T07. Resting-state EEG functional connectivity and outcome following mesial temporal lobe epilepsy surgery

Abstract

In this study we explore the reorganization of brain functional connectivity in patients with refractory mesial temporal lobe epilepsy that underwent surgery. We carried out a resting-state EEG functional connectivity analysis in a baseline period before and two years after the surgical intervention. Changes in synchronization features and graph theoretical properties were quantified by synchronization likelihood in patients with different surgical outcome, where outcome was defined as seizure-free (good outcome) or not seizure-free (poor outcome) 1 year after surgery. EEG segments were manually selected and included at least 2 min in closed eyes resting state. In all segments, synchronization likelihood (SL) and graph parameters in delta (1–4 Hz), theta (4–7 Hz), alpha1 (8–10 Hz), alpha2 (10–13 Hz), beta1 (13–15 Hz) and beta2 (15–20 Hz) frequency bands were calculated. Results showed that strength of the overall spatial synchronization was different 2 years after surgery in patients that were free of seizures. The change in synchronization was characterized by lower synchronization in alpha 1 but higher synchronization in alpha2. No changes between pre- and 2 years post-surgery periods were present in patients with seizures’ recurrence. Network properties as clustering coefficient and modularity in alpha2, beta1 and beta2 were higher postoperatively in the group free of seizures compared to baseline. Local efficiency was also higher in theta, alpha2 and beta bands. Interestingly the group with seizures’ recurrence showed a higher modularity only in the delta band but the clustering coefficient and the local efficiency were higher in all frequency bands 2 years after surgery. Outcome after surgery is related to a specific reorganization in brain networks as manifested in changes of functional connectivity and network topology. Reorganization toward a small-world network within the alpha2 and beta bands seems to be mediating seizure resolution.