Structural brain alterations associated with dyslexia predate reading onset

Cortical Structure in Pre-Readers at Cognitive Risk for Dyslexia: Baseline Differences and Response to Intervention

Early childhood is a critical period for structural brain development as well as an important window for the identification and remediation of reading difficulties. Recent research supports the implementation of interventions in at-risk populations as early as kindergarten or first grade, yet the neurocognitive mechanisms following such interventions remain understudied. To address this, we investigated cortical structure by means of anatomical MRI before and after a 12-week tablet-based intervention in: (1) at-risk children receiving phonics-based training (n = 29; n = 16 complete pre-post datasets), (2) at-risk children engaging with AC training (n = 24; n = 15 complete pre-post datasets) and (3) typically developing children (n = 25; n = 14 complete pre-post datasets) receiving no intervention. At baseline, we found higher surface area of the right supramarginal gyrus in at-risk children compared to typically developing peers, extending previous evidence that early anatomical differences exist in children who may later develop dyslexia. Our longitudinal analysis revealed significant post-intervention thickening of the left supramarginal gyrus, present exclusively in the intervention group but not the active control or typical control groups. Altogether, this study contributes new knowledge to our understanding of the brain morphology associated with cognitive risk for dyslexia and response to early intervention, which in turn raises new questions on how early anatomy and plasticity may shape the trajectories of long-term literacy development.

Leveraging brain science for impactful advocacy and policymaking: The synergistic partnership between developmental cognitive neuroscientists and a parent-led grassroots movement to drive dyslexia prevention policy and legislation

Reading proficiency is crucial for academic, vocational, and economic success and has been closely linked to health outcomes. Unfortunately, in the United States, a concerning 63% of fourth-grade children are reading below grade level, with approximately 7%-10% exhibiting a disability in word reading, developmental dyslexia. Research in developmental cognitive neuroscience indicates that individuals with dyslexia show functional and structural brain alterations in regions processing reading and reading-related information, with some of these differences emerging as early as preschool and even infancy. This suggests that some children start schooling with less optimal brain architecture for learning to read, emphasizing the need for preventative education practices. This article reviews educational policies impacting children with dyslexia and highlights a decentralized parent-led grassroots movement, Decoding Dyslexia, which centers the voices of those directly impacted by dyslexia. It utilizes civic engagement practices, advocacy and lobbying on local, federal, and social media platforms, and strong partnerships with scientists to drive systems-level change in educational practices, leading to dyslexia prevention legislation across the U.S. The ongoing partnership continues to address the profound gaps between scientific findings and policymaking to drive systems-level change for contemporary challenges in educational practices within a learning disabilities framework.

Revisiting the definition of dyslexia

The International Dyslexia Association definition of dyslexia was updated 20 years ago and has been referenced frequently in research and practice. In this paper, researchers from the Florida Center for Reading Research consider the components of the definition and make recommendations for revisions. These include recognizing the persistence of word-reading, decoding, and spelling difficulties, acknowledging the multifactorial causal basis of dyslexia, clarifying exclusionary factors, and denoting comorbidity with other developmental disorders. It is also suggested that the academic and psychosocial consequences of dyslexia be highlighted to reinforce a preventive service delivery model. Lastly, the inclusion of dyslexia within a specific learning disability category is supported.

Genetic Modifications of Developmental Dyslexia and Its Representation Using In Vivo, In Vitro Model

Dyslexia is a genetic and heritable disorder that has yet to discover the treatment of it, especially at the molecular and drug intervention levels. This review provides an overview of the current findings on the environmental and genetic factors involved in developmental dyslexia. The latest techniques used in diagnosing the disease and macromolecular factors findings may contribute to a higher degree of development in detangling the proper management and treatment for dyslexic individuals. Furthermore, this review tried to put together all the models used in the current dyslexia research for references in future studies that include animal models as well as in vitro models and how the previous research has provided consistent data across many years and regions. Thus, we suggest furthering the studies using an organoid model based on the existing gene polymorphism, pathways, and neuronal function input.

Beyond the language network: Associations between reading, receptive vocabulary, and grey matter volume in 10-year-olds

Most research on the neurostructural basis of language abilities in children stems from small samples and surface-based measures. To complement and expand the existent knowledge, we investigated associations between grey matter volume and language performance in a large sample of 9-to-11-year-old children, using data from the Adolescent Brain Cognitive Development (ABCD) Study (N = 1865) and an alternative measure of grey matter morphology. We estimated whole-brain grey matter volume for one half of the sample (N = 939) and tested for correlations with scores on a picture vocabulary and a letter and word reading test, with and without factoring in general intelligence and total grey matter volume as additional covariates. The initial analyses yielded correlations between grey matter in the right occipital fusiform gyrus, the right lingual gyrus, and the cerebellum for both vocabulary and reading. Employing the significant clusters from the first analyses as regions of interest in the second half of the cohort (N = 926) in correlational and multiple regression analyses suggests the cluster in the right occipital fusiform and lingual gyri to be most robust. Overall, the amount of variance explained by grey matter volume is limited and factoring in additional covariates paints an inconsistent picture. The present findings reinforce existent doubt with respect to explaining individual differences in reading and vocabulary performance based on unique contributions of macrostructural brain features.

An Overview on Electrophysiological and Neuroimaging Findings in Dyslexia

Objective: Dyslexia is a prevalent neurodevelopmental condition that is characterized by inaccurate and slow word recognition. This article reviews neural correlates of dyslexia from both electrophysiological and neuroimaging studies. Method : In this brief review, we provide electrophysiological and neuroimaging evidence from electroencephalogram (EEG) and magnetic resonance imaging (MRI) studies in dyslexia to understand functional and structural brain changes in this condition. Results: In both electrophysiological and neuroimaging studies, the most frequently reported functional impairments in dyslexia include aberrant activation of the left hemisphere occipito-temporal cortex (OTC), temporo-parietal cortex (TPC), inferior frontal gyrus (IFG), and cerebellar areas. EEG studies have mostly highlighted the important role of lower frequency bands in dyslexia, especially theta waves. Furthermore, neuroimaging studies have suggested that dyslexia is related to functional and structural impairments in the left hemisphere regions associated with reading and language, including reduced grey matter volume in the left TPC, decreased white matter connectivity between reading networks, and hypo-activation of the left OTC and TPC. In addition, neural evidence from pre-reading children and infants at risk for dyslexia show that there are abnormalities in the dyslexic brain before learning to read begins. Conclusion: Advances in comprehending the neural correlates of dyslexia could bring closer translation from basic to clinical neuroscience and effective rehabilitation for individuals who struggle to read. However, neuroscience still has great potential for clinical translation that requires further research.

