Dyslexia

Dyslexia

Reading and the brain

How humans read

Causes of dyslexia

Treating dyslexia

Future developments

Resources

Dyslexia is a disorder that falls under the broad category of learning disabilities. It is often described as a neurological syndrome in which otherwise normal people have difficulty reading and writing. Dyslexia is not defined exactly the same by specialists in the United States. However, the key feature in all definitions, whether it comes from the U.S. federal government, the World Health Organization, or other organizations, seems to be the person’s inability to read properly. The word dyslexia is derived from the Greek word dys (meaning poor or inadequate) and the word lexis (meaning words or language). Frequently, dyslexia is defined by what it is not—dyslexia is not mental retardation, a psychiatric or emotional disorder, or a vision problem. Dyslexia is not caused by poverty, psychological problems, lack of educational opportunities, or laziness; those who are identified as dyslectic have normal or above-normal intelligence, normal eyesight, and tend to come from average families.

There are dozens of symptoms associated with dyslexia. In reading and writing, those with dyslexia may skip words, reverse the order of letters in a word (for instance, writing or reading “was” for “saw”), or drop some letters from a word (for example, reading “run” instead of “running”). They may concoct strange spellings for common words, have difficulty remembering and following sequences (like reciting the alphabet in order), and have cramped, illegible handwriting. There is often a gap between what the person seems to be capable of doing and performance;

it is not unusual for a student with dyslexia to earn straight As in science and fail English.

Reading and the brain

Austrian physiologist, medical doctor, psychologist Sigmund Freud (1856–1939) wrote in 1900 that painful childhood experiences or hatred of one or both parents caused dyslexia. He reasoned that children who could not openly rebel against a harsh mother or father defied their parents by refusing to learn to read. Freud recommended psychoanalysis to resolve such emotional problems.

Today, experts reject the psychoanalytic explanation of dyslexia. Sophisticated brain imaging technology known as functional magnetic resonance imaging (fMRI) clearly shows inactivity in a large area that links the angular gyrus—the visual cortex and visual association areas where print or writing is interpreted— to areas in the superior temporal gyrus (Wernicke’s area) where language and phonetics are interpreted. In addition, during phonologic reading tasks, the area associated with spoken language (Broca’s area) showed activation in dyslexic readers where it did not in normal readers. Researchers believe this area may attempt to compensate for impairments in Wernicke’s area.

Investigators have studied those with brain lesions (abnormal growths such as tumors) in Wernike’s area. Although they had no reading difficulties before the lesion was large enough to detect, patients with brain lesions developed reading problems identical to those associated with dyslexia. Those with dyslexia also tend to have rapid, jerky, hard-to-control eye movements when they read—another indication of a misfire in the brain.

How humans read

Reading is a complicated chain of events coordinated in the brain. Imagine a busy, computerized railroad yard: trains pull in on hundreds of tracks from all directions. The cargo of each train is documented in a central tower and, then it is matched with a destination and assigned to one of dozens of tracks. Some trains may be sent to a holding area until their cargo is needed; others may be routed so they can make multiple stops. The computer system must analyze hundreds of pieces of information for each train pulling in, each train pulling out—so even a brief power failure can clog the railroad yard with thousands of trains, blocked from reaching their destination.

Scientists suspect a similar power failure in the brain is the cause of dyslexia. In normal reading, the eye sends pictures of abstract images (the printed word) to the brain. Each symbol is routed to various portions of the brain for processing or storage, symbols are interpreted and combined in combinations that make sense, then transferred to other portions of the brain that recognize the importance of the messages. Sometimes the messages are relayed to the lips, tongue, and jaw—reading aloud—or the fingers and hands—writing.

