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

The Face Processing Deficit in Developmental Dyslexia: A Meta-Analysis

Many studies have investigated face processing abilities in developmental dyslexia (DD) while conflicting evidence of both impaired and intact face processing has been reported. A systematic meta-analysis was conducted on the topic of the face processing abilities of DD. A total of 15 studies (34 effect sizes) were identified, representing data from 311 individuals with DD and 336 typically developing controls. A random-effects robust variance estimation model was used to synthesise the data. The average weighted standardised mean difference (Hedges' g) was 0.51 (95% confidence interval [0.24, 0.79], p = 0.001). A moderate level of heterogeneity was found while no publication bias was found between study-level effect sizes. Explorative meta-regression analyses showed that age, gender, and task type were not significant moderating factors. The results indicate that individuals with DD have face processing deficits compared with controls, suggesting domain-general deficits in DD and part of shared cognitive mechanisms underlying face and word processing.

Anatomically distinct regions in the inferior frontal cortex are modulated by task and reading skill

Inferior frontal cortex (IFC) is a critical region for reading and language. This part of the cortex is highly heterogeneous in its structural and functional organization and shows high variability across individuals. Despite decades of research, the relationship between specific IFC regions and reading skill remains unclear. To shed light on the function of IFC in reading, we aim to (1) characterize the functional landscape of text-selective responses in IFC, while accounting for interindividual variability; and (2) examine how text-selective regions in the IFC relate to reading proficiency. To this end, children with a wide range of reading ability (N=66; age 7-14 years, 34 female, 32 male) completed functional MRI scans while performing two tasks on text and non-text visual stimuli. Importantly, both tasks do not explicitly require reading, and can be performed on all visual stimuli. This design allows us to tease apart stimulus-driven responses from task-driven responses and examine where in IFC task and stimulus interact. We were able to identify three anatomically-distinct, text-selective clusters of activation in IFC, in the inferior frontal sulcus (IFS), and dorsal and ventral precentral gyrus (PrG). ​​These three regions showed a strong task effect that was highly specific to text. Furthermore, text-selectivity in the IFS and dorsal PrG was associated with reading proficiency, such that better readers showed higher selectivity to text. These findings suggest that text-selective regions in the IFC are sensitive to both stimulus and task, and highlight the importance of this region for proficient reading.Significance statement The inferior frontal cortex (IFC) is a critical region for language processing, yet despite decades of research, its relationship with reading skill remains unclear. In a group of children with a wide range of reading skills, we were able to identify three anatomically distinct text-selective clusters of activation in the IFC. ​​These regions showed a strong task effect that was highly selective to text. Text-selectivity was positively correlated with reading proficiency, such that better readers showed higher selectivity to text, even in tasks that did not require reading. These findings suggest that multiple text-selective regions within IFC are sensitive to both stimulus and task, and highlight the critical role of IFC for reading proficiency.

Towards a dynamic, comprehensive conceptualization of dyslexia

Here we build from the central strength of the existing definition of dyslexia-its emphasis on neurobiological origins-and proffer a set of seven core principles for a new, more comprehensive conceptualization of dyslexia. These principles derive from two major research directions: (1) the still evolving history of attempts to explain dyslexia, including in varied writing systems; and (2) the study of the reading brain circuit, its development, and its genetic and environmental influences. What emerges from connecting these two directions is a dynamic conceptualization of dyslexia that incorporates the extensive research on the heterogeneity of dyslexia and the interdependent contributions of multiple biological and socio-cultural risk and preventive factors. A new definition of dyslexia, therefore, needs to transcend both past unitary characterizations and past assumptions based largely on the English orthography. Such a conceptualization references the ways that different languages interact with the reading brain circuit to produce different sources of reading failure. Similarly, the characteristics and consequences of dyslexia that have been considered as secondary sequela (e.g., reduced reading comprehension, social-emotional issues) should be part of a more comprehensive narrative. Of critical importance, any definition of dyslexia should clarify persisting misconceptions that associate dyslexia with a lack of intelligence, potential to learn, or talents. Thus, the overall purpose of such a definition should serve as an instrument of knowledge and an enduring reason for pursuing growth in reading for the individual, the educator, and the public.

