Jolijn Vanderauwera

Disentangling the relation between left temporoparietal white matter and reading: A spherical deconvolution tractography study.

Diffusion tensor imaging (DTI) studies have shown that left temporoparietal white matter is related to phonological aspects of reading. However, DTI lacks the sensitivity to disentangle whether phonological processing is sustained by intrahemispheric connections, interhemispheric connections, or projection tracts. Spherical deconvolution (SD) is a nontensor model which enables a more accurate estimation of multiple fiber directions in crossing fiber regions. Hence, this study is the first to investigate whether the observed relation with reading aspects in left temporoparietal white matter is sustained by a particular pathway by applying a nontensor model. Second, measures of degree of diffusion anisotropy, which indirectly informs about white matter organization, were compared between DTI and SD tractography. In this study, 71 children (5–6 years old) participated. Intrahemispheric, interhemispheric, and projection pathways were delineated using DTI and SD tractography. Anisotropy indices were extracted, that is, fractional anisotropy (FA) in DTI and quantitative hindrance modulated orientational anisotropy (HMOA) in SD. DTI results show that diffusion anisotropy in both the intrahemispheric and projection tracts was positively correlated to phonological awareness; however, the effect was confounded by subjects’ motion. In SD, the relation was restricted to the left intrahemispheric connections. A model comparison suggested that FA was, relatively to HMOA, more confounded by fiber crossings; however, anisotropy indices were highly related. In sum, this study shows the potential of SD to quantify white matter microstructure in regions containing crossing fibers. More specifically, SD analyses show that phonological awareness is sustained by left intrahemispheric connections and not interhemispheric or projection tracts. Hum Brain Mapp 36:3273–3287, 2015.

Atypical structural asymmetry of the planum temporale is related to family history of dyslexia

Research on the neural correlates of developmental dyslexia indicates atypical anatomical lateralization of the planum temporale, a higher-order cortical auditory region. Yet whether this atypical lateralization precedes reading acquisition and is related to a familial risk for dyslexia is not currently known. In this study, we address these questions in 2 separate cohorts of young children and adolescents with and without a familial risk for dyslexia. Planum temporale surface area was manually labeled bilaterally, on the T1-weighted MR brain images of 54 pre-readers (mean age: 6.2 years, SD: 3.2 months; 33 males) and 28 adolescents (mean age: 14.7 years, SD: 3.3 months; 11 males). Half of the pre-readers and adolescents had a familial risk for dyslexia. In both pre-readers and adolescents, group comparisons of left and right planum temporale surface area showed a significant interaction between hemisphere and family history of dyslexia, with participants who had no family risk for dyslexia showing greater leftward asymmetry of the planum temporale. This effect was confirmed when analyses were restricted to normal reading participants. Altered planum temporale asymmetry thus seems to be related to family history of dyslexia.

Early dynamics of white matter deficits in children developing dyslexia

Neural anomalies have been demonstrated in dyslexia. Recent studies in pre-readers at risk for dyslexia and in pre-readers developing poor reading suggest that these anomalies might be a cause of their reading impairment. Our study goes one step further by exploring the neurodevelopmental trajectory of white matter anomalies in pre-readers with and without a familial risk for dyslexia (n = 61) of whom a strictly selected sample develops dyslexia later on (n = 15). We collected longitudinal diffusion MRI and behavioural data until grade 3. The results provide evidence that children with dyslexia exhibit pre-reading white matter anomalies in left and right long segment of the arcuate fasciculus (AF), with predictive power of the left segment above traditional cognitive measures and familial risk. Whereas white matter differences in the left AF seem most strongly related to the development of dyslexia, differences in the left IFOF and in the right AF seem driven by both familial risk and later reading ability. Moreover, differences in the left AF appeared to be dynamic. This study supports and expands recent insights into the neural basis of dyslexia, pointing towards pre-reading anomalies related to dyslexia, as well as underpinning the dynamic character of white matter.