Investigators have identified three major tracks (routes) for sending written messages to the brain for interpretation. The phonic route recognizes individual letters and, over time, builds a list of groups of letters that generally appear together. The direct route is a mental dictionary of whole words recognized as a unit; the lexical route breaks strings of letters into a base word, prefixes, and suffixes. The lexical route might, for example, break the word together into “to-get-her.” The areas of the brain are responsible for channeling words along these different routes, processing them, and then moving them along as a message that makes sense. They must coordinate thousands of pieces of information in normal reading. These bits of information are moved through the brain over neurons, the roadways of the nervous system, on neurotransmitters, naturally occurring chemicals that make it possible for messages to travel from one nerve cell to the next. In dyslexia, something jams the signals in the brain and interferes with the interpretation of the written word.

Causes of dyslexia

Researchers generally agree that genetics play a role in dyslexia. Studies of twins show that if one twin is dyslexic, the other is far more likely to have the disorder. Other studies show that dyslexia, that affects about 8% of the world population, tends to run in families. It is common for a child with dyslexia to have a parent or other close relative with the disorder. In the United States and England, about 10% of the population has dyslexic tendencies, where about 4% are severe and the other 6% are moderate in nature. In the United States, the major cause of illiteracy is dyslexia.

Because dyslexia affects males far more often than females (the rate is about three to one), investigators are exploring the relationship of male hormones to dyslexia. Several studies indicate that an excess of the male hormone testosterone prior to birth may slow the development of the left side of the fetus’s brain. Other researchers argue, however, that those with dyslexia rarely have problems with spoken language, which is also controlled by the left side of the brain and depends on some of the same areas that control reading and writing.

Treating dyslexia

Those with mild cases of dyslexia sometimes learn to compensate on their own, and many with dyslexia reach remarkable levels of achievement. Leonardo Da Vinci (1452–1519), the famous Renaissance inventor and artist who painted the Mona Lisa, is thought to have been dyslexic; so was German–American physicist Albert Einstein (1879–1955).

The severity of the disorder, early diagnosis, and prompt treatment seem to be the keys to overcoming the challenges of dyslexia. Linguistic and reading specialists can help those with dyslexia learn how to break reading and writing into specific tasks, how to better remember and apply reading skills, and how to independently develop reading and writing skills. Studies with community college students indicate that intensive sessions with a specialist significantly increase a student’s reading and writing skills, and experts believe earlier intervention is even more effective.

Although dyslexia occurs independently, it can spark social, behavioral, and emotional problems. Children with dyslexia may be frustrated by their inability to understand and embarrassed by their failure in the classroom. They may perceive themselves as stupid and develop problems with self-esteem and motivation.

Future developments

There is no cure for dyslexia, however, skilled specialists are using phonics, self-esteem techniques, and sequencing to reduce the severity of the problem. Researchers are also exploring the use of various drugs

KEY TERMS

Angular gyrus— A portion of the brain directly related to reading, located in the left side of the brain.

Frontal lobe— A portion of the brain that controls planning, problem solving, and writing. Broca’s area (the part of the brain that coordinates the movements of muscles used in speech) is located in the frontal lobe.

Occipital lobe— The portion of the brain that accepts visual signals and combines and interprets them.

Wernicke’s area— The portion of the left side of the brain that stores and retrieves words and word patterns.

known to affect chemical activity in the brain. Although MRI can not yet be used as a diagnostic tool, its use has proven the neurobiologic root to dyslexia and may help in devising methods of treatment.

Resources

BOOKS

Mortimore, Tilly. Dyslexia and Learning Style: A Practitioner’s Handbook. London, UK: Whurr, 2003.

Pollock, Joy. Day-to-day Dyslexia in the Classroom. London, UK, and New York: RoutledgeFalmer, 2004.

Shaywitz, Sally E. Overcoming Dyslexia: A New and Complete Science-based Program for Reading Problems at any Level. New York: Vintage Books, 2005.

Smythe, Ian, John Everatt, and Robin Salter, eds. International Book of Dyslexia: A Guide to Practice and Resources. Hoboken, NJ: Wiley, 2004.

OTHER

The International Dyslexia Association (IDA). “Home page of IDA.” <http://www.interdys.org/> (accessed October 9, 2006).

A. Mullig