There’s a Placebo Effect For Sleep
The placebo effect is known far and wide. Give somebody a sugar pill, tell them it’s aspirin, and they’ll feel better. What’s less well-known is that there’s evidence of the placebo effect in domains that go beyond the commonly known medical scenarios.
One study (pdf) found that hotel maids who were told their work was good exercise later scored higher than a control group on a range of health indicators. Another study found that when participants were told athletes had excellent vision, they demonstrated better vision when doing a more-athletic activity relative to a less-athletic activity. Many studies have also shown that placebo caffeine can have an impact. In one experiment caffeine placebos improved cognitive performance among participants who were in the midst of 28 hours of sleep deprivation.
Given that caffeine placebos can mitigate the effects of sleep deprivation, Christina Draganich and Kristi Erdal of Colorado College decided to take the logical next step and investigate whether the effects of sleep deprivation could be influenced by perceptions about sleep quality. In other words, could making people think their sleep quality was better or worse influence the cognitive effects of sleep?
In an initial experiment participants were given brief lesson on the relationship between sleep quality and cognitive functioning, and told the normal proportion of REM sleep was between 20% and 25%. Participants were then hooked up to a machine and told it would measure their pulse, heart rate, and brain frequency, after which a program would use the data to calculate the amount of REM sleep they had had the night before. (Very few participants reported having suspicions about the machine.) Some participants were told they got 16.2% REM sleep (below average sleep quality) and some were told they got 28.7% REM sleep (above average sleep quality.)
After being told what the machine said, participants self-reported their own perception of their sleep quality. Finally, participants were administered the “Paced Auditory Serial Addition Test” (PASAT), a cognitive exercised that required adding many numbers together.
Draganich and Erdal found that participants who were told they had below average sleep quality performed significantly worse on the PASAT. At the same time, self-reported sleep quality was unrelated to PASAT performance. A follow-up experiment that included additional controls and three other cognitive tests largely confirmed the initial findings. In addition, the performance of participants on a verbal fluency test called the COWAT showed that not only does telling people they had below average sleep quality lead to inferior performance, telling them they had above average sleep can lead to superior performance.
Given the global importance of getting a good night’s rest the idea of placebo sleep seems potentially far-reaching. For example, you always hear that you should get a lot of sleep before a big test or interview, but that grandmotherly piece advice becomes even more important if the knowledge that you got too little sleep can harm your performance in a way that goes beyond the direct negative impact of not getting enough sleep.
The sleep placebo also suggests that finding a way to improve your sleep may be more important than you think. If you’re able to convince yourself that your bedtime routine is working — whether it’s reading, exercising, or eating honey — you might see the cognitive benefits of improved sleep even on nights when you don’t actually sleep better.
Draganich C, & Erdal K (2014). Placebo Sleep Affects Cognitive Functioning. Journal of experimental psychology. Learning, memory, and cognition PMID: 24417326
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