The Role of Neural and Genetic Processes in Learning to Read and Specific Reading Disabilities: Implications for Instruction

To learn to read, the brain must repurpose neural systems for oral language and visual processing to mediate written language. We begin with a description of computational models for how alphabetic written language is processed. Next, we explain the roles of a dorsal sublexical system in the brain that relates print and speech, a ventral lexical system that develops the visual expertise for rapid orthographic processing at the word level, and the role of cognitive control networks that regulate attentional processes as children read. We then use studies of children, adult illiterates learning to read, and studies of poor readers involved in intervention, to demonstrate the plasticity of these neural networks in development and in relation to instruction. We provide a brief overview of the rapid increase in the field's understanding and technology for assessing genetic influence on reading. Family studies of twins have shown that reading skills are heritable, and molecular genetic studies have identified numerous regions of the genome that may harbor candidate genes for the heritability of reading. In selected families, reading impairment has been associated with major genetic effects, despite individual gene contributions across the broader population that appear to be small. Neural and genetic studies do not prescribe how children should be taught to read, but these studies have underscored the critical role of early intervention and ongoing support. These studies also have highlighted how structured instruction that facilitates access to the sublexical components of words is a critical part of training the brain to read.

A Scoping Review on Movement, Neurobiology and Functional Deficits in Dyslexia: Suggestions for a Three-Fold Integrated Perspective

Developmental dyslexia is a common complex neurodevelopmental disorder. Many theories and models tried to explain its symptomatology and find ways to improve poor reading abilities. The aim of this scoping review is to summarize current findings and several approaches and theories, focusing on the interconnectedness between motion, emotion and cognition and their connection to dyslexia. Consequently, we present first a brief overview of the main theories and models regarding dyslexia and its proposed neural correlates, with a particular focus on cerebellar regions and their involvement in this disorder. After examining different types of intervention programs and remedial training, we highlight the effects of a specific structured sensorimotor intervention named Quadrato Motor Training (QMT). QMT utilizes several cognitive and motor functions known to be relevant in developmental dyslexia. We introduce its potential beneficial effects on reading skills, including working memory, coordination and attention. We sum its effects ranging from behavioral to functional, structural and neuroplastic, especially in relation to dyslexia. We report several recent studies that employed this training technique with dyslexic participants, discussing the specific features that distinguish it from other training within the specific framework of the Sphere Model of Consciousness. Finally, we advocate for a new perspective on developmental dyslexia integrating motion, emotion and cognition to fully encompass this complex disorder.

Longitudinal changes in brain activation underlying reading fluency

Reading fluency-the speed and accuracy of reading connected text-is foundational to educational success. The current longitudinal study investigates the neural correlates of fluency development using a connected-text paradigm with an individualized presentation rate. Twenty-six children completed a functional MRI task in 1st/2nd grade (time 1) and again 1-2 years later (time 2). There was a longitudinal increase in activation in the ventral occipito-temporal (vOT) cortex from time 1 to time 2. This increase was also associated with improvements in reading fluency skills and modulated by individual speed demands. These findings highlight the reciprocal relationship of the vOT region with reading proficiency and its importance for supporting the developmental transition to fluent reading. These results have implications for developing effective interventions to target increased automaticity in reading.

Reduced pattern similarity in brain activation during orthographic processing in children with developmental dyslexia

Intra-individual variability of neural response has been found to be negatively associated with cognitive proficiency and automaticity. However, whether developmental dyslexia (DD) is marked by greater intra-individual neural variability remains unclear. Using a multivariate approach and dual-control group design, the current study aims to examine whether the pattern similarity of brain activation during a visual spelling task is abnormal in children with DD compared to age control and reading control children. We found that there was reduced intra-subject pattern similarity at the left occipito-temporal regions in children with DD than both control groups, suggesting a neural signature of DD. Furthermore, we found that pattern similarity was positively associated with stability of reaction time and reading fluency in both children with DD and typical control children, suggesting that neural stability supports behavioral stability and automaticity during reading.

Animal models of developmental dyslexia

As some critics have stated, the term “developmental dyslexia” refers to a strictly human disorder, relating to a strictly human capacity – reading – so it cannot be modeled in experimental animals, much less so in lowly rodents. However, two endophenotypes associated with developmental dyslexia are eminently suitable for animal modeling: Cerebral Lateralization, as illustrated by the association between dyslexia and non-righthandedness, and Cerebrocortical Dysfunction, as illustrated by the described abnormal structural anatomy and/or physiology and functional imaging of the dyslexic cerebral cortex. This paper will provide a brief review of these two endophenotypes in human beings with developmental dyslexia and will describe the animal work done in my laboratory and that of others to try to shed light on the etiology of and neural mechanisms underlying developmental dyslexia. Some thought will also be given to future directions of the research.

Researcher-practitioner partnerships and in-school laboratories facilitate translational research in reading

Educational neuroscience approaches have helped to elucidate the brain basis of Reading Disability (RD) and of reading intervention response; however, there is often limited translation of this knowledge to the broader scientific and educational communities. Moreover, this work is traditionally lab-based, and thus the underlying theories and research questions are siloed from classroom practices. With growing awareness of the neurobiological origins of RD and increasing popularity of putative "brain-based" approaches in clinics and classrooms, it is imperative that we create more direct and bidirectional communication between scientists and practitioners. Such direct collaborations can help dispel neuromyths, and lead to increased understanding of the promises and pitfalls of neuroscience approaches. Moreover, direct partnerships between researchers and practitioners can lead to greater ecological validity in study designs to improve upon the translational potential of findings. To this end, we have forged collaborative partnerships, and built cognitive neuroscience laboratories within independent reading disabilities schools. This approach affords frequent and ecologically valid neurobiological assessment as children's reading improves in response to intervention. It also permits the creation of dynamic models of leading and lagging relationships of students' learning, and identification of individual-level predictors of intervention response. The partnerships also provide in-depth knowledge of student characteristics and classroom practices, which, when combined with the data we acquire, may facilitate optimization of instructional approaches. In this commentary, we discuss the creation of our partnerships, the scientific problem we are addressing (variable response to reading intervention), and the epistemological significance of researcher-practitioner bi-directional learning.

A Spatiotemporal Map of Reading Aloud

Reading words aloud is a fundamental aspect of literacy. The rapid rate at which multiple distributed neural substrates are engaged in this process can only be probed via techniques with high spatiotemporal resolution. We probed this with direct intracranial recordings covering most of the left hemisphere in 46 humans (26 male, 20 female) as they read aloud regular, exception and pseudo-words. We used this to create a spatiotemporal map of word processing and to derive how broadband γ activity varies with multiple word attributes critical to reading speed: lexicality, word frequency, and orthographic neighborhood. We found that lexicality is encoded earliest in mid-fusiform (mFus) cortex, and precentral sulcus, and is represented reliably enough to allow single-trial lexicality decoding. Word frequency is first represented in mFus and later in the inferior frontal gyrus (IFG) and inferior parietal sulcus (IPS), while orthographic neighborhood sensitivity resides solely in IPS. We thus isolate the neural correlates of the distributed reading network involving mFus, IFG, IPS, precentral sulcus, and motor cortex and provide direct evidence for parallel processes via the lexical route from mFus to IFG, and the sublexical route from IPS and precentral sulcus to anterior IFG.SIGNIFICANCE STATEMENT Reading aloud depends on multiple complex cerebral computations: mapping from a written letter string on a page to a sequence of spoken sound representations. Here, we used direct intracranial recordings in a large cohort while they read aloud known and novel words, to track, across space and time, the progression of neural representations of behaviorally relevant factors that govern reading speed. We find, concordant with cognitive models of reading, that known and novel words are differentially processed through a lexical route, sensitive to frequency of occurrence of known words in natural language, and a sublexical route, performing letter-by-letter construction of novel words.

