Previous research had shown that sleep helps people consolidate their memories, fixing them in the brain so we can retrieve them later.  (Read about secrets of why we sleep in National Geographic magazine.)

But the new study, a review based on new studies as well as past research on sleep and memory, suggests that sleep also transforms memories in ways that make them somewhat less accurate but more useful in the long run.

For example, sleep-enabled memories may help people produce insights, draw inferences, and foster abstract thought during waking hours.

(Related: "Dreams Make You Smarter, More Creative, Studies Suggest.")

"The sleeping brain isn't stupid—it doesn't just consolidate everything you put into it,