You don't need to sleep. You just need to believe you've slept.

A new study suggests that there's such a thing as the "sleep placebo" effect. Just believing you've gotten a good night's sleep is enough to help you perform better on tests and feel more energetic.

Apparently, people who think they've slept well behave like people who have slept well too. Especially if an authority figure like a psychologist tells them that their sleep has been scientifically measured, and found to be the right kind.

Julie Beck sums up the study over at The Atlantic:

Participating undergrads first reported how deeply they'd slept the night before, on a scale of one to 10. The researchers then gave the participants a quick, five-minute lesson about sleep's effect on cognitive function, telling them it was just background information for the study. During the lesson, they said that adults normally spend between 20 and 25 percent of their sleep time in REM sleep, and that getting less REM sleep than that tends to cause lower performance on learning tests. They also said that those who spend more than 25 percent of their sleep time in REM sleep usually perform better on such tests.

Then participants were hooked up to equipment that they were told would read their pulse, heartrate, and brainwave frequency, though it actually just measured their brainwave frequency. They were told that these measurements would allow the researchers to tell how much REM sleep they'd gotten the night before . . .

Then one of the experimenters pretended to calculate that each participant got either 16.2 percent REM sleep or 28.7 percent REM sleep the previous evening. After getting their reading, participants took a test that measures "auditory attention and speed of processing, skills most affected by sleep deprivation," according to the study . . . Participants who were told they had above-average REM sleep performed better on the test, and those who were told their REM sleep was below average performed worse, even when researchers controlled for the subjects' self-reported sleep quality.

Obviously this wouldn't work if the students had actually been sleep deprived. Basically, it was a test of how your opinions on whether you'd slept "well" could influence your actual performance. It sounds like a study whose results are similar to those in tests of stereotype priming, where people who are told that they will succeed at a certain task tend to perform better at it than people who have been told they will fail.

As Beck notes, however, it's also a lesson in perspective. If you've gotten some sleep but focus on how tired you still feel, you may undermine your performance at work, on tests, or elsewhere.

Read more at The Atlantic