How brain research can help demystify dyslexia
How can brain research tools help us understand dyslexia, fine-tune its identification, and improve teaching methods?
By Gordon Sherman, Ph.D.
Neuroscientific tools, such as neuroimaging, promise to play a key role in the unfolding story of dyslexia - helping to clarify misconceptions, dispel controversy, and improve diagnosis and intervention.
Dyslexia results from a complex gene-environment interaction that begins in the womb and eventually modifies both the structure and function of the nervous system. This prompts the brain to develop according to a different blueprint. The result is a brain that does not process language in the usual way. Even with all we understand about this atypical development, mysteries remain.
Controversy and Confusion
Why do controversy and confusion often surround dyslexia? Partly because the work of the researchers, educators, and evaluators concerned with dyslexia often rests on inference - inferred assumptions about normal and atypical brain development and function.
Historically, to investigate the structure and neurophysiological function of brains, neuroscientists rely on the examination of brains obtained at autopsy or on studies of patients during neurosurgery. To understand learning and learning disabilities, clinicians and educators rely on closely observed behavior patterns. Scientists, clinicians, and educators study neural tissue or behaviors to infer what the brains of their patients, subjects, or students actually do in normal living and learning conditions.
Given the inexact nature of inference, many conclusions about dyslexia are subject to interpretation, and, thus, plagued by controversy. Since Pringle Morgan and James Hinshelwood first described dyslexia a little over 100 years ago, scientists, educators, and clinicians have debated dyslexia's definition, diagnosis, treatment, and even its existence.
Now, however, the brave new world of neuroimaging promises to put many dyslexia debates to rest. Much like the Hubble telescope enables us to see into remote corners of space, neuroimaging allows us to probe the frontiers of the human brain. As neuroimaging technology progresses, we will "see" the structure and functioning of living brains with increasing clarity - a scientific advancement beyond anything Morgan or Hinshelwood could have imagined.
Modern neuroimaging techniques, showing the activity of brain areas and networks, will help unravel the mysteries of dyslexia. While traditional neurological studies and clinical observations continue to provide valuable information, neuroimaging offers a window for viewing the structural and functional attributes of living and learning brains. Thus, neuroimaging promises to enhance the diagnosis of dyslexia, the design of educational programs, and the precision of prescriptive teaching.
Neuroimaging May Aid Diagnosis
Here is the most widely accepted definition of dyslexia:
Dyslexia is a specific learning disability that is neurological 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 phonological component of language that is often unexpected in relation to other cognitive abilities and the provision of effective classroom instruction. Secondary consequences may include problems in reading comprehension and reduced reading experience that can impede growth of vocabulary and background knowledge. Adopted by the IDA Board, November 2002 and by the National Institutes of Health, 2002 .
Although this definition has proven useful, particularly for research purposes, it does not give us a concrete understanding of dyslexia.
- Exactly what is different about the brain of a person with dyslexia? What are the brain-based mechanisms for the types and degrees of dyslexia?
- How do we diagnose dyslexia?
- How does the environment alter brain structure and function in dyslexia?
- What are the best methods of instruction for people with this learning disability?
Neuroimaging may lead us to a more precise definition of dyslexia, providing more specific information about its neurological basis and characteristics which, in turn, may yield additional diagnostic and educational insights.
Advanced neuroimaging tools also may aid in the diagnosis of dyslexia. Techniques such as PET (Positron Emission Tomography) and fMRI (Functional Magnetic Resonance Imaging) reveal the activity of the brain during tasks such as speaking, reading, and writing. If people with dyslexia show consistent and characteristic differences in brain function during such tasks, demonstrating a distinct "neurological profile," this information may lead to more precise identification and educational intervention.
Certainly, today's neuroimaging tools are too cumbersome and expensive, even too rudimentary, to be useful for common screening and diagnostic purposes. But who knows? Consider our remarkable evolution since Morgan and Hinshelwood. Technological advances making neuroimaging part of every child's kindergarten screening may be less science fiction than we might imagine.