During deep sleep, low-frequency brain waves set out from the frontal cortex and travel toward the back of the brain, in the process synchronizing many thousands of brain cells into a kind of neural symphony. This harmonizing of our neurons helps us distill and consolidate the blizzard of information we’ve taken in during the day. Memories are carried on these slow waves from sites of short-term daily storage to more permanent locations. Picture the mental desktop being cleared off and reorganized at the end of the workday, as the brain’s files are stowed in their proper place or trashed.
