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Dyslexia and Language Brain Areas

The learning disability dyslexia, which centers on difficulties in reading, once stumped scientists. Since dyslexics often have good intelligence and even may be gifted in some areas, it was thought that a little motivation could get them on the right track. Now researchers not only know that dyslexia is born of biology, but they also are getting closer to confirming the key brain areas that are affected. New insights will help pinpoint therapies and improve treatment.

Albert Einstein was a genius. And a dyslexic.
      The fact that the reading disability, dyslexia - often marked by deficits in the decoding of words - can affect smart people, even some famously knowledgeable, once perplexed scientists. Many assumed that laziness was the cause.
      Now research confirms that more than a kick in the butt is needed to jumpstart dyslexics' stall in reading. Studies show a biological basis for this disability that affects millions of American children and adults. One line of research indicates that dyslexics use the brain regions that process written language differently than those without the disorder.

New advances are leading to:

  • Earlier diagnosis and treatment of dyslexia.
  • Fine-tuning of therapies.
  • A better understanding of the nature of dyslexia.

      For decades after researchers first described dyslexia, many people contended that it stemmed from a "slacker" attitude. Then, almost a century later, scientists began to unearth hints that the disorder was backed by biology. In 1979 a report indicated that anatomical abnormalities existed in a dyslexic patient. The left side of the brain of the 20-year-old who died accidentally depicted disorganization in the cells that control language areas.
      The finding caused researchers to investigate the brain's involvement in dyslexia.
      Many scientists have identified brain regions related to dyslexia with high-tech imaging techniques that photograph the brain in action. The tools have helped them link the disability to speech sound processing, vision and language brain systems. Today researchers are systematically scrutinizing large numbers of dyslexics to determine which areas of the brain are the most involved and to understand how they relate to each other and contribute to different degrees and varieties of the disability. Dyslexia's symptoms, which may include deficits in spelling, in recognizing sounds in words, in processing rapid visual information and in saying words quickly when put on the spot, have made it difficult for researchers to tease apart the key brain regions involved.
      While the areas most central to the disability are still uncertain, many researchers suspect that the brain areas that control language play a critical role. One of these areas that keeps coming up in studies is the angular gyrus (AG). Located toward the back of the brain, the AG translates the mass of words and letters we encounter in day-to-day life into language.
      Some researchers believe the area, which is known to be involved in normal reading, is a key component of an overall "reading pathway" in the brain. Recent studies of a variety of reading and language tasks in dyslexic individuals showed less activity in the AG than those without the disability. The researchers suspect that this part of the brain does not function normally in dyslexics.
      Some scientists speculate that dyslexics use the area inadequately and may compensate by using other brain areas, such as the inferior frontal gyrus, which is located in the front of the brain, and is associated with spoken language. For example, dyslexics who say the words they are reading under their breath may rely heavily on this area to get through a passage of text, according to one theory.
      Many researchers also are using imaging techniques to see if the behavioral interventions sometimes used to treat those with dyslexia actually modify brain activity. One group is reviewing three separate interventions thought to target either the brain system that processes written language, the speech sound processing system or the visual system.
      The results could help confirm the brain areas that are common to the many forms of the disability and lead to a fine-tuning of interventions.

Several imaging studies of reading and language skills show that the AG is involved in dyslexia. One group of researchers currently is studying how dyslexics perform pig latin tasks compared to normal readers. Pig latin requires dissecting and reordering the sounds within a word. For example, if a word begins with a consonant, the first letter is moved to the end of the word and "ay" is added. "Pig" becomes "igpay." It is a difficult test for dyslexics because it challenges their ability to sound out written words as well as their memory skills. The image above shows that activity in the AG is increased in a normal reader who performs the pig latin task. The researchers suspect that the activity will be lower in dyslexic readers.

Image by Guinevere Eden, D.Phil, Georgetown University

For more information please contact Leah Ariniello, Science Writer, Society for Neuroscience, 11 Dupont Circle, NW, Suite 500, Washington DC 20036.