The Difference between Developmental Dyslexia and Dysgraphia: Recent Neurobiological Evidence

Abstract

Developmental dyslexia and developmental dysgraphia are considered to be distinct learning difficulties that affect the child's ability to learn. Dyslexia affects all aspects of written language, while the symptoms of dysgraphia appear to be confined to difficulties in writing. However, the distinction between the two learning difficulties is often obscured by the similar learning cognitive deficits manifested by individuals diagnosed with these difficulties. The aim of this review is to summarize and evaluate research concerning the neurobiological basis of the two difficulties with a view to assist researchers and practitioners in their classification of individuals with resembling deficits. In so doing, we bring together the findings of studies that have utilized powerful neuroimaging techniques such as functional Magnetic Resonance Imaging (fMRI). The evidence suggests that while individuals with dyslexia and dysgraphia share a left-hemisphere processing limitation resulted from the absence of a scanning mechanism for disembedding, encoding, and rehearsing visual patterns (e.g., words), there are important neurological differences that distinguish the two groups. Specifically, recent neurobiological studies have shown that children with developmental dysgraphia differ from their dyslexic counterparts in white matter integrity, functional connectivity revealed by fMRI, and white matter-gray matter correlations. These differences in the brain between children with developmental dyslexia and children with dysgraphia confirm the neurobiological distinction between these two special learning difficulties. Based on these neurobiological differences researchers and practitioners in the field should exercise special care not to treat the two disorders as the same in their research or professional practice.