The Difference Between Developmental Dyslexia and Dysgraphia: Recent Neurobiological Evidence

International Journal of Neuroscience and Behavioral Science 8(1): 1-5, 2020 http://www.hrpub.org DOI: 10.13189/ijnbs.2020.080101

The Difference between Developmental Dyslexia and Dysgraphia: Recent Neurobiological Evidence

Filippos Vlachos*, Elias Avramidis

Department of Special Education, University of Thessaly, Greece

Received December 17, 2019; Revised February 25, 2020; Accepted March 12,2020

Abstract Developmental dyslexia and developmental 1. Introduction dysgraphia are considered to be distinct learning difficulties that affect the child's ability to learn. Dyslexia Developmental dyslexia and developmental dysgraphia affects all aspects of written language, while the symptoms are closely related developmental disorders that can exist of dysgraphia appear to be confined to difficulties in together as well as separately [1]. Although the literature writing. However, the distinction between the two learning contains different classifications and definitions for these difficulties is often obscured by the similar learning two disorders, they are often used interchangeably by cognitive deficits manifested by individuals diagnosed practitioners in the field. with these difficulties. The aim of this review is to Developmental dyslexia is the most common learning summarize and evaluate research concerning the disability in school-aged children. It is genetic in origin neurobiological basis of the two difficulties with a view to with a neurobiological substrate. It is characterized by a assist researchers and practitioners in their classification of marked impairment in the development of reading skills individuals with resembling deficits. In so doing, we bring and affects a considerable number of children [2-4]. together the findings of studies that have utilized powerful Although difficulties in accurate and/or fluent word neuroimaging techniques such as functional Magnetic reading are at the core of the definition of developmental Resonance Imaging (fMRI). The evidence suggests that dyslexia, the latter is not just a reading disorder [3, 5]. It is while individuals with dyslexia and dysgraphia share a also a writing disorder because of the spelling mistakes that left-hemisphere processing limitation resulted from the emerge with the production of written texts; nevertheless, absence of a scanning mechanism for disembedding, the writing problems in developmental dyslexia remain under-recognised and under-treated [6]. Young children encoding, and rehearsing visual patterns (e.g., words), identified as at risk for being diagnosed with the disorder there are important neurological differences that may also experience delayed language development and distinguish the two groups. Specifically, recent have trouble learning to spell and write as they reach neurobiological studies have shown that children with school age. That is why in the case of a child struggling developmental dysgraphia differ from their dyslexic with reading or writing, it can be difficult to pinpoint counterparts in white matter integrity, functional exactly what the problem is. connectivity revealed by fMRI, and white matter-gray Developmental dysgraphia may be defined as a failure in matter correlations. These differences in the brain between the normal development of writing skills [7]. Writing skills children with developmental dyslexia and children with are below those expected for a person’s age or ability, dysgraphia confirm the neurobiological distinction despite appropriate education. It may contribute between these two special learning difficulties. Based on significantly to a child’s learning difficulty or learning these neurobiological differences researchers and disability and is a matter of both educational and medical practitioners in the field should exercise special care not to significance [8]. Some children diagnosed with treat the two disorders as the same in their research or developmental dysgraphia have developed strong verbal professional practice. skills to compensate for their writing issues and are often Keywords Developmental Dyslexia, Developmental strong readers. Because little is known about the disorder, Dysgraphia, Neurobiological Differences it often remains unidentified by educators and other professionals in the field. This could be partly attributed to the significant handwriting and spelling problems 2 The Difference between Developmental Dyslexia and Dysgraphia: Recent Neurobiological Evidence

