title: The influence of learning on sleep slow oscillations and associated spindles and ripples in humans and rats.
abstract: The mechanisms underlying off-line consolidation of memory during sleep are elusive. Learning of hippocampus-dependent tasks increases neocortical slow oscillation synchrony, and thalamocortical spindle and hippocampal ripple activity during subsequent non-rapid eye movement sleep. Slow oscillations representing an oscillation between global neocortical states of increased (up-state) and decreased (down-state) neuronal firing temporally group thalamic spindle and hippocampal ripple activity, which both occur preferentially during slow oscillation up-states. Here we examined whether slow oscillations also group learning-induced increases in spindle and ripple activity, thereby providing time-frames of facilitated hippocampus-to-neocortical information transfer underlying the conversion of temporary into long-term memories. Learning (word-pairs in humans, odor-reward associations in rats) increased slow oscillation up-states and, in humans, shaped the timing of down-states. Slow oscillations grouped spindle and rat ripple activity into up-states under basal conditions. Prior learning produced in humans an increase in spindle activity focused on slow oscillation up-states. In rats, learning induced a distinct increase in spindle and ripple activity that was not synchronized to up-states. Event-correlation histograms indicated an increase in spindle activity with the occurrence of ripples. This increase was prolonged after learning, suggesting a direct temporal tuning between ripples and spindles. The lack of a grouping effect of slow oscillations on learning-induced spindles and ripples in rats, together with the less pronounced effects of learning on slow oscillations, presumably reflects a weaker dependence of odor learning on thalamo-neocortical circuitry. Slow oscillations might provide an effective temporal frame for hippocampus-to-neocortical information transfer only when thalamo-neocortical systems are already critically involved during learning.
authors.affiliation: Department of Neuroendocrinology, University of Lübeck, Ratzeburger Allee 160, Haus 23a, 23538 Lübeck, Germany. moelle@kfg.uni-luebeck.de
authors.forename: Matthias
authors.initials: M
authors.lastname: Mölle
authors.forename: Oxana
authors.initials: O
authors.lastname: Eschenko
authors.forename: Steffen
authors.initials: S
authors.lastname: Gais
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Sara
authors.forename: Jan
authors.initials: J
authors.lastname: Born
mesh_terms: D000328:Adult; D000818:Animals; D001245:Association Learning / Q000502:physiology*; D002540:Cerebral Cortex / Q000502:physiology; D004569:Electroencephalography; D005071:Evoked Potentials / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009483:Neuropsychological Tests; D009812:Odorants; D010507:Periodicity; D051381:Rats; D017207:Rats, Sprague-Dawley; D012201:Reward; D012890:Sleep / Q000502:physiology*; D013057:Spectrum Analysis / Q000379:methods; D013223:Statistics as Topic; D055815:Young Adult