Sounds can penetrate deep sleep and enhance associated memories upon waking

ScienceDaily (2009-11-20) -- They were in a deep sleep, yet sounds, such as a teakettle whistle, somehow penetrated their slumber. The 25 sounds were reminders of earlier spatial learning, though the research participants were unaware of the sounds as they slept. Yet, upon waking, memory tests showed that spatial memories had changed. Deep sleep, then, is actually is a key time for memory processing, the study suggests.


http://www.sciencedaily.com/releases/2009/11/091119193632.htm