Epilepsy Research (2015) 113, 98—103 j ourna l h om epa ge: www.elsevier.com/locate/epilepsyres Responders to vagus nerve stimulation (VNS) in refractory epilepsy have reduced interictal cortical synchronicity on scalp EEG Clémentine Bodin a , Sandrine Aubert a , Géraldine Daquin b , Romain Carron c , Didier Scavarda d , Aileen McGonigal a , Fabrice Bartolomei a,e,* a CHU Timone, Service de Neurophysiologie Clinique, Assistance Publique des Hôpitaux de Marseille, Marseille F-13005, France b Hôpital Henri Gastaut, 13009 Marseille, France c CHU Timone, Stereotactic and Functional Neurosurgery Department, Assistance Publique des Hôpitaux de Marseille, Marseille F-13005, France d CHU Timone, Pediatric Neurosurgery Department, Assistance Publique des Hôpitaux de Marseille, Marseille F-13005, France e Institut de Neurosciences des Systèmes, INSERM UMR 1106, Marseille, France Received 15 February 2015; received in revised form 18 March 2015; accepted 28 March 2015 Available online 9 April 2015 KEYWORDS VNS; EEG; Functional connectivity; Synchrony; Epilepsy Summary EEG desynchronization has been proposed to be an important mechanism for antiepileptic effect of vagus nerve stimulation (VNS) but has never been clearly documented in human. The aim of this study was to evaluate impact of VNS on the synchronicity of inter- ictal EEG rhythms. We estimated synchronization between scalp EEG signals using phase lag index (PLI) in 19 patients with chronic VNS therapy. We estimated changes in synchronization between ON and OFF phases and between responder (R) and non-responder (NR) patients. We found that R have a lower global level of synchronization (EEG broadband) than NR (p < 0.0001) In addition, ON periods were characterized by lower values in comparison with OFF periods (p < 0.001). R had significantly lower global synchronization levels in delta and alpha frequency bands (p < 0.0001). ∗ Corresponding author at: CHU Timone, Service de Neurophysiologie Clinique, CHU Timone-264 Rue St Pierre, F-13005 Marseille, France. E-mail address: fabrice.bartolomei@ap-hm.fr (F. Bartolomei). http://dx.doi.org/10.1016/j.eplepsyres.2015.03.018 0920-1211/© 2015 Elsevier B.V. All rights reserved.