Differential effects of early and late nocturnal sleep on the consolidation of declarative and nondeclarative memory

Nocturnal sleep apparently promotes the translation of labile short-term memories into more stable long-term memories. The present studies suggest that the sleep-related consolidation of hippocampus-mediated memories benefits primarily from early nocturnal sleep. A reduced activation of hippocampal glucocorticoid receptors and a neocortico-hippocampal 'off-line' mode during this part of sleep may be of particular relevance for this phenomenon. In contrast, non hippocampus-mediated memories benefit primarily from late nocturnal sleep. In addition to a critical amount of REM sleep, other, yet unknown factors may contribute to the consolidation of non hippocampus-mediated memories during late nocturnal sleep.