The memory function of sleep
Susanne Diekelmann and Jan Born
Abstract | Sleep has been identified as a state that optimizes the consolidation of newly acquired information in memory, depending on the specific conditions of learning and the timing of sleep. Consolidation during sleep promotes both quantitative and qualitative changes of memory representations. Throughspecific patterns of neuromodulatory activity and electric field potential oscillations, slow-wave sleep (SWS) and rapid eye movement (REM) sleep support system consolidation and synaptic consolidation, respectively. During SWS, slow oscillations, spindles and ripples — at minimum cholinergic activity — coordinate the re-activation and redistribution of hippocampus-dependent memories to neocorticalsites, whereas during REM sleep, local increases in plasticity-related immediate-early gene activity — at high cholinergic and theta activity — might favour the subsequent synaptic consolidation of memories in the cortex.
Memories that are accessible to conscious recollection including memories for facts and episodes, for example, learning vocabulary or remembering events.Declarative memories rely on the hippocampus and associated medial temporal lobe structures, together with neocortical regions for long-term storage.
Memories for skills that result from repeated practice and are not necessarily available for conscious recollection, for example, riding a bike or playing the piano. Procedural memories rely on the striatum and cerebellum, althoughrecent studies indicate that the hippocampus can also be implicated in procedural learning. University of Lübeck, Department of Neuroendocrinology, Haus 50, 2. OG, Ratzeburger Allee 160, 23538 Lübeck, Germany. Correspondence to J. B. e‑mail: firstname.lastname@example.org‑luebeck.de doi:10.1038/nrn2762 Published online 4 January 2010
Although sleep is a systems-level process that affects the whole organism, itsmost distinctive features are the loss of behavioural control and consciousness. Among the multiple functions of sleep1, its role in the establishment of memories seems to be particularly important: as it seems to be incompatible with the brain’s normal processing of stimuli during waking, it might explain the loss of consciousness in sleep. Sleep promotes primarily the consolidation of memory,whereas memory encoding and retrieval take place most effectively during waking. Consolidation refers to a process that transforms new and initially labile memories encoded in the awake state into more stable representations that become integrated into the network of pre-existing long-term memories. Consolidation involves the active re-processing of ‘fresh’ memories within the neuronal networks thatwere used for encoding them. It seems to occur most effectively off-line, i.e. during sleep, so that encoding and consolidation cannot disturb each other and the brain does not ‘hallucinate’ during consolidation2. The hypothesis that sleep favours memory consolidation has been around for a long time3. Recent research in this field has provided important insights into the underlying mechanismsthrough which sleep serves memory consolidation4–7. In this Review, we first discuss findings from behavioural studies regarding the specific conditions that determine the access of a freshly encoded memory to sleep-dependent consolidation, and regarding the way in which sleep quantitatively and qualitatively changes new memory representations. We then consider the role of slow-wave sleep (SWS) andrapid eye movement (REM) sleep in memory consolidation (BOX 1). We
finish by comparing two hypotheses that might explain sleep-dependent memory consolidation on a mechanistic level, that is, the synaptic homeostasis hypothesis and the active system consolidation hypothesis.
Behavioural studies Numerous studies have confirmed the beneficial effect of sleep on declarative and procedural memory...
Leer documento completo
Regístrate para leer el documento completo.