Exploring boundary conditions of the listening comprehension-reading comprehension discrepancy index

Conversations about the nature of dyslexia and how dyslexia impacts reading and listening comprehension get to the heart of classification and identification models of dyslexia. Recently, this conversation has been expanded to include efforts to estimate the prevalence of dyslexia in the population through the introduction of a discrepancy index of listening comprehension and reading comprehension. This discrepancy index was proposed to serve as a proxy for dyslexia when estimating its prevalence in the population. Individuals whose reading comprehension is considerably lower than their listening comprehension are thought to exhibit unexpected reading deficits. However, the index could underrepresent certain groups within the population. The current study explored this possibility using data from a sample of 4078 public-school students. We hypothesized that students from historically marginalized or otherwise disenfranchised groups (i.e., poor and minority groups) would be less likely to have a positive listening comprehension - reading comprehension (LC-RC) discrepancy index. Based on the results of multilevel linear mixed effect modeling, socioeconomic status (SES) contributed to differential performance on the discrepancy index when it was calculated using residual scores. Moreover, African American students were identified as having a reliably lower discrepancy index regardless of how it was calculated. It appears that this index, which only looks at the comprehension of language and not production, may, in fact, disadvantage students for whom oral language production differs from General American English (GAE). These outcomes suggest that this measure may lack the sensitivity to identify bidialectal students with dyslexia.

Cross-Sectional Investigation of Brain Volume in Dyslexia

The goal of the study was to determine whether dyslexia is associated with differences in local brain volume, and whether these local brain volume differences show cross-sectional age-effects. We investigated the local volume of gray and white brain matter with voxel-based morphometry (VBM) as well as reading performance in three age groups of dyslexic and neurotypical normal reading subjects (children, teenagers and adults). Performance data demonstrate a steady improvement of reading skills in both neurotypical as well as dyslexic readers. However, the pattern of gray matter volumes tell a different story: the children are the only group with significant differences between neurotypical and dyslexic readers in local gray matter brain volume. These differences are localized in brain areas associated with the reading network (angular, middle temporal and inferior temporal gyrus as well as the cerebellum). Yet the comparison of neurotypical and normal readers over the age groups shows that the steady increase in performance in neurotypical readers is accompanied by a steady decrease of gray matter volume, whereas the brain volumes of dyslexic readers do not show this linear correlation between brain volume and performance. This is further evidence that dyslexia is a disorder with a neuroanatomical basis in the form of a lower volume of gray matter in parts of the reading network in early dyslexic readers. The present data point out that network shaping processes in gray matter volume in the reading network does take place over age in dyslexia. Yet this neural foundation does not seem to be sufficient to allow normal reading performances even in adults with dyslexia. Thus dyslexia is a disorder with lifelong consequences, which is why consistent support for affected individuals in their educational and professional careers is of great importance. Longitudinal studies are needed to verify whether this holds as a valid pattern or whether there is evidence of greater interindividual variance in the neuroanatomy of dyslexia.

Mother-child similarity in brain morphology: A comparison of structural characteristics of the brain's reading network

BACKGROUND

Substantial evidence acknowledges the complex gene-environment interplay impacting brain development and learning. Intergenerational neuroimaging allows the assessment of familial transfer effects on brain structure, function and behavior by investigating neural similarity in caregiver-child dyads.

METHODS

Neural similarity in the human reading network was assessed through well-used measures of brain structure (i.e., surface area (SA), gyrification (lG), sulcal morphology, gray matter volume (GMV) and cortical thickness (CT)) in 69 mother-child dyads (children's age~11 y). Regions of interest for the reading network included left-hemispheric inferior frontal gyrus, inferior parietal lobe and fusiform gyrus. Mother-child similarity was quantified by correlation coefficients and familial specificity was tested by comparison to random adult-child dyads. Sulcal morphology analyses focused on occipitotemporal sulcus interruptions and similarity was assessed by chi-square goodness of fit.

RESULTS

Significant structural brain similarity was observed for mother-child dyads in the reading network for lG, SA and GMV (r = 0.349/0.534/0.542, respectively), but not CT. Sulcal morphology associations were non-significant. Structural brain similarity in lG, SA and GMV were specific to mother-child pairs. Furthermore, structural brain similarity for SA and GMV was higher compared to CT.

CONCLUSION

Intergenerational neuroimaging techniques promise to enhance our knowledge of familial transfer effects on brain development and disorders.

Musical Performance in Adolescents with ADHD, ADD and Dyslexia—Behavioral and Neurophysiological Aspects

Research has shown that dyslexia and attention deficit (hyperactivity) disorder (AD(H)D) are characterized by specific neuroanatomical and neurofunctional differences in the auditory cortex. These neurofunctional characteristics in children with ADHD, ADD and dyslexia are linked to distinct differences in music perception. Group-specific differences in the musical performance of patients with ADHD, ADD and dyslexia have not been investigated in detail so far. We investigated the musical performance and neurophysiological correlates of 21 adolescents with dyslexia, 19 with ADHD, 28 with ADD and 28 age-matched, unaffected controls using a music performance assessment scale and magnetoencephalography (MEG). Musical experts independently assessed pitch and rhythmic accuracy, intonation, improvisation skills and musical expression. Compared to dyslexic adolescents, controls as well as adolescents with ADHD and ADD performed better in rhythmic reproduction, rhythmic improvisation and musical expression. Controls were significantly better in rhythmic reproduction than adolescents with ADD and scored higher in rhythmic and pitch improvisation than adolescents with ADHD. Adolescents with ADD and controls scored better in pitch reproduction than dyslexic adolescents. In pitch improvisation, the ADD group performed better than the ADHD group, and controls scored better than dyslexic adolescents. Discriminant analysis revealed that rhythmic improvisation and musical expression discriminate the dyslexic group from controls and adolescents with ADHD and ADD. A second discriminant analysis based on MEG variables showed that absolute P1 latency asynchrony |R-L| distinguishes the control group from the disorder groups best, while P1 and N1 latencies averaged across hemispheres separate the control, ADD and ADHD groups from the dyslexic group. Furthermore, rhythmic improvisation was negatively correlated with auditory-evoked P1 and N1 latencies, pointing in the following direction: the earlier the P1 and N1 latencies (mean), the better the rhythmic improvisation. These findings provide novel insight into the differences between music processing and performance in adolescents with and without neurodevelopmental disorders. A better understanding of these differences may help to develop tailored preventions or therapeutic interventions.

How Learning to Read Changes the Listening Brain

Reading acquisition reorganizes existing brain networks for speech and visual processing to form novel audio-visual language representations. This requires substantial cortical plasticity that is reflected in changes in brain activation and functional as well as structural connectivity between brain areas. The extent to which a child's brain can accommodate these changes may underlie the high variability in reading outcome in both typical and dyslexic readers. In this review, we focus on reading-induced functional changes of the dorsal speech network in particular and discuss how its reciprocal interactions with the ventral reading network contributes to reading outcome. We discuss how the dynamic and intertwined development of both reading networks may be best captured by approaching reading from a skill learning perspective, using audio-visual learning paradigms and longitudinal designs to follow neuro-behavioral changes while children's reading skills unfold.

