Structural brain alterations associated with dyslexia predate reading onset

Abstract

Functional magnetic resonance imaging studies have reported reduced activation in parietotemporal and occipitotemporal areas in adults and children with developmental dyslexia compared to controls during reading and reading related tasks. These patterns of regionally reduced activation have been linked to behavioral impairments of reading-related processes (e.g., phonological skills and rapid automatized naming). The observed functional and behavioral differences in individuals with developmental dyslexia have been complemented by reports of reduced gray matter in left parietotemporal, occipitotemporal areas, fusiform and lingual gyrus and the cerebellum. An important question for education is whether these neural differences are present before reading is taught. Developmental dyslexia can only be diagnosed after formal reading education starts. However, here we investigate whether the previously detected gray matter alterations in adults and children with developmental dyslexia can already be observed in a small group of pre-reading children with a family-history of developmental dyslexia compared to age and IQ-matched children without a family-history (N = 20/mean age: 5:9 years; age range 5:1–6:5 years). Voxel-based morphometry revealed significantly reduced gray matter volume indices for pre-reading children with, compared to children without, a family-history of developmental dyslexia in left occipitotemporal, bilateral parietotemporal regions, left fusiform gyrus and right lingual gyrus. Gray matter volume indices in left hemispheric occipitotemporal and parietotemporal regions of interest also correlated positively with rapid automatized naming. No differences between the two groups were observed in frontal and cerebellar regions. This discovery in a small group of children suggests that previously described functional and structural alterations in developmental dyslexia may not be due to experience-dependent brain changes but may be present at birth or develop in early childhood prior to reading onset. Further studies using larger sample sizes and longitudinal analyses are needed in order to determine whether the identified structural alterations may be utilized as structural markers for the early identification of children at risk, which may prevent the negative clinical, social and psychological outcome of developmental dyslexia.

Functional characteristics of developmental dyslexia in left-hemispheric posterior brain regions predate reading onset

“…It has been hypothesized that hypoactivation in DD within left temporoparietal and occipitotemporal areas of the brain are fundamental to the language disorder itself, as differences in these areas during reading tasks are apparent, even when comparing children with DD to younger, typical readers, who are on the same reading level (44). Our results support this hypothesis and one can further hypothesize that prereading children at risk for DD exhibit reduced gray-matter volume indices in left temporoparietal and occipitotemporal brain regions (62), which then lead to a disruption of the network typically involved in phonological processing and subsequent reading failure. Brain regions, which were included in subsequent region of interest analyses, are shown in boldface.…”

“…Furthermore, reduced gray-matter volume indices in temporoparietal and occipitotemporal brain regions have been reported in prereading children at risk for DD compared with their peers (62). The left temporoparietal region of the brain is known to be crucial for the integration of letter and speech sounds (68) and has consistently demonstrated activation during phonological processing tasks in typically reading children and adults (for reviews, see refs.…”

“…Voxel-based morphometry reveals differences in gray-matter volume indices in individuals with DD (compared with typical reading controls) in various areas of the brain, including left occipitotemporal and temporoparietal areas (44,(56)(57)(58)(59)(60)(61), bilateral fusiform (59), and lingual gyrus (LG) (58) as well as the cerebellum (56)(57)(58). Morphological abnormalities in these regions can be identified even before reading skills are present in children as young as 5 to 6 y of age, suggesting atypical early development or even a genetic basis for DD (62).…”

Print-specific multimodal brain activation in kindergarten improves prediction of reading skills in second grade

“…The corresponding N1 (~170ms) ERP attenuation and its magneto-encephalographic homologue also point to diminished sensitivity to print in dyslexics (Helenius et al, 1999;Kronbichler et al, 2006;Maurer et al, 2007;. Furthermore, the following evidence points to the potential of occipito-temporal activity for predicting reading skills at a young age: i) structural alterations within the VWFS of at-risk children before school enrolment (Raschle et al, 2011); ii) its importance in learning to read supported by the early and rapidly emerging sensitivity to letters or letter strings (Brem et al, 2010;Cantlon et al, 2011); iii) the neurophysiological differences between normal readers and dyslexics seen in the corresponding N1 ERP (Maurer et al, 2007). Because interventions for poor readers might be most beneficial when started in parallel with reading acquisition (Bradley and Bryant, 1983) the identification of predictors at preschool age would be particularly valuable.…”

“…An fMRI study by Specht and colleagues (Specht et al 2009) revealed a negative correlation of the strength of activation in the occipitotemporal cortex and the dyslexia risk index and a structural MRI study reported significantly reduced grey matter volume in the left occipito-temporal and bilateral parieto-temporal cortex, the left fusiform gyrus and the right lingual gyrus in familial at-risk children in preschool (Raschle et al, 2011). Interestingly, most areas with diminished grey matter volume in at-risk children, and especially the basal left occipito-temporal cortex often referred to as the visual word form system (VWFS) (Cohen et al, 2000;Vinckier et al, 2007), plays a key role in print processing when children learn to read (Brem et al, 2010;Maurer et al, 2006).…”