Here’s why sleep affects your memory (and how you can change it).

NPR goes, ahem, under the covers to trace the brain chemistry of sleep:

“One of the most profound effects of a night of sleep is the improvement in our ability to remember things,” says Ravi Allada, a sleep researcher at Northwestern University. Yet this connection hasn’t been well-understood, he says.

That’s changing, thanks to recent research from scientists including Jennifer Choi Tudor from the University of Pennsylvania. At the meeting, Tudor presented a study involving a brain chemical (known as 4EBP2) that is produced during sleep and is thought to play a role in remembering new information.

Previous experiments have shown that sleep-deprived mice have memory problems and lower levels of this chemical. So the team tried injecting the chemical into the brains of mice, then deprived them of sleep. “With the injection, their memory is normal,” Tudor says.

[Karim] Benchenane’s team set out to change each rat’s memory during sleep. They did this by stimulating the pleasure center in the animal’s brain each time the brain cell associated with a specific location became active. The idea was to form, in the brain, a positive association with one place in the cage. And sure enough, when the animals woke up, they went straight to that location, looking for a pleasurable reward.

The finding not only shows that new memories can be formed during sleep, Benchenane says — it also suggests a new way to treat people who have post-traumatic stress disorder and often have a negative association with a particular experience.