Is Dyslexia a Brain Disorder?

Abstract

Specific word reading difficulty, commonly termed ‘developmental dyslexia’, refers to the low end of the word reading skill distribution but is frequently considered to be a neurodevelopmental disorder. This term implies that brain development is thought to be disrupted, resulting in an abnormal and dysfunctional brain. We take issue with this view, pointing out that there is no evidence of any obvious neurological abnormality in the vast majority of cases of word reading difficulty cases. The available relevant evidence from neuroimaging studies consists almost entirely of correlational and group-differences studies. However, differences in brains are certain to exist whenever differences in behavior exist, including differences in ability and performance. Therefore, findings of brain differences do not constitute evidence for abnormality; rather, they simply document the neural substrate of the behavioral differences. We suggest that dyslexia is best viewed as one of many expressions of ordinary ubiquitous individual differences in normal developmental outcomes. Thus, terms such as “dysfunctional” or “abnormal” are not justified when referring to the brains of persons with dyslexia.

It’s Time to Be Scientific About Dyslexia

“…Clearly, reading disability has a neurobiological component, as does proficiency across all domains of human performance (Protopapas & Parrila, 2018). Reference to a neurobiological origin, therefore, neither offers explanatory power nor serves a diagnostic function (Sand & Bolger, 2019).…”

“…Many fail to understand that the contribution of neuroscience to the practical task of assessment and intervention of reading disability is still rudimentary (Sand & Bolger, 2019), and scientific understandings continue to be undermined by methodological difficulties and the selective use of evidence (M.L. Elliott et al, 2020; Protopapas & Parrila, 2018; Ramus, Altarelli, Jednoróg, Zhao, & Scotto di Covella, 2018).…”

Evolving Concepts of Dyslexia and Their Implications for Research and Remediation

“…The question of whether dyslexia makes up some special population, outside of the general distribution of reading skill, has been investigated for some time now. Over the past decades, it seems increasingly accepted that there is no distinct group and that dyslexia concerns the low end of the distribution of reading skill (Ahmed et al, 2012;Snowling, 2013; see Protopapas and Parrila, 2018, for more references).…”

“…It is a view that will not prevail, in my opinion, because despite many efforts there are no indications of abnormality at any level of description, either genetic or neurological or cognitive or linguistic. There is much evidence confirming the existence of differences between groups of people with and without reading problems across some of these domains, but this kind of evidence is nowhere near establishing neurodevelopmental failure (see Protopapas and Parrila, 2018, for extensive discussion). Unfortunately, this issue is muddled by some researchers, who inappropriately use terms such as "neurological disorder" based on average differences between groups with and without dyslexia, with no evidence of disturbance or malfunction of the nervous system.…”

“…This would not lead us to characterize the individuals with deviations from average performance as neurologically disordered. Likewise, group deviations -even extreme ones -from the average reading performance should hardly be characterized as "neurological disorders" but, rather, as expected occurrences in the context of individual variability (Protopapas and Parrila, 2018).…”