title: Interictal Hippocampal Spiking Influences the Occurrence of Hippocampal Sleep Spindles.
abstract: OBJECTIVE
  The significance of hippocampal sleep spindles and their relation to epileptic activity is still a matter of controversy. Hippocampal spindles have been considered a physiological phenomenon, an evoked response to afferent epileptic discharges, or even the expression of an epileptic manifestation. To address this question, we investigated the presence and rate of hippocampal spindles in focal pharmacoresistant epilepsy patients undergoing scalp-intracerebral electroencephalography (EEG).
  
  
  METHODS
  Sleep recording with scalp-intracerebral EEG.
  
  
  METHODS
  Tertiary referral epilepsy center.
  
  
  METHODS
  Twenty-five epilepsy patients (extratemporal: n = 6, temporal: n = 15, and multifocal including the temporal lobe: n = 4).
  
  
  METHODS
  N/A.
  
  
  RESULTS
  We analyzed associations between hippocampal spindles and hippocampal electrophysiological findings (interictal spiking, seizure onset zone) and magnetic resonance imaging volumetry. Sixteen of 25 patients (64%) had hippocampal spindles (extratemporal epilepsy: 6/6; temporal epilepsy: 10/15; and multifocal epilepsy: 0/4; P = 0.005). Median spindle rate was 0.6 (range, 0.1-8.6)/min in nonrapid eye movement sleep. Highest spindle rates were found in hippocampi of patients with extratemporal epilepsy (P < 0.001). A negative association was found between hippocampal spiking activity and spindle rate (P = 0.003). We found no association between the presence (n = 21) or absence (n = 17) of hippocampal seizure onset zone and hippocampal spindle rate (P = 0.114), and between a normal (n = 30) or atrophic (n = 8) hippocampus and hippocampal spindle rate (P = 0.195).
  
  
  CONCLUSIONS
  Hippocampal spindles represent a physiological phenomenon, with an expression that is diminished in epilepsy affecting the temporal lobe. Hippocampal spiking lowered the rate of hippocampal spindles, suggesting that epileptic discharges may at least in part be a transformation of these physiological events, similar to the hypothesis considering generalized spike-and-waves a transformation of frontal spindles.
authors.affiliation: Montreal Neurological Institute and Hospital, McGill University, Montreal, Québec, Canada.
authors.forename: Birgit
authors.initials: B
authors.lastname: Frauscher
authors.affiliation: Montreal Neurological Institute and Hospital, McGill University, Montreal, Québec, Canada.
authors.forename: Neda
authors.initials: N
authors.lastname: Bernasconi
authors.affiliation: Montreal Neurological Institute and Hospital, McGill University, Montreal, Québec, Canada.
authors.forename: Benoit
authors.initials: B
authors.lastname: Caldairou
authors.affiliation: Montreal Neurological Institute and Hospital, McGill University, Montreal, Québec, Canada.
authors.forename: Nicolás
authors.initials: N
authors.lastname: von Ellenrieder
authors.affiliation: Montreal Neurological Institute and Hospital, McGill University, Montreal, Québec, Canada.
authors.forename: Andrea
authors.initials: A
authors.lastname: Bernasconi
authors.affiliation: Montreal Neurological Institute and Hospital, McGill University, Montreal, Québec, Canada.
authors.forename: Jean
authors.initials: J
authors.lastname: Gotman
authors.affiliation: Montreal Neurological Institute and Hospital, McGill University, Montreal, Québec, Canada.
authors.forename: François
authors.initials: F
authors.lastname: Dubeau
mesh_terms: D000328:Adult; D004569:Electroencephalography; D004827:Epilepsy / Q000503:physiopathology*; D005260:Female; D006624:Hippocampus / Q000503:physiopathology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D012640:Seizures / Q000503:physiopathology; D012890:Sleep / Q000502:physiology*; D013702:Temporal Lobe / Q000503:physiopathology
keywords: MRI volumetry; epilepsy; hippocampus; intracerebral EEG; sleep physiology