Disruption of EEG resting state functional connectivity in patients with focal epilepsy

Mostafa M. Elkholy1*

Abstract
Background Epilepsy is a network disease and EEG could be used to evaluate dynamic inter-regional connectivity. The aim of the current study is to explore disruption of resting state EEG functional connectivity in focal epilepsy using coherence and phase lag degree. This cross-sectional study included 30 patients with focal epilepsy and 30 matched healthy controls. One to two minutes of EEG segmented into 2-s epochs during awake eye-closed state were analyzed using fast Fourier transform to yield four frequency bands: delta, theta, alpha and beta. Coherence and phase lag degree were computed between each pair of 19 EEG electrodes and were assessed at the intrahemispheric (frontal–parietal and frontal–temporal) and inter-hemispheric (frontal, temporal and parietal) levels. The frequency of interictal epileptiform discharges (IEDs) was calculated from a 60-min EEG recording session.

Results Compared to healthy controls, patients had lower theta coherence at left frontal–parietal (P = 0.017), lower delta coherence at inter-frontal (P = 0.045), higher theta phase lag at right frontal–parietal (P = 0.01) and lower delta phase lag at inter-temporal (P = 0.046) levels. Patients with left-sided epilepsy had lower theta coherence at left frontal– parietal (P = 0.026), higher theta phase lag at right frontal–parietal (P < 0.001), higher delta phase lag at right frontal– temporal (P = 0.036) and higher theta phase lag at inter-parietal (P = 0.028) levels. The frequency of IEDs correlated with phase lag of delta (P = 0.036, r = 0.406) and theta (P = 0.005, r = 0.513).

Conclusions Patients with focal epilepsy had significant interictal functional connectivity disruption detected by coherence and phase lag degree of delta and theta waves and correlated with frequency of IEDs.

Keywords Functional connectivity, Electroencephalography, Coherence, Phase lag, Focal epilepsy, Epileptic networks

NON-2024-1447