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Atypical Hemispheric Re-Organization of the Reading Network in High-Functioning Adults with Dyslexia: Evidence from Representational Similarity Analysis

Poster B62 in Poster Session B, Tuesday, October 24, 3:30 - 5:15 pm CEST, Espace Vieux-Port

Eddy Cavalli1, Valérie Chanoine2;4, Yufei Tan2;4, Jean-Luc Anton2;4, Bruno Giordano2;4, Felipe Pegado3;4, Johannes C. Ziegler2;4; 1Université Lyon 2, 2Aix Marseille Université, 3Université Paris Cité, 4ILCB, Aix Marseille Université and CNRS

It has been argued that university students with dyslexia compensate for their reading deficits by a neural re-organization of the typical reading network that emphasizes semantic similarity between words over orthographic similarity. To investigate the re-organization of neural word representations more directly, we used multivariate representational similarity analyses (RSA) to find out which brain regions of the reading network respond to orthographic and semantic similarity between 544 pairs of words and whether there were any differences between typical and dyslexic readers. In accordance with the re-organization hypothesis, we predicted greater similarity (i.e., correlation of neural dissimilarity matrices) in adult dyslexic than in typical readers in regions associated with semantic processing and weaker similarity in regions associated with orthographic processing. The results showed that all three subparts of the fusiform gyrus (FG1, FG2, FG3) bilaterally were sensitive to semantic information in typical readers, whereas less sensitivity in a posterior subpart of fusiform gyrus (FG1) in the left hemisphere was obtained for dyslexic readers. In typical readers, orthographic information was not only processed in the left fusiform gyrus (FG1, FG2, FG3) but also in left IFG. Adults with dyslexia, in contrast, did not show sensitivity to orthographic information in left IFG. However, they showed increased sensitivity to orthographic information in the right hemisphere FG1. Together, the results show abnormal orthographic processing in left IFG and right FG1 and reduced semantic information in left FG1. While we found evidence for compensatory re-organization in adult dyslexia, the present results do not support the hypothesis according to which adults with dyslexia rely more heavily on semantic information. Instead, they revealed atypical hemispheric organization of the reading network that do not extensively rely on the typical left language hemisphere.

Topic Areas: Disorders: Developmental, Language Development/Acquisition

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