Dyslexia: What Brain Research Reveals About Reading
By: Society for Neuroscience
Making a difference today
A staggering 5 to 15 percent of Americans—14.5 to 43.5 million children and adults—have dyslexia, a learning disability that makes it difficult to read, write, and spell, no matter how hard the person tries or how intelligent he or she is. For years—until advances in neuroscience helped reveal a biological basis for the disorder—people with dyslexia were called "dumb" or "lazy." We now know such labels to be cruelly inappropriate. People with dyslexia can be just as bright and motivated as their nondyslexic peers. They also can be found in all economic and ethnic groups.
In a world where reading and writing skills are in increasing demand, the impact of dyslexia on individuals—and on U.S. society—can be devastating. About 80 percent of learning disabled children eligible for special education services have significant reading difficulties, including dyslexia. According to the National Center for Education Statistics, the high school dropout rate for students with learning disabilities is more than twice what it is for other students (36 percent compared with 14 percent). One study is currently tracing individuals from age 5 to their late 20s and will look at the costs of dyslexia to society as a whole, especially in terms of intervention costs and employment opportunities.
Research brings greater understanding
During the last two decades, scientists have come to learn that the nature of dyslexia is very complex. The difficulties observed in reading arise from a core deficit in phonological awareness, a skill that is needed to associate spoken words with written language. Dyslexics have difficulty sounding out words as well. Approximately 80 percent of children who have delayed language development go on to have reading, writing, and spelling deficits. Research studies also have identified differences in the processing of visual and auditory information in dyslexic readers.
Our understanding of dyslexia exploded in the 1990s after the availability of functional brain imaging, a technology that allows scientists to observe the brain at work as a person reads, speaks, or processes phonological features of language. While watching brain images of volunteers as they attempted to transcribe letters into sounds, NIH-funded scientists found conclusive evidence that the areas in the brain that process written language work differently in people with dyslexia. Scientists are now isolating and mapping the many "reading pathways" in the brain involved in dyslexia. The identification of these pathways may lead to earlier and more effective interventions. Researchers also have uncovered evidence that specific regions of the human genome are involved in a number of reading-related processes within the brain. Such findings help to explain why dyslexia tends to run in families. Similarly, family genetic studies show a high concordance between oral and written language disorders in affected family members.
Earlier and better interventions
Early intervention is key to helping people with dyslexia learn to read and write well. Studies have shown that 74 percent of children who display reading problems in the third grade will remain poor readers into adulthood unless they receive special instruction on reading and phonological awareness. Many intervention methods are currently in use, and more studies need to be done to determine which interventions work best. With NIH funding, researchers are examining which methods might help the millions of Americans struggling with dyslexia and are using brain imaging technology to discover the biological mechanisms by which reading gains are achieved.
- A better understanding of the biological and genetic nature of dyslexia.
- Earlier diagnosis of dyslexia and prevention of reading disabilities.
- More effective and precisely targeted intervention treatments.
Making a difference tomorrow
During the past two decades, scientists have made remarkable advances in understanding the biological and genetic nature of dyslexia. They have also gained greater knowledge about the impact of environmental factors—particularly how children are taught to read—on the disorder. But myths and misunderstandings about dyslexia persist, causing many children—and adults— with this disability to remain undiagnosed and untreated, often with devastating results.
- As many as 43.5 million Americans may have dyslexia. Dyslexia occurs among people of all economic and ethnic backgrounds.
- About 3.5 percent of American students—slightly more than 2 million children—are receiving special educational services for a reading disorder.
- Dyslexia is the most common cause of reading, writing, and spelling difficulties.
- Youth with untreated dyslexia are more likely than their nondyslexic peers to drop out of high school and become unemployed, underemployed, or incarcerated.
Research equals hope for the future
Now that scientists have established that people with dyslexia have a glitch in their neurological wiring that makes reading extremely difficult for them, they are actively searching for a deeper understanding of how that wiring becomes disrupted. One line of study is looking at whether immune proteins in the brain may somehow cause the wiring to go awry. Researchers will also need to examine the role of hormones and neurotransmitters (chemicals that transport messages between nerve cells) in studies of the reading brain. In addition, genetic research into dyslexia continues at an exciting pace. Scientists already have found gene markers for dyslexia on several chromosomes. Knowledge of the genetic and possible biochemical causes of dyslexia will help experts more accurately diagnose—and treat—at-risk children. Using brain imaging technologies, researchers also hope to scientifically determine which types of reading methods and interventions are most effective in helping dyslexic children. Some studies suggest that certain types of intensive reading instruction, if offered early enough, may actually rewire the brain, causing the neurological factors that trigger dyslexia to be ameliorated or circumvented.
Hope for other disorders
Research into dyslexia could help solve many other neurological puzzles. Studies estimate that between 20 and 40 percent of people with dyslexia also have attention deficit/hyperactivity disorder (ADHD). Some dyslexics also suffer from poor math skills. Research tools available to neuroscientists studying dyslexia and its related conditions may also help explain neurodegenerative diseases such as Parkinson’s disease and multiple sclerosis. In addition, recent studies demonstrate that scientifically based reading interventions are able to rewire the dyslexic brain, giving scientists valuable insights into how to develop treatments to help the brain relearn tasks after a stroke or other brain injury.
Dyslexia is a lifelong reading disorder that can have a disastrous impact on a person’s self-image and ability to live up to his or her potential. With continued NIH funding for basic and clinical research, the future could bring more effective methods of diagnosing and treating dyslexia—and thus hope to millions of Americans who struggle daily with this disabling learning disorder.
- The discovery of a biological basis for dyslexia.
- The ability of scientists to identify with a high degree of accuracy those children who have dyslexia.
- The development of special therapies that can help people with dyslexia overcome some of their reading and writing difficulties.
Reprinted from Brain Research Success Stories, Society for Neuroscience, 2004.