7 - Brain bases of reading disabilities

Summary

Overview: For a century and a half, brain–behavior correlates in language were studied via the lesion approach, in which functional deficits after localized neurological damage are used to deduce the brain's organization. While much of the basic information gleaned from this research tradition still holds and new lesion-based discoveries continue to be made, modern advances with in vivo imaging techniques reveal that language processing in fact recruits many brain areas. In particular, different aspects of spoken and written language, such as orthography and semantics, require different kinds of neuropsychological processing. Given the complex distribution of language-related skills in the brain, the heterogeneity of dyslexic profiles is not surprising. In the end, it is likely that this very heterogeneity will prove key not just to unlocking the true nature of dyslexia but to understanding better the spoken and written language systems themselves.

The Editors

Since the late 1800s, scientists have known that there are specialized brain areas crucially involved in language reception and production, including understanding and producing written language. Reading impairments associated with a condition termed ‘visual word blindness’ were independently reported at the end of the nineteenth century by Scottish ophthalmologist James Hinshelwood and British physician Pringle Morgan (Hinshelwood 1895; Morgan 1896). These are generally considered the first behavioral accounts of the syndrome now called dyslexia. In the 1890s, based on lesion data collected by Monsieur Dejerine in adults, the left inferior parieto-occipital region along with the posterior section of the corpus callosum, called the splenium, were implicated as brain regions playing a special role in this disorder.