Reprint of blog with 2018 Update
By: Jennifer Preschern, MA CCC-SLP, MA Learning Disabilities
Dyslexia: We've all heard this term. But what is it?
“Dyslexia is a specific learning disability that is neurobiological 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.” (International Dyslexia Association-IDA).
Before diving into dyslexia, let's look at the brain systems needed to read fluently.
How Do We Read?
Good readers predominately use their left hemisphere to access reading. The three basic systems needed for reading are shown above: Broca's area (green), Wernicke's area (red), and the occipital temporal word form area (yellow). It is important to note that when children first encounter text, they process it through the right hemisphere, which makes a gestalt or overall picture of the experience. Through text practice, phoneme awareness training, and language enrichment, teachers literally change the brain to bring the print processing to the left hemisphere, which is more adept at processing language and other rule governed information( Linkersdörfer, 2016).
Education also helps children to break the brains' biological wiring for "invariant object recognition," or the brain's natural inclination to recognize an object as the same regardless of the perspective from which the object is observed. It is for this reason that many young children(and older children with dyslexia) create letter reversals, identifying "b" for "d" or "p" for "q." It is not that they see letters differently, they have simply not suppressed this biological wiring yet and learned that orientation matters for letters (Dehaene,2010).
Inside the brain, specific regions are not as discrete and observable at the picture above shows. The brain is actually composed of individual neurons, as pictured below.
Neurons have small gaps between them, and they use chemicals, called neurotransmitters, to communicate with one another. In order to communicate more effectively, our bodies cover the long axonal tails of neurons with myelin. Myelin is a fatty sheath that acts like pavement on a highway or a super-conducter. It allows the neurotransmitters to flow more quickly and easily.
Early brain organization related to reading development includes the increase of myelin connections between the three main areas related to reading, and the pruning of excess neurons to make the connections more directional. In the brain, the myelin looks white, thus it's called the "white matter."
Two main brain connection pathways have been identified in good readers: the arcuate fasiculus (shown in blue below) and the Inferior Longitudinal Fasciculus (ILF) (shown in yellow below).
The arcuate fasiculus connects Broca's area (word forms-semantics, phonological awareness, phonics-orthographic awareness) to Wernicke's area (language comprehension). The ILF connects both these areas to the occipital lobe, which is used to process visual information. As you can see in the picture below, these white matter connections literally look like a road connecting the front and back areas of the brain.
As children age, research shows the arcuate fasiculus and IFL become more directional. Increasing directionality is akin to paving a straight road, rather than having an unpaved dirt road that spills out in some places and wanders in others. Researchers measure these changes through looking at fractional anisotropy (FA), which is a technique that measures the fiber density of neurons, the diameter of the neuronal axons, and the myelination of the neurons.
As shown above, the fractional anistrophy of the arcuate fasciulus and IFL increase with age for both above average readers (shown in black ) and below average readers (shown in grey). Furthermore, the connections for above average readers increase in a linear fashion, while poor readers have more ups and downs in their development. For both groups, development is approximately linear from ages 7-15 years old
Dyslexia: Where is the Breakdown?
In children with dyslexia, their white matter tracks, as described above, are not as directional nor as dense as children with solid reading ability(Zhaoa, 2016).
A 2018 study by Pedro Paz- Alanzo, et. Al. looked specifically at brain activiation under fMRI of 41 participants with dyslexia during a demanding reading task. “Readers with dyslexia exhibited hypo-activation associated with phonological processing in parietal regions; with orthographic processing in parietal regions, Broca's area (pars opercularis and triangularis), vOT and thalamus; and with semantic processing in the AG and hippocampus.” Basically, this study proves that readers with dyslexia have under-active processing in the left hemisphere for the main processing involved in reading: phonological, orthographic, semantic. It’s the strongest evidence to date that shows dyslexia is caused by lack of functional connectivity in the brain, and that students with dyslexia are not efficiently using networks in their left hemisphere to read.
Dyslexia = inefficient processing in the left hemisphere
Research recommends an integrative approach to dyslexia treatment aimed at connecting all networking areas(Kershner, 2016). This includes systematic word study instruction in:
Orthographic Awareness (Phonics)
Morphology: Word Roots, Prefixes, Suffixes
Mental Images of Words: connectionist-mnemonic strategies for memorization of words that do not follow orthographic patterns
Can Instruction Change the Brain?
While not with students, one study looked at whether experts in phonetics, as defined by adults with 1-4 years of formal training in phonetics, would have different brain structures than non-experts. Researchers found that yes! Training in phonetics, or sounds, creates changes in white matter fibers in fronto-temporal functional hubs, areas in left-hemisphere that are important for phonetic processing.
In another study that directly assessed the impact of phonics instruction, researchers from Stanford University(Yoncheva & McCadliss, 2017) taught students new words using either a phonics based approach or a whole word approach. Then, they looked at brain wave activity while students were reading these words at a later date. Their research showed that teaching students to read using a phonics based approach activated brain wave activity in the left hemisphere, while teaching using a whole word approach causes activity in the right hemisphere.
Training in sounds and phonics can change the brain, but using a whole word approach keeps processing in the inefficient right hemisphere.
Which Program is Best?
Programs don’t teach kids, teachers do. However, having materials that are grounded in research is crucial.
