title: Nodal approach reveals differential impact of lateralized focal epilepsies on hub reorganization.
abstract: The impact of the hemisphere affected by impairment in models of network disease is not fully understood. Among such models, focal epilepsies are characterised by recurrent seizures generated in epileptogenic areas also responsible for wider network dysfunction between seizures. Previous work focusing on functional connectivity within circumscribed networks suggests a divergence of network integrity and compensatory capacity between epilepsies as a function of the laterality of seizure onset. We evaluated the ability of complex network theory to reveal changes in focal epilepsy in global and nodal parameters using graph theoretical analysis of functional connectivity data obtained with resting-state fMRI. Graphs of functional connectivity networks were derived from 19 right and 13 left focal epilepsy patients and 15 controls. Topological metrics (degree, local efficiency, global efficiency and modularity) were computed for a whole-brain, atlas-defined network. We also calculated a hub disruption index for each graph metric, measuring the capacity of the brain network to demonstrate increased connectivity in some nodes for decreased connectivity in others. Our data demonstrate that the patient group as a whole is characterised by network-wide pattern of reorganization, even while global parameters fail to distinguish between groups. Furthermore, multiple metrics indicate that epilepsies with differently lateralized epileptic networks are asymmetric in their burden on functional brain networks; with left epilepsy patients being characterised by reduced efficiency and modularity, while in right epilepsy patients we provide the first evidence that functional brain networks are characterised by enhanced connectivity and efficiency at some nodes whereas reduced in others.
authors.affiliation: Aix-Marseille Université, CNRS, CRMBM UMR 7339, 13005 Marseille, France; APHM, Hôpital de la Timone, Pôle d'Imagerie Médicale, CEMEREM, 13005 Marseille, France. Electronic address: ben.ridley@univ-amu.fr.
authors.forename: Ben Gendon Yeshe
authors.initials: BG
authors.lastname: Ridley
authors.affiliation: Aix-Marseille Université, CNRS, CRMBM UMR 7339, 13005 Marseille, France; APHM, Hôpital de la Timone, Pôle d'Imagerie Médicale, CEMEREM, 13005 Marseille, France. Electronic address: celiarousseau.rousseau@gmail.com.
authors.forename: Celia
authors.initials: C
authors.lastname: Rousseau
authors.affiliation: Aix-Marseille Université, CNRS, CRMBM UMR 7339, 13005 Marseille, France; APHM, Hôpital de la Timone, Pôle d'Imagerie Médicale, CEMEREM, 13005 Marseille, France. Electronic address: jonathan.wirsich@univ-amu.fr.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Wirsich
authors.affiliation: Aix-Marseille Université, CNRS, CRMBM UMR 7339, 13005 Marseille, France; APHM, Hôpital de la Timone, Pôle d'Imagerie Médicale, CEMEREM, 13005 Marseille, France. Electronic address: arnaud.le-troter@univ-amu.fr.
authors.forename: Arnaud
authors.initials: A
authors.lastname: Le Troter
authors.affiliation: Aix-Marseille Université, CNRS, CRMBM UMR 7339, 13005 Marseille, France; APHM, Hôpital de la Timone, Pôle d'Imagerie Médicale, CEMEREM, 13005 Marseille, France. Electronic address: elisabeth.soulier@univ-amu.fr.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Soulier
authors.affiliation: Aix-Marseille Université, CNRS, CRMBM UMR 7339, 13005 Marseille, France; APHM, Hôpital de la Timone, Pôle d'Imagerie Médicale, CEMEREM, 13005 Marseille, France. Electronic address: sylviane.gouny@univ-amu.fr.
authors.forename: Sylvianne
authors.initials: S
authors.lastname: Confort-Gouny
authors.affiliation: APHM, Hôpital de la Timone, Service de Neurophysiologie Clinique, 13005 Marseille, France; Aix-Marseille Université, INSERM, Institut de Neuroscience des Systèmes U1106, 13005 Marseille, France. Electronic address: fabrice.bartolomei@ap-hm.fr.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Bartolomei
authors.affiliation: Aix-Marseille Université, CNRS, CRMBM UMR 7339, 13005 Marseille, France; APHM, Hôpital de la Timone, Pôle d'Imagerie Médicale, CEMEREM, 13005 Marseille, France. Electronic address: jean-phillipe.ranjeva@univ-amu.fr.
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Ranjeva
authors.affiliation: Centre National de la Recherche Scientifique, Grenoble Image Parole Signal Automatique, 38402 Grenoble, France. Electronic address: sophie.achard@gipsa-lab.inpg.fr.
authors.forename: Sophie
authors.initials: S
authors.lastname: Achard
authors.affiliation: Aix-Marseille Université, CNRS, CRMBM UMR 7339, 13005 Marseille, France; APHM, Hôpital de la Timone, Pôle d'Imagerie Médicale, CEMEREM, 13005 Marseille, France. Electronic address: maxime.guye@ap-hm.fr.
authors.forename: Maxime
authors.initials: M
authors.lastname: Guye
mesh_terms: D000328:Adult; D000368:Aged; D001921:Brain / Q000503:physiopathology*; D001931:Brain Mapping / Q000379:methods*; D004828:Epilepsies, Partial / Q000503:physiopathology*; D005260:Female; D007839:Functional Laterality; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009415:Nerve Net / Q000503:physiopathology; D055815:Young Adult
keywords: Epilepsy; Functional connectivity; Graph theory; Hemispheric asymmetry; Network modelling; Resting-state