There is almost no end to the ways that the placebo phenomenon can manifest. In one instance researchers tricked participants into thinking they’d had more sleep than they actually had, and then observed how this affected their performance the next day. The researchers achieved this deception by wiring their participants up to various physiological measures and then giving some of them false feedback on how much REM sleep they’d had. After hearing that they’d had an impressive amount of sleep, participants performed better on tests of language and arithmetic.