Developmental dyslexia, neurolinguistic theory and deviations in brain morphology

Abstract

Although some form of central nervous system involvement is presumed, evidence establishing a relationship between dyslexia and neurological dysfunction has been correlational. Recently, neuroimaging and postmortem studies have begun to provide direct evidence implicating neuropathological structures in dyslexia. This article reviews computed tomography (CT) and magnetic resonance imaging (MRI) studies examining deviations in brain morphology which appear to be associated with neurolinguistic functioning. Methodological and technical issues are discussed. Based on their own and others research, the authors conclude that dyslexies show variations in specific brain regions, namely, reversed or symmetrical plana temporale (L ≤ R), smaller insular length bilaterally, and symmetrical frontal regions. Moreover, recent studies by the senior author and colleagues suggest that specific reading tasks are associated with specific variations in brain morphology. Symmetrical frontal widths was related to poorer passage comprehension, and reversed frontal area symmetry was related to poor word attack skills. Though many conceptual and technical issues remain unresolved, neuroimaging procedures appear to provide direct evidence supporting the importance of deviations in normal patterns of brain morphology in dyslexia.