Neurobiology and Dyslexia: What We Know About the Brain and Learning
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Please scroll down to the bottom of this page to view the transcript of questions that were asked and Dr. Eden's answers.
Dyslexia is believed to have a biological basis, caused by an unusual organization of certain neuronal connections or brain cells.
Understanding how the brain processes information at the neurological level is a key component in figuring out how to support learners with dyslexia effectively and can help answer questions like: "How does the brain of someone with dyslexia process information?" or "How do brain scans help researchers understand dyslexia?"
Join Dr. Guinevere Eden, of the Center for the Study of Learning at Georgetown University, as she demystifies the connection between neurobiology and learning disabilities.
Dr. Eden has provided this fMRI scan to help us understand what brain activiry can look like following reading interventions:
Changes in brain activity following reading intervention in adults with developmental dyslexia
(Eden et al., Neuron, 2004)
Read more about Guinevere Eden, Ph.D.
According to the National Institute on Deafness and Other Communication Disorders at the National Institutes of Health, “In children, auditory processing difficulty may be associated with conditions such as dyslexia, attention deficit disorder, autism, autism spectrum disorder, specific language impairment, pervasive developmental disorder, or developmental delay. Sometimes this term has been misapplied to children who have no hearing or language disorder but have challenges in learning.”
Researchers are still debating the question regarding the potential relationship between reading deficits and auditory perceptual processing abilities. Some have argued that dyslexia and specific language impairment (SLI) are the result of deficits in the processing of rapid and brief sounds. However, collectively the research studies published in this field have come up with different, conflicting results and therefore we cannot be certain that this theory is accurate. The reason why scientists have been unable to come up with a unanimous answer to this question is due to several factors. The experimental tasks that have been used to assess auditory processing vary in their nature and do not seem to lead to reliable (reproducible) results. There appear to be large individual differences in auditory processing abilities, making it difficult to come up with a conclusion that can be generalized to all children with reading disorders. Finally, a theoretic framework that has guided much of this research and posits a relationship between verbal and non-verbal auditory processing abilities has been heavily debated based on theoretical grounds. This issue needs to be resolved urgently, because it has important implications for interventional approaches; attempts to remediate reading problems in dyslexia by targeting auditory processing has, in general, not been as successful as might have been hoped for a few years ago.
For more research information on this matter I recommend the work by Dr. Dorothy Bishop at the University of Oxford, especially the reviews by McArthur and Bishop, Dyslexia, 2001 and Dawes and Bishop, in press, International Journal of Language and Communication Disorders. When it comes to Central Auditory Processing Disorders, it has been argued that this diagnosis is reserved for perceptual dysfunction that is specific to the auditory modality. In this way CADP is distinguishable from language-based learning disabilities like dyslexia. However, depending on who evaluates the child, these boundaries sometimes become unclear and it can be a problem with regards to reaching a fitting diagnosis and appropriate avenue for intervention.
This is an excellent question. When brain imaging technology first became available, researchers such as Dr. Flowers at Wake Forest University and Dr. Rumsey at the National Institutes of Health used these technologies to study participants with dyslexia. However, these studies only involved adults as the brain imaging technology required the use of radioactive tracers and were not suitable for use in children. So an important question arose as to whether the brain patterns identified through this research were indicative of the location of the aberrations associated with dyslexia, or if researchers were in fact studying the neuronal consequence of a lifelong experience with reading difficulties in these adults.
In the 1990s, fMRI became available as a non-invasive brain imaging tool and researchers have used it to study children; so we can now examine the concordance with the published literature of children and adults with dyslexia. Studies in which children performed reading or phonological (largely rhyming) tasks in response to visually presented stimuli have yielded widespread activation differences: dyslexic children underactivated multiple left frontal, temporal, and parietal regions as well as their right hemisphere homologues. This symmetry differs from the largely left-lateralized findings reported in the studies of adults with dyslexia.
To date we have no studies that directly compare adults and children with dyslexia on these types of tasks. However, a recent study conducted at Yale University in children with dyslexia between the ages 7 to 18 years provides some clues and is consistent with the notion that the differences in children seem to be presented in both brain hemispheres (Shaywitz et al., Annals of Neurology, 2007). When these results are considered in the context of the age-related changes that occur in children who don’t have dyslexia, the authors suggest that the patterns in brain activity observed in the older dyslexics is a reflection of their use of a different strategy when it comes to processing print.
