Elsevier

Biological Psychiatry

Volume 57, Issue 11, 1 June 2005, Pages 1301-1309
Biological Psychiatry

Advancing the neuroscience of ADHD
Dyslexia (Specific Reading Disability)

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Converging evidence from a number of lines of investigation indicates that 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, particularly the development of functional magnetic resonance imaging, provide evidence of a neurobiological signature for dyslexia, specifically a disruption of two left hemisphere posterior brain systems, one parieto-temporal, the other occipito-temporal, with compensatory engagement of anterior systems around the inferior frontal gyrus and a posterior (right occipito-temporal) system. Furthermore, good evidence indicates a computational role for the left occipito-temporal system: the development of fluent (automatic) reading. The brain systems for reading are malleable and their disruption in dyslexic children may be remediated by provision of an evidence-based, effective reading intervention. In addition, functional magnetic resonance imaging studies of young adults with reading difficulties followed prospectively and longitudinally from age 5 through their mid twenties suggests that there may be two types of reading difficulties, one primarily on a genetic basis, the other, and far more common, reflecting environmental influences. These studies offer the promise for more precise identification and effective management of dyslexia in children, adolescents and adults.

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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