Advancing the neuroscience of ADHDDyslexia (Specific Reading Disability)
Section snippets
Definition and History
Developmental dyslexia is characterized by an unexpected difficulty in reading in children and adults who otherwise possess the intelligence and motivation considered necessary for accurate and fluent reading. More formally, “Dyslexia is a specific learning disability that is neurobiological in origin. It is characterized by difficulties with accurate and/or fluent word recognition and by poor spelling and decoding abilities. These difficulties typically result from a deficit in the
Outcome
Deficits in phonological coding continue to characterize dyslexic readers even in adolescence; performance on phonological processing measures contributes most to discriminating dyslexic and average adolescent readers, and average and superior readers as well (Shaywitz et al 1999). Children with dyslexia neither spontaneously remit nor do they demonstrate a lag mechanism for “catching up” in the development of reading skills. That is not to say that many dyslexic readers do not become quite
Neurobiological Studies
To a large degree these advances in understanding the cognitive basis of dyslexia have informed and facilitated studies examining the neurobiological underpinnings of reading and dyslexia. Thus, a range of neurobiologic investigations using postmortem brain specimens (Galaburda et al 1985), and more recently, brain morphometry (Brown et al 2001; Eliez et al 2000; Filipek 1996) and diffusion tensor MRI imaging (Klingberg et al 2000) suggests that there are differences in the
Conclusions and Implications
Within the last two decades overwhelming evidence from many laboratories has converged to indicate the cognitive basis for dyslexia: dyslexia represents a disorder within the language system and more specifically within a particular subcomponent of that system, phonological processing. Recent advances in imaging technology and the development of tasks which sharply isolate the subcomponent processes of reading now provide for the first time, a neurobiological signature for dyslexia: a
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