Neural systems supporting typical and atypical reading – separating developmental processes from dyslexia specific effects

Neural systems supporting typical and atypical reading – separating developmental processes from dyslexia specific effects

First Author: Katarzyna Chyl -- Nencki Institute of Experimental Biology
Additional authors/chairs: 
Agnieszka Dębska; Magdalena Łuniewska; Katarzyna Jednoróg
Keywords: Developmental dyslexia, functional MRI, Reading acquisition
Abstract / Summary: 

Purpose
It is known that dyslexics process print in a suboptimal way, hypoactivating left hemispheric (LH) language circuit (i.e. IFG, STG, FG) when compared to their peers. This pattern of brain activation is present also in the typically developing, less proficient readers. Here, we aim to uncover print processing patterns typical for dyslexics that are not merely associated with the reading expertise.

Method
We matched two control groups with 25 dyslexics (DR): typical readers (TR) who entered the study on the same reading skill as DRs, but later did well in reading; and advanced readers (AR) who at the beginning of the study were able to read as well as dyslexics two years later. All children at the beginning of the study (TP1, M age = 6.7) and 2 years later (TP3) took part in fMRI study, in which words were visually presented. With TR and DR groups we were able to track developmental trajectories of impaired and typical reading development. AR TP3> TR TP3 comparisons allowed to observe reading-related effects, while AR TP1 > DR TP3 – effects not related to the performance.

Results
We did not observe neural differences between DRs and TRs for reading processing, when both groups read on low lever. 2 years later differences were found: DRs hypoactivated LH IFG and FG when compared to TRs. When DRs were compared to younger ARs currently reading on the same level, again LH IFG and FG was hypoactivated in DRs. Comparison between two control groups (ARs and TRs) reading differently showed that also poorer readers underactivate language circuit, but those effects are non-overlapping with effects present in dyslexics.

Conclusions
Decreased activation of left vOT and IFG could to be a specific marker of dyslexic brain response to print. This hypoactivation cannot be explained solely by lower reading skills. Our study provides an evidence that neural processes underlying reading in dyslexics do not merely associate with their smaller expertise in reading.