Predicting Reading From Behavioral and Neural Measures - A Longitudinal Event-Related Potential Study

Fluent reading is characterized by fast and effortless decoding of visual and phonological information. Here we used event-related potentials (ERPs) and neuropsychological testing to probe the neurocognitive basis of reading in a sample of children with a wide range of reading skills. We report data of 51 children who were measured at two time points, i.e., at the end of first grade (mean age 7.6 years) and at the end of fourth grade (mean age 10.5 years). The aim of this study was to clarify whether next to behavioral measures also basic unimodal and bimodal neural measures help explaining the variance in the later reading outcome. Specifically, we addressed the question of whether next to the so far investigated unimodal measures of N1 print tuning and mismatch negativity (MMN), a bimodal measure of audiovisual integration (AV) contributes and possibly enhances prediction of the later reading outcome. We found that the largest variance in reading was explained by the behavioral measures of rapid automatized naming (RAN), block design and vocabulary (46%). Furthermore, we demonstrated that both unimodal measures of N1 print tuning (16%) and filtered MMN (7%) predicted reading, suggesting that N1 print tuning at the early stage of reading acquisition is a particularly good predictor of the later reading outcome. Beyond the behavioral measures, the two unimodal neural measures explained 7.2% additional variance in reading, indicating that basic neural measures can improve prediction of the later reading outcome over behavioral measures alone. In this study, the AV congruency effect did not significantly predict reading. It is therefore possible that audiovisual congruency effects reflect higher levels of multisensory integration that may be less important for reading acquisition in the first year of learning to read, and that they may potentially gain on relevance later on.

Developmental Factors That Predict Head Movement During Resting-State Functional Magnetic Resonance Imaging in 3-7-Year-Old Stuttering and Non-stuttering Children

Early childhood marks a period of dynamic neurocognitive development. Preschool-age coincides with the onset of many childhood disorders and is a developmental period that is frequently studied to determine markers of neurodevelopmental disorders. Magnetic resonance imaging (MRI) is often used to explore typical brain development and the neural bases of neurodevelopmental disorders. However, acquiring high-quality MRI data in young children is challenging. The enclosed space and loud sounds can trigger unease and cause excessive head movement. A better understanding of potential factors that predict successful MRI acquisition would increase chances of collecting useable data in children with and without neurodevelopmental disorders. We investigated whether age, sex, stuttering status, and childhood temperament as measured using the Child Behavioral Questionnaire, could predict movement extent during resting-state functional MRI (rs-fMRI) in 76 children aged 3–7 years, including 42 children who stutter (CWS). We found that age, sex, and temperament factors could predict motion during rs-fMRI scans. The CWS were not found to differ significantly from controls in temperament or head movement during scanning. Sex and age were significant predictors of movement. However, age was no longer a significant predictor when temperament, specifically effortful control, was considered. Controlling for age, boys with higher effortful control scores moved less during rs-fMRI procedures. Additionally, boys who showed higher negative affectivity showed a trend for greater movement. Considering temperament factors in addition to age and sex may help predict the success of acquiring useable rs-fMRI (and likely general brain MRI) data in young children in MR neuroimaging.

Atypical processing in neural source analysis of speech envelope modulations in adolescents with dyslexia

Different studies have suggested that language and developmental disorders such as dyslexia are associated with a disturbance of auditory entrainment and of the functional hemispheric asymmetries during speech processing. These disorders typically result from an issue in the phonological component of language that causes problems to represent and manipulate the phonological structure of words at the syllable and/or phoneme level. We used Auditory Steady-State Responses (ASSRs) in EEG recordings to investigate the brain activation and hemisphere asymmetry of theta, alpha, beta and low-gamma range oscillations in typical readers and readers with dyslexia. The aim was to analyse whether the group differences found in previous electrode level studies were caused by a different source activation pattern or conversely was an effect that could be found on the active brain sources. We could not find differences in the brain locations of the main active brain sources. However, we observed differences in the extracted waveforms. The group average of the first DSS component of all signal-to-noise ratios of ASSR at source level was higher than the group averages at the electrode level. These analyses included a lower alpha synchronisation in adolescents with dyslexia and the possibility of compensatory mechanisms in theta, beta and low-gamma frequency bands. The main brain auditory sources were located in cortical regions around the auditory cortex. Thus, the differences observed in auditory EEG experiments would, according to our findings, have their origin in the intrinsic oscillatory mechanisms of the brain cortical sources related to speech perception.

Children with developmental dyslexia show elevated parasympathetic nervous system activity at rest and greater cardiac deceleration during an empathy task

Reading difficulties are the hallmark feature of dyslexia, but less is known about other areas of functioning. Previously, we found children with dyslexia exhibited heightened emotional reactivity, which correlated with better social skills. Whether emotional differences in dyslexia extend to the parasympathetic nervous system-an autonomic branch critical for attention, social engagement, and empathy-is unknown. Here, we measured autonomic nervous system activity in 24 children with dyslexia and 24 children without dyslexia, aged 7 - 12, at rest and during a film-based empathy task. At rest, children with dyslexia had higher respiratory sinus arrhythmia (RSA) than those without dyslexia. Cardiac deceleration during the empathy task was greater in dyslexia and correlated with higher resting RSA across the sample. Children with dyslexia produced more facial expressions of concentration during film-viewing, suggesting greater engagement. These results suggest elevated resting parasympathetic activity and accentuated autonomic and behavioral responding to others' emotions in dyslexia.

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

Developmental dyslexia is defined by reading impairments that are disproportionate to intelligence, motivation, and the educational opportunities considered necessary for reading. Its cause has traditionally been considered to be a phonological deficit, where people have difficulties with differentiating the sounds of spoken language. However, reading is a multidimensional skill and relies on various cognitive abilities. These may include high-level vision—the processes that support visual recognition despite innumerable image variations, such as in viewpoint, position, or size. According to our high-level visual dysfunction hypothesis, reading problems of some people with dyslexia can be a salient manifestation of a more general deficit of high-level vision. This paper provides a perspective on how such non-phonological impairments could, in some cases, cause dyslexia. To argue in favor of this hypothesis, we will discuss work on functional neuroimaging, structural imaging, electrophysiology, and behavior that provides evidence for a link between high-level visual impairment and dyslexia.

Development of white matter microstructure and executive functions during childhood and adolescence: a review of diffusion MRI studies

Diffusion magnetic resonance imaging (dMRI) provides indirect measures of white matter microstructure that can be used to make inferences about structural connectivity within the brain. Over the last decade, a growing literature of cross-sectional and longitudinal studies have documented relationships between dMRI indices and cognitive development. In this review, we provide a brief overview of dMRI methods and how they can be used to study white matter and connectivity and review the extant literature examining the links between dMRI indices and executive functions during development. We explore the links between white matter microstructure and specific executive functions: inhibition, working memory and cognitive shifting, as well as performance on complex executive function tasks. Concordance in findings across studies are highlighted, and potential explanations for discrepancies between results, together with challenges with using dMRI in child and adolescent populations, are discussed. Finally, we explore future directions that are necessary to better understand the links between child and adolescent development of structural connectivity of the brain and executive functions.

