Abstracts

Rationale: Extra-temporal functional brain networks could be altered in medial temporal lobe epilepsy (MTLE). It is not yet clear whether such a large-scale network change is a cause or result of epilepsy. We hypothesized that interictal epileptiform discharges (IED) cause extra-temporal network alteration in MTLE patients. The spatiotemporal relationship between IED and functional connectivity (FC) was investigated by using simultaneous EEG-fMRI in this study. Methods: A total 16 MTLE patients with histologically-confirmed hippocampal sclerosis (Left: 8, Right: 8) were assigned in this study. Eye-closed resting state EEG-fMRI was recorded preoperatively. Time-series data was segmented into 5 different epochs around IED; pre-IED: -10 to 0 sec, IED: 0 to 10s, post-IED: 10 to 20s, rest: at least 30s before and 45s after IED. Total 160 epochs of 32 IEDs without overlaps were analyzed. Affected medial temporal lobe structures (hippocampus and para-hippocampal gyrus: PHG) were set as seed in seed-to-voxel analysis to calculate FC. Then, FCs were statistically compared between epochs. Results: FCs between PHG and the ipsilateral frontal lobe, contralateral posterior temporal lobe and precuneous were significantly decreased during post-IED epoch than pre-IED epoch (cluster threshold: p＜0.05, FDR). Although there was no statistical significance to the rest epoch, the FC was stronger in a negative correlation during post IED epoch than rest and pre IED epoch (the mean value of FC during rest, pre and post IED was -0.17, -0.10 and -0.28, respectively). Conclusions: Our data suggested FC between the medial temporal lobe and extra-temporal lobe could be altered by IED as pathologic result. Funding: This study is supported by The Japan epilepsy research foundation (JERF18001) and Japan Brain Foundation.