Högskolan i Skövde

Sleep is a complex phenomenon far from fully known, but one important function is to improve memory. Sleep allows the brain to work with memory processes. Sleep consist of different sleep stages divided into two big parts: rapid-eye-movement sleep and non-rapid-eye movement sleep. Memory is an important cognitive function that can be divided into declarative and non-declarative memory. The aim of this thesis will be to investigate the relationship between sleep and declarative memory consolidation. There is compelling evidence that links sleep with better memory consolidation. Consolidation is an active process where the newly encoded information is being transferred to long-term memory, which is stored throughout the neocortex. Hippocampus serves as a temporal memory storage for new memories and is active in transferring to neocortex during sleep. Reactivation and reorganization of encoded information seem to play an essential role in successful consolidation. Memories become more resilient to interference after a reactivation. Different memory systems are supported by different sleep stages, for example, hippocampus-dependent memory is benefitted mostly by slow-wave sleep and rapid-eye-movement sleep for memory not dependent on the hippocampus. Sleep stages are producing different brain-waves patterns with several neurotransmitters that help memories to transfer to long-term memory. Slow oscillations in neocortex are dominant in slow-wave sleep and are beneficial for consolidation. Declarative memory retrieval is enhanced by a period of sleep compared to wakefulness, and this effect is not limited to the day after learning but lasts longer. Intense learning increases sleep spindles, which also is important for consolidation. Not enough sleep disturb memory processes.