title: Differentiation of specific ripple patterns helps to identify epileptogenic areas for surgical procedures.
abstract: OBJECTIVE
  High frequency oscillations (HFOs) at 80-500 Hz are promising markers of epileptic areas. Several retrospective studies reported that surgical removal of areas generating HFOs was associated with a good seizure outcome. Recent reports suggested that ripple (80-200 Hz) HFO patterns co-existed with different background EEG activities. We hypothesized that the coexisting background EEG pattern may distinguish physiological from epileptic ripples.
  
  
  METHODS
  Rates of HFOs were analyzed in intracranial EEG recordings of 22 patients. Additionally, ripple patterns were classified for each channel depending either as coexisting with a flat or oscillatory background activity. A multi-variate analysis was performed to determine whether removal of areas showing the above EEG markers correlated with seizure outcome.
  
  
  RESULTS
  Removal of areas generating high rates of 'fast ripples (>200 Hz)' and 'ripples on a flat background activity' showed a significant correlation with a seizure-free outcome. In contrast, removal of high rates of 'ripples' or 'ripple patterns in a continuously oscillating background' was not significantly associated with seizure outcome.
  
  
  CONCLUSIONS
  Ripples occurring in an oscillatory background activity may be suggestive of physiological activity, while those on a flat background reflect epileptic activity.
  
  
  CONCLUSIONS
  Consideration of coexisting background patterns may improve the delineation of the epileptogenic areas using ripple oscillations.
authors.affiliation: Epilepsy Center, University Medical Center Freiburg, Mathildenstrasse 1, Breisacher Str. 64, 79106 Freiburg, Germany. Electronic address: karokerber@gmx.de.
authors.forename: Karolin
authors.initials: K
authors.lastname: Kerber
authors.affiliation: Epilepsy Center, University Medical Center Freiburg, Mathildenstrasse 1, Breisacher Str. 64, 79106 Freiburg, Germany. Electronic address: matthias.duempelmann@uniklinik-freiburg.de.
authors.forename: Matthias
authors.initials: M
authors.lastname: Dümpelmann
authors.affiliation: Institute for Complex Systems and Mathematical Biology, University of Aberdeen, Meston Building, AB24 3UE Aberdeen, UK.
authors.forename: Björn
authors.initials: B
authors.lastname: Schelter
authors.affiliation: Medical Physics, University Medical Center Freiburg, Breisacher Str. 60a, 79106 Freiburg, Germany. Electronic address: Pierre.levan@uniklinik-freiburg.de.
authors.forename: Pierre
authors.initials: P
authors.lastname: Le Van
authors.affiliation: Department of Neuropediatrics and Muscular Disease, University Medical Center Freiburg, University of Freiburg, Mathildenstrasse 1, 79106 Freiburg, Germany. Electronic address: rudolf.korinthenberg@uniklinik-freiburg.de.
authors.forename: Rudolf
authors.initials: R
authors.lastname: Korinthenberg
authors.affiliation: Epilepsy Center, University Medical Center Freiburg, Mathildenstrasse 1, Breisacher Str. 64, 79106 Freiburg, Germany. Electronic address: andreas.schulze-bonhage@uniklinik-freiburg.de.
authors.forename: Andreas
authors.initials: A
authors.lastname: Schulze-Bonhage
authors.affiliation: Department of Neuropediatrics and Muscular Disease, University Medical Center Freiburg, University of Freiburg, Mathildenstrasse 1, 79106 Freiburg, Germany. Electronic address: julia.jacobs@uniklinik-freiburg.de.
authors.forename: Julia
authors.initials: J
authors.lastname: Jacobs
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D004567:Electrodes, Implanted; D004569:Electroencephalography / Q000379:methods*; D004827:Epilepsy / Q000601:surgery*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D011300:Preoperative Care / Q000379:methods*; D012189:Retrospective Studies; D012640:Seizures / Q000175:diagnosis*; D016896:Treatment Outcome; D055815:Young Adult
keywords: Depth electrodes; Epilepsy surgery; Fast ripple; High frequency oscillation; Refractory epilepsy; Spikes