Science of Dyslexia
Physicians began researching dyslexia in the late 19th century, yet the cause of this condition, which makes learning to read and write unexpectedly difficult for some people, remained a mystery for more than a century.
In recent decades, genetic research and brain scans using functional magnetic resonance imaging (fMRI) on individuals with dyslexia have shed light on this complex and often hereditary reading disorder. As widespread understanding continues to expand, so too do opportunities for individuals affected by dyslexia to become independent, fluent readers.
Research has found that individuals with dyslexia show neurological differences in both their structure (gray and white matter) and their function. Treatment studies have shown changes in the reading circuitry with effective instruction. fMRI studies before and after intervention show that gray and white matter changes (Keller et al., 2009; Krafnik, Flowers, Napoliello, & Eden, 2011) and brain function changes (Shaywitz et al., 2004; Simos et al., 2002; Temple et al., 2003; Eden et al., 2004; Meyler et al., 2009).
Guinevere Eden, Ph.D., professor and director of the Center for the Study of Learning at Georgetown University, and her colleagues were the first to apply fMRI to the study of dyslexia. In the video Dyslexia and the Brain, created by Understood, she explains which parts of the brain are used for reading, the differences in brain function between individuals with and without dyslexia, and how the brain function of a child with dyslexia changes when proper reading instruction is implemented.
As noted in the IDA fact sheet Dyslexia and the Brain, magnetic resonance imaging (MRI) is a commonly used tool to capture images that illustrate brain anatomy (e.g., the amount of gray and white matter, the integrity of white matter), brain metabolites (chemicals used in the brain for communication between brain cells), and brain function (where large pools of neurons are active). fMRI is based on the physiological principle that activity in the brain (where neurons are “firing”) is associated with an increase of blood flow to that specific part of the brain.
There is a neurological basis to dyslexia. The entire brain is used in the act of reading. However, language tasks are more specific to the left hemisphere.
Figure 1 shows the left hemisphere of the brain, and highlights areas used by typically developing readers with left hemisphere specialization for reading and language.
An fMRI image will show areas of the brain that have any increased activity while a reading and/or language task is being performed. For example, imagine an individual performs tasks with real words and nonwords while in an fMRI machine. Blood goes to areas of the brain that are activated during these tasks. With fMRIs, researchers can look at where blood goes, demonstrating the activation in proficient vs. struggling readers. Although typically developing readers develop left hemisphere specialization for reading and language, one of the frequent findings in neuroimaging of children with dyslexia is that they fail to develop this pattern. Instead, they develop an altered circuit involving greater reliance on right hemisphere and frontal lobe areas.
Key Research Findings
Since 2000, key research findings have shown:
- Biophysical and structural differences exist in the brains of individuals with dyslexia.
- Developmental dyslexia is genetic.
- Every individual has brain-based strengths and weaknesses.
- Dyslexia is not related to intelligence.
- Inherited genes, particularly those that may interfere with development of specific fibers in the left hemisphere of the brain that are involved with mapping sounds and word/letter recognition, may predispose an individual to dyslexia.
- Early intervention is best because the powerful plasticity of the brain in developmental years enables young children to more easily adapt to the MSL learning method.
- Research-based educational interventions create changes in brain circuitry.
In its 2017 report, The State of Learning Disabilities: Understanding the 1 in 5, the National Center for Learning Disabilities (NCLD) notes that “new research is deepening our understanding of the differences in brain structure and function in children with learning and attention issues. Brain scans and other tools are also helping researchers measure the biological impact that instructional interventions have on children who learn differently, including those with dyslexia, ADHD, and other issues.”
At the Gabrieli Laboratory at the Massachusetts Institute of Technology, ongoing research is being conducted in partnership with local organizations, schools, and clinics to provide solutions for parents, educators, and clinicians who work with children. Neuroscientist John Gabrieli, Ph.D., director of the Martinos Imaging Center within the McGovern Institute for Brain Research at MIT, is using brain imaging to study differences in children with dyslexia and how reading instruction affects the brain. Findings suggest that a combination of evidence-based teaching practices and cognitive neuroscience measures could prevent reading failure in a majority of children who show signs of dyslexia at an early age.
Research at Boston Children’s Hospital’s Laboratories of Cognitive Neuroscience focuses on children with or at risk for various developmental disorders, particularly language-based learning disabilities such as dyslexia. Experts there in neuroscience, psychology, and education collaborate with clinical experts in fields such as developmental pediatrics and child neurology. In this space, Nadine Gaab, Ph.D., leads the Gaab Laboratory, where a team of researchers focuses on language, reading, and brain development in children with a family history of dyslexia, as well as the connections between dyslexia and ADHD. Data derived from these studies will ultimately translate into earlier identification, improved therapies, and better outcomes for children with dyslexia, ADHD, and autism.
In their article, The Emerging Field of Educational Neuroscience is Changing the Landscape of Dyslexia Research and Practice, researchers Fumiko Hoeft and Chelsea Myers note that scientific research will continue to influence-and ultimately improve-teaching methods and curricula to enable students with dyslexia to thrive academically and personally.
References (click to show)
Eden, G. F., Jones, K. M., Cappell, K., Gareau, L., Wood, F. B., Zeffiro, T. A., … Flowers, D. L. (2004). Neural changes following remediation in adult developmental dyslexia. Neuron, 44(3), 411–422.
Keller, T. A., & Just, M. A. (2009). Altering cortical connectivity: Remediation-induced changes in the white matter of poor readers. Neuron, 64(5), 624-631.
Krafnick, A. J., Flowers, D. L., Napoliello, E. M., & Eden, G. F. (2011). Gray matter volume changes following reading intervention in dyslexic children. Neuroimage, 57(3), 733-741.
Meyler, A., Keller, T.A., Cherkassky, V.I., Gabrieli, J.D.E., & Just, M.A. (2008). Modifying the brain activation of poor readers during sentence comprehension with extended remedial instruction: A longitudinal study of neuroplasticity. Neuropsychologia, 46, 2580-2592.
Shaywitz, B. A., Shaywitz, S. E., Blachman, B. A., Pugh, K. R., Fulbright, R. K., Skudlarski, P., … Gore, J. C. (2004). Development of left occipitotemporal systems for skilled reading in children after a phonologically based intervention. Biological Psychiatry, 55(9), 926-933.
Simos, P. G., Fletcher, J. M., Bergman, E., Breier, J. I., Foorman, B. R., Castillo, E. M., … Papanicolaou, A. C. (2002). Dyslexia-specific brain activation profile becomes normal following successful remedial training. Neurology, 58(8), 1203-1213.
Temple, E., Deutsch, G. K., Poldrack, R. A., Miller, S. L., Tallal, P., Merzenich, M. M. & Gabrieli, J. D. E. (2003). Neural deficits in children with dyslexia ameliorated by behavioral remediation: Evidence from functional MRI. Proceedings of the National Academy of Sciences, 100(5), 2860-2865.