Functional and morphological correlates of developmental dyslexia: A multimodal investigation of the ventral occipitotemporal cortex

BACKGROUND AND PURPOSE

The ventral occipitotemporal cortex (vOT) is a region crucial for reading acquisition through selective tuning to printed words. Developmental dyslexia is a disorder of reading with underlying neurobiological bases often associated with atypical neural responses to printed words. Previous studies have discovered anomalous structural development and function of the vOT in individuals with dyslexia. However, it remains unclear if or how structural abnormalities relate to functional alterations.

METHODS

In this study, we acquired structural, functional (words and faces processing), and diffusion MRI data from 26 children with dyslexia (average age = 10.4 ± 2.0 years) and 14 age-matched typically developing readers (average age = 10.4 ± 1.6 years). Morphological indices of local gyrification, neurite density (i.e., dendritic arborization structure), and orientation dispersion (i.e., dendritic arborization orientation) were analyzed within the vOT region that showed preferential activation in typically developing readers for words (as compared to face stimuli).

RESULTS

The two cohorts diverged significantly in both functional and structural measures. Compared to typically developing controls, children with dyslexia did not show selectivity for words in the left vOT (contrast: words > false fonts). This lack of tuning to printed words was associated with greater neurite dispersion heterogeneity in the dyslexia cohort, but similar neurite density. These group differences were not present in the homologous contralateral area, the right vOT.

CONCLUSIONS

Our findings provide new insight into the neurobiology of the lack of vOT word tuning in dyslexia by linking behavior, alterations in functional activation, and neurite organization.

Neuro-Behavioral Correlates of Executive Dysfunctions in Dyslexia Over Development From Childhood to Adulthood

Dyslexia is a neurobiological learning disability in the reading domain that has symptoms in early childhood and persists throughout life. Individuals with dyslexia experience difficulties in academia and cognitive and emotional challenges that can affect wellbeing. Early intervention is critical to minimize the long-term difficulties of these individuals. However, the behavioral and neural correlates which predict dyslexia are challenging to depict before reading is acquired. One of the precursors for language and reading acquisition is executive functions (EF). The present review aims to highlight the current atypicality found in individuals with dyslexia in the domain of EF using behavioral measures, brain mapping, functional connectivity, and diffusion tensor imaging along development. Individuals with dyslexia show EF abnormalities in both behavioral and neurobiological domains, starting in early childhood that persist into adulthood. EF impairment precedes reading disability, therefore adding an EF assessment to the neuropsychological testing is recommended for early intervention. EF training should also be considered for the most comprehensive outcomes.

Gray matter correlates of reading fluency deficits: SES matters, IQ does not

Brain correlates of reading ability have been intensely investigated. Most studies have focused on single-word reading and phonological processing, but the brain basis of reading fluency remains poorly explored to date. Here, in a voxel-based morphometry study with 8-year-old children, we compared fluent readers (n = 18; seven boys) with dysfluent readers with normal IQ (n = 18; six boys) and with low IQ (n = 18; ten boys). Relative to dysfluent readers, fluent readers had larger gray matter volume in the right superior temporal gyrus and the two subgroups of dysfluent readers did not differ from each other, as shown in frequentist and Bayesian analyses. Pairwise comparisons showed that dysfluent readers of normal and low IQ did not differ in core reading regions and that both subgroups had less gray matter volume than fluent readers in occipito-temporal, parieto-temporal and fusiform areas. We also examined gray matter volume in matched subgroups of dysfluent readers differing only in socioeconomic status (SES): lower-SES (n = 14; seven boys) vs. higher-SES (n = 14; seven boys). Higher-SES dysfluent readers had larger gray matter volume in the right angular gyrus than their lower-SES peers, and the volume of this cluster correlated positively with lexico-semantic fluency. Age, sex, IQ, and gray matter volume of the right angular cluster explained 68% of the variance in the reading fluency of higher-SES dysfluent readers. In sum, this study shows that gray matter correlates of dysfluent reading are independent of IQ, and suggests that SES modulates areas sub-serving lexico-semantic processes in dysfluent readers-two findings that may be useful to inform language/reading remediation programs.

Rapid serial naming: Developmental trajectory and relationship with the Bangor Dyslexia Test in Spanish students

This study aimed to analyse the developmental trajectory of the accuracy and speed of naming among dyslexics and developing readers from 1st to 6th grade of primary education. It examined how familiarity with the stimulus influences the performance of different naming tasks in both groups and evaluated the link between naming speed and the Bangor Dyslexia Test. With a descriptive and correlational design, eight naming tasks and the Bangor Dyslexia Test (Miles, 1982; Outón & Suárez, 2010) were administered to a sample of 198 dyslexics and 245 developing readers. The results showed that the dyslexics were slower and more inaccurate in all the naming tasks, compared with the developing readers of the same age. Greater difficulty was observed with the less familiar stimuli. It became evident that naming performance improved with age among both groups of subjects. Finally, a greater number of significant and positive correlations were found between the naming tasks and the Bangor Dyslexia Test in the dyslexic group; the strongest relationship was obtained by naming letters.

Altered gray matter development in pre-reading children with a family history of reading disorder

Reading disorders are common in children and can impact academic success, mental health, and career prospects. Reading is supported by network of interconnected left hemisphere brain regions, including temporo-parietal, occipito-temporal, and inferior-frontal circuits. Poor readers often show hypoactivation and reduced gray matter volumes in this reading network, with hyperactivation and increased volumes in the posterior right hemisphere. We assessed gray matter development longitudinally in pre-reading children aged 2-5 years using magnetic resonance imaging (MRI) (N = 32, 110 MRI scans; mean age: 4.40 ± 0.77 years), half of whom had a family history of reading disorder. The family history group showed slower proportional growth (relative to total brain volume) in the left supramarginal and inferior frontal gyri, and faster proportional growth in the right angular, right fusiform, and bilateral lingual gyri. This suggests delayed development of left hemisphere reading areas in children with a family history of dyslexia, along with faster growth in right homologues. This alternate development pattern may predispose the brain to later reading difficulties and may later manifest as the commonly noted compensatory mechanisms. The results of this study further shows our understanding of structural brain alterations that may form the neurological basis of reading difficulties.

Structural brain dynamics across reading development: A longitudinal MRI study from kindergarten to grade 5

Primary education is the incubator for learning academic skills that help children to become a literate, communicative, and independent person. Over this learning period, nonlinear and regional changes in the brain occur, but how these changes relate to academic performance, such as reading ability, is still unclear. In the current study, we analyzed longitudinal T1 MRI data of 41 children in order to investigate typical cortical development during the early reading stage (end of kindergarten-end of grade 2) and advanced reading stage (end of grade 2-middle of grade 5), and to detect putative deviant trajectories in children with dyslexia. The structural brain change was quantified with a reliable measure that directly calculates the local morphological differences between brain images of two time points, while considering the global head growth. When applying this measure to investigate typical cortical development, we observed that left temporal and temporoparietal regions belonging to the reading network exhibited an increase during the early reading stage and stabilized during the advanced reading stage. This suggests that the natural plasticity window for reading is within the first years of primary school, hence earlier than the typical period for reading intervention. Concerning neurotrajectories in children with dyslexia compared to typical readers, we observed no differences in gray matter development of the left reading network, but we found different neurotrajectories in right IFG opercularis (during the early reading stage) and in right isthmus cingulate (during the advanced reading stage), which could reflect compensatory neural mechanisms.

