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Brain Research Produces Clues on
Possible Causes of Dyslexia

May 21 2003 - An eighty-year-old theory about the neurobiological basis of reading disability has been partly confirmed by researchers using functional magnetic resonance imaging (fMRI) to study brain activity in children. The technique also sheds new light on how the activities of different brain regions change as children become accomplished readers. Their findings are reported in the May 18 online publication of the journal Nature Neuroscience.

Clinician and prominent dyslexia researcher, Dr. Samuel Orton, hypothesized in 1925 that normally developing readers suppress visual images reported by the right hemisphere of the brain that could potentially interfere with input from the left. Researchers at Georgetown University Medical Center using fMRI found that children do in fact "turn off" the right side of the visual parts of the brain as they become accomplished readers. This finding confirms an aspect of Orton's theory - born out of observations of individuals with reading disability - is correct.

For the first time, they also were able to show that different phonological skills are related to activity in different parts of the brain when children read. Phonological skills allow readers to sound out words by correctly associating sounds with written symbols. They are critical for children learning to read and are often found to be impaired in children with developmental dyslexia.

The observation adds support to the theory that there may be several neurobiological profiles corresponding to different subtypes of dyslexia - each associated with varying deficits in one or more of these different phonological skills.

"Reading is the single most important skill our children learn - it impacts virtually every aspect of a child's life," said Dr. Guinevere Eden, associate professor of pediatrics and director of Georgetown University's Center for the Study of Learning. "Despite the extraordinary effort that goes into teaching children to read, very little is known about the neurobiology of reading acquisition in children. This study is important because we need to understand the brain basis of learning in kids who read well in order to understand why some children, like those with dyslexia, don't."

Dr. Eden and colleagues Peter Turkeltaub, Lynn Gareau, and Dr. Tom Zeffiro of Georgetown, and Dr. Lynn Flowers of Wake Forest University, studied 41 people aged between six and 22 using fMRI to examine which parts of the brain were employed when they saw words. Using a method where subjects were asked to locate tall letters within a word - forcing them to read the words implicitly - the researchers correlated brain activity with scores on reading tests to see if more advanced readers had more activity in certain brain areas than less experienced readers, and vice versa. Then they studied brain activity during reading related to scores on tests of phonological skills.

The fMRI scans showed that young children just learning to read used the left temporal regions of their brains; increases in age and the associated gains in reading, were characterized by a suppression of the visual areas of the right hemisphere - supporting Orton's theory.

The study also showed that the same locus in the left temporal lobe engaged during reading in younger children is also more active if children are good at phonemic awareness, such as understanding that "pop" without "p" is "op." These measures are frequently employed for behavioral evaluation of children at risk for developing reading problems and these new findings provide an anatomical correlate of this ability.

"Work like this can provide important background information to develop new research-based teaching programs that can ultimately help all children to become proficient readers and identify those who are need of specific interventions," said Peter Turkeltaub, primary author of this study. "This is an exciting area of research in which scientists converge with educators and parents to achieve the common goal of helping children achieve the reading skills they need to succeed in life."

Dr. Eden's team will continue to study the neurobiological basis for reading. And Eden and her colleagues will soon begin related research, supported by the NIH and the International Dyslexia Association - founded in the memory of Samuel Orton, involving the largest longitudinal study ever undertaken in the US to study brains in children as they develop into readers. A "brain bank" will enable researchers to undertake more comprehensive dyslexia and neurobiological research.

This research was funded by the National Institutes of Health.

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