“Placebo Sleep” Can Improve Thinking

The placebo effect works for medicine, exercise, and vision. Now, apparently, it works for sleep. According to a recent study, if people are told they got “above average” quality sleep, they were better at performing cognitive tests.

Could a placebo effectively treat sleep apnea?

To see whether the placebo effect worked for sleep, researchers took a group of 164 subjects and set them up in a fake sleep lab where their sleep could be” monitored” using electrodes. Before going to bed, the subjects were told about the impact of REM sleep on cognition, and that more REM sleep would help them think better. They were told that average sleep consisted of 20-25% REM sleep. In the morning, each subject was asked to rate their sleep, then was told whether the monitoring showed their sleep quality to be below average (about 17% REM sleep) or above average (about 28% REM sleep).

Subjects were then given four tests. On two of the tests–Paced Auditory Serial Addition Test (PASAT, in which people have to add up a series of numbers) and Controlled Oral Word Association Task (COWAT, a verbal fluency test in which people are supposed to think of as many words as possible beginning with a certain letter)–people did better or worse depending on the quality of sleep they’d been told they had. Two other tests–the digit span task (in which people are asked to remember a string of numbers) and the symbol digit modalities test (in which people are asked to match numbers and figures)–were unaffected by sleep ratings. None of the test scores were predicted by self-reported sleep quality.