Some researches believe that memory consolidation occurs during sleep, and specifically that it is during sleep that the slow interweaving of information into cortical networks takes place. Although it has not yet been demonstrated that the hippocampal playback during sleep is actually read and used by the cortex, the existing data are consistent with the possibility. (LeDoux, Joseph. Synaptic Self, How Our Brains Become Who We Are. p 105-108. NY: Penguin Books, 2002.)

Refer to Sleep and the Brain for additional information.