title: Different mechanisms of ripple-like oscillations in the human epileptic subiculum.
abstract: OBJECTIVE
  Transient high-frequency oscillations (HFOs; 150-600Hz) in local field potentials generated by human hippocampal and parahippocampal areas have been related to both physiological and pathological processes. The cellular basis and effects of normal and abnormal forms of HFOs have been controversial. This lack of agreement is clinically significant, because HFOs may be good markers of epileptogenic areas. Better defining the neuronal correlate of specific HFO frequency bands could improve electroencephalographic analyses made before epilepsy surgery.
  
  
  METHODS
  Here, we recorded HFOs in slices of the subiculum prepared from human hippocampal tissue resected for treatment of pharmacoresistant epilepsy. With combined intra- or juxtacellular and extracellular recordings, we examined the cellular correlates of interictal and ictal HFO events.
  
  
  RESULTS
  HFOs occurred spontaneously in extracellular field potentials during interictal discharges (IIDs) and also during pharmacologically induced preictal discharges (PIDs) preceding ictal-like events. Many of these events included frequencies >250Hz and so might be considered pathological, but a significant proportion were spectrally similar to physiological ripples (150-250Hz). We found that IID ripples were associated with rhythmic γ-aminobutyric acidergic and glutamatergic synaptic potentials with moderate neuronal firing. In contrast, PID ripples were associated with depolarizing synaptic inputs frequently reaching the threshold for bursting in most pyramidal cells.
  
  
  CONCLUSIONS
  Our data suggest that IID and PID ripple-like oscillations (150-250Hz) in human epileptic hippocampus are associated with 2 distinct population activities that rely on different cellular and synaptic mechanisms. Thus, the ripple band could not help to disambiguate the underlying cellular processes.
authors.affiliation: Brain and Spine Institute, Pitié-Salpêtrière Hospital, Paris, France; Pierre and Marie Curie University, Paris.
authors.forename: Catalina
authors.initials: C
authors.lastname: Alvarado-Rojas
authors.forename: Gilles
authors.initials: G
authors.lastname: Huberfeld
authors.forename: Michel
authors.initials: M
authors.lastname: Baulac
authors.forename: Stéphane
authors.initials: S
authors.lastname: Clemenceau
authors.forename: Stéphane
authors.initials: S
authors.lastname: Charpier
authors.forename: Richard
authors.initials: R
authors.lastname: Miles
authors.forename: Liset Menendez
authors.initials: LM
authors.lastname: de la Prida
authors.forename: Michel
authors.initials: M
authors.lastname: Le Van Quyen
mesh_terms: D000293:Adolescent; D000328:Adult; D004569:Electroencephalography / Q000379:methods*; D004827:Epilepsy / Q000175:diagnosis* / Q000503:physiopathology* / Q000601:surgery; D005260:Female; D006624:Hippocampus / Q000503:physiopathology* / Q000601:surgery; D006801:Humans; D008297:Male; D008564:Membrane Potentials / Q000502:physiology*; D008875:Middle Aged; D009924:Organ Culture Techniques; D055815:Young Adult