Atypical neural synchronization to speech envelope modulations in dyslexia

HIGHLIGHTSAuditory steady‐state responses measure synchronization of neural oscillations in the auditory cortices.Specific oscillatory bands are addressed using different speech envelope modulations.Dyslexic readers show reduced alpha synchronization to syllabic rates (10 Hz).Dyslexic readers show enhanced beta synchronization to phonemic rates (20 Hz).Bottom‐up and top‐down neural processes relate auditory synchronization to reading and phonology. ABSTRACT A fundamental deficit in the synchronization of neural oscillations to temporal information in speech could underlie phonological processing problems in dyslexia. In this study, the hypothesis of a neural synchronization impairment is investigated more specifically as a function of different neural oscillatory bands and temporal information rates in speech. Auditory steady‐state responses to 4, 10, 20 and 40 Hz modulations were recorded in normal reading and dyslexic adolescents to measure neural synchronization of theta, alpha, beta and low‐gamma oscillations to syllabic and phonemic rate information. In comparison to normal readers, dyslexic readers showed reduced non‐synchronized theta activity, reduced synchronized alpha activity and enhanced synchronized beta activity. Positive correlations between alpha synchronization and phonological skills were found in normal readers, but were absent in dyslexic readers. In contrast, dyslexic readers exhibited positive correlations between beta synchronization and phonological skills. Together, these results suggest that auditory neural synchronization of alpha and beta oscillations is atypical in dyslexia, indicating deviant neural processing of both syllabic and phonemic rate information. Impaired synchronization of alpha oscillations in particular demonstrated to be the most prominent neural anomaly possibly hampering speech and phonological processing in dyslexic readers.

Longitudinal changes in mathematical abilities and white matter following paediatric mild traumatic brain injury.

Abstract Primary objective: Paediatric traumatic brain injury (TBI) has been associated with acute and long-term mathematical difficulties. Little is known about the recovery of these impairments in children with mild TBI (mTBI) and their underlying pathophysiology, such as white matter abnormalities. Research design: A prospective longitudinal study followed the recovery of mathematical abilities and white matter in children with mTBI from the sub-acute (1 month post-injury) to chronic stage (6–8 months post-injury) of recovery. Methods and procedures: Twenty children with mTBI and 20 matched controls completed mathematics tests. Diffusion Tensor Imaging (DTI) metrics of white matter pathways corpus callosum (CC), superior and longitudinal fasciculi were examined with DTI-tractography. Main outcomes and results: Mathematical difficulties and white matter abnormalities in the CC observed shortly after the injury resolved after 6–8 months of recovery. Children with mTBI continued to show working memory deficits. Longitudinal DTI data suggest continued maturation of the CC in controls, but little maturation of the damaged CC in children with mTBI. Conclusions: Children with mTBI recovered in terms of mathematical abilities and white matter. These children continued to show working memory deficits, which might interfere with learning at school.

Neural organization of ventral white matter tracts parallels the initial steps of reading development: A DTI tractography study

HighlightsPre‐reading cognitive measures are sustained by broad ventral white matter network.The left ventral IFOF serves as a lexical reading route.The left IFOF is specialized for orthographic knowledge before reading instruction.Ventral white matter is not involved in phonological processing. ABSTRACT Insight in the developmental trajectory of the neuroanatomical reading correlates is important to understand related cognitive processes and disorders. In adults, a dual pathway model has been suggested encompassing a dorsal phonological and a ventral orthographic white matter system. This dichotomy seems not present in pre‐readers, and the specific role of ventral white matter in reading remains unclear. Therefore, the present longitudinal study investigated the relation between ventral white matter and cognitive processes underlying reading in children with a broad range of reading skills (n = 61). Ventral pathways of the reading network were manually traced using diffusion tractography: the inferior fronto‐occipital fasciculus (IFOF), inferior longitudinal fasciculus (ILF) and uncinate fasciculus (UF). Pathways were examined pre‐reading (5–6 years) and after two years of reading acquisition (7–8 years). Dimension reduction for the cognitive measures resulted in one component for pre‐reading cognitive measures and a separate phonological and orthographic component for the early reading measures. Regression analyses revealed a relation between the pre‐reading cognitive component and bilateral IFOF and left ILF. Interestingly, exclusively the left IFOF was related to the orthographic component, whereas none of the pathways was related to the phonological component. Hence, the left IFOF seems to serve as the lexical reading route, already in the earliest reading stages.

White matter pathways mediate parental effects on children's reading precursors

HighlightsParental reading relates to offspring’s white matter (WM) and phonological skills.Fathers’ reading and SES influence children’s early reading via ventral WM.Mothers display no mediating role via WM.SES relates to children’s early reading via WM and to mothers’ reading.Parent‐offspring associations might be partly genetically driven. Abstract Previous studies have shown that the link between parental and offspring’s reading is mediated by the cognitive system of the offspring, yet information about the mediating role of the neurobiological system is missing. This family study includes cognitive and diffusion MRI (dMRI) data collected in 71 pre‐readers as well as parental reading and environmental data. Using sequential path analyses, which take into account the interrelationships between the different components, we observed mediating effects of the neurobiological system. More specifically, fathers’ reading skills predicted reading of the child by operating through a child’s left ventral white matter pathway. For mothers no clear mediating role of the neural system was observed. Given that our study involves children who have not yet learned to read and that environmental measures were taken into account, the paternal effect on a child’s white matter pathway is unlikely to be only driven by environmental factors. Future intergenerational studies focusing on the genetic, neurobiological and cognitive level of parents and offspring will provide more insight in the relative contribution of parental environment and genes.

