106 Functional Network Analysis in Surgical Epilepsy Patients Using Magnetoencephalography

INTRODUCTION: Intractable focal epilepsy is a devastating disorder with profound effects on cognition and quality of life. Epilepsy surgery can lead to seizure freedom in patients with focal epilepsy; however, sometimes it fails owing to an incomplete delineation of the epileptogenic zone (EZ). Brain networks in epilepsy can be studied with resting-state functional connectivity (RSFC) analysis, yet previous investigations using functional MRI or electrocorticography have produced inconsistent results. Magnetoencephalography (MEG) allows noninvasive whole-brain recordings, and can be used to study both long-range network disturbances in focal epilepsy and regional connectivity at the EZ. METHODS: In MEG recordings from presurgical epilepsy patients, we examined: (1) global functional connectivity maps in patients vs controls, and (2) regional functional connectivity maps at the region of resection, compared with the homotopic nonepileptogenic region in the contralateral hemisphere. RESULTS: Sixty-one patients were studied, including 30 with mesial temporal lobe epilepsy and 31 with focal neocortical epilepsy. Compared with a group of 31 controls, epilepsy patients had decreased RSFC in widespread regions, including perisylvian, posterior temporoparietal, and orbitofrontal cortices (P < .01, false discovery rate-corrected). Decreased mean global connectivity was related to longer duration of epilepsy and higher frequency of consciousness-impairing seizures (P < .01, linear regression). Furthermore, patients with increased regional connectivity within the resection site (n = 24) were more likely to achieve postoperative seizure freedom (87.5% with Engel I outcome) than those with neutral (n = 15, 64.3% seizure free) or decreased (n = 23, 47.8% seizure free) regional connectivity (P < .02, χ2). CONCLUSION: Widespread global decreases in functional connectivity are observed in patients with focal epilepsy and may reflect deleterious long-term effects of recurrent seizures. Furthermore, enhanced regional functional connectivity at the area of resection may help predict seizure outcome and aid surgical planning.