Resting-State and Task-Based Functional Brain Connectivity in Developmental Dyslexia

Abstract

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.

Individual Differences in Adult Reading Are Associated with Left Temporo-parietal to Dorsal Striatal Functional Connectivity

“…In the present study, right hemisphere connectivity between AG and pericalcarine cortex positively correlated with phonemic decoding. Aberrant connectivity of visual regions in RD has also been shown in several recent reports (van der Mark et al 2011;Finn et al 2013;Fan et al 2014;Schurz et al 2014). Deficits in basic visual processing have long been linked with RD, particularly in the magnocellular pathway (Demb et al 1998).…”

“…Remediated readers showed more negative connectivity between left fusiform gyrus and right medial prefrontal cortex relative to typical and nonremediated dyslexic readers (Koyama et al 2013). Several regions that are typically anticorrelated with the left IPL, including anterior cingulate, post-central gyrus, right hippocampus, and precuneus, are less anticorrelated or positively correlated in RD readers across reading and resting tasks (Schurz et al 2014). While interpretation of differences in negative connectivity can be more challenging, findings involving negative connectivity in RD, psychiatric (Cullen et al 2014;Stegmayer et al 2014), and neurodevelopmental disorders (Jung et al 2014) suggest that variability in negative connectivity may be an important predictor of symptoms and warrants further research.…”

“…In the present study, we also found a correlation between left TPJ to IFG connectivity and PDE scores, at a statistical threshold appropriate for an a priori ROI. Findings regarding the relationship between task-independent functional connectivity of left temporo-parietal cortex and left IFG and reading skill have been mixed (Koyama et al 2011(Koyama et al , 2013Boets et al 2013;Finn et al 2013;Schurz et al 2014). Connectivity between BA39 and Broca's region has been shown to correlate more strongly with reading measures during reading tasks relative to rest (Hampson et al 2006), though consistent connectivity differences in RD across both task and resting conditions has also been shown (Schurz et al 2014).…”

“…Findings regarding the relationship between task-independent functional connectivity of left temporo-parietal cortex and left IFG and reading skill have been mixed (Koyama et al 2011(Koyama et al , 2013Boets et al 2013;Finn et al 2013;Schurz et al 2014). Connectivity between BA39 and Broca's region has been shown to correlate more strongly with reading measures during reading tasks relative to rest (Hampson et al 2006), though consistent connectivity differences in RD across both task and resting conditions has also been shown (Schurz et al 2014). It is also notable that several studies have used residualized task-based scans rather than resting scans (Boets et al 2013;Finn et al 2013), potentially contributing to inconsistent findings across "task-independent" connectivity studies.…”

“…As previous work has shown reduced functional connectivity between left inferior frontal gyurs (IFG) and parietal language regions in individuals with RD or weaker reading skill (Koyama et al 2011;Boets et al 2013;Schurz et al 2014), we examined positive associations between PDE scores and connectivity from all left hemisphere seed regions to the left IFG at a reduced threshold of P < 0.001 uncorrected.…”