title: Gamma Oscillations and Their Cross-frequency Coupling in the Primate Hippocampus during Sleep.
abstract: OBJECTIVE
  The mechanism by which sleep consolidates memory is unclear. Based on the two-stage model of memory consolidation, different functions for slow wave sleep (SWS) and rapid eye movement (REM) sleep have been proposed; thus, state-dependent changes of neural oscillations in the hippocampus might clarify this fundamental question.
  
  
  METHODS
  We recorded hippocampal local field potentials from freely behaving monkeys via telemetry and analyzed their nonstationary oscillations using Hilbert-Huang transform.
  
  
  RESULTS
  By applying a recently developed empirical mode decomposition analysis, we found strong cross-frequency coupling between high-frequency and slow wave oscillations during SWS and a prominent increase of gamma band activity in short bursts during REM sleep in unanesthetized primates' hippocampus.
  
  
  CONCLUSIONS
  Spatiotemporal integration through coupled oscillations during slow wave sleep might be a physiological basis of system consolidation, whereas gamma bursts during rapid eye movement sleep might be related to synaptic consolidation in the local hippocampal neural circuit.
authors: Supportive Center for Brain Research, National Institute for Physiological Sciences, Okazaki, Japan.|The Graduate University for Advanced Studies (SOKENDAI), Shonan Village, Hayama, Kanagawa, Japan.
authors: Saori
authors: S
authors: Takeuchi
authors: Human Brain Research Center, Kyoto University Graduate School of Medicine, Shogoin, Sakyo-ku, Kyoto, Japan.
authors: Tatsuya
authors: T
authors: Mima
authors: Supportive Center for Brain Research, National Institute for Physiological Sciences, Okazaki, Japan.
authors: Rie
authors: R
authors: Murai
authors: McGovern Institute for Brain Research, Massachusetts Institute of Technology, Cambridge, MA.
authors: Hideki
authors: H
authors: Shimazu
authors: Tamagawa University Brain Science Institute, Tokyo 194-8610, Japan.
authors: Yoshikazu
authors: Y
authors: Isomura
authors: Supportive Center for Brain Research, National Institute for Physiological Sciences, Okazaki, Japan.|The Graduate University for Advanced Studies (SOKENDAI), Shonan Village, Hayama, Kanagawa, Japan.
authors: Toru
authors: T
authors: Tsujimoto
mesh_terms: D000818:Animals; D005260:Female; D065818:Gamma Rhythm / Q000502:physiology*; D006624:Hippocampus / Q000166:cytology / Q000502:physiology*; D008251:Macaca; D008297:Male; D000069077:Memory Consolidation / Q000502:physiology; D012890:Sleep / Q000502:physiology*; D012895:Sleep, REM / Q000502:physiology
keywords: Hilbert-Huang transform; REM sleep; cross-frequency coupling; hippocampus; monkey