Authors: Alfred Mansour, Susan M. Bowyer, Annette E. Richard, John E. Moran, Laszlo A. Erdodi, Amy Olszewski, Lesley Pawluk, Daniel Jacobson, Kelly Vogt, Aimee M. Moore, Renée Lajiness-O’Neill.
Publication: Psychology (Scientific Research Publishing (SCIRP)). Vol.5 No.16, pp 1879-1910 2014 | DOI: 10.4236/psych.2014.516193
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.
Mansour, A., Bowyer, S., Richard, A., Moran, J., Erdodi, L., Olszewski, A., Pawluk, L., Jacobson, D., Vogt, K., Moore, A. & Lajiness-O’Neill, R. (2014). Magnetoencephalography Coherence Source Imaging in Dyslexia: Activation of Working Memory Pathways. Psychology, 5, 1879-1910. doi: 10.4236/psych.2014.516193.
In contrast to controls, individuals with dyslexia tended to recruit prefrontal cortical regions earlier over more posterior temporal or parietal cortical gyri as the superior temporal gyrus and the supramarginal gyrus, regardless of whether they were processing orthographic or non-orthographic information. Specifically, individuals with dyslexia showed an early activation in the superior frontal gyrus (209 ms), whereas control subjects showed an earlier activation in the language-related posterior cortical regions (supramarginal gyrus = 227 ms; superiortemporal gyrus = 290 ms), prior to engaging superior frontal gyrus (325 ms) during the performance of the verbal working memory task. Similarly, during the spatial working task, individuals with dyslexia showed an early latency of activation in the precentral gyrus (167 ms) compared to controls (343 ms), who initiated in more posterior cortical regions of the supramarginal gyrus (236 ms) and superior temporal gyrus (233 ms) during the SWM task.