title: High frequency oscillations and high frequency functional network characteristics in the intraoperative electrocorticogram in epilepsy.
abstract: High frequency oscillations (HFOs; > 80 Hz), especially fast ripples (FRs, 250-500 Hz), are novel biomarkers for epileptogenic tissue. The pathophysiology suggests enhanced functional connectivity within FR generating tissue. Our aim was to determine the relation between brain areas showing FRs and 'baseline' functional connectivity within EEG networks, especially in the high frequency bands.
  
  
  
  We marked FRs, ripples (80-250 Hz) and spikes in the electrocorticogram of 14 patients with refractory temporal lobe epilepsy. We assessed 'baseline' functional connectivity in epochs free of epileptiform events within these recordings, using the phase lag index. We computed the Eigenvector Centrality (EC) per channel in the FR and gamma band network. We compared EC between channels that did or did not show events at other moments in time.
  
  
  
  FR-band EC was higher in channels with than without spikes. Gamma-band EC was lower in channels with ripples and FRs.
  
  
  
  We confirmed previous findings of functional isolation in the gamma-band and found a first proof of functional integration in the FR-band network of channels covering presumed epileptogenic tissue.
  
  
  
  'Baseline' high-frequency network parameters might help intra-operative recognition of epileptogenic tissue without the need for waiting for events. These findings can increase our understanding of the 'architecture' of epileptogenic networks and help unravel the pathophysiology of HFOs.
authors.affiliation: Brain Center Rudolf Magnus, Department of Neurology and Neurosurgery, UMC Utrecht, P.O. box 85500, 3508 GA Utrecht, The Netherlands.
authors.forename: W J E M
authors.initials: WJ
authors.lastname: Zweiphenning
authors.affiliation: Brain Center Rudolf Magnus, Department of Neurology and Neurosurgery, UMC Utrecht, P.O. box 85500, 3508 GA Utrecht, The Netherlands.
authors.forename: M A
authors.initials: MA
authors.lastname: van 't Klooster
authors.affiliation: Brain Center Rudolf Magnus, Department of Pediatric Neurology, UMC Utrecht, P.O. box 85500, 3508 GA Utrecht, The Netherlands.
authors.forename: E
authors.initials: E
authors.lastname: van Diessen
authors.affiliation: Brain Center Rudolf Magnus, Department of Neurology and Neurosurgery, UMC Utrecht, P.O. box 85500, 3508 GA Utrecht, The Netherlands.
authors.forename: N E C
authors.initials: NE
authors.lastname: van Klink
authors.affiliation: Brain Center Rudolf Magnus, Department of Neurology and Neurosurgery, UMC Utrecht, P.O. box 85500, 3508 GA Utrecht, The Netherlands.
authors.forename: G J M
authors.initials: GJ
authors.lastname: Huiskamp
authors.affiliation: Brain Center Rudolf Magnus, Department of Neurology and Neurosurgery, UMC Utrecht, P.O. box 85500, 3508 GA Utrecht, The Netherlands.
authors.forename: T A
authors.initials: TA
authors.lastname: Gebbink
authors.affiliation: Brain Center Rudolf Magnus, Department of Neurology and Neurosurgery, UMC Utrecht, P.O. box 85500, 3508 GA Utrecht, The Netherlands.
authors.forename: F S S
authors.initials: FS
authors.lastname: Leijten
authors.affiliation: Brain Center Rudolf Magnus, Department of Neurology and Neurosurgery, UMC Utrecht, P.O. box 85500, 3508 GA Utrecht, The Netherlands.
authors.forename: P H
authors.initials: PH
authors.lastname: Gosselaar
authors.affiliation: Brain Center Rudolf Magnus, Department of Pediatric Neurology, UMC Utrecht, P.O. box 85500, 3508 GA Utrecht, The Netherlands; Biomedical MR Imaging and Spectroscopy Group, Center for Image Sciences, UMC Utrecht, P.O. box 85500, 3508 GA Utrecht, The Netherlands; Stichting Epilepsie Instellingen Nederland, Heemstede, P.O. box 540, 2130 AM Hoofddorp, The Netherlands.
authors.forename: W M
authors.initials: WM
authors.lastname: Otte
authors.affiliation: Department of Clinical Neurophysiology, Neuroscience Campus Amsterdam, VU University Medical Center, Postbus 7057, 1007 MB Amsterdam, The Netherlands.
authors.forename: C J
authors.initials: CJ
authors.lastname: Stam
authors.affiliation: Brain Center Rudolf Magnus, Department of Pediatric Neurology, UMC Utrecht, P.O. box 85500, 3508 GA Utrecht, The Netherlands.
authors.forename: K P J
authors.initials: KP
authors.lastname: Braun
authors.affiliation: Brain Center Rudolf Magnus, Department of Neurology and Neurosurgery, UMC Utrecht, P.O. box 85500, 3508 GA Utrecht, The Netherlands; Stichting Epilepsie Instellingen Nederland, Heemstede, P.O. box 540, 2130 AM Hoofddorp, The Netherlands.
authors.forename: G J M
authors.initials: GJ
authors.lastname: Zijlmans
mesh_terms: D000293:Adolescent; D000328:Adult; D058256:Brain Waves / Q000502:physiology*; D002648:Child; D002675:Child, Preschool; D000069280:Electrocorticography / Q000379:methods*; D004827:Epilepsy / Q000503:physiopathology* / Q000601:surgery; D005260:Female; D065818:Gamma Rhythm / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009415:Nerve Net / Q000503:physiopathology*; D055815:Young Adult
keywords: (io)ECoG, (intra-operative) electrocorticography; EC, eigenvector centrality; EEG, electroencephalography; Epilepsy; Epilepsy surgery; Epileptogenic zone; FR, fast ripple, 250–500 Hz; Functional network analysis; HFO, high frequency oscillation, > 80 Hz; High Frequency Oscillations; IPSP, inhibitory postsynaptic potential; PLI, phase lag index; SOZ, seizure onset zone; TLE, temporal lobe epilepsy