New neurological research that uses an emerging MRI technique shows that the difficulties children with dyslexia often experience with written language may be linked to structural differences within an important bundle of white matter in the brain’s left-hemisphere language network, known to play a role in oral language. “It brings us a little bit closer to understanding how dyslexia happens,” says Sheryl Rimrodt. (Credit: iStockphoto)

VANDERBILT (US)—Children with dyslexia often struggle with reading, writing, and spelling. A new study suggests the difficulties may be linked to structural differences in the part of their brain known to play a role in oral language.

Using an emerging MRI technique, called diffusion tensor imaging (DTI), researchers discovered the variations in an important bundle of white matter in the left-hemisphere language network. Details are reported in the journal Cortex.

White matter is made up of fibers that can be thought of as the wiring that allows communication between brain cells; the left-hemisphere language network is made up of bundles of these fibers and contains branches that extend from the back of the brain (including vision cells) to the front parts that are responsible for articulation and speech.

“When you are reading, you are essentially saying things out loud in your head,” explains Laurie Cutting, the Patricia and Rodes Hart Chair at the Peabody College of education and human development at Vanderbilt University. “If you have decreased white matter integrity in this area, the front and back part of your brain are not talking to one another. This would affect reading, because you need both to act as a cohesive unit.”

Cutting and colleague Sheryl Rimrodt, assistant professor of developmental medicine, used the DTI technique to map the course of an important white matter bundle in this network and discovered that it ran through a frontal brain region known to be less well-organized in the dyslexic brain.

They also found that fibers in that frontal part of the tract were oriented differently in dyslexia.

“Finding a convergence of MRI evidence that goes beyond identifying a region of the brain that differs in dyslexia to linking that to an identifiable structure and beginning to explore physical characteristics of the region is very exciting,” Rimrodt says.

“It brings us a little bit closer to understanding how dyslexia happens.”

Researchers from Johns Hopkins University and the Kennedy Krieger Institute collaborated on the work that was funded by the Johns Hopkins School of Medicine General Clinical Research Center, the Kennedy Krieger Institute’s Learning Disability Research Center and F.M. Kirby Research Center for Functional Brain Imaging, the National Institute for Neurological Disorders and the Eunice Kennedy Shriver National Institute of Child Health and Human Development.

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