Written by: Maya Lebowitz
Image from dana.org
Dyslexia, a neurobiological disorder, is associated with difficulty in processing the orthography (the written form) and phonology (the sound structure) of language, but it does not affect general intelligence. Some misconceptions about the cause of dyslexia are poverty, developmental delay, and learning a second language. Neuroimaging studies have revealed that dyslexics’ brains have concrete structural differences.
Dyslexia affects the development of the left temporal lobe, which is located just behind the ear. Magnetic resonance imaging (MRI) scanners, which can photograph the brain, allow for a more specific understanding of the anatomical distinctions in dyslexic brains. The brain is made up of two types of material: gray matter and white matter. Gray matter is mostly composed of nerve cells, and its primary function is to process information. Meanwhile, white matter is found in the deeper structures of the brain and consists of connective fibers covered in myelin. White matter is also responsible for information transfer around the brain. The coating facilitates communication between neurons.
In 2001, upon investigating the communication between neurons, researchers James R. Booth Phd and Douglas D. Burman Phd, found that dyslexics have less gray matter in the left hemisphere of their brain than those that are not dyslexic. This deficiency could cause the problems with the sound structure of language. Additionally, scientists have revealed that many people with dyslexia also have less white matter in corresponding areas as non-dyslexic individuals. This is important because more white matter is correlated with enhanced reading skills.
Laurie Cutting, a human development educator at Vanderbilt University, illustrated the disadvantages of decreased white matter: “When you are reading, you are essentially saying things out loud in your head. If you have decreased white matter integrity in this area, the front and back part of your brain are not talking to one another. This would affect reading because you need both to act as a cohesive unit.” Other structural analyses of the brain have concluded that while most brains of people who are not dyslexic are asymmetrical, with the left hemisphere being larger than the same area on the right, Heim and Keil (2004) found that people with dyslexia are symmetrical (right equals left) or asymmetry in the other direction (right larger than left). Although research to detect the exact cause of dyslexia is ongoing, current data suggests that there are clear differences in the structure of the dyslexic brain which adversely impact reading and spelling.
While structural differences are important, understanding the dyslexic brain requires understanding how it functions. In 1996, functional magnetic resonance imaging (fMRI), a noninvasive method that measures physiological signs of neural activation, was first used to study dyslexia. fMRI uses a strong magnet to pinpoint blood flow, the technology has been widely used to study the brain’s role in reading, phonology, orthography and semantics. The technique is functional because patients are asked to perform tasks; thus, what is being looked at is a functioning brain. Several studies that compared the brain activation patterns of readers with and without dyslexia using fMRI, have found potentially important patterns of differences. While dyslexics have underactive areas where they are weaker, in order to compensate, they have overactivation in other areas.
The results of studies conducted worldwide suggest that altered left-hemisphere areas, including ventral occipito-temporal, temporo-parietal, and inferior frontal cortices (and their connections), confirm the universality of dyslexia across different world languages. Researchers are investigating how genes associated with dyslexia might affect development of and communication among regions of the brain by using animals that have been bred to have genes. Differences in brain anatomy and brain function have been observed in people who carry dyslexia-associated genes, even in those who have good reading skills. At the anatomical, physiological, and molecular levels researchers are trying to find the exact chemical connection to dyslexia. Using a MRI-based technique, spectroscopy, brain metabolites that play a role in allowing neurons to communicate can be visualized. There are several metabolites that are thought to be different in people with dyslexia. In other words the brain of a dyslexic has a different distribution of metabolic activation than the brain of one who does not when performing the same language task. This is because there is a failure of the left hemisphere rear brain systems to function properly when reading.
Dyslexic’s brains have structural and functional differences than those that do not. This can cause a lot of challenges for those with dyslexia. In order to compensate, many dyslexics show greater activation in the lower frontal areas of the brain. This means that while dyslexics might have trouble reading they are often talented in other areas such as seeing the bigger picture, improved pattern recognition, sharper peripheral vision, highly creative, and have strong spatial relationships, all of these things use the right side of the brain. While dyslexia makes some aspects of learning more difficult, the differences in a dyslexics brain give them a different perspective of the world.
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