Dyslexia and the Brain Today

Once mistakenly thought to be unmotivated or unintelligent, people with dyslexia are now understood to have a brain disability that causes difficulties with reading, writing, spelling, and speaking. It doesn’t matter where people are from or what language they learn: the condition affects 15 to 20 percent of the world’s population.

Brain-imaging studies show that, while reading, most people activate areas in the left temporal cortex and other regions of the left hemisphere. Dyslexic readers, on the other hand, underactivate these regions. (Each image shows the left side of the brain.)

The importance of reading skills in modern society puts people with dyslexia in grave danger of falling behind.

• Dyslexia is the most common learning disability, affecting 80 percent of people with such conditions, and is the most common reason for enrolling in special education services.
• Because dyslexia affects language skills, people of all intelligence levels may have it. The stigma associated with it prevents many individuals from seeking help, while others do not receive suitable treatment due to limited resources.
• Children with untreated dyslexia often fall behind in school and are at greater risk for dropping out of high school, failing to go to college, or experiencing chronic unemployment.

Brain researchers supported by the National Institutes of Health and other funding agencies are developing a more thorough understanding of the condition and finding better ways to diagnose and treat it.

Research Brings Greater Understanding

The majority of dyslexia cases involve developmental dyslexia — a condition that begins early in life and lasts indefinitely. (Sometimes people develop dyslexia later because of a brain injury, such as a stroke or lesion.) It is usually detected during childhood or adolescence based on behavioral symptoms such as poor pronunciation, lack of verbal fluency, trouble learning letters or foreign languages, and subpar spelling.

Researchers have found that the condition affects phonological processing, the ability to break words down in units of sound and associate these sounds with words. But much about the exact nature of dyslexia remains uncertain.

Recently, scientists have gained insights into the biological mechanisms of dyslexia using functional brain imaging. Compared to typical readers, groups of dyslexic readers show abnormalities in several brain regions and pathways associated with language (for instance, the left temporo-parietal cortex), including those responsible for "fluent" or automatic reading — the ability to read without thinking about each individual word. Some people also have abnormalities in white matter connections between brain regions, including reduced connections in the back left half of the brain and increased connections between the two hemispheres.

Scientists are refining methods for early detection of dyslexia, in some cases even before reading begins, in order to minimize or prevent reading difficulties. Researchers, for instance, have found that many children who begin speaking later than average have dyslexia more often. In addition to special education and tutoring programs, treatment options include new strategies based on neuroplasticity (the brain’s ability to form new connections) that aim to strengthen basic sensory processing and cognitive skills.