Now this is pretty cool. New research just came out showing that we can hear sounds during deep sleep, and that those sounds can influence how we consolidate our memories.

One of the chief benefits of deep sleep is its effect on our minds, helping us to organize our memories and what went on during the day, refresh our brains, and prepare for another day of learning new things.

During a study at Northwestern University, researchers introduced sounds to volunteer nappers, and then determined afterward how those sounds affected their memories. The participants weren't aware of these sounds as they slept, but it was clear from the test results that the sounds, which ranged from a teakettle whistle to a cat's meow, were indeed "heard" by the brain and had an impact on how those people organized their memories. The actual details to how they designed the test are a bit complex, but the scientists were able to measure the ability of certain sounds to literally direct and even enhance a person's memories.