Rates for scanning at a clinical center are typically quite high ranging from $400 to more than $2,000 per half hour. We pay about $500 per hour to utilize the research dedicated MRI system at Georgetown University for our research studies. It is important to point out that functional brain imaging techniques, such as functional magnetic resonance imaging (fMRI), are currently used for research purposes, to elucidate the brain basis of mental functions such as reading. Currently, it is not appropriate to think of them as a diagnostic tool for dyslexia.
fMRI is used in other areas of research where the clinical applications are more obvious, such as pre-surgical planning, and here the possibility of insurance coverage potentially exists, but is not guaranteed (Medicare has billing codes for fMRI, but this does not guarantee that insurance companies will follow suit).
I will answer your question in two parts, from the perspective of identifying a provider and also with a view of how dyslexia is identified in an adult. As an adult, you need to find a reputable adult literacy organization that uses appropriate methods for the identification (and remediation) of dyslexia. Some nationally represented organizations, such as the International Dyslexia Association (IDA) can supply regional information about professionals who evaluate adults. Also, professional tutors will know of such people. Depending on where you live, you could also contact your local university to inquire if there is an ongoing reading research protocol for which you might qualify.
Adults are tested in the same way as children, using tests of real and non word decoding, fluency, comprehension, phonological awareness and working memory. The profile of dyslexia can be different in adults, even severely dyslexic ones, as they may have compensated by memorizing a number of words by sight (although they still have trouble figuring out unfamiliar ones) and have developed good strategies for understanding text by guessing and using context (although this may slow them down). Adults with dyslexia usually still have trouble with phonological awareness tasks as well as poor knowledge of the rules that govern pronunciation. Often they are very poor spellers, even so much so that a spell checker can't guess at the word. Like children with dyslexia, if fluency is a problem their deficits are enhanced. A well-informed evaluator should also be on the lookout for psychological problems, such as depression, which occurs at a significantly higher rate than the population base rate.
Currently fMRI is not used in this way. I receive emails every week from parents who inquire where ther child can receive an fMRI scan to diagnose their dyslexia. This sometimes comes from a frustration of not receiving the needed psycho-educational tests that should be used to identify struggling readers and parents hope that a brain image could serve to convince a school to provide accommodations. We use fMRI as a research tool and not for diagnostic purposes.
However, with the rapid advances that are taking place in brain imaging technology, the potential for this type of application will grow. We and others have already conducted studies where we generate computer algorithms that are trained on fMRI data sets obtained from subjects with and without dyslexia and then we apply the algorithm to a new set of data and see how successful it is in identifying those individuals in the data set that have a diagnosis of dyslexia based on their reading performance. From the technological perspective, the limitations of fMRI have involved issues around group data as opposed to data from a single person. Most studies publish findings based on group maps as this is one way to obtain sufficient statistical power from a technology that extracts a very tiny signal inferring brain activity. Should the technology be good enough so that brain imaging data are reproducible and can be interpreted robustly at the level of the individual, then your question will become very pertinent.
At that time we will need to decide whether information about brain physiology has an edge over behavioral evaluation. My personal opinion is that research protocols which employ brain imaging technology will be important to help us understand why there is variability amongst people with dyslexia and whether the brain patterns that we obtain are predictive of later reading outcome or indicative of which intervention might be most beneficial to an individual. In the context of knowledge about how the human brain works, such studies can allow us to understand why certain brain regions are recruited for reading and in response to reading intervention and the results can inform educational practices. But this research needs to be conducted in parallel with behavioral evaluations.
For practical purposes, the degree to which brain imaging would be used for decisions on a subject-by subject case will not only depend on how robust this approach is, but also whether it is cost effective (even though costs associated with MRI technology have come down, they are still relatively expensive when compared to behavioral testing). In the end we are studying the brain as a way to understand the behaviors that children and adults with dyslexia exhibit; and it is behavior that we are interested in when it comes to ascertaining whether students are making gains in reading. This needs to be taken to heart when we make decisions about which interventions are effective. It is easy to be seduced by intervention approaches that advertise brain changes in students with dyslexia, but if the students don’t demonstrate practical gains in reading, then brain images lose their relevance.
For more information about how to seek an evaluation for a child, see NCLD's Parent Guide to IDEA.
There is evidence of visual perceptual and motor planning differences in people with dyslexia. Much research activity is currently dedicated to these individually (i.e. specifically focused on the visual or motor system) and some researchers have formulated theories that account for the coexistence of both visual and motor problems (in addition to the more widely accepted cognitive problems in the domain of phonological coding, rapid naming and verbal working memory).
