Authors: Shaywitz, S. E., Mody, M., & Shaywitz, B. A..
Article: Neural Mechanisms in Dyslexia.
Publication: Current Directions in Psychological Science (Sage Journals). 15(6), 278–281 2006 | DOI: 10.1111/j.1467-8721.2006.00452.x
Within the last two decades, evidence from many laboratories has converged to indicate the cognitive basis for dyslexia: Dyslexia is a disorder within the language system and, more specifically, within a particular subcomponent of that system, phonological processing. Converging evidence from a number of laboratories using functional brain imaging indicates that there is a disruption of left-hemisphere posterior neural systems in child and adult dyslexic readers when they perform reading tasks. The discovery of a disruption in the neural systems serving reading has significant implications for the acceptance of dyslexia as a valid disorder—a necessary condition for its identification and treatment. Brain-imaging findings provide, for the first time, convincing, irrefutable evidence that what has been considered a hidden disability is “real,” and these findings have practical implications for the provision of accommodations, a critical component of management for older children and young adults attending postsecondary and graduate programs. The utilization of advances in neuroscience to inform educational policy and practices provides an exciting example of translational science being used for the public good.
Developmental dyslexia is defined as an unexpected difficulty in
reading in children and adults who otherwise possess the intelligence and motivation considered necessary for accurate and fluent reading and who also have had reasonable reading instruction.
However, during a task using real words, brain-activation patterns in the two groups of disabled readers diverged. In this semantic-category task, subjects are asked to judge, for example, if corn and rice are in the same category (yes, they are both foods) or if lion and tree are in the same category (they are not). During this task, accuracy-improved readers demonstrated the
typical disruption of left-hemisphere posterior systems. In contrast, similar to nonimpaired readers, persistently poor readers activated these posterior systems even though their reading performance was significantly poorer than that of nonimpaired readers on every reading task administered.
Both groups began school with comparable reading scores, but compared to accuracyimproved readers, persistently poor readers had poorer cognitive
(primarily verbal) ability; attended more disadvantaged schools; and tended to come from lower-socioeconomic-status homes. Thus, persistently poor readers resemble those with what is termed general reading backwardness, who tend to have lower cognitive ability and to come from more disadvantaged circumstances, while accuracy-improved readers appear to relate best to dyslexia, where the reading difficulties are unexpected.
Alternatively, accuracy-improved and persistently poor readers may both be genetically vulnerable but the higher cognitive ability, better verbal ability, and, perhaps, exposure to more effective reading instruction may serve as protective factors to help compensate for accuracy-improved readers’ decoding difficulties. Thus, a larger vocabulary and strong reasoning
abilities may help a struggling reader to use the context around an unknown word to figure out its meaning.
To date, most studies have focused on word-level reading; an important next question concerns elucidating and understanding the more complex and distributed neural organization for comprehending connected text. Here, studies using sentence level tasks engaging semantic or syntactic neural systems are beginning to tease apart the components of a cohesive operational system for reading comprehension.
Shaywitz, S. E., Mody, M., & Shaywitz, B. A. (2006). Neural Mechanisms in Dyslexia. Current Directions in Psychological Science, 15(6), 278–281.