Sleep and Memory

Abstract Current behavioural evidence indicates that sleep plays a central role in memory consolidation. Neural events during post‐learning sleep share key features with both early and late stages of memory consolidation. For example, recent studies have shown neuronal changes during post‐learning sleep which reflect early synaptic changes associated with consolidation, including activation of shared intracellular pathways and modifications of synaptic strength. Sleep may also play a role in later stages of consolidation involving propagation of memory traces throughout the brain. However, to date the precise molecular and physiological aspects of sleep required for this process remain unknown. The behavioural effects of sleep may be mediated by the large‐scale, global changes in neuronal activity, synchrony and intracellular communication that accompany this vigilance state, or by synapse‐specific ‘replay’ of activity patterns associated with prior learning. Key concepts Memory consolidation involves plastic changes at the synaptic and brain systems levels; these changes occur over timescales of minutes (synaptic consolidation) to days or months (systems consolidation). Cellular changes occurring during early post‐learning sleep suggest that synaptic consolidation may occur preferentially during sleep. Brain‐imaging and gene‐expression studies have provided limited evidence that sleep may facilitate the gradual redistribution of memory traces throughout the brain. Sleep may facilitate consolidation through large‐scale changes in neural activity, neurotransmission or gene expression associated with rapid eye movement (REM) and non‐REM (NREM) vigilance states. It remains unclear whether sleep‐dependent consolidation is mediated by permissive (global) or instructive (synapse‐specific) mechanisms.