Thursday, April 22, 1999 Published at 07:35 GMT 08:35 UK
Dyslexia linked to nerve damage
Dyslexics have trouble with reading
Dyslexia may be caused by damage to nerve cells in the brain, a scientist has claimed.
Dr John Stein, from Oxford University, has found damage in the optic nerves of dyslexic children, and believes other areas of the brain's nervous system may also be affected.
His controversial idea also appears to account for other trouble experienced by some dyslexic children, such as subtle hearing problems.
Dr Stein, according to New Scientist magazine, also believes that the damage occurs in the brain of the developing foetus and may be caused by the mother's immune system.
Dyslexia sufferers have trouble reading and writing, even though they might be intellectually bright.
Because there is so much natural variability in how fast children learn to read and write, the condition is often not properly diagnosed.
People with dyslexia have no difficulty understanding the meaning of words, recognising individual letter shapes, and seeing anything other than text.
This has led many scientists to say that dyslexia is caused by a specific problem with the language centres in the brain.
He believes that during foetal development, something damages or attacks the vulnerable young nerve cells responsible for relaying information about fast-changing events.
If he is right, this could explain a whole host of other lesser known problems that researchers and people who work with dyslexic children have associated with the condition, such as clumsiness, poor balance and coordination.
To test his theory, Dr Stein asked people to watch two computer screens displaying tiny dots moving around at random.
He found that dyslexics were less likely to spot synchronised movement of the dots than people who were not suffering from the condition.
Dr Stein found that the poorer the ability to spot a change in motion, the worse the reading and spelling.
Large nerve cells
Dr Stein believes that dyslexics suffer from a defect in a set of very large nerve cells known as magno-cells.
These cells rapidly transmit electrical impulses from the retina in the eye to the brain so that it can recognise rapid changes or movement.
Other researchers have shown that the magno-cells in dyslexics operate more slowly than usual, and postmortem examinations have revealed abnormalities in the shape and position of the cells.
The magno-cell defects could make reading difficult because they make it impossible to process the quick eye movements needed to decipher text.
Dr Stein has found that many dyslexics find it difficult to hold their eyes steady between movements, probably because the magno-cells are failing to send proper signals to the brain.
Dr Stein believes that the magno-cells are damaged in the womb by antibodies produced by the mother's immune system which attack the cells and stunt their development.
He believes other nervous pathways governing hearing and coordination may also be affected.