ON DYSLEXIA AND FUNCTIONAL DISRUPTION IN BRAIN ORGANIZATION (Proc. Natl. Acad. Sci. US 3 Mar 98)

Dyslexia is impaired reading ability when the reading competence is below that expected from the individual's general intelligence and there is no impairment of vision. It has been proposed that dyslexic children and adults lack phonologic awareness, an awareness that strings of letters (orthography) are connected to corresponding units of speech (phonologic constituents) that they represent. In biology, magnetic resonance imaging is a technique involving images produced by mobile protons of a tissue excited by the application of a magnetic field, and when used in functional cerebral imaging, the basis of the technique is that it images very small metabolic, blood-flow, and perfusion-diffusion changes in vivo, in real time, and with no risk to the subject, with the essential idea of mapping activity in the brain in response to external stimuli or during sensory, perceptual, or cognitive events. ... ...

Now Shaywitz et al (15 authors at 2 installations, US) report a study to find the location and extent of the functional disruption in neural systems that underlies dyslexia. Functional magnetic resonance imaging was used to compare brain activation patterns in dyslexic and nonimpaired subjects as they performed tasks that made progressively greater demands on phonologic analysis. Brain activation patterns differed significantly between the groups, with dyslexic readers showing underactivation in certain specific brain areas and overactivation in other specific brain areas. The authors suggest their results support a conclusion that the impairment in dyslexia is phonologic and that brain activation patterns may provide a neural signature for this impairment.
Sally E. Shaywitz (sally.shaywitz@yale.edu)