dysTalk What Causes Dyslexia - Talks - dysTalk

About the speaker: John Stein is a professor of neuroscience in Oxford University Medical School. He is particularly interested in the auditory and visual perceptual impairments suffered by dyslexic children.

Further information about this Talk

Key Points Covered in This Talk:

The Impairment of Magnocells: 

• The Genetic Cause: People inherit genes (we think there are at least nine genes) that give you a vulnerability to problems with reading. Those genes cause a problem with the development of a particular kind of nerve cell in the brain that is important for reading. These nerve cells are called magnocells. They are important for timing visual events and timing auditory events (for instance the sounds in speech). The cells are impaired in people with dyslexia, ADHD, developmental dyspraxia, developmental dysphasia (otherwise known as specific language impairment), autism spectrum disorders and recently have been shown in schizophrenia and possibly manic depressive psychosis. What this is saying is that there is a system of nerve cells in the brain that, if they are impaired in their development, give you a vulnerability to any one of these conditions. Most common of these is dyslexia. The impaired magnocells are not the only cause of dyslexia, there has to be other problems as well.
• Nutrition of The Brain: Contributing to dyslexic problems are problems with the nutrition of the brain. Essential fatty acids (derived from fish oils) constitute around 20% of the makeup of the brain. Unfortunately, nowadays, we eat very little fish. This creates a problem because the essential fatty acids that come from fish oils and are incorporated in the brain are moved in and out of the membranes and other places in the brain, and if you don't replace them then the workings of the brain are impaired and be part of the cause of dyslexia. This is why it is often suggested that people with dyslexic or ADHD problems are actually given supplements of these essential fatty acids.
• The Immune System: This is another contributing factor that causes dyslexia. We know that all these conditions are associated with what are called auto-immune problems, such as allergies, eczema, hay fever. It is probable that a related system to the one that controls your immune system is the one that controls the development of this particular kind of nerve cell. For instance we know that mothers produce anti-bodies to these magnocells and if you inject these antibodies into pregnant mice, the offspring of the mother will develop incoordintation and the symptoms that are related to what happens to people with dyslexia.

Why These Magnocells Are important:

Magnocells are very important for the focusing of attention. Not only visual attention, but also auditory attention.

• Auditory Attention: If you are listening to someone speaking and you want to understand them, what you have to do is hear the sounds that they are producing and order them in your mind. That means focusing your attention on each of the sounds as they come out and that enables you to understand it. People with developmental dysphasia or specific language impairment often have a problem picking up the order of sounds. This leads to a problem with auditory memory, so they have problems with hearing the order of the sounds. If you read non-words (e.g. flagistafwop) to children with these problems they simply would not be able to repeat it back. Non-word repetition is a good sign of this particular problem. This is also found in many people with dyslexia. Therefore you need to be able to focus your auditory attention in order to sequence sounds properly and many dyslexic and dysphasic children have a problem with their auditory magnocellular system.
• Visual Attention: This relates very much to reading. Here what you have is a problem with focusing your attention and hence your eye control on the letters you are reading. If you want to read the word "dog" you have got to be able to focus on the "d" then the "o" and then the "g" in the right order. If your attention and eye movements are less steady than they should be, you might not know that when you are looking at the "d" you're looking at the "d" or you might think the "g" is where the "d" is. You therefore might make the mistake of misreading "god" for "dog" or "was" for "saw" and make letter transpositions. This is very characteristic of beginning readers but goes on a lot longer in dyslexics. This is because the visual magnocellular system is impaired in dyslexics.