Neuroimaging Reveals Heterogeneous Neural Correlates of Reading Deficit in Individuals with Dyslexia Consistent with a Multiple Deficit Model

Abstract

Neuroimaging has become a powerful way of studying in vivo brain function and structure. The aim here is to comprehensively review Reid's fMRI study which is the first to use a multiple case approach to investigate individual differences among 18 participants with dyslexia (DPs) and 16 control participants (CPs) and to directly test the predictions of the main dyslexia theories on reading deficit. The results show that the neural correlates of reading deficit for all DPs (except one) are consistent with more than one theory, supporting a multiple deficit model. Striking individual differences between DPs were found; even if the neural correlates of reading deficit in two DPs were consistent with the same theory, the affected brain areas could differ. To make progress, research on causes of reading deficit in dyslexia would need to (1) focus on the multiple deficit model, (2) use neuroimaging to test a further refined set of brain areas (including areas hypothesised by other dyslexia theories) in longitudinal designs, (3) control the effects of co-occurring neurodevelopmental disorders, (4) use high-field MRI (including diffusion techniques), multiband fMRI and MEG with optically pumped magnetometers, (5) progress imaging genetics and (6) pursue neuroimaging intergenerational transmission of brain circuity.

Neuroimaging Findings for Developmental Coordination Disorder (DCD) in Adults: Critical Evaluation and Future Directions

“…Otherwise the results would be confounded by the effect of co-occurring developmental disorders and no claims could be made with regard to the effects of DCD. For a similar argument regarding research on developmental dyslexia see [77,78].…”

“…The issue of individual differences is crucial in studying and understanding heterogeneous developmental disorders; however, it is usually (with few exceptions, e.g. [77,78]) neglected. As stated earlier in this chapter, DCD is a heterogeneous disorder, hence reliance on between-group comparisons (with a group consisting of participants with DCD (DCDPs) being most likely heterogeneous) might obscure the results for underrepresented or rarer cases.…”

“…Such research is more advanced regarding other developmental disorders, e.g. ADHD and developmental dyslexia [78]. Finally, it needs to be underscored that the biological complexity of DCD cannot be disregarded and genome-wide measurements, together with investigations of individual genes and pathways, are crucial in ascertaining the underlying mechanisms of neurodevelopmental disorders, such as DCD [105].…”

“…Additionally, after controlling for brain size, patients with increasing X or Y chromosome dosage also tend to have a disproportionally reduced size of cerebellum, pallidum and amygdala [117][118][119]. As discussed above, cerebellar abnormalities have been reported in neuroimaging studies involving DCDAs [51,52] and children with DCD [82,120,121], but also other developmental disorders, such dyslexia [77,78,122] and ADHD [123]. Furthermore, studies on children with DCD have revealed functional abnormalities in the basal ganglia and pallidum [124,125].…”

Words as Visual Objects: Neural and Behavioral Evidence for High-Level Visual Impairments in Dyslexia

“…Accordingly, reading problems have been associated with a wide variety of difficulties, such as a temporal processing deficit [ 8 , 9 , 10 ], slowed visual processing [ 11 ], developmental impairments of magnocellular neurons [ 12 ], visual attentional deficits [ 13 ], and difficulties with rapid automatized naming (RAN) [ 14 , 15 ]. Moreover, two persons showing the same pattern of reading deficits can have very different neural responses to reading [ 16 ], and there appear to be several distinct, additive risk factors for reading disability [ 17 ]. Lastly, the influence of phonological awareness in dyslexia seems to be modulated by the orthography of languages, where it is less associated with reading outcomes in languages with shallow, or more transparent, orthographies [ 18 ].…”