Decoding the role of the cerebellum in the early stages of reading acquisition

Numerous studies have consistently reported functional activation of the cerebellum during reading tasks, especially in the right cerebellar hemisphere. However, it remains unclear whether this region is also involved in reading during the earliest stages of reading acquisition. Here, we investigated whether and how the cerebellum contributes to reading acquisition. We tested 80 5-6-year-old kindergarteners, who performed a visual word matching task during which functional MRI (fMRI) data were collected. We found that bilateral cerebellar hemispheres were significantly activated during visual word processing. Moreover, activation of left cerebellar lobule VII extending to lobule VIII negatively and significantly correlated with current reading ability, whereas activation of right cerebellar lobule VII extending to lobule VIII significantly and positively correlated with future reading ability. Functional decoding via functional connectivity patterns further revealed that left and right cerebellar lobules connected with different cerebral cortex regions. Our results suggest a division of labor between the left and right cerebellar lobules in beginning readers.

Neural processing of vision and language in kindergarten is associated with prereading skills and predicts future literacy

The main objective of this longitudinal study was to investigate the neural predictors of reading acquisition. For this purpose, we followed a sample of 54 children from the end of kindergarten to the end of second grade. Preliterate children were tested for visual symbol (checkerboards, houses, faces, written words) and auditory language processing (spoken words) using a passive functional magnetic resonance imaging paradigm. To examine brain-behavior relationships, we also tested cognitive-linguistic prereading skills at kindergarten age and reading performance of 48 of the same children 2 years later. Face-selective response in the bilateral fusiform gyrus was positively associated with rapid automatized naming (RAN). Response to both spoken and written words at preliterate age was negatively associated with RAN in the dorsal temporo-parietal language system. Longitudinally, neural response to faces in the ventral stream predicted future reading fluency. Here, stronger neural activity in inferior and middle temporal gyri at kindergarten age was associated with higher reading performance. Our results suggest that interindividual differences in the neural system of language and reading affect literacy acquisition and thus might serve as a marker for successful reading acquisition in preliterate children.

Visual search efficiency and functional visual cortical size in children with and without dyslexia

Dyslexia is characterised by poor reading ability. Its aetiology is probably multifactorial, with abnormal visual processing playing an important role. Among adults with normal reading ability, there is a larger representation of central visual field in the primary visual cortex (V1) in those with more efficient visuospatial attention. In this study, we tested the hypothesis that poor reading ability in school-aged children (17 children with dyslexia, 14 control children with normal reading ability) is associated with deficits in visuospatial attention using a visual search task. We corroborated the psychophysical findings with neuroimaging, by measuring the functional size of V1 in response to a central 12° visual stimulus. Consistent with other literature, visual search was impaired and less efficient in the dyslexic children, particularly with more distractor elements in the search array (p = 0.04). We also found atypical interhemispheric asymmetry in functional V1 size in the dyslexia group (p = 0.02). Reading impaired children showed poorer visual search efficiency (p = 0.01), needing more time per unit distractor (higher ms/item). Reading ability was also correlated with V1 size asymmetry (p = 0.03), such that poorer readers showed less left hemisphere bias relative to the right hemisphere. Our findings support the view that dyslexic children have abnormal visuospatial attention and interhemispheric V1 asymmetry, relative to chronological age-matched peers, and that these factors may contribute to inter-individual variation in reading performance in children.

Validation of The Reading House and Association With Cortical Thickness

BACKGROUND AND OBJECTIVES

The American Academy of Pediatrics recommends literacy and school readiness promotion during well visits. The Reading House (TRH) is a children's book-based screener of emergent literacy skills in preschool-aged children. Vocabulary, rhyming, and rapid naming are core emergent skills, and reading abilities are associated with thicker cortex in the left hemisphere. Our objective was to expand validity of TRH relative to these skills and explore association with cortical thickness.

METHODS

Healthy preschool-aged children completed MRI including a T1-weighted anatomic scan. Before MRI, TRH and assessments of rapid naming (Comprehensive Test of Phonological Processing, Second Edition), rhyming (Pre-Reading Inventory of Phonological Awareness), vocabulary (Expressive Vocabulary Test, Second Edition), and emergent literacy (Get Ready to Read!) were administered. Analyses included Spearman-ρ correlations (r _ρ) accounting for age, sex, and socioeconomic status (SES). MRI analyses involved whole-brain measures of cortical thickness relative to TRH scores, accounting for covariates.

RESULTS

Seventy children completed assessments (36-63 months old; 36 female) and 52 completed MRI (37-63 months; 29 female). TRH scores were positively correlated with Comprehensive Test of Phonological Processing, Second Edition (r _ρ = 0.61), Expressive Vocabulary Test, Second Edition (r _ρ = 0.54), Get Ready to Read! (r _ρ = 0.87), and Pre-Reading Inventory of Phonological Awareness scores (r _ρ = 0.64; all P < .001). These correlations remained statistically significant across age, sex, and SES groups. TRH scores were correlated with greater thickness in left-sided language and visual cortex (P-family-wise error <.05), which were similar for higher SES yet more bilateral and frontal for low SES, reflecting a less mature pattern (P-family-wise error <.10).

CONCLUSIONS

These findings expand validation evidence for TRH as a screening tool for preschool-aged children, including associations with emergent skills and cortical thickness, and suggest important differences related to SES.

Dyslexia in the 21st century

PURPOSE OF REVIEW

Within the past decade tremendous advances have occurred in our understanding of dyslexia.

RECENT FINDINGS

Reliable data now validate the definition of dyslexia as an unexpected difficulty in reading in an individual who has the ability to be a much better reader. That dyslexia is unexpected is now codified in US federal law (PL 115-391). Replicated studies using functional brain imaging have documented a neural signature for dyslexia. Epidemiologic, longitudinal data now demonstrate that dyslexia is highly prevalent, affecting 20% of the population, affecting boys and girls equally. These data further demonstrate that the achievement gap between dyslexic and typical readers is now evident as early as first grade and persists. Evidence-based, efficient, inexpensive screening tools now offer the possibility of universal screening to identify children at risk for dyslexia as early as first grade. Specialized schools which focus on dyslexic students provide welcoming communities, ensuring that dyslexic children will not only survive but thrive.

SUMMARY

Taken together, these findings indicate that we must act and act now to ensure that this 21st century knowledge of dyslexia is disseminated to educators, policy makers, and most of all to parents of dyslexic children.

Imaging the rapidly developing brain: Current challenges for MRI studies in the first five years of life

Rapid and widespread changes in brain anatomy and physiology in the first five years of life present substantial challenges for developmental structural, functional, and diffusion MRI studies. One persistent challenge is that methods best suited to earlier developmental stages are suboptimal for later stages, which engenders a trade-off between using different, but age-appropriate, methods for different developmental stages or identical methods across stages. Both options have potential benefits, but also biases, as pipelines for each developmental stage can be matched on methods or the age-appropriateness of methods, but not both. This review describes the data acquisition, processing, and analysis challenges that introduce these potential biases and attempts to elucidate decisions and make recommendations that would optimize developmental comparisons.

