The neural basis of specific reading disability (SRD) remains only partly understood. A dozen studies have used voxel-based morphometry (VBM) to investigate gray matter volume (GMV) differences between SRD and control children, however, recent meta-analyses suggest that few regions are consistent across studies. We used data collected across three countries (France, Poland, and Germany) with the aim of both increasing sample size (236 SRD and controls) to obtain a clearer picture of group differences, and of further assessing the consistency of the findings across languages. VBM analysis reveals a significant group difference in a single cluster in the left thalamus. Furthermore, we observe correlations between reading accuracy and GMV in the left supramarginal gyrus and in the left cerebellum, in controls only. Most strikingly, we fail to replicate all the group differences in GMV reported in previous studies, despite the superior statistical power. The main limitation of this study is the heterogeneity of the sample drawn from different countries (i.e., speaking languages with varying orthographic transparencies) and selected based on different assessment batteries. Nevertheless, analyses within each country support the conclusions of the cross-linguistic analysis. Explanations for the discrepancy between the present and previous studies may include: (1) the limited suitability of VBM to reveal the subtle brain disruptions underlying SRD; (2) insufficient correction for multiple statistical tests and flexibility in data analysis, and (3) publication bias in favor of positive results. Thus the study echoes widespread concerns about the risk of false-positive results inherent to small-scale VBM studies.

BackgroundTo date, the neural correlates of phonological word stress processing are largely unknown.MethodsIn the present study, we investigated the processing of word stress and vowel quality using an identity matching task with pseudowords.ResultsIn line with previous studies, a bilateral fronto-temporal network comprising the superior temporal gyri extending into the sulci as well as the inferior frontal gyri was observed for word stress processing. Moreover, we found differences in the superior temporal gyrus and the superior temporal sulcus, bilaterally, for the processing of different stress patterns. For vowel quality processing, our data reveal a substantial contribution of the left intraparietal cortex. All activations were modulated by task demands, yielding different patterns for same and different pairs of stimuli.ConclusionsOur results suggest that the left superior temporal gyrus represents a basic system underlying stress processing to which additional structures including the homologous cortex site are recruited with increasing difficulty.

Despite decades of research, the anatomical abnormalities associated with developmental dyslexia are still not fully described. Studies have focused on between-group comparisons in which different neuroanatomical measures were generally explored in isolation, disregarding potential interactions between regions and measures. Here, for the first time a multivariate classification approach was used to investigate grey matter disruptions in children with dyslexia in a large (N = 236) multisite sample. A variety of cortical morphological features, including volumetric (volume, thickness and area) and geometric (folding index and mean curvature) measures were taken into account and generalizability of classification was assessed with both 10-fold and leave-one-out cross validation (LOOCV) techniques. Classification into control vs. dyslexic subjects achieved above chance accuracy (AUC = 0.66 and ACC = 0.65 in the case of 10-fold CV, and AUC = 0.65 and ACC = 0.64 using LOOCV) after principled feature selection. Features that discriminated between dyslexic and control children were exclusively situated in the left hemisphere including superior and middle temporal gyri, subparietal sulcus and prefrontal areas. They were related to geometric properties of the cortex, with generally higher mean curvature and a greater folding index characterizing the dyslexic group. Our results support the hypothesis that an atypical curvature pattern with extra folds in left hemispheric perisylvian regions characterizes dyslexia. Hum Brain Mapp 38:900-908, 2017. © 2016 Wiley Periodicals, Inc.

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We investigated whether phonological deficits are a consequence of magnocellular processing deficits in dyslexic and control children. In Experiment 1, children were tested for reading ability, phonological awareness, visuo-magnocellular motion perception, and attention shifting (sometimes considered as magnocellular function). A two-step cluster analysis of the behavioural scores revealed four clusters of children. Phonological awareness was correlated with attention (cluster musical sharp1) or motion detection (cluster musical sharp2), whereas attention and motion detection were correlated in cluster musical sharp3. In cluster musical sharp4, all variables were uncorrelated. In Experiment 2, the same variables plus auditory discrimination were tested with fMRI in a sub-sample of Experiment 1. Although dyslexics had reduced activation in visual or auditory cortex during motion detection or auditory discrimination, respectively, they had increased right frontal activation in areas 44 and 45 in all 'magnocellular' (including auditory) tasks. In contrasts, during phonological decisions, there was higher activation for good readers than dyslexics in left areas 44 and 45. Together, the two experiments give insight into the interplay of phonological and magnocellular processing during reading. Distinct left versus right frontal effects reveal partly different underlying neural mechanisms. These data contradict the view that phonological processing deficits in dyslexia necessarily result from impaired magnocellular functioning.