title: Sleep-stage correlates of hippocampal electroencephalogram in primates.
abstract: It has been demonstrated in the rodent hippocampus that rhythmic slow activity (theta) predominantly occurs during rapid eye movement (REM) sleep, while sharp waves and associated ripples occur mainly during non-REM sleep. However, evidence is lacking for correlates of sleep stages with electroencephalogram (EEG) in the hippocampus of monkeys. In the present study, we recorded hippocampal EEG from the dentate gyrus in monkeys overnight under conditions of polysomnographical monitoring. As result, the hippocampal EEG changed in a manner similar to that of the surface EEG: during wakefulness, the hippocampal EEG showed fast, desynchronized waves, which were partly replaced with slower waves of intermediate amplitudes during the shallow stages of non-REM sleep. During the deep stages of non-REM sleep, continuous, slower oscillations (0.5-8 Hz) with high amplitudes were predominant. During REM sleep, the hippocampal EEG again showed fast, desynchronized waves similar to those found during wakefulness. These results indicate that in the monkey, hippocampal rhythmic slow activity rarely occurs during REM sleep, which is in clear contrast to that of rodents. In addition, the increase in the slower oscillations of hippocampal EEG during non-REM sleep, which resembled that of the surface EEG, may at least partly reflect cortical inputs to the dentate gyrus during this behavioral state.
authors.affiliation: Department of Integrative Neuroscience, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan.
authors.forename: Ryoi
authors.initials: R
authors.lastname: Tamura
authors.affiliation: Department of Otorhinolaryngology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nishida
authors.affiliation: Department of Systems Neuroscience, School of Medicine, Fukushima Medical University, Fukushima, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Eifuku
authors.affiliation: Faculty of Health Sciences, Mejiro University, Saitama, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Fushiki
authors.affiliation: Department of Otorhinolaryngology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan.
authors.forename: Yukio
authors.initials: Y
authors.lastname: Watanabe
authors.affiliation: Department of Integrative Neuroscience, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan.
authors.forename: Kumiko
authors.initials: K
authors.lastname: Uchiyama
mesh_terms: D000818:Animals; D004569:Electroencephalography; D006624:Hippocampus / Q000502:physiology*; D008251:Macaca / Q000502:physiology*; D012894:Sleep Stages