Neurological Models of Dyslexia

Abstract

The reading network is only partially understood and even less is known regarding how the network functions when reading is impaired. Dyslexia is characterized by poor phonological processing and affects roughly 5-12% of the population. The Dorsal-Ventral and Cerebellar-Deficit models propose distinct behavioral and structural differences in young adults with dyslexia. Behavioral assessments were used to determine if deficits for young adults with dyslexia were restricted to the literacy domain or dispersed among reading and associated behavioral domains. Diffusion tensor imaging (DTI) was used determine the extent to which white matter pathways and gray matter regions differ structurally in young adults with dyslexia. The present study also investigated whether brain-behavior relationships exist and are consistent with the theoretical models of reading in this population. Findings show that young adults with dyslexia exhibited deficits in both literacy and associated behavioral domains, including verbal working memory and motor function. Structural findings showed increased fractional anisotropy in the left anterior region (the aslant) and decreased fractional anisotropy in left posterior regions (inferior occipital fasciculus and vertical occipital fasciculus) of the reading network for young adults with dyslexia. Brain-behavior associations were found between the right inferior frontal gyrus and decoding for those with dyslexia. These findings provide support for the use of an altered reading network by young adults with dyslexia, as outlined by the Dorsal-Ventral model of reading. Limited structural and behavior findings support of the Cerebellar-Deficit model of reading, findings that warrant additional investigation.