the junctions between the occipital and temporal lobes and the temporal and parietal lobes in the back of the brain when compared with controls. The left temporoparietal region is critical for integration of letter and speech sounds.
"We already know that older children and adults with dyslexia have dysfunction in the same brain regions," said senior investigator Nadine Gaab, PhD, also of the laboratories of cognitive neuroscience, in a statement. "What this study tells us is that the brain's ability to process language sounds is deficient even before children have reading instruction."
In both the at-risk and control groups, children with high activation in these brain areas had better prereading skills, such as rhyming, knowing letters and letter sounds, knowing when two words start with the same sound and being able to separate sounds within a word (like saying "cowboy" without the "cow").
The children at risk for dyslexia showed no increase in activation of frontal brain regions, as has been seen in older children and adults with dyslexia. This suggests that these regions become active only when children begin reading instruction, as the brain tries to compensate for other deficits.
“Our results suggest that these behavioral and neural differences in children at risk for developmental dyslexia must reflect a mechanism that develops within the first few years of life or may even have a biological origin,” the researchers wrote.
"We hope that identifying children at risk for dyslexia around preschool or even earlier may help reduce the negative social and psychological consequences these kids often face," said Raschle.
While various neuropsychological interventions are available for dyslexia, the condition generally isn't diagnosed until the child has reached third grade, when they are less effective, Gaab added. “Identifying a learning disability around mid-elementary school is oftentimes too late, as the delayed development may have already affected a child’s vocabulary skills and motivation to read,” according to Raschle et al.
"Families often know that their child has dyslexia as early as kindergarten, but they can't get interventions at their schools," Gaab said. "If we can show that we can identify these kids early, schools may be encouraged to develop programs."
Gaab and Raschle plan to follow the children over time to see if the brain patterns they observed correlate with a later diagnosis of dyslexia.