title: Slow oscillations orchestrating fast oscillations and memory consolidation.
abstract: Slow-wave sleep (SWS) facilitates the consolidation of hippocampus-dependent declarative memory. Based on the standard two-stage memory model, we propose that memory consolidation during SWS represents a process of system consolidation which is orchestrated by the neocortical <1Hz electroencephalogram (EEG) slow oscillation and involves the reactivation of newly encoded representations and their subsequent redistribution from temporary hippocampal to neocortical long-term storage sites. Indeed, experimental induction of slow oscillations during non-rapid eye movement (non-REM) sleep by slowly alternating transcranial current stimulation distinctly improves consolidation of declarative memory. The slow oscillations temporally group neuronal activity into up-states of strongly enhanced neuronal activity and down-states of neuronal silence. In a feed-forward efferent action, this grouping is induced not only in the neocortex but also in other structures relevant to consolidation, namely the thalamus generating 10-15Hz spindles, and the hippocampus generating sharp wave-ripples, with the latter well known to accompany a replay of newly encoded memories taking place in hippocampal circuitries. The feed-forward synchronizing effect of the slow oscillation enables the formation of spindle-ripple events where ripples and accompanying reactivated hippocampal memory information become nested into the single troughs of spindles. Spindle-ripple events thus enable reactivated memory-related hippocampal information to be fed back to neocortical networks in the excitable slow oscillation up-state where they can induce enduring plastic synaptic changes underlying the effective formation of long-term memories.
authors.affiliation: Department of Neuroendocrinology, University of Lübeck, Lübeck, Germany. moelle@kfg.uni-luebeck.de
authors.forename: Matthias
authors.initials: M
authors.lastname: Mölle
authors.forename: Jan
authors.initials: J
authors.lastname: Born
mesh_terms: D004558:Electric Stimulation; D004569:Electroencephalography; D006624:Hippocampus / Q000502:physiology*; D006801:Humans; D008568:Memory / Q000502:physiology*; D008959:Models, Neurological; D010507:Periodicity; D012890:Sleep / Q000502:physiology*