Enhanced visceromotor emotional reactivity in dyslexia and its relation to salience network connectivity

Dyslexia is a neurodevelopmental disorder mainly defined by reading difficulties. During reading, individuals with dyslexia exhibit hypoactivity in left-lateralized language systems. Lower activity in one brain circuit can be accompanied by greater activity in another, and, here, we examined whether right-hemisphere-based emotional reactivity may be elevated in dyslexia. We measured emotional reactivity (i.e., facial behavior, physiological activity, and subjective experience) in 54 children ages 7-12 with (n = 32) and without (n = 22) dyslexia while they viewed emotion-inducing film clips. Participants also underwent task-free functional magnetic resonance imaging. Parents of children with dyslexia completed the Behavior Assessment System for Children, which assesses real-world behavior. During film viewing, children with dyslexia exhibited significantly greater reactivity in emotional facial behavior, skin conductance level, and respiration rate than those without dyslexia. Across the sample, greater emotional facial behavior correlated with stronger connectivity between right ventral anterior insula and right pregenual anterior cingulate cortex (pFWE<.05), key salience network hubs. In children with dyslexia, greater emotional facial behavior related to better real-world social skills and higher anxiety and depression. Our findings suggest there is heightened visceromotor emotional reactivity in dyslexia, which may lead to interpersonal strengths as well as affective vulnerabilities.

Shared Neural Substrates Underlying Reading and Visual Matching: A Longitudinal Investigation

The role of visual skills in reading acquisition has long been debated and whether there is shared neurobiological basis between visual skills and reading is not clear. This study investigated the relationship between Visual Matching and reading and their shared neuroanatomical basis. Two hundred and ninety-three typically developing Mandarin-speaking children were followed in a longitudinal study from ages 4 to 11 years old. A subsample of 79 children was further followed up at 14 years old when the MRI data were collected. Results showed that the development of Visual Matching from ages 6 to 8 predicted reading accuracy at age 11. In addition, both the development of Visual Matching and reading accuracy were associated with cortical surface area of a cluster located in fusiform gyrus. These findings suggested that the mapping from visual codes to phonological codes is important in learning to read and that left fusiform gyrus provided neural basis for such mapping. Implications of these findings in light of a new approach toward the neurocognitive mechanisms underlying reading development are discussed.

Longitudinal Effects of the Home Learning Environment and Parental Difficulties on Reading and Math Development Across Grades 1-9

This study focuses on parental reading and mathematical difficulties, the home literacy environment, and the home numeracy environment as well as their predictive role in Finnish children’s reading and mathematical development through Grades 1–9. We examined if parental reading and mathematical difficulties directly predict children’s academic performance and/or if they are mediated by the home learning environment. Mothers (n = 1590) and fathers (n = 1507) reported on their reading and mathematical difficulties as well as on the home environment (shared reading, teaching literacy, and numeracy) when their children were in kindergarten. Tests for reading fluency, reading comprehension, and arithmetic fluency were administered to children in Grades 1, 2, 3, 4, 7, and 9. Parental reading difficulties predicted children’s reading fluency, whereas parental mathematical difficulties predicted their reading comprehension and arithmetic fluency. Familial risk was associated with neither formal nor informal home environment factors, whereas maternal education had a significant relationship with both, with higher levels of education among mothers predicting less time spent on teaching activities and more time spent on shared reading. In addition, shared reading was significantly associated with the development of reading comprehension up to Grades 3 and 4, whereas other components of the home learning environment were not associated with any assessed skills. Our study highlights that taken together, familial risk, parental education, and the home learning environment form a complex pattern of associations with children’s mathematical and reading skills.

Developmental dyslexia: A new look at clinical features and brain mechanisms

Developmental dyslexia is the commonest "specific learning disorder" (DSM-5) or "developmental learning disorder with impairment in reading" (ICD-11). This impairment in reading acquisition is related to a defect in the installation of cognitive precursors necessary to master the grapheme-phoneme conversion. Its origin is largely genetic, but many environmental factors seem capable of modulating symptom intensity. Three types of presentation, roughly equal in occurrence, are useful to distinguish according to the associated disorders (language, attentional, and/or motor coordination), thus suggesting, at least in part, potentially different mechanisms at their origin. In adolescence and adulthood the clinical presentation tends to bear a more uniform pattern, covering a large range of severity depending on each person's ability to compensate for their deficit. Research has demonstrated dysfunction of specific brain areas during reading-related tasks (using fMRI), essentially in the left cerebral hemisphere, but also atypical patterns of connectivity (using diffusion imaging), further supplemented by functional connectivity studies at rest. The current therapeutic recommendations emphasize the need for multidisciplinary care, giving priority, depending on the clinical form, to the language, psychomotor, or neuropsychologic aspects of rehabilitation. Various training methods whose effectiveness has been scientifically tested are reviewed, emphasizing those exploiting the hypothesis of a lack of intermodal connectivity between separate cognitive systems.

Putative protective neural mechanisms in prereaders with a family history of dyslexia who subsequently develop typical reading skills

Developmental dyslexia affects 40-60% of children with a familial risk (FHD+) compared to a general prevalence of 5-10%. Despite the increased risk, about half of FHD+ children develop typical reading abilities (FHD+Typical). Yet the underlying neural characteristics of favorable reading outcomes in at-risk children remain unknown. Utilizing a retrospective, longitudinal approach, this study examined whether putative protective neural mechanisms can be observed in FHD+Typical at the prereading stage. Functional and structural brain characteristics were examined in 47 FHD+ prereaders who subsequently developed typical (n = 35) or impaired (n = 12) reading abilities and 34 controls (FHD-Typical). Searchlight-based multivariate pattern analyses identified distinct activation patterns during phonological processing between FHD+Typical and FHD-Typical in right inferior frontal gyrus (RIFG) and left temporo-parietal cortex (LTPC) regions. Follow-up analyses on group-specific classification patterns demonstrated LTPC hypoactivation in FHD+Typical compared to FHD-Typical, suggesting this neural characteristic as an FHD+ phenotype. In contrast, RIFG showed hyperactivation in FHD+Typical than FHD-Typical, and its activation pattern was positively correlated with subsequent reading abilities in FHD+ but not controls (FHD-Typical). RIFG hyperactivation in FHD+Typical was further associated with increased interhemispheric functional and structural connectivity. These results suggest that some protective neural mechanisms are already established in FHD+Typical prereaders supporting their typical reading development.

Differential activation of the visual word form area during auditory phoneme perception in youth with dyslexia

Developmental dyslexia is a learning disorder characterized by difficulties reading words accurately and/or fluently. Several behavioral studies have suggested the presence of anomalies at an early stage of phoneme processing, when the complex spectrotemporal patterns in the speech signal are analyzed and assigned to phonemic categories. In this study, fMRI was used to compare brain responses associated with categorical discrimination of speech syllables (P) and acoustically matched nonphonemic stimuli (N) in children and adolescents with dyslexia and in typically developing (TD) controls, aged 8-17 years. The TD group showed significantly greater activation during the P condition relative to N in an area of the left ventral occipitotemporal cortex that corresponds well with the region referred to as the "visual word form area" (VWFA). Regression analyses using reading performance as a continuous variable across the full group of participants yielded similar results. Overall, the findings are consistent with those of previous neuroimaging studies using print stimuli in individuals with dyslexia that found reduced activation in left occipitotemporal regions; however, the current study shows that these activation differences seen during reading are apparent during auditory phoneme discrimination in youth with dyslexia, suggesting that the primary deficit in at least a subset of children may lie early in the speech processing stream and that categorical perception may be an important target of early intervention in children at risk for dyslexia.

