Authors: Matthias Schurz, Heinz Wimmer, Fabio Richlan, Philipp Ludersdorfer, Johannes Klackl, Martin Kronbichler.
Publication: Cerebral Cortex (Oxford University Press). Volume 25, Issue 10, Pages 3502–3514 2015 | DOI: 10.1093/cercor/bhu184
Reading requires the interaction between multiple cognitive processes situated in distant brain areas. This makes the study of functional brain connectivity highly relevant for understanding developmental dyslexia. We used seed-voxel correlation mapping to analyse connectivity in a left-hemispheric network for task-based and resting-state fMRI data. Our main finding was reduced connectivity in dyslexic readers between left posterior temporal areas (fusiform, inferior temporal, middle temporal, superior temporal) and the left inferior frontal gyrus. Reduced connectivity in these networks was consistently present for 2 reading-related tasks and for the resting state, showing a permanent disruption which is also present in the absence of explicit task demands and potential group differences in performance. Furthermore, we found that connectivity between multiple reading-related areas and areas of the default mode network, in particular the precuneus, was stronger in dyslexic compared with nonimpaired readers.
Matthias Schurz, Heinz Wimmer, Fabio Richlan, Philipp Ludersdorfer, Johannes Klackl, Martin Kronbichler, Resting-State and Task-Based Functional Brain Connectivity in Developmental Dyslexia, Cerebral Cortex, Volume 25, Issue 10, October 2015, Pages 3502–3514, https://doi.org/10.1093/cercor/bhu184
Besides findings of stronger connectivity in nonimpaired compared with dyslexic readers, we also found the opposite pattern for some of our seed areas. Connectivity between multiple reading-related areas (FFG, ITG, MTG, and IPL) and posterior cortical midline areas (precuneus/cuneus) were stronger in dyslexic compared with nonimpaired readers. These group differences were mainly driven by stronger positive correlations in dyslexic reader.
Another finding of stronger connectivity in dyslexic readers was linked to IFG pars opercularis–left IPL/angular gyrus and IFG pars opercularis–right angular gyrus.
In our study, the criterion for assigning participants to the dyslexia group was a difference in reading fluency. This is because we tested readers of German, which has high regularity in grapheme-phoneme mappings (shallow orthography).