High Tech Lullabye

Synchronized sounds sharpen sleep

In the study, the researchers exposed the sleepers to light rhythmic noise both in sync and out of sync with their brain's oscillations during deep sleep. The in-sync sounds appear to have strengthened the brain rhythms, the researchers found, while also strengthening memories: volunteers were better able to retain word associations they had learned the night before. The out-of-sync sounds didn't have any effect. 

Huh. I thought that's what snoring did. IntraCranial reverberation.