Sleep strengthens memories

Memories in human subjects were reactivated by presenting associated odor cues either during slow-wave sleep or wakefulness. The experimental design also tested memory stability. Reactivation during slow-wave sleep stabilized the memories, increasing their resistance to interference. Reactivation during wakefulness had the opposite effect.
Diekelmann S et al.: Labile or stable: opposing consequences for memory when reactivated during waking and sleep. Nature Neuroscience [Epub ahead of print, Jan 23, 2011] doi:10.1038/nn.2744
http://www.ncbi.nlm.nih.gov/pubmed/21258327