30 May 2014

Placebo Sleep

Welcome back. I’ve written about sleep a few times (Time to Sleep, Sleep and Memory, Sleep Patterns), but it’s always been about, well, sleep, the real thing. Today’s sleep discourse is more about the power of suggestion.
Perception versus reality.
(multiple websites)

Suppose I had some way of convincing you that you slept well or didn’t sleep well last night regardless of how well you actually slept. (You snored all night, dear; you must have slept like a log.) Do you think that would affect your mental acuity? Would it be enough to make you sharper or--sorry--blunter, again, regardless of how well you actually slept?

That’s what investigators from the Colorado College in Colorado Springs set out to learn.


The researchers conducted two experiments. The first presented a lesson on the relationship between sleep quality and cognitive functioning to 50 undergraduates and then had the students rate how well they slept the previous night.

In the lesson, students were advised that rapid eye movement (REM) sleep typically occupies 20% to 25% of total sleep, and that those who experience more than 25% do better on learning and memory tests, while those who experience less than 20% do worse.

Each student was then attached to a machine, which the students were led to believe would measure brain activity, pulse and the like to determine how much REM sleep they had experienced the previous night. (You just can’t trust psychology researchers.) After being presented fictitious readings of either 16.2% or 28.7% REM sleep, the students were given a Paced Auditory Serial Addition Test, which assesses auditory information processing speed and flexibility, as well as calculation ability.

I know you’re anxious to hear the results, but since the second experiment, done with 114 undergraduates, followed essentially the same steps as the first experiment, let me lay that out and take the two experiments together.

The main difference between the experiments for our purposes is that the second employed three other cognitive tests: the Controlled Oral Word Association Test, which assesses verbal fluency; Digital Span, which determines the longest list of numbers one can repeat in correct order; and Symbol Digit Modality Test, which gauges the time to pair abstract symbols with specific numbers.


Students who were informed they had experienced below average sleep quality by being given the lower REM sleep value, 16.2%, did significantly worse on the Paced Auditory Serial Addition and Controlled Oral Word Association tests than did students who were informed their sleep quality was above average by being given the higher REM value, 28.7%.

In contrast to the statistically significant effect of the REM sleep values, the students’ self-rated values of sleep quality showed no relation to test performance.

The assigned REM values did not predict students' scores on the Digit Span Test, which was expected, but it also failed to predict performance on the Symbol Digit Modalities Test, which was not expected. The research continues.

Wrap Up

The study, which set out to determine if perceived sleep quality affects cognitive function, successfully demonstrated the placebo effect, where the outcome is attributed to the belief in the treatment--mindset, perception or expectation--rather than to the treatment itself. Placebos aren’t limited to sugar pills. Thanks for stopping by.


-Colorado College study in the Journal of Experimental Psychology: Learning, Memory, and Cognition: www.ncbi.nlm.nih.gov/pubmed/24417326
-Articles on the study on Smithsonian Magazine and Salon websites:

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