International Journal of Epilepsy 2016; 03(01): 42-62
DOI: 10.1016/j.ijep.2015.12.013
Thieme Medical and Scientific Publishers Private Ltd. 2017

Altered connectivity in focal epilepsy

Chun Kee Chung
1   Department of Neurosurgery, Seoul National University Hospital, Seoul, Republic of Korea
2   Interdisciplinary Program in Neuroscience, Seoul National University College of Natural Science, Seoul, Republic of Korea
3   Department of Neurosurgery, Seoul National University College of Medicine, Seoul, Republic of Korea
4   Department of Brain and Cognitive Sciences, Seoul National University College of Natural Sciences, Seoul, Republic of Korea
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Publication Date:
12 May 2018 (online)

According to the recent studies, epileptic brains have specific alterations in connectivity and network topology both in functional and structural networks, which have led to the recent hypothesis that epilepsy is a brain network disease rather than a focal disease. To characterize the functional brain networks in epilepsy from an electrophysiological perspective, we investigated resting-state functional networks identified by using magnetoencephalography (MEG) signals in epilepsy patients with focal cortical dysplasia (FCD) and mesial temporal lobe epilepsy (mTLE) with hippocampal sclerosis (HS). By virtue of the high temporal resolution of MEG, we investigated the various frequency bands such as theta, alpha, beta, and gamma frequency bands. At the sensor level study of FCD, we found that FCD brains had increased functional connectivity in the beta and gamma frequency bands at the resting state compared with those in healthy controls. Interestingly, patients exhibited different network characteristics depending on the type of FCD. At the source level study of FCD, we found that FCD alters whole brain functional cortical hubs compared to healthy controls in various frequency bands, which are indicative of network reorganization of brain networks. At the source level study of mTLE with HS, we found altered electrophysiological functional hubs in mTLE patients. Since we detected network hubs in both hippocampal and extra-hippocampal areas, it is probable that mTLE is a large-scale network disorder rather than a focal disorder. In conclusion, resting-state brain network studies in epilepsy might helpful enhancing our understanding of the epileptic brain as a network disease.