Abstracts

Rationale: Interictal MEG is a useful tool for localization of epileptiform activity in patients with medically refractory epilepsy. Brain functional connectivity analysis plays an important role in understanding the organized behavior of brain regions beyond mapping and localization of their activities. In this study, we analyzed interictal MEG spikes from epilepsy patients, and investigated causal interactions between localized epileptiform activities and connected brain regions using functional connectivity analysis.Methods: Interictal MEG data from three medically intractable epilepsy patients were recorded by Magnes 2500 WH (148 MEG channels, 4D Neuroimaging). For each patient, 8 interictal spikes were selected after band-pass filtering. MEG sensors were co-registered with the standard Montreal Neurological Institute (MNI) brain and a spherical head model was used in forward modeling. For each spike, cortical source imaging with minimum norm estimation was used to identify epileptiform sources. Directional connectivity among cortical regions of interest was estimated using directed transfer function and visualized over the cortical surface using eConnectome software package.Results: Epileptogenic brain areas were identified by experienced epileptologists using MRI and intracranial EEG. The patients had surgical resection of the epileptogenic zones, and were either seizure free or had significant seizure reduction with medicine after surgery. Identified epileptiform activities were overlapping with surgically resected regions. The activity propagated from identified foci to connected brain regions, might through the language, motor or sensory region, probably causing interictal brain disorders. Estimated directional connectivity among source regions and propagated regions agreed with the propagations. Fig. 1 shows source connectivity analysis results of an interictal spike from a patient.Conclusions: Cortical source connectivity analysis of interictal MEG data was used to study interictal discharge propagation and underlying mechanisms. Interictal discharge sources identified were in agreement with surgically resected regions in the patients studied. The present results suggest the potential application of MEG source connectivity analysis in localizing epileptogenic foci and understanding epileptic brain networks.