Imagine You Slept Better Than You Did

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Telling yourself you got a good night's rest may make a difference in how you think and feel: In a study in the Journal of Experimental Psychology, scientists told one group of subjects that they had logged an above-average amount of REM sleep, while a second group was told they didn't get enough. Then everyone was given a test that measured their cognitive function. The above-average sleepers performed better than those told they'd slept poorly. "Simply hearing that you had high-quality sleep may trigger automatic responses, like heightened energy, that your brain has come to associate with being well rested," says study coauthor Kristi Erdal, PhD.

—Jessica Migala