Biology 202, Spring 2005
Second Web Papers
On Serendip

Both genetic and neurodevelopmental factors play a role in the manifestation of key symptoms of dyslexia in children (1). Adults can develop dyslexia as a result of brain injury later in life, however the true disorder of developmental dyslexia stems from an initial disruption in brain function during development. Key symptoms of dyslexia include reversals, elisions or omissions of letters, slow or hesitant reading, and incorrect order of syllables in word or words in a sentence (4). These symptoms stem from an apparent insufficiency in the phonological component of language; the function of sounds within a language. Dyslexic individuals cannot make the innate connection that specific letters or groups of letters relate to individual sounds of spoken language (2). A person with dyslexia can possess a completely normal and well-developed vocabulary and understand the definition of many words; however their brain cannot perform an important step in the process of reading thereby preventing the connection of a written word with a spoken word from their vocabulary bank.

The process of reading contains two important steps in normally functioning readers; decoding and identification (2). The process of decoding involves recognizing individual phonemes in words and connecting them to the spoken sounds that they represent. Once a word has been decoded a normal individual can then identify the word and connect it to its meaning which is stored in a knowledge "bank". In the case of a dyslexic child, a breakdown occurs in the decoding process therefore no connection can be made between the phonemic pieces of words and their corresponding sounds (2). A deficiency in decoding prevents the identification of a word as a recognizable part of stored language. For example, a dyslexic individual can know the meaning of a certain word, however they will not be able to decode that word as it is written and therefore cannot connect the printed word to his or her definition. Many researchers believe that this breakdown occurs because the process of speech and connecting definitions to the sound of language is natural, while reading is a complex process that must be taught (2).

Phonological processing can be found in the left hemisphere posterior brain system, and it is in this area that a disruption of activity can be found during reading. Recent studies have used functional magnetic resonance imaging to measure changes in blood flow to brain and metabolic activity to map brain function and activity patterns during phonological tasks(2). As predicted the patterns and location of brain activity vary among nonimpaired readers and dyslexic individuals. A positive correlation was found to exist between a child's reading skill and the amount of activation in the left occipito-temporal word form area, while a negative correlation was found to exist between the amount of activation and reading skill in the right occipito-temporal word form region (2). In other words, the more activation present in the right occipito-temporal region while reading the more likely it is that a person possesses poor reading skills and is using other areas of their brain to compensate.

Much research has been conducted to determine whether or not reading intervention or therapy can help dyslexics with word recognition and decoding. The effectiveness of the intervention would thereby prove whether or not the language areas responsible for dyslexia are malleable enough to be altered in order to create more normal activity levels for the improvement of reading. Teaching techniques that focus on phonologically based intervention such as multisensory intervention have been found to produce increased reading ability and also changes in the brain corresponding to the improvement. The International Dyslexia Association purports multisensory intervention which uses visual, auditory, and tactile cues to improve the ability of the brain to trigger memories of specific letters or patterns to their assigned sounds (3). This treatment aims to create more connections and activity in the normal areas of the brain associated with reading, thereby increasing recognition ability. Findings show that not only does phonologically based intervention increase reading proficiency it also increases activity in key areas of the brain. Children not only increase this activity during intervention but are able to maintain it after the fact (2). This leads researchers to believe that these areas of the brain are particularly malleable and can be trained to function in a more desirable manner.

References

1) Hynd, George W. "The Dyslexic Brain." Science 263 (1994): 841-842.

2) Shaywitz, Sally E., Bennet Shaywitz. "Dyslexia (Specific Reading Disability)." Society of Biological Psychiatry 2005.

3)The International Dyslexia Association

4)Dyslexia Online

5) Witelson, Sandra F. "Developmental Dyslexia: Two Right Hemispheres and None Left." Science 195 (1977): 309-311.


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