title: Initiation of sleep-dependent cortical-hippocampal correlations at wakefulness-sleep transition.
abstract: Sleep is involved in memory consolidation. Current theories propose that sleep-dependent memory consolidation requires active communication between the hippocampus and neocortex. Indeed, it is known that neuronal activities in the hippocampus and various neocortical areas are correlated during slow-wave sleep. However, transitioning from wakefulness to slow-wave sleep is a gradual process. How the hippocampal-cortical correlation is established during the wakefulness-sleep transition is unknown. By examining local field potentials and multiunit activities in the rat hippocampus and visual cortex, we show that the wakefulness-sleep transition is characterized by sharp-wave ripple events in the hippocampus and high-voltage spike-wave events in the cortex, both of which are accompanied by highly synchronized multiunit activities in the corresponding area. Hippocampal ripple events occur earlier than the cortical high-voltage spike-wave events, and hippocampal ripple incidence is attenuated by the onset of cortical high-voltage spike waves. This attenuation leads to a temporary weak correlation in the hippocampal-cortical multiunit activities, which eventually evolves to a strong correlation as the brain enters slow-wave sleep. The results suggest that the hippocampal-cortical correlation is established through a concerted, two-step state change that first synchronizes the neuronal firing within each brain area and then couples the synchronized activities between the two regions.
authors.affiliation: Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas; and.
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Haggerty
authors.affiliation: Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas; and Department of Neuroscience, Baylor College of Medicine, Houston, Texas dji@bcm.edu.
authors.forename: Daoyun
authors.initials: D
authors.lastname: Ji
mesh_terms: D000818:Animals; D056547:CA1 Region, Hippocampal / Q000502:physiology*; D008297:Male; D009434:Neural Pathways / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D051381:Rats; D020318:Rats, Long-Evans; D012894:Sleep Stages / Q000502:physiology*; D014793:Visual Cortex / Q000502:physiology*; D014851:Wakefulness / Q000502:physiology*
keywords: high-voltage spike waves; hippocampus; memory consolidation; ripples; sleep