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."
