title: Sleep in the human hippocampus: a stereo-EEG study.
abstract: BACKGROUND
  There is compelling evidence indicating that sleep plays a crucial role in the consolidation of new declarative, hippocampus-dependent memories. Given the increasing interest in the spatiotemporal relationships between cortical and hippocampal activity during sleep, this study aimed to shed more light on the basic features of human sleep in the hippocampus.
  
  
  RESULTS
  We recorded intracerebral stereo-EEG directly from the hippocampus and neocortical sites in five epileptic patients undergoing presurgical evaluations. The time course of classical EEG frequency bands during the first three NREM-REM sleep cycles of the night was evaluated. We found that delta power shows, also in the hippocampus, the progressive decrease across sleep cycles, indicating that a form of homeostatic regulation of delta activity is present also in this subcortical structure. Hippocampal sleep was also characterized by: i) a lower relative power in the slow oscillation range during NREM sleep compared to the scalp EEG; ii) a flattening of the time course of the very low frequencies (up to 1 Hz) across sleep cycles, with relatively high levels of power even during REM sleep; iii) a decrease of power in the beta band during REM sleep, at odds with the typical increase of power in the cortical recordings.
  
  
  CONCLUSIONS
  Our data imply that cortical slow oscillation is attenuated in the hippocampal structures during NREM sleep. The most peculiar feature of hippocampal sleep is the increased synchronization of the EEG rhythms during REM periods. This state of resonance may have a supportive role for the processing/consolidation of memory.
authors.affiliation: Department of Psychology, University of Rome La Sapienza, Roma, Italy.
authors.forename: Fabio
authors.initials: F
authors.lastname: Moroni
authors.forename: Lino
authors.initials: L
authors.lastname: Nobili
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Curcio
authors.forename: Fabrizio
authors.initials: F
authors.lastname: De Carli
authors.forename: Fabiana
authors.initials: F
authors.lastname: Fratello
authors.forename: Cristina
authors.initials: C
authors.lastname: Marzano
authors.forename: Luigi
authors.initials: L
authors.lastname: De Gennaro
authors.forename: Franco
authors.initials: F
authors.lastname: Ferrillo
authors.forename: Massimo
authors.initials: M
authors.lastname: Cossu
authors.forename: Stefano
authors.initials: S
authors.lastname: Francione
authors.forename: Giorgio
authors.initials: G
authors.lastname: Lo Russo
authors.forename: Mario
authors.initials: M
authors.lastname: Bertini
authors.forename: Michele
authors.initials: M
authors.lastname: Ferrara
mesh_terms: D000328:Adult; D004569:Electroencephalography; D005260:Female; D006624:Hippocampus / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D012890:Sleep / Q000502:physiology*