Effect of interictal epileptiform discharges on EEG coherence and phase lag in patients with focal epilepsy

Document Type : Original Article

Author

Department of Clinical Neurophysiology (Neuro-Diagnostic and Research Center), Faculty of Medicine, Beni-Suef University, Egypt

Abstract

Background and Aim: Epilepsy is a network disease, and its pathological networks could be related to the interictal epileptiform discharges (IEDs). The aim is to explore the effect of IEDs on EEG functional connectivity metrics (coherence and phase lag degree) in patients with focal epilepsy. Methods: The study included 14 patients with focal epilepsy and 14 matched healthy controls. EEGs of the patients were segmented into two-second epochs: a. epochs containing IEDs, b. resting epochs with no IEDs. The selected epochs were analyzed using Fast Fourier Transform to yield four frequency bands: Delta, Theta, Alpha and Beta. Coherence and phase lag degree were computed between the EEG electrodes and were assessed at the intra-hemispheric (frontal-parietal and frontal-temporal) and inter-hemispheric (frontal, temporal and parietal) levels. The frequency of IEDs was calculated from a sixty-minute EEG recording session. Results: Patients had significant IED-related connectivity disruption in the form of higher phase lag degree at both intra-hemispheric and inter-hemispheric levels of the following frequencies: delta (P=0.022) and theta (P=0.041) at the left frontal-parietal, beta at the left frontal-temporal (P=0.009), theta at the inter-hemispheric frontal (P=0.003), delta (P=0.006), and beta (P=0.041) frequency bands at the inter-hemispheric temporal level. The frequency of IEDs correlated with phase lag degree of theta (P=0.004, r= 0.720) frequency over the right frontal-parietal level. Conclusions: Patients with focal epilepsy showed dynamic IED-related changes in EEG functional connectivity mainly demonstrated by increase of phase lag degree of delta and theta frequency over the frontal and temporal regions.

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References

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