title: No effect of odor-induced memory reactivation during REM sleep on declarative memory stability.
abstract: Memory reactivations in hippocampal brain areas are critically involved in memory consolidation processes during sleep. In particular, specific firing patterns of hippocampal place cells observed during learning are replayed during subsequent sleep and rest in rodents. In humans, experimentally inducing hippocampal memory reactivations during slow-wave sleep (but not during wakefulness) benefits consolidation and immediately stabilizes declarative memories against future interference. Importantly, spontaneous hippocampal replay activity can also be observed during rapid eye movement (REM) sleep and some authors have suggested that replay during REM sleep is related to processes of memory consolidation. However, the functional role of reactivations during REM sleep for memory stability is still unclear. Here, we reactivated memories during REM sleep and examined its consequences for the stability of declarative memories. After 3 h of early, slow-wave sleep (SWS) rich sleep, 16 healthy young adults learned a 2-D object location task in the presence of a contextual odor. During subsequent REM sleep, participants were either re-exposed to the odor or to an odorless vehicle, in a counterbalanced within subject design. Reactivation was followed by an interference learning task to probe memory stability after awakening. We show that odor-induced memory reactivation during REM sleep does not stabilize memories against future interference. We propose that the beneficial effect of reactivation during sleep on memory stability might be critically linked to processes characterizing SWS including, e.g., slow oscillatory activity, sleep spindles, or low cholinergic tone, which are required for a successful redistribution of memories from medial temporal lobe regions to neocortical long-term stores.
authors.affiliation: Division of Biopsychology, Institute of Psychology, University of Zurich Zurich, Switzerland.
authors.forename: Maren J
authors.initials: MJ
authors.lastname: Cordi
authors.affiliation: Department of Medical Psychology, Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen Tübingen, Germany.
authors.forename: Susanne
authors.initials: S
authors.lastname: Diekelmann
authors.affiliation: Department of Medical Psychology, Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen Tübingen, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Born
authors.affiliation: Division of Biopsychology, Institute of Psychology, University of Zurich Zurich, Switzerland ; Psychiatric University Hospital, Zurich Center for Interdisciplinary Sleep Research (ZiS), University of Zurich Zurich, Switzerland ; Division of Cognitive Biopsychology and Methods, Department of Psychology, University of Fribourg Fribourg, Switzerland.
authors.forename: Björn
authors.initials: B
authors.lastname: Rasch
keywords: declarative object location task; hippocampus; memory stability; rapid eye movement sleep; reactivation