MEG Coherence and DTI Connectivity in mTLE

Abstract

Purpose Magnetoencephalography (MEG) is a noninvasive imaging method for localization of focal epileptiform activity in patients with epilepsy. Diffusion tensor imaging (DTI) is a noninvasive imaging method for measuring the diffusion properties of the underlying white matter tracts through which epileptiform activity is propagated. This study investigates the relationship between the cerebral functional abnormalities quantified by MEG coherence and structural abnormalities quantified by DTI in mesial temporal lobe epilepsy (mTLE). Methods Resting state MEG data was analyzed using MEG coherence source imaging (MEG-CSI) method to determine the coherence in 54 anatomical sites in 17 adult mTLE patients with surgical resection and Engel class I outcome, and 17 age- and gender- matched controls. DTI tractography identified the fiber tracts passing through these same anatomical sites of the same subjects. Then, DTI nodal degree and laterality index were calculated and compared with the corresponding MEG coherence and laterality index. Results MEG coherence laterality, after Bonferroni adjustment, showed significant differences for right versus left mTLE in insular cortex and both lateral orbitofrontal and superior temporal gyri (p<0.017). Likewise, DTI nodal degree laterality, after Bonferroni adjustment, showed significant differences for right versus left mTLE in gyrus rectus, insular cortex, precuneus and superior temporal gyrus (p<0.017). In insular cortex, MEG coherence laterality correlated with DTI nodal degree laterality (R2 = 0.46; p = 0.003) in the cases of mTLE. None of these anatomical sites showed statistically significant differences in coherence laterality between right and left sides of the controls. Coherence laterality was in agreement with the declared side of epileptogenicity in insular cortex (in 82% of patients) and both lateral orbitofrontal (88%) and superior temporal gyri (88%). Nodal degree laterality was also in agreement with the declared side of epileptogenicity in gyrus rectus (in 88% of patients), insular cortex (71%), precuneus (82%) and superior temporal gyrus (94%). Combining all significant laterality indices improved the lateralization accuracy to 94% and 100% for the coherence and nodal degree laterality indices, respectively. Conclusion The associated variations in diffusion properties of fiber tracts quantified by DTI and coherence measures quantified by MEG with respect to epileptogenicity possibly reflect the chronic microstructural cerebral changes associated with functional interictal activity. The proposed methodology for using MEG and DTI to investigate diffusion abnormalities related to focal epileptogenicity and propagation may provide a further means of noninvasive lateralization.

The Temporal Instability of Resting State Network Connectivity in Intractable Epilepsy

“…It is worth noting that our instability finding is consistent with diffusion tensor white matter showing that TLE patients express abnormalities in precuneus regions and precuneus-to-mesialtemporal tracts [Campos et al, 2015;Liao et al, 2011;Nazem-Zadeh et al, 2016]. Our data suggest that regardless of the side of the epilepsy, the precuneus displays instability in the setting of both left and right epileptogenic regions compared to controls (i.e., our precuneus/middle temporal cortex finding).…”

“…Moreover, instability in some of these precuneus connections was associated with disease duration, raising the possibility that connections to this key brain and DMN hub may become more temporally unstable as the seizures of TLE become more intractable and chronic. It is worth noting that our instability finding is consistent with diffusion tensor white matter showing that TLE patients express abnormalities in precuneus regions and precuneus-to-mesialtemporal tracts [Campos et al, 2015;Liao et al, 2011;Nazem-Zadeh et al, 2016]. This may suggest that the instability we found associated with the precuneus potentially stems from white matter deficits.…”

Cervical Dystonia and Executive Function: A Pilot Magnetoencephalography Study

“…After transformation to a time-frequency representation, the strength of network interactions can be determined by calculating the coherence, which is a measure of synchrony between signals from different regions for each FFT frequency. Using MEG-Coherence Source Imaging (MEG-CSI), Elisevich et al found regions of high coherence primarily located in the cerebral cortex and localized in the epileptogenic regions, and a seizure-free outcome was associated with removal of these highly coherent networks [ 15 , 16 , 17 ].…”

The Effect of Botulinum Toxin on Network Connectivity in Cervical Dystonia: Lessons from Magnetoencephalography

“…Anatomical identification in these regions was implemented using MEG tools. 8 Coherence results were assessed within a given hemisphere (intrahemispheric) and between the two hemispheres (interhemispheric).…”