title: Electrical stimulation for cortical mapping reduces the density of high frequency oscillations.
abstract: BACKGROUND
  High frequency oscillations (HFOs, 80-500 Hz) are EEG biomarkers for epileptogenic areas. HFOs are also indicators of disease activity as HFO rates increase after reduction of antiepileptic medication. Electrical stimulation (ES) can be used for diagnostic purposes as well as therapy in patients with refractory epilepsy. This study investigates the occurrence and changes of HFOs during ES in patients with refractory epilepsy.
  
  
  OBJECTIVE
  Analysis of the effects of ES using intracranial ES on the occurrence of epileptic HFOs.
  
  
  METHODS
  Patients underwent ES for diagnostic purposes. Ripples (80-200 Hz) and fast ripples (200-500 Hz) were visually marked in a baseline EEG segment prior to ES, after each period of ES as well as after the end of ES. In patients in whom ES triggered a seizure a pre- and postictal segment was marked. Rates of HFOs were compared for the different time periods using a Spearman's correlation and Wilcoxon rank sum test (p<0.05).
  
  
  RESULTS
  12 patients with 911 EEG channels were analyzed. Ripple (r=-0.42, p<0.001) as well as fast ripple (r=-0.21, p<0.001) rates decreased significantly over the course of stimulation. This phenomenon was not focal over the seizure onset or neighboring contacts but even observed over distant contacts.
  
  
  CONCLUSIONS
  ES resulted in a gradual decrease of HFO-Rates over time. The decrease of HFOs was not limited to SOZ areas. If HFOs are considered as markers of disease activity the reduction in HFO-rates as a result of intracranial ES has to be interpreted as a reduction of disease activity.
authors.affiliation: Department of Neuropediatrics and Muscular Disease, University Medical Center Freiburg, Germany. Electronic address: julia.jacobs@gmx.de.
authors.forename: Julia
authors.initials: J
authors.lastname: Jacobs
authors.affiliation: Department of Neuropediatrics and Muscular Disease, University Medical Center Freiburg, Germany; Epilepsy Center, University Medical Center Freiburg, Germany.
authors.forename: Tilin
authors.initials: T
authors.lastname: Golla
authors.affiliation: Department of Neuropediatrics and Muscular Disease, University Medical Center Freiburg, Germany.
authors.forename: Malenka
authors.initials: M
authors.lastname: Mader
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: Epilepsy Center, University Medical Center Freiburg, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Dümpelmann
authors.affiliation: Department of Neuropediatrics and Muscular Disease, University Medical Center Freiburg, Germany.
authors.forename: Rudolf
authors.initials: R
authors.lastname: Korinthenberg
authors.affiliation: Epilepsy Center, University Medical Center Freiburg, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Schulze-Bonhage
mesh_terms: D000328:Adult; D001921:Brain / Q000503:physiopathology*; D001931:Brain Mapping / Q000379:methods*; D058256:Brain Waves / Q000502:physiology*; D004558:Electric Stimulation / Q000379:methods*; D004567:Electrodes, Implanted; D004569:Electroencephalography / Q000379:methods*; D004827:Epilepsy / Q000175:diagnosis / Q000503:physiopathology; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D055815:Young Adult
keywords: Electrical stimulation; Fast ripple; Refractory epilepsy; Ripple