The question which remains a source of considerable debate is whether these sensorimotor deficits are integral to causing the reading problems or should be considered to be epiphenomena of dyslexia (see Zeffiro and Eden, Trends in Neuroscience, 2001). Intervention approaches that target the motor or visual system as a way to bring about gains in reading, have often been considered to be controversial.
Children who suffer seizures can exhibit a range of cognitive weaknesses and this may include reading. Because of their neurological history, such a child would not be considered to have dyslexia using a classical definition, because their reading problems are attributed to the brain trauma associated with the seizures.
How you approach this depends on the age and temperament of your child and the support that is available to them through the school and your family. One thing we have experienced through our volunteers research participants is that children like to learn about what is going on in their brains and how this could explain why they experience reading difficulties. Anybody could integrate science in their explanation and remind the child that the brain really has a tremendously difficult job in mastering reading (and in us grown-ups mastering remembering things!). Reading is not something that comes to us naturally and when the brain reads, it has to draw on numerous cognitive resources and coordinates them in ways that allow us to draw meaning from print. The brain areas that end up chiming in for this to occur, were not specifically designed to read; and researchers speculate why they get involved in the first place. So when this process does not work out, it is not the fault of the child, it is merely that their brain is not well aligned to a skill that has intense cultural value in the time in which we live in (but it did not a few thousand years ago).
I remind our participants that we are all different. The brain areas that are involved in reading are not always the same for different individuals. Also, when we look at studies from other writing systems, for example those used by Chinese readers, they use different regions of their brain for reading. That is because a visuospatial character requires a different type of brain support than an alphabetic writing system. Chinese children learn about 600 characters in first grade, where our brains have to understand the job of the 26 letters of the alphabet. Once you contemplate the complexities of the reading brain, it is astonishing that it works at all!
Another thing that children need to learn eventually is that dyslexia is a life-long condition. With proper help these kids can learn to read and/or write, but they will always encounter problems when they are in certain situations (brought about by fatigue, stress, or anxiety provoking situations). In these cases it is probably wiser to be prepared for dealing with the situation rather than not to plan on them occurring at all. A resource to help build self esteem in your child is, "Building Self Esteem."
Recently, I had the opportunity to visit a group of high school students with learning disabilities in Colorado, who had come to terms with their diagnosis, were comfortable with their identity and this allowed them to effectively advocate for themselves and communicate clearly to others what their disability was about. Early introduction to the facts is probably a good start to this trajectory of a childhood and adolescence that is based on understanding and not on self doubt.
Signs that dyslexia lies in a child’s future can manifest quite early in life. Firstly, we know which children are at risk for dyslexia and these children should be given special attention: children born to a parent with dyslexia has a 35-40% of having dyslexia. For these and other children there are now several tools available to assess the risk of a child of developing dyslexia. NCLD has provided the Get Ready to Read! screening tool, which through a series of questions for children in the year before they enter kindergarten can be used to determine whether they have the early literacy skills they need to become readers. The field tests for this tool were conducted by Drs. Grover J. Whitehurst and Christopher Lonigan. The tool addresses inside-out skills (knowing the names of letters of the alphabet and what sounds letters make) and outside-in skills (vocabulary and knowledge of the outside world).
Another tool is the Predictive Assessment of Reading, which was developed and nationally standardized by Drs. Frank Wood and Lynn Flowers. The PAR is a brief (15 to 20 minutes) test for children as young as kindergarten, to predict future reading achievement out to grade 12. It assesses those skills that research has shown are central to early reading development, such as naming vocabulary, naming speed, phonemic awareness, letter and word recognition. The Phonological Awareness Literacy Screening (PALS) was created through the Virginia Early Intervention Reading Initiative at the University of Virginia’s Curry School of Education. Individual children’s scores are tabulated with links to the activities on the Website that support any student deficits. Another state based initiative comes from Texas, the Texas Primary Reading Inventory. The kit includes a teacher’s guide, an intervention activities guide, magnetic board and set of magnetic letters, laminated story cards, and twenty-six student record sheets for K, 1, and 2 classrooms. The use of these tools for identifying children “at risk” for dyslexia is important as it reduces the time lag for effective actions to be taken and avoids waiting until the child is so far behind that it becomes very difficult for him or her to get caught up.
NCLD also has a Checklist of LD Signs and Symptoms that may be helpful.