exhibited in dysgraphic learners which often lead to developmental dysgraphia, Döhla and Heim suggest practitioners to confuse developmental dysgraphia with the that phonological awareness plays an important role in more commonly found developmental dyslexia, despite the both dyslexia and dysgraphia. Additionally, they assume dysgraphic learners’ unimpaired reading skills. that further predictors such as working memory, auditory The Diagnostic and Statistical Manual of Mental processing, visual attention, and language impairment Disorders (4th edition) distinguishes between three play an important role in reading and writing as well [1]. categories of learning disabilities, namely: reading Another recent review synthesized neuroimaging disability, mathematical disability and ‘disorder of written studies carried out in adults and in children with and expression’, together with a fourth category, ‘learning without learning disabilities with a view to identifying the disability not otherwise specified’. Developmental neural network involved in handwriting and reading. This dysgraphia as a disorder of written expression is review concluded that the mastery of handwriting is based characterised by “writing skills (that) …are substantially on the involvement of a network of brain structures which below those expected given the person's chronological age, is built upon the joint learning of writing and reading. A measured intelligence, and age-appropriate education” [9]. part of this graphomotor network is brought into play However, in this definition there is a lack of clarity as to during the identification of letters through visual reading. whether writing refers only to the motor skill of writing Additionally, both writing and reading form the basis for (which is the traditional interpretation) or whether it also the accomplishment of more complex language tasks includes the orthographic skill of spelling [10]. involving orthographic knowledge such as the In the 5th edition of the Diagnostic and Statistical composition of texts [12]. Manual of Mental Disorders (DSM-V), developmental In another review, Nicolson and Fawcett sought to dysgraphia no longer exists as a separate category but falls identify the similarities and differences between under the category of "specific learning disorder." This developmental dyslexia and dysgraphia. They concluded category refers to difficulties in learning and to limited that both of these learning disabilities reflect lack of academic skills, as indicated by the presence of at least one automaticity at the cognitive level, which can be attributed of the following symptoms that have persisted for at least 6 to impaired circuits of procedural learning located at the months despite the provision of interventions that target cerebellum. Accordingly, the authors suggest that ‘pure’ those difficulties: inaccurate or slow and effortful word dysgraphia reflects an impairment of the cerebellar-motor reading; or difficulty understanding the meaning of what is circuit and ‘pure’ dyslexia reflects an impairment of the read, or with spelling, or with written expression, or cerebellar-language circuit [10]. mastering number sense, number facts, or calculation; or In regards to the neurobiological cause of difficulties with mathematical reasoning [11]. developmental dyslexia and dysgraphia, in a previous In sum, both developmental dyslexia and developmental published study, Mather proposed the concurrent dysgraphia affect the child's ability to learn. It must be tapping/line orientation procedure. This procedure aimed stressed, however, that although they are considered to be to investigate brain-processing differences in early two distinct learning difficulties that affect the child's adolescence with dysgraphia, dyslexia and good learning ability in a very different way, little is known readers/spellers. This study demonstrated that individuals about their neurological differences. The aim of this review with dyslexia and dysgraphia are different from healthy is to summarize and evaluate recent empirical research, individuals, having a print-scanning deficit in common. which supports the distinction between developmental From this study the author concluded that individuals with dyslexia and dysgraphia not only at the behavioral but also dyslexia and dysgraphia share a left-hemisphere at the neurobiological level. processing limitation resulted from the absence of a scanning mechanism for disembedding, encoding, and rehearsing visual patterns (e.g., words). This limitation 2. Similarities and Differences could have arisen due to introducing written language prematurely to children late in developing left-hemisphere Dyslexia affects all aspects of written language, while motor dominance [13]. the symptoms of dysgraphia appear to be confined to Apart from the above mentioned findings in children, difficulties in handwriting [1]. For this reason, in the another study examined the cognitive mechanisms and process of diagnosing dysgraphia and in order to give a neural substrates of phonological dyslexia and dysgraphia, student the corresponding characterization, it is also in a large cohort of adult patients with focal damage to necessary that reading ability and spelling should not be perisylvian cortical regions that had affected phonological deficient. In a recent review, Döhla and Heim concluded processing. Lesion-deficit correlations indicated that that both learning disabilities have diverse comorbidities phonological dyslexia and dysgraphia may be produced and predictors within and outside the language domain in by a damage in a variety of perisylvian cortical regions, common. Examining how far existing knowledge about consistent with distributed network models of the cognitive causes of developmental dyslexia also apply phonological processing. Their results provide empirical

