Anatomy of the Temporal Processing Deficit in Developmental Dyslexia

Abstract

The acquisition of reading competence requires important environmental input as well as the brain machinery to process a variety of types of information at multiple levels. The development of the architecture of this machinery is under the control of multiple genetic and epigenetic factors. It is not surprising, therefore, that developmental reading disorders could arise from dysfunction in many areas and at many levels. However, it appears that many children who fail to acquire reading competence easily and fully suffer from a specific type of developmental brain anomaly that can affect linguistic and low level auditory and/or visual processing. The present chapter will examine the effects of this anomaly on brain anatomy and behavior and will look at the perceptual and cognitive consequences of minor cortical malformations in the visual and auditory systems, as they relate to reading acquisition. Furthermore, the developmental mechanisms associated with these malformations will be described in the context of other developmental disorders. Finally, etiologic factors leading to the formation of these malformations will be reviewed, including genetic and epigenetic influences acting during the period of neuronal migration to the cerebral cortex. The chapter will take examples from human autopsy studies as well as from studies involving experimental animal models.