Abstract
This study investigates the functional connectivity of neuronal networks critical for working memory in individuals with dyslexia by means of magnetoenchephalographic (MEG) coherence imaging. Individuals with dyslexia showed an early onset of activation in anterior cortical regions (precentral gyrus and the superior frontal gyrus), which differed from controls where activation initiated in posterior cortical regions (supramarginal gyrus and superior temporal gyrus). Further, individuals with dyslexia showed lower brain activity in the right superior temporal gyrus and right middle temporal gyrus than controls during a spatial working memory (SWM) task. In contrast, during a verbal working memory (VWM) task, individuals with dyslexia showed lower activity in the right insular cortex and right superior temporal gyrus and higher, likely compensatory, activity in the right fusiform gyrus, left parahippocampal gyrus, and left precentral gyrus. When performing a SWM task, individuals with dyslexia showed significantly lower coherent activity and synchronization in 1) right frontal connectivity, 2) right fronto-temporal connectivity, 3) left and right frontal connectivity, 4) left temporal and right frontal connectivity, and 5) left occipital and right frontal connectivity. MEG coherence source imaging (CSI) by frequency bands showed lower mean coherence values in individuals with dyslexia compared to controls for each frequency range during the SWM task. In contrast, during the VWM task, individuals with dyslexia showed higher coherent low frequency (3 - 15 Hz) and lower coherent high frequency (30 - 45 Hz) synchronization than control subjects. Logistic regression of coherent activity by group membership was significant, with an overall predictive success of 84.4% (88.9% for controls and 77.8% for dyslexia). Coherence between the right lateral orbitofrontal and middle orbitofrontal gyri pair substantially contributed to group membership. The results suggest a pattern of aberrant connectivity as evidenced by the early onset and reliance on prefrontal cortical areas, the differential activation of fronto-temporal brain systems, and an altered pattern of functional connectivity in the frontotemporal pathways mediating these behaviors.
Highlights
An estimated 5% to 17% of school age children have significant difficulties learning to read despite average or above average intelligence, adequate educational opportunities, and environmental support (Shaywitz et al, 1998; Vellutino, Fletcher, Snowling, & Scanlon, 2004)
MEG coherence significantly differed between individuals with dyslexia and matched-controls when performing a working memory paradigm and these results depended on the stimulus presentation
MEG activation was initiated in more posterior cortical regions such as the supramarginal gyrus and superior temporal gyrus during the performance of a Spatial Working Memory (SWM) task
Summary
An estimated 5% to 17% of school age children have significant difficulties learning to read despite average or above average intelligence, adequate educational opportunities, and environmental support (Shaywitz et al, 1998; Vellutino, Fletcher, Snowling, & Scanlon, 2004). Phonological processing (word decoding) occurs at 250 - 330 milliseconds and involves the activation of left middle and superior temporal gyri and the parietal cortical regions (supramarginal gyrus, angular gyrus). Oral output or the articulation of a word or speech sound occurs after 330 milliseconds and results in activation of Broca’s area in the left inferior frontal gyrus and bilateral sensorimotor areas. These MEG localizations and latencies have been corroborated using several different MEG analysis techniques (Bowyer et al, 2004; Simos et al, 2002)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