As with many things, the best thing educators and others can do is educate themselves about dyslexia on a continuing basis. Do not assume that you were taught all that you need to know about dyslexia during your training to become an educator. There are many available resources for learning about dyslexia, and they need not be expensive. Also, there are mechanisms by which you can attend conferences and seminars through the support of your school and these opportunities for professional development will allow you to expand your knowledge about all aspects that a dyslexic student is faced with.
We are fortunate that these resources are available to us (this is not the case in many other parts of the world where learning disabilities are not recognized) and so we need to take advantage of them. For example, I attend the annual conference of the International Dyslexia Association every year and am energized each time how much new information is offered by our participants every year.
For more information, see NCLD’s article on Working with Dyslexia.
This is an important question for a number of reasons. Firstly, we want to know how permanent any behavioral benefits are for any reading intervention. Secondly, from a neuroscience perspective we want to know whether there is a dynamic aspect to the brain-based correlate of successful reading intervention. Thirdly what role do software programs play in successful intervention?
Unfortunately there are few studies that address any of these questions. There are some behavioral studies that have compared software programs with non-computerized programs immediately after completion of the intervention and at long-term follow-up. For example Dr. Pam Hook and colleagues (Hook et al., Annals of Dyslexia, 2001) compared children receiving a computer-based training with those involved in a non-computerized phonics program and matched longitudinal controls. Only those children receiving the non-computerized phonics program made significant gains in Word Attack, and both programs led to similar immediate gains in phonemic awareness. The computer-based training group made gains in spoken language and syntax immediately after intervention, but the gains were not maintained by the children at the two-year follow-up.
There is only one study to date that employed brain imaging to study children following reading intervention (consisting of daily, individual tutoring) immediately after the intervention was completed and one year thereafter (Shaywitz et al., Biological Psychiatry, 2004). Unfortunately the control groups were not scanned at the one year follow up, so the results can only be interpreted with reservations. However, the importance of conducting such studies is well recognized and there hopefully will be more efforts in this area to allow us to fill this void.
I've read a little about brain imaging and dyslexia. I have three questions:
1. How do you define dyslexia? I'm under the assumption that even individuals with poor word reading in context, versus simply poor word reading in isolation, qualify for a diagnosis of dyslexia, but I have not seen this new definition in practice in my setting.
2. Is brain scanning an effective tool for individuals who are "mildly" dyslexic (I guess I'm asking if the functioning of the brain is different for different severity ratings)?
3. Have you identified any tools that practitioners can use that are highly correlated with the result you find through brain imaging.
Here is the official definition of dyslexia developed in collaboration between the National Institute of Child Health and Human Development (NICHD) and the International Dyslexia Association (IDA) in 2002. “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.”
Individuals with dyslexia may exhibit poor word reading in context as well as in isolation. The reason we like to administer tests that present words in isolation is that we then now that the word could not have been read through the use of context and this allows us to evaluate decoding skills (of real words and pseudowords). It is also important to measure reading of connected text, as this provides valuable information, not only on reading accuracy, but also of reading fluency and comprehension.
With regards to your second question, brain imaging data can be correlated with information that has been obtained outside of the scanner. In this way researchers generate correlations between reading ability captured on a standardized score (such as the Woodcock Johnson Test) and the amount of brain activity generated in response to a task that involves reading. This is a useful way to assess brain-behavior relationships and to answer questions such as yours. It has also been used to correlate brain activity with the amount of gains made on measures of reading following reading intervention.
Thirdly, many tools that practitioners use have come out of research conducted in the last 30 years using behavioral approaches. Longitudinal studies, such as those conducted by Drs. Wagner and Torgesen in children, captured the skills that support reading have lead to the development of measures that identify children at risk for reading disability. We integrate these kinds of measures in our own research, integrate them with measures of brain function and hope that the neuroimaging results will allow us to understand why some educational practices are more promising than others.
Math in particular has received increased attention in recent years and there has been a much needed increase of research funds to support this work. As is the case for brain imaging studies of reading, the behavioral literature on number processing has provided the foundation for developing brain imaging paradigms. Using this approach, researchers such as Dr. Stan Dehaene in Paris have identified which brain areas are involved in different aspects of mathematical computations (Dehaene at al., Current Opinion in Neurobiology, 2004). It is also known that brain areas recruited in mental arithmetic change throughout development (Rivera, Cerebral Cortex 2005;) and are different in students with math disabilities.
When it comes to children who have both reading and math disability, it has been debated whether these two disabilities are attributed to one and the same underlying cognitive deficit, or if each disability is attributed to a different cognitive weakness, both having arisen independently. Future brain imaging research is likely to be helpful in shedding some light onto this question.