Functional MRI Studies View Dyslexia in Action

Dyslexia is a specific learning disorder that affects a person's ability to read. It is the most common learning disability in the United States. Some researchers feel that dyslexia may affect as many as 20% of all Americans; historically approximately 6% of school-age children have been estimated to have dyslexia.

Dyslexia affects people of all occupations and economic circumstances. Albert Einstein, Thomas Edison, stockbroker Charles Schwab, and actor Tom Cruise have been suspected to have dyslexia, although careful historical analyses of some of these cases have suggested different causes for their learning struggles. Scientists know that people with dyslexia have difficulty understanding language sounds, recognizing words in print, and spelling accurately. What is not known are the precise problems within the brain that cause dyslexia.

fMRI Studies the Learning Brain
Currently, scientists are trying to understand those problems by conducting a variety of studies. Functional magnetic resonance imaging (fMRI) studies of multisensory processing in people with dyslexia are helping to provide a better understanding of how the brain functions in a person with dyslexia. One such study has been ongoing at the Medical College of Wisconsin for the past three years, under the direction of Jeffrey R. Binder, MD, Professor of Neurology at the Medical College. Robert F. Newby, PhD, Associate Professor of Neurology at the Medical College, has also been on the research team.

Using fMRI, which is painless and non-invasive, Dr. Binder and colleagues study computer-generated images of the brains of dyslexic and non-dyslexic children as they make use of language (phonological) sounds to process language. The research team observes the children, asking them to respond via the push of a button to different sounds that test phonological skills essential to reading. These include an understanding of the sound structure of language and the silent sounding-out of printed words for storage in working memory.

The brain images revealed by studies using fMRI show that people with dyslexia seem to process language information in a different area of the brain than people who do not have dyslexia. "The left hemisphere of the brain is better at perceiving and recognizing and classifying events, especially speech sounds," according to Dr. Binder. "Auditory characteristics of speech change very rapidly. That turns out to be important for learning to read because, if the different speech sounds are not characterized well enough by the brain, it is hard for the person to learn to associate different sounds and different words," he said.

Language Processing is Likely Key
Scientists across the US conducting similar research are beginning to arrive at some conclusions. "There is beginning to be a convergence of opinion on what is going on with the brains of people with dyslexia," said Dr. Newby, who also conducts neuropsychological evaluations of many children with dyslexia. "There are two themes, but most of the research centers are finding that the brain processing difficulty is a language processing problem. And most research indicates that the left hemisphere of the brain is involved, but it is still a matter of scientific debate. There continue to be some investigations about other processing functions such as vision," he said.

The imaging studies have provided much-needed information for those who develop treatments for dyslexic readers. "It is very clear from many good studies that the majority of children who are at risk for dyslexia display certain symptoms or risk markers. The symptoms can include delayed speech, slowness to develop knowledge of the alphabet, and the mixing up of sounds in multisyllabic words, such as 'aminal' vs. 'animal'," Dr. Newby said.

Early Identification, Training Can Boost Reading Skills
If risk markers can be identified early enough, the worst effects of dyslexia can be prevented by appropriate intervention in pre-school or early elementary school. "When children receive sufficient training, they become normal or close to normal readers. If early intervention, such as traditional phonics training, would be used to treat these children, some researchers believe that 95% of cases could be alleviated," Dr. Newby added.

On the other hand, if the problem is not treated, reading difficulty is likely to persist into adulthood. "If you have a five-year-old child who has a certain degree of dyslexia and they receive a certain number of hours of phonemic awareness training, they will make a certain gain. If you wait four years, it takes four times as many hours. That is why early intervention and early identification are so important," he explained.

Over the last five years or so, a lot of attention has been directed toward training people to recognize special sounds. "Other training strategies are aimed at solidifying a child's concept of the parts that make up a word. The emphasis on phonetics seems to be very effective. The more time spent in reading programs, the more effective they are," Dr. Binder said.

While research is not yet conclusive, dyslexia is most likely genetic in origin, according to Dr. Newby. "If one parent or other immediate family member is dyslexic, there is increased risk that at least one of the children is dyslexic. Because dyslexia is likely to be caused by multiple genes, actual genetic tests and genetic markers are still being researched," he said.

"We believe that not all children with dyslexia have the same problem. Some have auditory problems; some have other problems," Dr. Binder said. "What we are discovering is that dyslexia is probably not one condition, but a number of conditions. Imaging studies will be the key to understanding dyslexia."

JoAnn Petaschnick
HealthLink Contributing Writer

This article includes information from the National Institutes of Health.