title: High frequency oscillations (80-500 Hz) in the preictal period in patients with focal seizures.
abstract: OBJECTIVE
  Intracranial depth macroelectrode recordings from patients with focal seizures demonstrate interictal and ictal high frequency oscillations (HFOs, 80-500 Hz). These HFOs are more frequent in the seizure-onset zone (SOZ) and reported to be linked to seizure genesis. We evaluated whether HFO activity changes in a systematic way during the preictal period.
  
  
  METHODS
  Fifteen minutes of preictal intracranial electroencephalography (EEG) recordings were evaluated in seven consecutive patients with well-defined SOZ. EEG was filtered at 500 Hz and sampled at 2,000 Hz. Ripples (80-250 Hz) and fast ripples (250-500 Hz) were visually marked, and spectral analysis was performed in seizure-onset as well as nonseizure-onset channels. Linear regressions fitted to the power trends corresponding to intervals of 1, 5, and 15 min before the seizure onset was calculated.
  
  
  RESULTS
  Total rates of HFOs were significantly higher in the SOZ than outside. Preictal increases and decreases in HFO rates and band power could be detected in all patients, and they were not limited to the SOZs. These measures were very variable, and no systematic trends were observed when comparing patients or seizures in the same patient.
  
  
  CONCLUSIONS
  High frequencies in the range of 80-500 Hz are present during the preictal period and are more prominent in the SOZ. They do not change in a systematic way before seizure onset for the horizons we tested. The 80-500 Hz band may be used for the localization of seizure-onset areas but may be more difficult to use for seizure prediction purposes.
authors.affiliation: Montreal Neurological Institute and Hospital, McGill University, Montreal, Québec, Canada.
authors.forename: Julia
authors.initials: J
authors.lastname: Jacobs
authors.forename: Rina
authors.initials: R
authors.lastname: Zelmann
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Jirsch
authors.forename: Rahul
authors.initials: R
authors.lastname: Chander
authors.forename: Claude-Edouard Châtillon François
authors.initials: CE
authors.lastname: Dubeau
authors.forename: Jean
authors.initials: J
authors.lastname: Gotman
mesh_terms: D001921:Brain / Q000503:physiopathology*; D001931:Brain Mapping / Q000379:methods*; D004567:Electrodes, Implanted; D004569:Electroencephalography / Q000706:statistics & numerical data*; D005583:Fourier Analysis; D006801:Humans; D008137:Longitudinal Studies; D011336:Probability; D012640:Seizures / Q000175:diagnosis* / Q000503:physiopathology; D012815:Signal Processing, Computer-Assisted; D013057:Spectrum Analysis / Q000706:statistics & numerical data; D013238:Stereotaxic Techniques