Δυσλεξία και εγκεφαλική ασυμμετρία: ανασκόπηση μελετών ανατομικής και λειτουργικής απεικόνισης

Abstract

Developmental dyslexia is a learning disorder that is marked by reading achievement that falls substantially below that expected given the individual's chronological age, measured intelligence, and age-appropriate education (ICD-10, WHO, 1993). It is estimated to affect 5-17% of the student population. It is a disorder that is neurological in nature (Habib, 2000. Σίμος, Μουζάκη, & Παπανικολάου, 2004), but which requires educational intervention. Recently, there has been considerable progress in the investigation of the neurobiological underpinnings of dyslexia. Yet, even today Orton’s 1925 hypothesis, postulating that individuals with dyslexia have not adequately developedthe typical left cerebral lateralization for language and are symmetrical or right-hemispheric dominant for language, remains timely and is under investigation. The present narrative review presents research studies that have investigated the inadequate lateralization hypothesis using anatomical and functional brain imaging. Findings show, for the largest part, that individuals with dyslexia do indeed show anatomical and functional differences in the language networks of the left hemisphere, compared to typical readers. In conclusion, inadequate lateralization is an important neurobiological factor for the development of dyslexia, albeit it is not the only one.