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

Abstract

Individuals with developmental dyslexia (DD) show a disruption in posterior left-hemispheric neural networks during phonological processing. Additionally, compensatory mechanisms in children and adults with DD have been located within frontal brain areas. However, it remains unclear when and how differences in posterior left-hemispheric networks manifest and whether compensatory mechanisms have already started to develop in the prereading brain. Here we investigate functional networks during phonological processing in 36 prereading children with a familial risk for DD (n = 18, average age = 66.50 mo) compared with age and IQ-matched controls (n = 18; average age = 65.61 mo). Functional neuroimaging results reveal reduced activation in prereading children with a family-history of DD (FHD + ), compared with those without (FHD − ), in bilateral occipitotemporal and left temporoparietal brain regions. This finding corresponds to previously identified hypoactivations in left hemispheric posterior brain regions for school-aged children and adults with a diagnosis of DD. Furthermore, left occipitotemporal and temporoparietal brain activity correlates positively with prereading skills in both groups. Our results suggest that differences in neural correlates of phonological processing in individuals with DD are not a result of reading failure, but are present before literacy acquisition starts. Additionally, no hyperactivation in frontal brain regions was observed, suggesting that compensatory mechanisms for reading failureare not yet present. Future longitudinal studies are needed to determine whether the identified differences may serve as neural premarkers for the early identification of children at risk for DD.is a specific learning disability that affects about 5-17% of all children (1, 2). DD is characterized by difficulties with accurate and fluent word recognition and poor spelling and decoding performance. DD cannot be accounted for by poor vision, hearing, or a lack of motivation. Molecular-genetic, twin, and family studies have shown a marked familial risk for DD, with an increasing prevalence in families with one or more members with a diagnosis of DD or reading difficulties (e.g., refs. 3 and 4). In addition, several DD susceptibility genes crucial for early brain development have been reported (5-8). DD can have severe social and psychological consequences (9-11) and may impact a child's life beyond their academic pursuits. Studies have shown that children with learning disabilities are less likely to complete high school (12) and are more likely to enter the juvenile justice system (13).Most researchers, clinicians, and reading specialists agree that DD typically results from a weakness in the ability to manipulate oral speech sounds of language (2,14). Individuals with DD are often unable to access the underlying sound structures of words, creating a difficulty in mapping sounds to written language (15-18). Phonological processing skills have been found to be a key predictor of later reading ability in pr...

Dysfunction of the auditory thalamus in developmental dyslexia

“…Previous neuroimaging studies on reading and phonological tasks have reported, in dyslexic participants relative to controls, higher activity in IFG (47,48) and less activation mostly in the left parietotemporal, left occipitotemporal, and left frontal areas (49)(50)(51), although this is not the case in all studies (e.g., refs. 52, 53).…”

Enhancement of brain event-related potentials to speech sounds is associated with compensated reading skills in dyslexic children with familial risk for dyslexia

“…An fMRI study in at-risk kindergartners reported hypoactivations at left posterior regions before formal reading instruction at brain areas corresponding to previously identified areas in adult and school-aged dyslexics (Raschle, Zuk & Gaab, 2012). Brain activity at left occipito-temporal and temporo-parietal areas was positively correlated with pre-reading skills in both groups.…”

“…It has been also seen that several dissimilar genetic profiles can lead to similarly manifesting phenotypes of dyslexia (Pennington, 2006;Willcutt et al, 2010). Many brain studies show anatomic and functional abnormalities in the brains of at-risk children before formal reading instruction, even at birth (e.g., Clark et al, 2014;Guttorm et al, 2001;Guttorm et al, 2003;Raschle, Zuk & Gaab, 2012;van Zuijen et al, 2012). It has been claimed, however, that the dissimilarities seen between the brain responses of dyslexics and controls at school age and as adults could in fact be caused by differences in reading experiences instead of being inherited.…”

An Electrophysiological Study of Print Processing in Kindergarten: The Contribution of the Visual N1 as a Predictor of Reading Outcome

“…Furthermore, the combination of the right prefrontal activation in a rhyming task and the white matter organization in the left superior longitudinal fasciculus informed about the long-term reading gains of children with developmental dyslexia (Hoeft et al, 2011). Lately, it has been shown that structural as well as functional (Raschle, Zuk, & Gaab, 2012) differences related to dyslexia are already detectable in preschool children, before they learn to read (Raschle, Chang, & Gaab, 2010). In children with a high familial risk of developing reading problems, a reduced amount of grey matter was found in the bilateral parietotemporal and left occipito-temporal regions (Raschle et al, 2010).…”