The following articles, written by Drs. Sally and Bennett Shaywitz, further detail their scientific discoveries in the neuroscience of dyslexia. Each one is available for download in PDF format.
Neural Mechanisms in Dyslexia
by Sally E. Shaywitz, Maria Mody, and Bennett A. Shaywitz
ABSTRACT: 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 post-secondary 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.
Age-Related Changes in Reading Systems of Dyslexic Children,
by Bennett A. Shaywitz, MD, Pawel Skudlarski, PhD, John M. Holahan, PhD, Karen E. Marchione, RN, R. Todd Constable, PhD, Robert K. Fulbright, MD, Daniel Zelterman, PhD, Cheryl Lacadie, BS, and Sally E. Shaywitz, MD.
Objective: To examine age-related changes in the neural systems for reading in nonimpaired and dyslexic children and adolescents.
Methods: Functional magnetic resonance imaging was used to study age-related changes in the neural systems for reading in a cross-sectional sample of 232 right-handed children 7 to 18 years of age (113 dyslexic readers and 119 nonimpaired readers) as they read pseudowords.
Results: In nonimpaired readers, systems in the left anterior lateral occipitotemporal area developed with age, whereas systems in the right superior and middle frontal regions decreased. In contrast, in dyslexic readers, systems in the left posterior medial occipitotemporal regions developed with age. Older nonimpaired readers were left lateralized in the anterior lateral occipitotemporal area; there was no difference in asymmetry between younger and older dyslexic readers.
Interpretation: These findings offer a possible neurobiological explanation for the differences in reading acquisition between
dyslexic and nonimpaired readers and provide further evidence of the critical role of the left occipitotemporal region in the development of reading.
Neural Systems for Compensation and Persistence: Young Adult Outcome of Childhood Reading Disability
Sally E. Shaywitz, Bennett A. Shaywitz, Robert K. Fulbright, Pawel Skudlarski, W. Einar Mencl, R. Todd Constable, Kenneth R. Pugh, John M. Holahan, Karen E. Marchione, Jack M. Fletcher, G. Reid Lyon, and John C. Gore
Introduction: 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. It represents one of the most common problems affecting children and adults; in the United States, the prevalence of dyslexia is estimated to range from 5% to 17% of school-age children (Shaywitzes, 1998). There is now a strong consensus that the central difficulty in dyslexia reflects a deficit within the language system and, more particularly, in a lower level component, phonology, which has to do with the ability to access the underlying sound structure of words (Shaywitz, 1998; Shaywitz, 1996; Wagner and Torgesen, 1987). In young school-age children, a deficit in phonology represents the most reliable and specific correlate of dyslexia (Fletcher, et al., 1994; Morris et al., 1998). Such findings form the basis for the most successful and evidence-based interventions designed to improve reading (Report of the National Reading Panel, 2000).
In this study, we wanted to learn whether and how two groups of young adults who were poor readers as children, a relatively compensated group and a group, with persistent reading difficulties, differed from nonimpaired readers. In addition, we wanted to determine if there were any factors distinguishing the compensated from persistently poor readers that might account for their different outcomes. To this end, we took advantage of the availability of a cohort who are participants in the Connecticut Longitudinal Study, a representative sample that has been prospectively followed since 1983 when they were age 5 years and who have had their reading performance assessed yearly throughout their primary and secondary schooling (Shaywitz SE et al., 1992; Shaywitz et al., 1999; Shaywitz et al., 1990).
Disruption of Posterior Brain Systems for Reading in Children with Developmental Dyslexia
Bennett A. Shaywitz, Sally E. Shaywitz, Kenneth R. Pugh, W. Einar Mencl, Robert K. Fulbright, Pawel Skudlarski, R. Todd Constable, Karen E. Marchione, Jack M. Fletcher, G. Reid Lyon, and John C. Gore
Introduction: Dyslexia is characterized by an unexpected difficulty in reading in children and adults who otherwise possess the intelligence, motivation, and schooling considered necessary for accurate and fluent reading (Shaywitz 1998). It represents one of the most common problems affecting children and adults with prevalence rates ranging from 5 to 17.5% (Shaywitz 1998). Such data have led “the National Institute of Child Health and Human Development (NICHD) within the National Institutes of Health (NIH) [to] consider reading failure to reflect not only an educational problem, but a significant public health problem as well” (Lyon 1998).
There is now a strong consensus that the central difficulty in dyslexia reflects a deficit within the language system and, more particularly, in a lower level component, phonology, which has to do with the ability to access the underlying sound structure of words (Liberman and Shankweiler 1991; Shaywitz 1996, 1998; Wagner and Torgesen 1987). Results from large and well-studied populations with reading disability confirm that in young school-age children, a deficit in phonologic analysis represents the most reliable (Fletcher et al 1994; Stanovich and Siegel 1994) and specific (Morris et al 1998) correlate of dyslexia. Such findings form the basis for the most successful and evidence-based interventions designed to improve reading (Report of the National Reading Panel 2000). A range of neurobiological investigations using postmortem brain specimens (Galaburda et al 1985), brain morphometry (Filipek 1996), and diffusion tensor magnetic resonance imaging (MRI; Klingberg et al 2000) suggests that there are differences in the left temporoparieto-occipital brain regions between dyslexic and nonimpaired readers. Converging evidence using functional brain imaging in adult dyslexic readers also shows a failure of left hemisphere posterior brain systems to function properly during reading (Brunswick et al., 1999; Helenius et al., 1999; Horwitz et al., 1998; Paulesu et al 2001; Pugh et al 2000; Rumsey et al., 1992, 1997; Salmelin et al., 1996; Shaywitz et al., 1998; Simos et al., 2000). In addition, some functional brain imaging studies show differences in brain activation in frontal regions in dyslexic compared with nonimpaired readers; in some studies dyslexic readers are more active in frontal regions (Brunswick et al.,1999; Rumsey et al., 1997; Shaywitz et al., 1998), and in others nonimpaired readers are more active in frontal regions (Corina et al., 2001; Georgiewa et al., 1999; Gross-Glenn et al., 1991; Paulesu et al., 1996).
These previous functional imaging studies of dyslexia were in adults, and the findings in adults were used to infer what might be found in children with dyslexia, without actually studying them. To determine whether these findings are the result of a lifetime of poor reading or whether they are there during the period of literacy acquisition, we
used functional magnetic resonance imaging (fMRI) to compare dyslexic and nonimpaired children during tasks that required phonologic analysis, that is, tapped the problems experienced by dyslexic children in sounding out words.