Abstracts

Rationale: Medically-refractory focal epilepsy results in profound effects on cognition and quality of life. While epilepsy surgery can lead to seizure freedom in focal epilepsy patients, sometimes it fails due to an incomplete localization of the epileptogenic zone (EZ). Brain networks in epilepsy can be interrogated with resting-state functional connectivity (RSFC) analysis, although previous studies using electrocorticography or functional MRI have produced inconsistent results. Magnetoencephalography (MEG) allows noninvasive recordings across the entire cortex, and can be used to study both long-range network alterations in focal epilepsy and regional connectivity at the EZ.Methods: In MEG recordings from preoperative epilepsy patients, we examined both global functional connectivity maps in patients versus controls, as well as regional functional connectivity maps at the area of resection, compared to the homotopic non-epileptogenic region in the contralateral hemisphere.Results: We studied 61 patients, including 30 with mesial temporal lobe epilepsy and 31 with focal neocortical epilepsy. Compared to matched controls, epilepsy patients had decreased RSFC in widespread areas, including peri-sylvian, posterior temporo-parietal, and orbitofrontal cortices (p < 0.01, t-test). Reduced mean global connectivity was related to longer duration of epilepsy and higher frequency of consciousness-impairing seizures (p < 0.01, linear regression). In addition, patients with increased regional connectivity within the resection site (n = 24) were more likely to achieve seizure freedom after surgery (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 < 0.02, chi-square).Conclusions: Patients with focal epilepsy harbor widespread global decreases in functional connectivity, which may reflect deleterious long-term effects of recurrent seizures. Enhanced regional functional connectivity at the area of resection may aid surgical planning and help predict seizure outcome.