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.
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.
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.
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.
Neuroimaging also may help us discern the precise instructional elements that work best for teaching students with dyslexia how to read, write, and spell.
For example, some propose that supplementary non-language treatments directed at the visual and auditory systems benefit the struggling reader. This, however, remains controversial. It has been difficult to establish the efficacy of these approaches. Imaging the brain before and after using these techniques may provide the clues necessary to determine if they do benefit learning.
While science has verified structured-language instruction, researchers have yet to study the "multisensory" component educational therapists and teachers often include, particularly for students with dyslexia. Multisensory instruction conveys information through multiple input channels (visual, auditory, and kinesthetic/tactile) and enlists various multisensory strategies to enhance memory storage and retrieval. Multiple sensory channels feed comprehensive and concrete information to the language-processing network of the brain. Theoretically, multisensory instruction bypasses sensory-system weaknesses, conveys information to an atypical language system in more decipherable and indelible forms, and provides various "triggers" for memory.
In multisensory instruction, a student might be instructed to look at a letter (visual), listen to its sound (auditory), associate the letter and its sound with a picture of a "key word" that "unlocks" its sound (e.g., apple/short a - visual/auditory), say the letter with its sound (kinesthetic/auditory) and perhaps its key word, and write the word and perhaps move or gesture in some way that represents the key word, letter, or sound (kinesthetic). A variety of structured-language/multisensory programs employ versions of such methods, usually in inventive and systematic ways. Their goal is to achieve multiple pathways and associations for input, storage, and retrieval to offset weaknesses in sensory, language, and memory systems.
Clinical experience with this technique points to a powerful effect. From what we know about the brain and dyslexia, multisensory instruction would seem to be an important component in teaching students with this learning condition, perhaps even beneficial for all students. But science has not yet addressed the efficacy of multisensory instruction. "Seeing" the brain at work through neuroimaging may help establish the merits of this instruction and enable educators to refine its elements. Neuroimaging may help us understand the apparent magic of multisensory instruction.
Neuroimaging techniques reveal a brain far more complex than previously thought. For example, the language network appears to involve more than a few "key centers" and may be distributed in other brain regions, contrary to earlier hypotheses. We have also learned how the brains of people with dyslexia change while engaged in basic language tasks after receiving structured-language educational interventions. In general, these changes entail shifting to a more efficient, unilateral mode of processing. In other articles in this series we will discuss these remarkable findings in greater detail.
Will advancements in neuroimaging dispel all the controversies and confusions surrounding dyslexia? Probably not. They will, however, bring us breathtakingly closer to understanding the mysteries of the brain. Along the way, these advancements will help us demystify dyslexia, sharpen its definition, fine-tune its diagnosis, and verify the efficacy of educational interventions. Indeed, we are on the threshold of a brave new world - one where neuroscience and education will combine to unlock and enhance human potential in powerful new ways. Morgan and Hinshelwood would have been astonished! We, however, need only a little vision to find and cross the threshold.