Abstracts

Rationale: Previous reports revealed extra-temporal functional brain networks could be altered in medial temporal lobe epilepsy (MTLE). Little is known what affects such large-scale network changes. We hypothesized that interictal epileptiform discharges (IED) would be a cause of the network alteration in MTLE patients. The relationship between IED frequency 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. FC between multiple ROIs (medial temporal lobe: MTL, lateral temporal lobe: LTL, prefrontal cortex: PFC, premotor area, sensorimotor cortex, parietal lobe and occipital lobe) were analyzed. Then, correlation between FC and the frequency of simultaneously-recorded IED was calculated. The correlation to the IED frequency during extra scanner EEG (light sleep stage) and to that of intraoperative electrocorticogram (ECoG) was also analyzed. Results: The IED frequency during fMRI recording was negatively correlated with the FC between affected para-hippocampal gyrus and bilateral PFC, LTL (r<-0.6, p<0.05). Conversely, there were no significant correlations with FCs between MTL and other ROIs. The IED frequency both during extra scanner EEG and intra-operative ECoG was negatively correlated with FC between bilateral LTL and PFC predominantly in the affected side (r<-0.51, p<0.05). Conclusions: Our data suggested frequent IED could decrease FC within the temporal lobe and that between the temporal lobe and prefrontal cortex. Funding: Japan Epilepsy Research Foundation (JERF) 2018 (No. JERF TENKAN 18001)