Is dyslexia a neurodevelopmental disorder? Is it possible to talk about a developmental disorder in the case of reading, but not in the case of chess? Is the brain development of dyslexic individuals atypical?
According to Gorka Fraga González, Iliana I. Karipidis, and Jurgen Tijms (2018), the answer to these questions is "yes", although the notion of dyslexia as a neurodevelopmental disorder has been repeatedly brought into question by several authors (e.g., Elliott, 2006; Lopes, 2012; Protopapas & Parrila, 2018), based on the following arguments:
- reading proficiency is distributed along a continuum, and the break point which separates dyslexics from non-dyslexics is artificial and arbitrary, thus there is no need to create a category of dyslexic readers;
- the brain differences between dyslexics and non-dyslexics is purely individual (it does not contemplate group differences), and reading has a biological basis, like any other cognitive ability;
- dyslexia has its origin in poor teaching and may be corrected with adequate teaching methods;
- reading is not an innate ability, but a skill to be learned, within the framework of a certain writing system (which is itself a social product);
- learning to read is not, therefore, any different from learning to sing or play chess.
Harm and dysfunction in dyslexia
González, Kapiridis and Tijms refute all arguments against the concept of dyslexia as a neurodevelopmental disorder, although they stress that their own view is not incompatible with the place of dyslexia at the tail of the continuum of reading ability. First, they point out that the notion of dyslexia meets two of the fundamental criteria for being considered a mental disorder according to the criteria of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) of the American Psychiatric Association: (1) it constitutes a dysfunction of the neuropsychological processes involved in reading, and (2) it impairs the functioning of the individual in society at a level that can be considered clinically significant.
Regarding harm, González, Kapiridis, and Tijms stress that reading is an essential skill for functioning in modern societies, whether in school, at work, or in private life. It is an essential skill to obtain socio-economic success in a knowledge society.
Failure to become a fluent reader has a significant impact on the quality of life of individuals, limiting one's possibilities and increasing the risk of psychosocial problems, including anxiety and depression, which proves its clinical relevance.
With regard to dysfunctionality, the authors highlight the existence of an increasing number of studies on the neurobiological bases of dyslexia, suggesting the atypicality of the development of the brain networks of dyslexic subjects (e.g. Tamboer, Vorst, Ghebreab, & Scholte, 2016; Yu, Zuk, & Gaab, 2018). These anomalies are dysfunctional because they are persistent, and atypical because they are not present in most individuals. However, as with anxiety or depression, this does not necessarily imply a discontinuous distribution of reading competence, i.e. that there are categories of readers.
A growing number of studies (e.g. Richlan, Kronbichler, & Wimmer, 2011; Shaywitz & Shaywitz, 2008) conducted with Functional Magnetic Resonance (fMRI) have shown that dyslexics exhibit anomalous specialisation of the visual areas for word recognition, phonological processing in the auditory cortex, and integration of grapheme and phonemes in multisensory areas. However, González, Kapiridis, and Tijms point out that a recent meta-analysis on neuroanatomy of dyslexic subjects found inconsistencies across studies, possibly because selection criteria in many of them equate dyslexia to poor reading. Nevertheless, the authors consider that there is compelling evidence suggesting that impairments in dyslexia may originate from atypical specialisation of brain networks, which start quite early in development and tend to extend.
The perspective of dyslexia as a neurodevelopmental disorder is beneficial and has clinical and educational implications, according to González, Kapiridis, and Tijms. A first benefit relates to the specification of deficits at a level that behavioural description cannot achieve. A second benefit is the early detection of problems, increasing the probability of success of the intervention. On the other hand, neurodevelopmental tests predict reading difficulties better than behavioural tests. Finally, neurodevelopmental tests also better predict the effectiveness of the intervention.
In sum, González, Kapiridis, and Tijms point out that, unlike other learned abilities of considerable complexity, such as playing chess, difficulties in learning how to read have a clear impact on the well-being of individuals, and are therefore particularly harmful. On the other hand, they believe that there is enough evidence to state that these difficulties are caused by the atypical specialisation of brain networks, which have an early start and are persistent over time. The neurobiological mechanisms that impede the proper acquisition of reading skills are therefore dysfunctional. The fact it is both harmful and dysfunctional makes the case for dyslexia as a neurodevelopmental disorder.
Also, according to these authors, the view of dyslexia as a mental disorder is essential to facilitate adequate support to individuals which would not otherwise be provided.
Finally, González, Kapiridis, and Tijms consider that although a neurodevelopmental approach seems to suggest a categorical approach to dyslexia, there will be advantages in conceiving the problem as dimensional (i.e., as a continuum and not as a dichotomous yes/no category) and in accommodating the idea that there may not be one single cause for all reading problems.
Elliott, J. G., «Dyslexia: diagnoses, debates and diatribes», Education Canada, 46, 2006, pp. 14-17.
González, G., F. , Karipidis, I. I., & Tijms, J., «Dyslexia as a neurodevelopmental disorder and what makes it different from a chess disorder», Brain Sciences, 8, 2018.
Lopes, J., «Biologising reading problems: the specific case of dyslexia», Contemporary Social Science: Journal of the Academy of Social Sciences, 7, 2012, pp. 215-229.
Protopapas, A., & Parrila, R., «Is dyslexia a brain disorder?», Brain Sciences, 8, 2018.
Richlan, F., Kronbichler, M., & Wimmer, H., «Meta-analyzing brain dysfunctions in dyslexic children and adults», NeuroImage, 56(3), 2011, pp. 1735-1742.
Shaywitz, S. E., & Shaywitz, B. A., «Paying attention to reading: The neurobiology of reading and dyslexia», Development and Psychopathology, 20, 2008, pp. 1329-1349.
Tamboer, P., Vorst, H. C. M., Ghebreab, S., & Scholte, H. S., «Machine learning and dyslexia: Classification of individual structural neuro-imaging scans of students with and without dyslexia», NeuroImage: Clinical, 11, 2016, pp. 508-514.
Yu, X., Zuk, J., & Gaab, N., «What Factors Facilitate Resilience in Developmental Dyslexia? Examining Protective and Compensatory Mechanisms Across the Neurodevelopmental Trajectory», Child Development Perspectives, 12, 2018, pp. 240-246.