Investigating Dyslexia through Diffusion Tensor Imaging across Ages: A Systematic Review

Dyslexia is a neurodevelopmental disorder that presents a deficit in accuracy and/or fluency while reading or spelling that is not expected given the level of cognitive functioning. Research indicates brain structural changes mainly in the left hemisphere, comprising arcuate fasciculus (AF) and corona radiata (CR). The purpose of this systematic review is to better understand the possible methods for analyzing Diffusion Tensor Imaging (DTI) data while accounting for the characteristics of dyslexia in the last decade of the literature. Among 124 articles screened from PubMed and Scopus, 49 met inclusion criteria, focusing on dyslexia without neurological or psychiatric comorbidities. Article selection involved paired evaluation, with a third reviewer resolving discrepancies. The selected articles were analyzed using two topics: (1) a demographic and cognitive assessment of the sample and (2) DTI acquisition and analysis. Predominantly, studies centered on English-speaking children with reading difficulties, with preserved non-verbal intelligence, attention, and memory, and deficits in reading tests, rapid automatic naming, and phonological awareness. Structural differences were found mainly in the left AF in all ages and in the bilateral superior longitudinal fasciculus for readers-children and adults. A better understanding of structural brain changes of dyslexia and neuroadaptations can be a guide for future interventions.

The odd one out - Orthographic oddball processing in children with poor versus typical reading skills in a fast periodic visual stimulation EEG paradigm

The specialization of left ventral occipitotemporal brain regions to automatically process word forms develops with reading acquisition and is diminished in children with poor reading skills (PR). Using a fast periodic visual oddball stimulation (FPVS) design during electroencephalography (EEG), we examined the level of sensitivity and familiarity to word form processing in ninety-two children in 2nd and 3rd grade with varying reading skills (n = 35 for PR, n = 40 for typical reading skills; TR). To test children's level of "sensitivity", false font (FF) and consonant string (CS) oddballs were embedded in base presentations of word (W) stimuli. "Familiarity" was examined by presenting letter string oddballs with increasing familiarity (CS, pseudoword - PW, W) in FF base stimuli. Overall, our results revealed stronger left-hemispheric coarse sensitivity effects ("FF in W" > "CS in W") in TR than in PR in both topographic and oddball frequency analyses. Further, children distinguished between orthographically legal and illegal ("W/PW in FF" > "CS in FF") but not yet between lexical and non-lexical ("W in FF" vs "PW in FF") word forms. Although both TR and PR exhibit visual sensitivity and can distinguish between orthographically legal and illegal letter strings, they still struggle with nuanced lexical distinctions. Moreover, the strength of sensitivity is linked to reading proficiency. Our work adds to established knowledge in the field to characterize the relationship between print tuning and reading skills and suggests differences in the developmental progress to automatically process word forms.

Applications of advanced diffusion MRI in early brain development: a comprehensive review

Brain development follows a protracted developmental timeline with foundational processes of neurodevelopment occurring from the third trimester of gestation into the first decade of life. Defining structural maturational patterns of early brain development is a critical step in detecting divergent developmental trajectories associated with neurodevelopmental and psychiatric disorders that arise later in life. While considerable advancements have already been made in diffusion magnetic resonance imaging (dMRI) for pediatric research over the past three decades, the field of neurodevelopment is still in its infancy with remarkable scientific and clinical potential. This comprehensive review evaluates the application, findings, and limitations of advanced dMRI methods beyond diffusion tensor imaging, including diffusion kurtosis imaging (DKI), constrained spherical deconvolution (CSD), neurite orientation dispersion and density imaging (NODDI) and composite hindered and restricted model of diffusion (CHARMED) to quantify the rapid and dynamic changes supporting the underlying microstructural architectural foundations of the brain in early life.

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.