Abstracts

Rationale: It was observed that the mean level of phase synchronization of cortical activity is related to cortical excitability in humans. Also, abnormal cortical excitability is believed to be an important cause of the initiation and spread of epileptic seizures. Therefore, this study aimed to evaluate phase synchronization of EEG current dipole activities to assess cortical excitability during epilepsy treatment with Geodesic Transcranial Electrical Neuromodulation (GTEN). Methods: Three patients with focal epilepsy were treated by GTEN in its safety and feasibility trial at the University of Washington Harborview Hospital in Seattle. For each patient, the treatment plan describes the targeted brain regions of interest (ROI) in terms of a list of current dipoles. In each treatment session, EEG was recorded before and after treatment. From these EEG recordings, epileptiform discharges were marked as spike events by an experienced epileptologist. Around these spike events, EEG was segmented by 10-second windows and source localized with sLORETA. For each spike marked before treatment, local phase synchronization was calculated for each dipole in the ROI with respect to its nearest neighbors. Average phase synchronization was then calculated across all spikes; and total phase synchronization of the ROI before treatment was then calculated as the sum of individual dipole results. Similarly, total phase synchronization of the ROI after treatment was calculated. The change of total phase synchronization before and after GTEN is finally calculated for analysis. Results: For one of the three patients analyzed, phase synchronization at the high gamma frequency was consistently reduced across the five treatment days (after versus before treatment, mean: -17.0% ; standard deviation: 11.7%).  It may be relevant that this patient reported the greatest seizure reduction and subjective improvement following GTEN treatment. Conclusions: Phase synchronization measured in EEG source space might be used as a non-invasive approach to assess and monitor cortical excitability during epilepsy treatment. Further studies with additional clinical data would be necessary to validate this hypothesis. Funding: Funded by EGI.