Why reading is so difficult
Dyslexia is a learning disorder that affects the ability to read, write, spell and/or use numbers. With modern imaging methods, clear differences between the brains of dyslexics and controls could be identified. Researchers at Yale University and the University of Texas Medical School have presented a detailed map of the dyslexic brain showing which areas are responsible for the disorder (Proceedings of the National Academy of Sciences, March 3, 1998). With the help of magnetic resonance imaging, which shows in high-resolution images which areas of the brain are active while the test person has to solve a task, they were able to compare the activity patterns of people who have dyslexia and non-disordered controls.
The words of the spoken language are made up of individual sounds, the phonemes. During the hearing process, the brain automatically recombines these sounds into words - a process that occurs eight to ten times a second in normal conversations. Dyslexics have difficulty translating the process to printed text. In the English language, the 26 letters of the alphabet, alone or in combination, represent the 44 phonemes of spoken English. Dyslexics cannot make a proper connection between the letters, the sounds and the words.
Sally E. Shaywitz of Yale University and her colleagues studied 29 dyslexic and 32 normal readers. She presented subjects with increasingly difficult tasks and tracked brain activity during phonological analysis. In order not to be deceived by pure memory skills with known words, she also had nonsensical words that rhyme - like "lete" and "jeat" - read.
During the tasks, a large area at the back of the brain was less active in the dyslexic than in the control group. This region connects the visual cortex to the parts responsible for language (superior temporal gyrus, Wernike's region). In contrast, increased activity was recorded in the front section. This part, known as the Brocas Region, is associated with the spoken language. The activity did not increase in the controls. Shaywitz suspects that dyslexics try to compensate for their dysfunction in one part of the brain by doing something else.
The results confirm previous results for alexia, an acquired reading disorder caused by tumor, injury or stroke.
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