Bennett Shaywitz, MD
Charles and Helen Schwab Professor of Pediatrics (Neurology)Cards
About
Research
Overview
The Neurobiology of dyslexia. Converging evidence from many laboratories around the world using functional brain imaging, first positron emission tomography (PET) in the 1980s and then functional magnetic resonance imaging (fMRI) in the 1990s, for the first time has made visible what previously was a hidden disability. In one of the first studies of fMRI in dyslexia, we studied 144 children, approximately half of whom had dyslexia and half of whom were typical readers. Our findings indicated significantly greater activation in posterior reading systems in typical readers than in readers with dyslexia during a task tapping phonologic analysis. These data from fMRI studies in groups of children with dyslexia have been replicated in reports from many investigators and show a failure of left-hemisphere posterior brain systems to function properly during reading, particularly the systems in the left-hemisphere occipitotemporal regions. Good evidence suggests that the left hemisphere occipitotemporal region acts as an interactive node for reading, assimilating the orthography (the way the word looks), the phonology (the way the word sounds) and the semantics (what the word means). Other investigative groups studying prereaders with a family history of dyslexia have demonstrated that the inefficient functioning of posterior neural systems actually predate the poor reading providing evidence that the differences in brain function and structure are present even before the children learn to read. Furthermore, these functional brain imaging findings are universal, occurring in languages using alphabetic and logographic orthographies. Connectivity analyses of fMRI data represent the most recent evolution in characterizing brain networks in dyslexia. Measures of functional connectivity are designed to detect differences in brain regions with similar magnitudes of activation but whose activity is differentially synchronized with other brain systems across subject groups and/or types of stimuli. Using functional connectivity analyses involving the whole brain, we found that compared to typical readers, in dyslexic readers, connectivity was disrupted to the word-form area (critical to reading fluency), and between posterior reading systems and attention systems in frontal regions. We provide a more detailed discussion of brain imaging in Overcoming Dyslexia, 2nd edition by Sally Shaywitz and Jonathan Shaywitz published in 2020), These brain imaging studies provide neurobiological evidence that illuminates and clarifies current understanding of the nature of dyslexia and its treatment. For example, brain imaging has taken dyslexia from what had previously been considered a hidden disability to one that is visible; the findings of inefficient functioning in posterior reading systems are often referred to as a ‘neural signature for dyslexia’. These findings should eliminate any thoughts of whether dyslexia is real or a ‘valid’ diagnosis; even more so, these cutting-edge converging functional brain imaging data from imaging laboratories worldwide should encourage the use of the word ‘dyslexia,’ for it has meaning and relevance at levels reaching to the basic functional neural architecture in reading and its inefficient functioning in struggling readers. A final caveat: While functional brain imaging has produced very consistent and replicated studies in dyslexic compared to typical readers anatomic brain imaging has not produced as clear a picture.
Medical Research Interests
Academic Achievements & Community Involvement
News & Links
Media
- Non-impaired readers (left) activate three important language areas on the left side of the brain, one anterior (Broca’s area) and two posterior (parietotemporal, above, and occipitotemporal, below). These two posterior regions are significantly less activated and function inefficiently in dyslexic readers (right).
News
- February 08, 2024
New Study Highlights Potential Missed Diagnoses of Dyslexia in African American Students
- February 05, 2024
Study Following Students with Dyslexia Examines Reading Development from Childhood to Adulthood
- March 03, 2022Source: Yale News
School closures impaired reading for disadvantaged children
- March 24, 2021
YSM faculty elected to National Academy of Medicine and AAAS