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Atypical Brain Activity Detected In People With Dyslexia

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/ADVANCE/ BETHESDA, Md., July 3, 1996 -- Brain imaging studies at the National Institute of Mental Health (NIMH) have revealed dramatic evidence of a deficit in the brain's visual system in people with dyslexia, a disorder that affects the reading ability of millions of American school children and adults. While it has been commonly believed that only the language-related areas of the brain are affected in dyslexia, this study adds to the growing body of research pointing to dysfunction of another portion of the brain known as V5/MT. Using functional magnetic resonance imaging (fMRI), NIH scientists Guinevere Eden, D.Phil., and colleagues demonstrated in a small controlled study of adult males that people with dyslexia showed no activation in the V5/MT brain area, which specializes in movement perception. Dr. Eden's research confirms that people with dyslexia, hobbled by problems with reading, writing, and spelling, have trouble processing specific visual information. "We found that maps of brain activity measured while subjects were given a visual task of looking at moving dots were very different in individuals with dyslexia compared to normal control subjects," said Dr. Eden. The eight control subjects showed robust activity in brain region V5/MT when viewing a moving dot pattern. Almost no activity was present in those areas in people with dyslexia. In fact, a clear finding in all six subjects showing no response in the V5/MT area is a step toward improving the understanding, diagnosis, and eventually, treatment for the disorder. "This research confirms that dyslexia is a discrete brain disorder, not, as some people have believed, a by-product of a poor education or upbringing," said NIMH Director Steven H. Hyman, M.D. Furthermore, if confirmed by additional research, functional brain imaging may be used as a tool for early and accurate diagnosis of this common and disabling disorder. Whether the motion perception deficit uncovered by this study contributes to the reading disability characteristic of dyslexia is still unknown. It is possible that the visual disturbances we found and the reading disturbances others have found may be caused by an underlying, common information processing deficit," said Dr. Eden. According to the research team, the anatomical changes underlying these functional differences are thought to occur during the early stages of development, when regional functional specialization occurs. Abnormal function in the specialized brain area V5/MT explains previously reported visual behavioral problems in dyslexia. The above bold is mine. It sounds good but ignores the reality that external factors such as a visual problem that could be removed with dyslexia glasses very well might have caused the brain to develop differently for some dyslexics. Below ,in my bold, Dr Eden does seem to leave the doorway open for this possibility. This is a long way from statements that dyslexia and vision are not related at all which she has made in the past and have been accepted by many others in the field of dyslexia.  Future research will provide further insights into the details of visual end language deficits and their effects on reading. Dr. Eden's study suggests a broader definition of the underlying mechanisms of dyslexia, thus opening the way for development of special help and effective treatment for more people with the disorder. All of the dyslexic subjects in this study had a childhood history of reading disability, a measurable reading deficit, a discrepancy of at least 2 standard deviations between their reading and verbal IO, and poorer phonological awareness compared to controls, and none had neurological disorders. Normal controls were closely matched to dyslexics in age, education, socioeconomic status, and IQ. The technique of functional magnetic resonance imaging is based on the principle that blood flow, rich in oxygen, increases locally in active areas of the brain. Usually used to obtain information on structural details of the brain, EMRI can also pinpoint regions where oxygenation levels are changing as a result of neural activity. The procedure is noninvasive, as it exploits a magnetic tracer, namely hemoglobin, that is a normal constituent of blood. The study, "Abnormal Processing of visual Motion Processing in Dyslexia Revealed by Functional Brain Imaging," was published July 4 in Nature. Co-authors are Judith M. Rumsey, Ph.D., and Jose Ma. Masog, M.D., of NIMH, Thomas A. Zeffiro, M.D., Ph.D., and John W. VanMeter, Ph.D., of Sensor Systems, Inc., and Roger Woods, M.D., of U.C.L.A. CONTACT: Constance Burr, 301-443-4536, or home, 202-543-1567, or Elaine Baldwin, home, 301-942-3666, of the National Institute of Mental Health

 

During the first four months of life, there is so much happening inside the human brain -- so many cells growing, dividing, and firing, so many structures maturing and taking appropriate shapes, so many important connections being made -- that, according to Dr. Guinevere Eden, "it is almost surprising that you don't actually hear all the commotion inside the infant's head!"