The best instructional program on the market right now for educators that integrates these areas is called "SPELL-Links" by Learning by Design. "SPELL-Links leverages the brain's innate, biological wiring and organization for oral language. Unlike traditional phonics and word study programs which begin with the written letter and teach students to match the letter to a sound, with SPELL-Links students first learn how to attend to the sound structure of spoken English words and then how to connect and combine sounds, letter patterns, and meanings to read and spell words. This is exactly how the brain works in good readers and writers!"
Things that DO NOT Work
Even though the research is clear about how the brain reads and what works, there are many educators who attempt to help children with dyslexia in others ways. A few things that do not work:
Whole Language Approaches: Whole language comes in many different names. If a child is learning decoding strategies like "look at the picture, skip it and come back, sound it out (with little instruction as to the orthography besides initial sounds, blends, and digraphs), or ask a teacher" and progress is measured by movement on "leveled texts," they are being instructed through a whole language approach. While this may lead to small gains, as part of building the white matter tracks is simply reading more, relying solely on a whole language approach is not best practice for children with dyslexia. For a discussion on this, see here.
Changing Fonts: In 2008 Christian Boer, a Dutch artist, developed a special font ("Dyslexie") to facilitate reading in children and adults with dyslexia. The font has received a lot of media attention worldwide, even though there was no research to support it. So does it work? There are still limited studies on this area. One recent study with only 39 participants shows "that low-progress readers performed better (i.e., read 7% more words per minute) in Dyslexie font than in standardly spaced Arial font. However, when within-word spacing and between-word spacing of Arial font was matched to that of Dyslexie font, the difference in reading speed was no longer significant. It concludes that the efficacy of Dyslexie font is not because of its specially designed letter shapes, but because of its particular spacing settings(Marinus, 2016)."
Color Overlays: Some educators believe that putting different colors over print may help students read. Several studies have proved this false. For example, sixty-one schoolchildren (aged 7-12 years) with reading difficulties were assessed by an Irlen diagnostician. Researchers looked at reading rate across 3 conditions: using an overlay of a prescribed color; using an overlay of a nonprescribed color; and using no overlay. The data concludes that there was no difference across groups in reading rate. (Ritchie, 2011).
Advocating in School
In many public schools, dyslexia is housed under the generic catch-all terms "learning disabilities" or "reading disability." This is not a problem, as long as educators are providing treatment that works.
All students need access to high quality literature. Whole language approaches may be suitable for children with learning disabilities who struggle with reading comprehension, yet possess adequate reading decoding skills. However, whole language is not enough for students who struggle with decoding. Parents and educators alike need to advocate for systematic word study instruction, as this is the most efficient way to change the brain of children with dyslexia.
Some good news is that the Common Core now mandates that schools include systematic word study instruction for all children under the "Reading Foundations" Standards. Here is some information on what these standards look like in practice for Kindergarten:
Spell Talk: Spell Talk is a free international group of reading researchers, teachers, speech language pathologists, and parents sharing resources and ideas about reading. Spell Talk releases weekly research references with the group via a listserve. Members are invited to pose questions to the group on any reading related topic.
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Linkersdörfer, 2015. "The association between gray matter volume and reading proficiency: a longitudinal study of beginning readers." J Cogn Neurosci. 2015
Marinus, E. "A Special Font for People with Dyslexia: Does it Work and, if so, why?" Dyslexia, 2016.
Mascheretti S, Neurogenetics of developmental dyslexia: from genes to behavior through brain neuroimaging and cognitive and sensorial mechanisms. Transl Psychiatry. 2017
Kershner, John. Network dynamics in dyslexia: Review and implications for remediation Research in Developmental Disabilities Volume 59, December 2016, Pages 24–34
Meyer, Ann. Keller, T., Keller, V., Cherkassky, L, Lee, D., Hoeft, F., Whitfield-Gabriel, S., Just, A. Ann (2007). Brain Activation during Sentence Comprehension among Good and Poor Readers. Cereb Cortex. Vol. 12, 2780-2787.
Paz-Alonso P.M., Oliver, LU., Caballero-Gaudes, Quiñones, I, Suárez-Coalla, P., Duñabeitia J., Cuetos, F., Carreiras(2018). Neural Correlates of Phonological, Orthographic and Semantic Reading Processing in Dyslexia NeuroImage: Clinical, 20, 433-447. doi.org/10.1016/j.nicl.2018.08.018
Ritchie, S. "Irlen colored overlays do not alleviate reading difficulties." Pediatrics, 2011.
Vandermosten, M., Price, C., Golestani, N. Cathy J. Plasticity of white matter connectivity in phonetics experts. Brain Structure and Function, 221(7), 3825-3833. doi.org/10.1007/s00429-015-1114-8
Yoncheva, Y., Wise, Jessica., McCadliss, B. (2015). Hemispheric Specialization for Visual Words is Shaped by Attention to Sublexical Units During Initial Learning. Brain and Language. Volume 145. Page 23
Zaixu Cui, “Disrupted white matter connectivity underlying developmental dyslexia: A machine learning approach” Human Brain Mapping. January, 2016.
Zhaoa, J “Altered hemispheric lateralization of white matter pathways in developmental dyslexia: Evidence from spherical deconvolution tractography” Cortex Volume 76, March 2016, Pages 51–62