Chapter 29 - Memory Processing in Relation to Sleep

Abstract

Although each of us empirically recognizes the utmost importance of sleep for the quality of our everyday life, the functions of sleep have long remained shrouded in mystery. Beyond its putative physiologic functions, there is now growing evidence that sleep plays a prominent role in brain plasticity and memory consolidation processes. According to this proposal, memory traces formed during a learning episode are not immediately stored in their ultimate form. Rather, they initially remain in a labile, fragile state during which they can be easily disrupted or interrupted. Over time and during sleep, memory traces subsequently undergo a series of transformations during which they will be consolidated and fully integrated into long-term memory. In this chapter, we present experimental data that provide support for the hypothesis that sleep exerts a promoting effect on plastic processes of memory consolidation. Several sources of support for this hypothesis are described in this chapter, including (1) studies assessing the effects of posttraining sleep deprivation on memory consolidation and on the reorganization of the neural substrates of long-term memories; (2) the effects of learning on posttraining sleep and reexpression of behavior-specific neural patterns during posttraining sleep; and (3) the effects of within-sleep stimulation on sleep patterns and overnight memories. Despite advances that have refined our understanding of the relationships between sleep and cognitive processes, the underlying mechanisms still remain to be fully elucidated. Further steps are now required to understand how sleep disorders and pathologies accompanied by sleep disturbances affect cognitive functions and especially learning and memory consolidation in humans, eventually leading to remedial interventions.