title: Interictal high-frequency oscillations (80-500 Hz) are an indicator of seizure onset areas independent of spikes in the human epileptic brain.
abstract: OBJECTIVE
  High-frequency oscillations (HFOs) known as ripples (80-250 Hz) and fast ripples (250-500 Hz) can be recorded from macroelectrodes inserted in patients with intractable focal epilepsy. They are most likely linked to epileptogenesis and have been found in the seizure onset zone (SOZ) of human ictal and interictal recordings. HFOs occur frequently at the time of interictal spikes, but were also found independently. This study analyses the relationship between spikes and HFOs and the occurrence of HFOs in nonspiking channels.
  
  
  METHODS
  Intracerebral EEGs of 10 patients with intractable focal epilepsy were studied using macroelectrodes. Rates of HFOs within and outside spikes, the overlap between events, event durations, and the percentage of spikes carrying HFOs were calculated and compared according to anatomical localization, spiking activity, and relationship to the SOZ.
  
  
  RESULTS
  HFOs were found in all patients, significantly more within mesial temporal lobe structures than in neocortex. HFOs could be seen in spiking as well as nonspiking channels in all structures. Rates and durations of HFOs were significantly higher in the SOZ than outside. It was possible to establish a rate of HFOs to identify the SOZ with better sensitivity and specificity than with the rate of spikes.
  
  
  CONCLUSIONS
  HFOs occurred to a large extent independently of spikes. They are most frequent in mesial temporal structures. They are prominent in the SOZ and provide additional information on epileptogenicity independently of spikes. It was possible to identify the SOZ with a high specificity by looking at only 10 min of HFO activity.
authors.affiliation: Montreal Neurological Institute and Hospital, Montreal, Canada. julia.jacobs@gmx.de
authors.forename: Julia
authors.initials: J
authors.lastname: Jacobs
authors.forename: Pierre
authors.initials: P
authors.lastname: LeVan
authors.forename: Rahul
authors.initials: R
authors.lastname: Chander
authors.forename: Jeffery
authors.initials: J
authors.lastname: Hall
authors.forename: François
authors.initials: F
authors.lastname: Dubeau
authors.forename: Jean
authors.initials: J
authors.lastname: Gotman
mesh_terms: D000679:Amygdala / Q000503:physiopathology; D001921:Brain / Q000503:physiopathology*; D004569:Electroencephalography; D004576:Electromyography; D004585:Electrooculography; D004827:Epilepsy / Q000175:diagnosis / Q000503:physiopathology*; D006801:Humans; D008279:Magnetic Resonance Imaging