Tuesday, January 11, 2011
1/11/2011 03:31:00 AM Publicado por Alquimia
Brain scans may be able to predict which children with dyslexia are likely to improve their reading skills over time, according to a new study led by MIT and Stanford researchers.
Some 5 to 17 percent of U.S. children suffer from dyslexia, a learning disorder that makes it difficult to read. Many dyslexic children are able to make substantial improvements in reading ability, but how they do so is not well-understood, and standardized reading tests cannot predict which children are likely to become stronger readers.
If the findings are confirmed in larger studies, brain scans could be used as a prognostic tool to predict reading improvement in dyslexic children. They could also help scientists and educators develop new teaching methods that take advantage of the brain pathways that dyslexic children appear to use to compensate for their disability, says John Gabrieli, MIT professor of brain and cognitive sciences. Such strategies may be able to help dyslexic children regardless of which brain patterns they show.
Gabrieli, who is also a member of MIT’s McGovern Institute for Brain Research, is a senior author of the paper on the work appearing in the Proceedings of the National Academy of Sciences the week of Dec. 20. The lead author is Fumiko Hoeft of Stanford University School of Medicine.
Experts disagree on a precise definition of dyslexia, with the consensus view being that children with dyslexia have difficulty learning to read, despite normal intelligence. Preschool-age children who will go on to become dyslexic often exhibit weakness in analyzing the sounds of language, such as whether or not words rhyme. As they get older, dyslexic children have difficulty associating sounds with letters, and decoding written words. However, around 25 to 50 percent of dyslexic children eventually develop compensatory strategies that enable them to read well enough to do their schoolwork.
Over the past decade, a type of brain scan known as functional magnetic resonance imaging (fMRI) has allowed researchers to learn a great deal about the brain regions that may be involved in dyslexia. However, so far this has not led to any direct benefits for patients, says Gabrieli. “I got interested in how brain imaging could do something that would get you closer to helping people,” he says.
In the new paper, Gabrieli and colleagues studied 25 dyslexic children, all ranging from 11 to 14 years old, as well as 20 normal readers of the same ages. Each subject’s brain was imaged as he or she decided whether pairs of words rhymed.
Two and a half years later, the researchers examined the reading ability of the same dyslexic children. They found that the children who improved the most were those who had the most activity in the right prefrontal cortex and also the strongest white-matter connections in the right prefrontal cortex during the first test (white matter consists of nerve bundles that carry messages from one area to another). The combination of these two brain measures was an even stronger predictor than either one alone. These brain regions were unrelated to reading gains in typical children.
Dyslexic children may be using the right prefrontal cortex, which is believed to be involved in visual memory, to memorize words, says Gabrieli. In contrast, normal readers use the right prefrontal cortex less and less as they move from memorizing words to figuring out words “on the fly” by translating letters into sounds. That task requires language-processing areas located in the left hemisphere.
The role of the extra-strong organization in the right-hemisphere white matter is still a mystery, says Gabrieli. In the left prefrontal cortex, white matter connects language areas. However, it’s not known what the corresponding white matter in the right prefrontal cortex does, or how activity in those areas would help dyslexic children read, says Gabrieli.
The new findings suggest that dyslexic children who overcome their reading difficulties somehow bypass brain regions normally used for reading, says Gabrieli. “It seems like they’re better off using a completely different strategy,” he says.
That could prompt educators to develop new ways of teaching dyslexic students, focusing on the appropriate brain regions, says Gabrieli. “Current interventions try to get kids to use typical approaches to reading. But you may be better off promoting a different approach to reading altogether in older children,” he says. One possibility would be to emphasize a more visual approach, similar to “speed reading,” as opposed to teaching dyslexic children to translate letters into sounds.
“Those children who did not improve might have the most to gain if instructions were developed that took into account alternative reading strategies, instead of trying to get struggling readers to read like good readers,” says Gabrieli. “Those who improved might have discovered on their own what works for them, and those who failed to improve might most be in need of explicit instruction and support to try a different strategy.”
Manuel Casanova, professor of psychiatry at the University of Louisville, says the study’s most important contribution is revealing that the behavioral and intelligence measures commonly used to evaluate a dyslexic child’s chances of improvement — such as IQ tests and standardized reading tests — are not reliable. “The conventional wisdom until now has been behavioral measurements,” says Casanova. “I am blown away by the fact that IQ is not predictive of the ability to improve.”
However, he points out that evaluating children at a younger age, when they are more likely to be able to improve, would be more useful to doctors and educators.
Gabrieli plans to repeat his fMRI study in younger children with dyslexia, and he is also studying the prognostic ability of fMRI in other brain disorders. He is optimistic that fMRI has potential to help doctors select the best treatment for individual patients, not just for dyslexics but those who suffer from many other brain disorders such as depression, anxiety and schizophrenia.