Morphological awareness and visual processing of derivational morphology in high-functioning adults with dyslexia: An avenue to compensation?

This study examined the processing of derivational morphology and its association with measures of morphological awareness and literacy outcomes in 30 Dutch-speaking high-functioning dyslexics, and 30 controls, matched for age and reading comprehension. A masked priming experiment was conducted where the semantic overlap between morphologically related pairs was manipulated as part of a lexical decision task. Measures of morphological awareness were assessed using a specifically designed sentence completion task. Significant priming effects were found in each group, yet adults with dyslexia were found to benefit more from the morphological structure than the controls. Adults with dyslexia were found to be influenced by both form (morpho-orthographic) and meaning (morphosemantic) properties of morphemes while controls were mainly influenced by morphosemantic properties. The reports suggest that morphological processing is intact in high-functioning dyslexics and a strength when compared to controls matched for reading comprehension and age. Thus, reports support morphological processing as a potential factor in the reading compensation of adults with dyslexia. However, adults with dyslexia performed significantly worse than controls on morphological awareness measures.

Evaluation of methods for volumetric analysis of pediatric brain data: The childmetrix pipeline versus adult-based approaches

Pediatric brain volumetric analysis based on Magnetic Resonance Imaging (MRI) is of particular interest in order to understand the typical brain development and to characterize neurodevelopmental disorders at an early age. However, it has been shown that the results can be biased due to head motion, inherent to pediatric data, and due to the use of methods based on adult brain data that are not able to accurately model the anatomical disparity of pediatric brains. To overcome these issues, we proposed childmetrix, a tool developed for the analysis of pediatric neuroimaging data that uses an age-specific atlas and a probabilistic model-based approach in order to segment the gray matter (GM) and white matter (WM). The tool was extensively validated on 55 scans of children between 5 and 6 years old (including 13 children with developmental dyslexia) and 10 pairs of test-retest scans of children between 6 and 8 years old and compared with two state-of-the-art methods using an adult atlas, namely icobrain (applying a probabilistic model-based segmentation) and Freesurfer (applying a surface model-based segmentation). The results obtained with childmetrix showed a better reproducibility of GM and WM segmentations and a better robustness to head motion in the estimation of GM volume compared to Freesurfer. Evaluated on two subjects, childmetrix showed good accuracy with 82–84% overlap with manual segmentation for both GM and WM, thereby outperforming the adult-based methods (icobrain and Freesurfer), especially for the subject with poor quality data. We also demonstrated that the adult-based methods needed double the number of subjects to detect significant morphological differences between dyslexics and typical readers. Once further developed and validated, we believe that childmetrix would provide appropriate and reliable measures for the examination of childrens brain.

Multi-method brain imaging reveals impaired representations of number as well as altered connectivity in adults with dyscalculia

ABSTRACT Two hypotheses have been proposed about the etiology of neurodevelopmental learning disorders, such as dyslexia and dyscalculia: representation impairments and disrupted access to representations. We implemented a multi‐method brain imaging approach to directly investigate these representation and access hypotheses in dyscalculia, a highly prevalent but understudied neurodevelopmental disorder in learning to calculate. We combined several magnetic resonance imaging methods and analyses, including univariate and multivariate analyses, functional and structural connectivity. Our sample comprised 24 adults with dyscalculia and 24 carefully matched controls. Results showed a clear deficit in the non‐symbolic magnitude representations in parietal, temporal and frontal regions, as well as hyper‐connectivity in visual brain regions in adults with dyscalculia. Dyscalculia in adults was thereby related to both impaired number representations and altered connectivity in the brain. We conclude that dyscalculia is related to impaired number representations as well as altered access to these representations. HighlightsDyscalculia affects 5–7% of population and is as prevalent as dyslexia.We applied wide variety of neuroimaging techniques to investigate this hypothesis.First neuroimaging study with adults diagnosed with dyscalculia.Impaired non‐symbolic number representations are observed across cortex.Increased functional connectivity between temporo‐occipital regions in dyscalculia.