title: Epileptic networks are strongly connected with and without the effects of interictal discharges.
abstract: Epilepsy is increasingly considered as the dysfunction of a pathologic neuronal network (epileptic network) rather than a single focal source. We aimed to assess the interactions between the regions that comprise the epileptic network and to investigate their dependence on the occurrence of interictal epileptiform discharges (IEDs).
  
  
  
  We analyzed resting state simultaneous electroencephalography-functional magnetic resonance imaging (EEG-fMRI) recordings in 10 patients with drug-resistant focal epilepsy with multifocal IED-related blood oxygen level-dependent (BOLD) responses and a maximum t-value in the IED field. We computed functional connectivity (FC) maps of the epileptic network using two types of seed: (1) a 10-mm diameter sphere centered in the global maximum of IED-related BOLD map, and (2) the independent component with highest correlation to the IED-related BOLD map, named epileptic component. For both approaches, we compared FC maps before and after regressing out the effect of IEDs in terms of maximum and mean t-values and percentage of map overlap.
  
  
  
  Maximum and mean FC maps t-values were significantly lower after regressing out IEDs at the group level (p < 0.01). Overlap extent was 85% ± 12% and 87% ± 12% when the seed was the 10-mm diameter sphere and the epileptic component, respectively.
  
  
  
  Regions involved in a specific epileptic network show coherent BOLD fluctuations independent of scalp EEG IEDs. FC topography and strength is largely preserved by removing the IED effect. This could represent a signature of a sustained pathologic network with contribution from epileptic activity invisible to the scalp EEG.
authors.affiliation: Functional Brain Mapping Lab, Faculty of Medicine, University of Geneva, Geneva, Switzerland.
authors.forename: Giannina R
authors.initials: GR
authors.lastname: Iannotti
authors.affiliation: Department of Radiology and Medical Informatics, University Hospital of Geneva, Geneva, Switzerland.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Grouiller
authors.affiliation: Developmental Imaging and Biophysics Section, UCL Institute of Child Health, London, United Kingdom.
authors.forename: Maria
authors.initials: M
authors.lastname: Centeno
authors.affiliation: Developmental Imaging and Biophysics Section, UCL Institute of Child Health, London, United Kingdom.
authors.forename: David W
authors.initials: DW
authors.lastname: Carmichael
authors.affiliation: Support Center of Advanced Neuroimaging (SCAN), Institute for Diagnostic and Interventional Neuroradiology, University Hospital Inselspital, Bern, Switzerland.
authors.forename: Eugenio
authors.initials: E
authors.lastname: Abela
authors.affiliation: Support Center of Advanced Neuroimaging (SCAN), Institute for Diagnostic and Interventional Neuroradiology, University Hospital Inselspital, Bern, Switzerland.
authors.forename: Roland
authors.initials: R
authors.lastname: Wiest
authors.affiliation: Pediatric Neurology, Child and Adolescent Department, University Hospitals and Faculty of Medicine of Geneva, Geneva, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Korff
authors.affiliation: Neurology Clinic, University Hospital and Faculty of Medicine of Geneva, Geneva, Switzerland.
authors.forename: Margitta
authors.initials: M
authors.lastname: Seeck
authors.affiliation: Functional Brain Mapping Lab, Faculty of Medicine, University of Geneva, Geneva, Switzerland.
authors.forename: Christoph
authors.initials: C
authors.lastname: Michel
authors.affiliation: Neurology Clinic, University Hospital and Faculty of Medicine of Geneva, Geneva, Switzerland.
authors.forename: Francesca
authors.initials: F
authors.lastname: Pittau
authors.affiliation: Neurology Clinic, University Hospital and Faculty of Medicine of Geneva, Geneva, Switzerland.
authors.forename: Serge
authors.initials: S
authors.lastname: Vulliemoz
mesh_terms: D000293:Adolescent; D001921:Brain / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D001931:Brain Mapping; D002648:Child; D004569:Electroencephalography; D004827:Epilepsy / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009434:Neural Pathways / Q000000981:diagnostic imaging / Q000503:physiopathology; D010100:Oxygen / Q000097:blood; D012146:Rest / Q000502:physiology; D012815:Signal Processing, Computer-Assisted; D055815:Young Adult
chemical_list: D010100:Oxygen
keywords: EEG-fMRI; Epilepsy; Functional connectivity; IED; Independent component analysis