Lower Interhemispheric Coherence in Adults with Surgically Treated Severe Generalized Epilepsy than in Patients Without Epilepsy: A Scalp EEG Study

Background: Interhemispheric coherence, a coherence value between symmetrically opposite electroencephalography (EEG) electrodes, can be considered as a representation of connectivity through commissural fibers. In general, these commissural fibers are the major pathway of communication between hemispheres. However, in patients with drug-resistant generalized epilepsy (GE), these fibers also play an important role in propagating seizure activities to the contralateral hemisphere. The differences in interhemispheric coherence between epilepsy patients and patients without epilepsy (non-E) remain poorly understood. This study compared interhemispheric coherence values between these groups and discussed the potential usage of coherence analysis in the field of epilepsy. Methods: We retrospectively collected EEG data from patients with severe non-lesional GE over 20 years old who underwent corpus callosotomy. To compare interhemispheric coherence, EEG data from 10 non-E patients were prepared. In each patient, EEG data during non-rapid eye movement (NREM) sleep were collected. Interhemispheric coherence in eight pairs of electrodes in five frequency bands was calculated. Interhemispheric coherence values were compared between GE and non-E groups. Results: In each frequency band and electrode pair, interhemispheric coherence values of P3-P4 in delta, C3-C4 in theta, C3-C4 in alpha, F3-F4 and C3-C4 in beta, and C3-C4 and P3-P4 in gamma frequency band were significantly lower for GE than for non-E. The overall interhemispheric coherence value was significantly lower for GE than for non-E. Conclusions: Interhemispheric coherence values were lower for severe GE than for non-E in adults during NREM sleep.