All that brain development is what permits people eventually to read and dance, talk and throw a frisbee. But not everyone can perform all these activities correctly or with ease.

Some people, for example, have difficulties reading. Many of them have a condition called developmental dyslexia. They can run into serious problems at school, at work, and in social situations, because reading is so central to everyday living.

The most common myth about dyslexia is that the affected person mistakes "was" for "saw" and "tip" for "pit." But dyslexia is more complicated than that. "There is a huge language component to dyslexia," says Eden, but, she adds, that is about the only thing that people interested in dyslexia agree upon.

Children with dyslexia describe how the letters and words on the printed page seem to jump around, superimpose themselves on one another, become indistinguishable (b looks like d, for example), or in other ways prove unmanageable. "It's like the words are walking," said one child with dyslexia.

At the end of the 19th century, two doctors in Britain -- a physician working in a school and an eye doctor -- described a condition that they called "congenital word blindness." Children with the condition couldn't read, even though they were of normal intelligence. Soon, another eye doctor proposed that word blindness arose when the area of the brain that was responsible for the "visual memory of words" had not developed properly (1).

In 1928, Samuel Orton, a neurologist in Iowa, described 15 children who shared some unusual quirky characteristics. In addition to confusing the letter b with d and the letter p with q, some could read more easily if they held pages up to a mirror, and a few were rapid mirror writers. Orton proposed that the term "strephosymbolia," which means "twisted symbols," replace "congenital word blindness" to describe their disability. He was optimistic that many of the children could be taught to read with new methods that exploited their other senses -- touch and hearing -- which were not impaired. He suggested that strephosymbolia (which was later dropped as a term and replaced by "dyslexia") might develop when proper connections in the brain did not (1).

The human brain consists of a patchwork of regions that carry out different activities. At least 32 regions (labeled with a "V") are thought to participate in vision. Region V5, for example, seems to be crucial for tracking moving objects; V1 and V2 recognize colors and patterns. A number of studies in recent years have targeted a visual pathway that includes V5 as a trouble zone in people with dyslexia.

Eden and her coworkers have now confirmed this association. They used a technique called functional magnetic resonance imaging (fMRI) to look at brain activities in men with dyslexia and in men with no known reading problems. As the men watched moving dots march around a movie screen, V5 became active only in the brains of those who read normally; the movements did not trigger V5 activity in those with dyslexia. Next, the men were shown motionless dots in various patterns; in this test, V1 and V2 glowed similarly in the brains of all the men, whether they were normal readers or had dyslexia (2).

Eden's dramatic pictures indicate that, indeed, V5 is not working the way it should in men with dyslexia. Can V5 inactivity account for the inability of these individuals to make sense of the flow of words on the written page, or are these independent phenomena?

V5 is part of the broader "magnocellular -- large cell -- system" that processes fast-moving objects. One interpretation is that a specific magnocellular cell type develops abnormally in people with dyslexia (3).

The magnocellular system works together with the "parvocellular -- small cell -- system" to make vision possible (4). The parvocellular system processes patterns and colors. Perhaps their coordination is incomplete or offbeat in dyslexia, so the handling of words is faulty. Whatever the cause of developmental dyslexia, the outcome is tortured or unsuccessful reading.

Developmental dyslexia is a condition said to be "unexpected (5)," because the people with it are smart enough to read and typically have had ample exposure to books and reading instruction. For some, the language difficulties are confined to reading; for others, writing, spelling, and speaking are also problematic (5). Most do not have wide-ranging developmental disabilities.

Lots of people -- kids and adults with dyslexia, their friends and family members (many of whom also have dyslexia), educators, psychiatrists, physiologists, behavioral scientists, policy makers, neuropsychologists -- are interested in dyslexia. They want to know where the problems lie, why they develop, and what can be done about them. Eden and her coworkers now have provided an answer to one of the "wheres."

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