Gray Matter Structure Is Associated with Reading Skill in Typically Developing Young Readers

Research using functional and structural magnetic resonance imaging has identified areas of reduced brain activation and gray matter volume in children and adults with reading disability, but associations between cortical structure and individual differences in reading in typically developing children remain underexplored. Furthermore, the majority of research linking gray matter structure to reading ability quantifies gray matter in terms of volume, and cannot specify unique contributions of cortical surface area and thickness to these relationships. Here, we applied a continuous analytic approach to investigate associations between distinct surface-based properties of cortical structure and individual differences in reading-related skills in a sample of typically developing young children. Correlations between cortical structure and reading-related skills were conducted using a surface-based vertex-wise approach. Cortical thickness in the left superior temporal cortex was positively correlated with word and pseudoword reading performance. The observed positive correlation between cortical thickness in the left superior temporal cortex and reading may have implications for the patterns of brain activation that support reading.

The emergence of dyslexia in the developing brain

Developmental dyslexia, a severe deficit in literacy learning, is a neurodevelopmental learning disorder. Yet, it is not clear whether existing neurobiological accounts of dyslexia capture potential predispositions of the deficit or consequences of reduced reading experience. Here, we longitudinally followed 32 children from preliterate to school age using functional and structural magnetic resonance imaging techniques. Based on standardised and age-normed reading and spelling tests administered at school age, children were classified as 16 dyslexic participants and 16 controls. This longitudinal design allowed us to disentangle possible neurobiological predispositions for developing dyslexia from effects of individual differences in literacy experience. In our sample, the disorder can be predicted already before literacy learning from auditory cortex gyrification and aberrant downstream connectivity within the speech processing system. These results provide evidence for the notion that dyslexia may originate from an atypical maturation of the speech network that precedes literacy instruction.

The Functional Neuroanatomy of Developmental Dyslexia Across Languages and Writing Systems

The present article reviews the literature on the functional neuroanatomy of developmental dyslexia across languages and writing systems. This includes comparisons of alphabetic languages differing in orthographic depth as well as comparisons across alphabetic, syllabic, and logographic writing systems. It provides a synthesis of the evidence for both universal and language-specific effects on dyslexic functional brain activation abnormalities during reading and reading-related tasks. Specifically, universal reading-related underactivation of dyslexic readers relative to typical readers is identified in core regions of the left hemisphere reading network including the occipito-temporal, temporo-parietal, and inferior frontal cortex. Orthography-specific dyslexic brain abnormalities are mainly related to the degree and spatial extent of under- and overactivation clusters. In addition, dyslexic structural gray matter abnormalities across languages and writing systems are analyzed. The neuroimaging findings are linked to the universal and orthography-dependent behavioral manifestations of developmental dyslexia. Finally, the present article provides insights into potential compensatory mechanisms that may support remediation across languages and writing systems.

The left inferior longitudinal fasciculus supports orthographic processing: Evidence from a lesion-behavior mapping analysis

Orthographic processing is a critical stage in visual word recognition. However, the white-matter pathways that support this processing are unclear, as prior findings might have been confounded by impure behavioral measures, potential structural reorganization of the brain, and limited sample sizes. To address this issue, we investigated the correlations between the integrity of 20 major tracts in the whole brain and the pure orthographic index across 67 patients with short-term brain damage. The integrity of the tracts was measured by the lesion volume percentage and the mean fractional anisotropy value. The orthographic index was calculated as the residual of the orthographic tasks after regressing out corresponding nonorthographic tasks and the orthographic factor from the principal component analysis (PCA) on the basis of four orthographic tasks. We found significant correlations associated with the left inferior longitudinal fasciculus (ILF), even after controlling for the influence of potential confounding variables. These observations strengthen evidence for the vital role of the left ILF in orthographic processing.

Correlation between diffusion tensor imaging measures and the reading and cognitive performance of Arabic readers: dyslexic children perspective

PURPOSE

To investigate the correlation between the diffusion tensor imaging (DTI) measures and the reading, spelling, writing, rapid naming, memory, and motor abilities in Arabic dyslexic children. This could verify the influence of possible white matter alterations on the abilities of those children.

METHODS

Twenty native Arabic-speaking children with dyslexia (15 males and 5 females; 8.2 years ± 1) underwent DTI of the brain on 1.5 T scanner. Diffusion-weighted images were acquired in 32 noncollinear direction. Tractography of the arcuate fasciculus (AF) was performed. Region of interest (ROI)-based approach was also used. Regions encompass superior longitudinal fasciculus (SLF), anterior and superior corona radiata (CR), and posterior limb of internal capsule (PLIC) were analyzed. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were measured. The aptitudes of those children were evaluated by the dyslexia assessment test. These abilities were statistically correlated with the FA and ADC of the AF and other ROIs.

RESULTS

The reduction of FA of right AF was related to worse overall reading and related abilities performance. The ADC of right SLF was negatively correlated with memory abilities. The ADC of right PLIC was positively correlated with writing performance. Other relations were also found.

CONCLUSION

White matter microstructural DTI measurements in the right AF, right PLIC, SLF, and left anterior and superior CR are correlated to reading, spelling, writing, memory, and rapid naming abilities of the participants. The DTI measures could be promising regarding their use as a biomarker for follow-up in developmental dyslexia.

Children With Dyslexia and Familial Risk for Dyslexia Present Atypical Development of the Neuronal Phonological Network

Learning to read changes the brain language system. Phonological processing is the language domain most crucial for reading, but it is still unknown how reading acquisition modifies the neural phonological network in children who either develop dyslexia or are at risk of dyslexia. For the two first years of formal education, we followed 90 beginning readers with (n = 55) and without (n = 35) familial risk of dyslexia who became typical readers (n = 70) or developed dyslexia (n = 20). We used functional magnetic resonance imaging to identify the neural correlates of phonological awareness using an auditory rhyme judgment task. This task was applied when participants were starting formal education, and repeated 2 years later. By applying two alternative group splits, we analyzed the effects of dyslexia and the effects of familial risk of dyslexia separately. We found that the phonological brain network undergoes reorganization during the first 2 years of formal education. This process proceeds differently depending on the presence of a familial history of dyslexia and reading impairment. Typical readers without risk for dyslexia activate structures responsible for phonological processing already at the beginning of literacy. This group shows reduced brain activation over time during phonological processing, perhaps due to automatization of phonological skills. Children who develop reading impairment present a delay in the development of phonological structures such as the bilateral superior temporal gyri, left middle temporal gyrus, right insula and right frontal cortex, where we observed time and group interaction. Finally, typical readers with familial risk of dyslexia also present an atypical development of the neural phonological structures, visible both at the beginning of reading instruction and 2 years later. These children used a presumably efficient neural mechanism of phonological processing, based on the activation of the precentral and postcentral gyri, and achieved a typical level of phonological awareness.