Developmental dyslexia: contribution of modern neuropsychology.

In France about 1 million children are thought to present learning disabili ties for reading that in most cases correspond to developmental dyslexias. These are specific and constitutional deficits that prevent rapid and autom atic reading abilities from developing, in spite of a normal intelligence a nd normal visual and auditory acuity. The most frequent form of dyslexia is called "phonological dyslexia" as it results from a deficit of perception and manipulation of phonemes (i.e. "phonological awareness"). Functional ne uro-imaging has great potential for helping understand such functional defi cits that are likely to be caused by microscopic abnormalities such as micr o-polygyria localised in the perisylvian cortex. Tomographic methods have s hown deficits of activation of these cortical areas. Electrophysiological m ethods revealed abnormalities of various events such as MMN or N400, and mo re recently, delayed latencies of earlier markers suggesting deficits of en coding short-lived features of speech signal.