Abstracts

Rationale: Epilepsy is common in patients with circumscribed brain abnormalities, such as primary brain tumours and hippocampal sclerosis. The mechanism of seizure onset that is induced by these abnormalities remains poorly understood. It has been suggested that the interaction of the ictal zone with surrounding brain areas is pivotal in the initiation and particularly in the propagation of seizures. A way to explore the interactions between brain areas is to look at functional interactions or functional connectivity. Furthermore, the brain can be seen as a complex network of interacting brain regions. Modern network theory can be used to analyze the characteristics of this network. We compare functional networks derived from MEG recordings in lesional epilepsy patients to those in healthy controls. Furthermore, we report on the relationship between functional connectivity and network characteristics on the one hand, and clinical characteristics on the other hand in lesional epilepsy patients. Methods: Resting-state eyes-closed MEG-recordings of 35 lesional epilepsy patients and 36 healthy controls were analyzed. The phase lag index (PLI) was used to assess functional connectivity in conventional frequency bands and weighted networks were constructed. Group differences between patients and controls in PLI and network parameters were calculated, and the correlation between functional connectivity, network measures, and clinical characteristics was established. Results: Clustering in the theta and lower alpha bands was increased in lesional epilepsy patients. Furthermore, longer theta band path lengths were correlated with higher seizure frequency, longer epilepsy history, and use of multiple anti-epileptic drugs. Finally, theta band clustering and path length differed between patient with different lesion pathology. Conclusions: Interictal functional network topology in lesional epilepsy patients is altered compared to controls, in particular in the theta band. Furthermore, network topology is correlated with several clinical epilepsy characteristics.