What Are the Effects of Dyslexia on the Brain?

Andrew Kirmayer

People with dyslexia have trouble with reading words and understanding language. Word recognition and the ability to relate letters and sounds are compromised to varying degrees depending on how severe the condition is. The effects of dyslexia on the brain are mostly found in the left hemisphere, where distinct regions control speech, reading, and language processing. By using medical imaging techniques, differences in the amount of material in certain parts of the brain can be seen in people that are dyslexic. Brain specialists focus on areas of the brain where words are decoded and processed during reading.

"Happy Days" actor Henry Winkler, who played Fonzie, is a popular celebrity who was diagnosed with dyslexia.
"Happy Days" actor Henry Winkler, who played Fonzie, is a popular celebrity who was diagnosed with dyslexia.

Dyslexia on the brain is analyzed by comparing the amount of white and gray matter to normal brains. The outer layer of the brain is made up of gray matter in which nerve cells process all of the information coming in from the senses. White matter found deeper inside are designed for fast communication between different parts of the brain. Those with dyslexia tend to have less of both gray and white matter in the left parietotemproral area, where words are decoded. One of the symptoms of dyslexia includes not being able to understand the sound of words, which could arise from the structural differences in this part of the brain.

Medical techniques such as functional magnetic resonance imaging (fMRI) can analyze the brains of children with signs of dyslexia. The effects of dyslexia on the brain can be seen with images that show lower levels of activity in places that control reading and language ability. In addition to structural differences from the normal brain, seen in computerized axial tomography (CAT) scans and positron emission tomography (PET), variations in metabolic processes are related to dyslexia on the brain. Also, the rear left parts of the brain are less active, but the frontal areas on the left side compensate with more activity than normal.

By studying effects of dyslexia on the brain, and seeing how activities such as juggling and playing musical instruments can physically change it, researchers are finding new treatment options. The ability of the brain to compensate when one hemisphere is removed has also made dyslexia treatment more optimistic, because the structure of the brain can change even in adults. Certain kinds of therapy can stimulate regions where the effects of dyslexia on the brain are present. These can help someone with the condition to compensate for his or her reading and language problems.

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