Developmental dyslexia: gray matter abnormalities in the occipitotemporal cortex

Functional neuroimaging studies have consistently demonstrated less activation of the left occipitotemporal cortex in dyslexic readers. This region is considered critical for skilled reading and damage to it in adult readers leads to severe deficits in reading ability. In contrast to these findings, structural abnormalities in the occipitotemporal cortex were not consistently found to date. We used optimized Voxel Based Morphometry with T1 weighted MR images to investigate gray matter volume in 13 dyslexic and 15 nonimpaired reading adolescents (age 14-16). Less gray matter volume for dyslexic readers was found in the left and right fusiform gyrus, the bilateral anterior cerebellum and in the right supramarginal gyrus. Decreased gray matter volume in the left and right fusiform gyrus of dyslexic readers highlights the importance of this brain region for developmental dyslexia. The structural abnormalities in the right occipitotemporal cortex suggest that dyslexia may be such a persistent disorder because an occipitotemporal reading area, critical for skilled reading, cannot develop in any hemisphere. The extended areas of reduced gray matter volume in dyslexic readers in the cerebellum suggest that structural abnormalities in the cerebellum are also strongly associated with dyslexia and warrant further investigation.