title: Interictal scalp fast oscillations as a marker of the seizure onset zone.
abstract: OBJECTIVE
  This study aims to identify if oscillations at frequencies higher than the traditional EEG can be recorded on the scalp EEG of patients with focal epilepsy and to analyze the association of these oscillations with interictal discharges and the seizure onset zone (SOZ).
  
  
  METHODS
  The scalp EEG of 15 patients with focal epilepsy was studied. We analyzed the rates of gamma (40-80 Hz) and ripple (>80 Hz) oscillations, their co-occurrence with spikes, the number of channels with fast oscillations inside and outside the SOZ, and the specificity, sensitivity, and accuracy of gamma, ripples, and spikes to determine the SOZ.
  
  
  RESULTS
  Gamma and ripples frequently co-occurred with spikes (77.5% and 63% of cases). For all events, the proportion of channels with events was consistently higher inside than outside the SOZ: spikes (100% vs 70%), gamma (82% vs 33%), and ripples (48% vs 11%); p < 0.0001. The mean rates (events/min) were higher inside than outside the SOZ: spikes (2.64 ± 1.70 vs 0.69 ± 0.26, p = 0.02), gamma (0.77 ± 0.71 vs 0.20 ± 0.25, p = 0.02), and ripples (0.08 ± 0.12 vs 0.04 ± 0.09, p = 0.04). The sensitivity to identify the SOZ was spikes 100%, gamma 82%, and ripples 48%; the specificity was spikes 30%, gamma 68%, and ripples 89%; and the accuracy was spikes 43%, gamma 70%, and ripples 81%.
  
  
  CONCLUSIONS
  The rates and the proportion of channels with gamma and ripple fast oscillations are higher inside the SOZ, indicating that they can be used as interictal scalp EEG markers for the SOZ. These fast oscillations are less sensitive but much more specific and accurate than spikes to delineate the SOZ.
authors.affiliation: Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada. lupatrizia@yahoo.com.br
authors.forename: L P
authors.initials: LP
authors.lastname: Andrade-Valenca
authors.forename: F
authors.initials: F
authors.lastname: Dubeau
authors.forename: F
authors.initials: F
authors.lastname: Mari
authors.forename: R
authors.initials: R
authors.lastname: Zelmann
authors.forename: J
authors.initials: J
authors.lastname: Gotman
mesh_terms: D000328:Adult; D016477:Artifacts; D001921:Brain / Q000473:pathology / Q000503:physiopathology*; D003627:Data Interpretation, Statistical; D004569:Electroencephalography; D004827:Epilepsy / Q000503:physiopathology; D005260:Female; D006801:Humans; D008297:Male; D012640:Seizures / Q000473:pathology / Q000503:physiopathology*; D012890:Sleep / Q000502:physiology; D055815:Young Adult