Sometimes elements of the outside world sneak into our dreams, like when a car alarm becomes a squawking pterodactyl. Researchers in Germany recently explored another subtle yet reliable avenue for affecting dream content: your nose.
Michael Schredl and collaborators pumped either hydrogen sulfide (the smell of rotten eggs) or phenylethyl alcohol (the scent of a rose) into subjects' noses for 10 seconds during REM sleep, then woke them a minute later and asked them about their dreams. The brain's olfactory bulb connects directly to the emotion-processing amygdala, so the scientists expected a strong effect on overall dream tone. Indeed, people rarely made any explicit reference to smells, but flowers induced much more pleasant dreams than rotten eggs did.