Morken, F. 1 , Helland, T. 1 , Hugdahl, K. 1, 2, 3 & Specht, K. 1, 4
1 Department of Biological and Medical Psychology, University of Bergen, Bergen, Norway
2 Division of Psychiatry, Haukeland University Hospital, Bergen, Norway
3 Department of Radiology, Haukeland University Hospital, Bergen, Norway
4 Department of Clinical Engineering, Haukeland University Hospital, Bergen, Norway
Dyslexia is a disorder preventing efficient acquisition of reading and writing skills. Longitudinal studies are of essence in order to understand this developmental disorder fully. This study investigated effective connectivity in a left hemisphere reading network through the Pre-literacy (6 years), Emergent literacy (8 years) and Literacy (12 years) stages of reading development, comparing a group with dyslexia and a group with typical reading skills. We used Dynamic Causal Modeling (DCM) in the analysis of functional magnetic resonance imaging (fMRI) data. The network model consisted of five regions: Inferior frontal gyrus (IFG), Pre-central gyrus, Superior temporal gyrus, Inferior parietal lobule, and Occipito-temporal cortex (OT). Connectivity measures were estimated for each connection, and subjected to factorial ANOVA. Results showed differences between groups in five connections - two to and from the IFG, and three to and from the OT. The typical group showed stable or slightly decreasing connectivity, whereas the dyslexia group showed a marked decrease (IFG) or increase (OT) from 6 to 8 years, followed by approximation to the values of the typical group by age 12. This was interpreted as a delay in entering the Pre-literacy and Emergent literacy stages.