International Journal of Neuroscience and Behavioral Science 8(1): 1-5, 2020 3

support for shared-components models of written students with dysgraphia and students with dyslexia language processing, according to which the same central differed in white matter integrity, fMRI functional cognitive systems support both reading and spelling. [14]. connectivity, and white matter-gray matter correlations. Overall, the above mentioned studies indicate that Such findings provide evidence that the two specific writing and reading share common brain and cognitive learning difficulties are not the same, because functional networks. Such findings suggest that developmental links were not the same in children with dyslexia and dyslexia and dysgraphia might have a similar those with dysgraphia, either in writing or in cognitive neurobiological basis. tasks [20]. Another study examined whether students in grades 4 to 9 with persistent problems with written language 3. Recent Neurobiological Evidence beyond the first three school grades could be classified into one of the three Specific Learning Disability (SLD) Many neuroimaging studies indicate that the disruption diagnostic categories defined on the basis of level of of left hemisphere posterior brain systems underlies the language impairment: developmental dysgraphia symptoms of developmental dyslexia [15-17]. Such (impaired subword handwriting), developmental dyslexia findings are in line with the suggestion of the greater right (impaired word spelling and reading), or oral and written hemisphere involvement in the expression of language learning disability (impaired oral and written developmental dyslexia revealed by behavioral studies syntax comprehension and expression). In this study, [18]. language impairment was assessed through administering As regards dysgraphia, a review of the neural correlates normed tests and parent questionnaires as well as of dysgraphia derived from lesion studies and studies examining the students’ recorded developmental and using neuroimaging and assessment of minor neurological educational histories. Furthermore, this study examined dysfunction concluded that our knowledge on the neural whether these three diagnostic groups might also have substrate of paediatric dysgraphia is limited. The limited different neuroimaging profiles in relation to fMRI available data suggest that at least some of the children functional connectivity in brain locations associated with with developmental dysgraphia have dysfunctions in processing and producing written words on a extensive supraspinal networks, involving cortical areas in word-specific spelling task to other brain locations. The all regions of the brain, while in others, dysfunction may findings confirmed unique diagnostic patterns based on be restricted to either the cerebellum or specific cortical impairments in levels of language. Moreover, these results sites [19]. provided converging fMRI functional connectivity brain However, the advent of more sophisticated evidence that those with developmental dysgraphia, neuroimaging technologies over the last years, allowed developmental dyslexia, oral and written language brain activation to be measured objectively. Recent learning disability, and controls differ in their neuroimaging studies provide evidence on the distinction neuroimaging profiles. Additionally, the three SLD between these two specific learning difficulties at the groups differed in the number of functional connections neurobiological level. made from the same local brain region to other brain In a recent study, researchers using fMRI (functional regions during a common word-specific spelling task. Magnetic Resonance Imaging: a magnetic resonance Based on behavioral and brain evidence, researchers imaging-based technique that makes it possible to detect concluded that developmental dysgraphia, developmental the brain areas that are involved in a task) and DTI dyslexia, and oral and written language learning disability (Diffusion Tensor Imaging: a neuroimaging technique appear to be discreet SLDs, even if they share some which makes it possible to estimate the location, commonalities [21]. orientation, and anisotropy of the brain's white matter In sum, both the aforementioned studies provide tracts) examined three groups of children (dyslexics, evidence that the brain differences observed in dysgraphics and typical developers) aged 9-15 years. developmental dysgraphia and developmental dyslexia on Having administered graphic tasks, they concluded that written language tasks are consistent with their behavioral the three groups differed from each other in graphic and impairments in handwriting and/or in word spelling. cognitive tasks. The control group had more interfaces to the white matter, which facilitate functional links to the gray matter for language and cognitive work. Conversely, 4. Discussion & Conclusions children with developmental dyslexia and developmental dysgraphia showed less white matter connections and There is a considerable overlap between dyslexia and more functional links to gray matter sites - in other words, dysgraphia since they are both developmental language their brains had to work harder to achieve the same tasks. disorders that can manifest themselves in similar ways. For As the researchers note, their brains were less effective in example, in both disorders converting phonemes (sounds) language processing. Additionally, the results showed that into graphemes (letters in written form) constitute major

4 The Difference between Developmental Dyslexia and Dysgraphia: Recent Neurobiological Evidence

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