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.
So should you fill your room with fragrances at night? "Unfortunately, the olfactory system rapidly adapts," Schredl says. For people with recurrent nightmares, he instead suggests imagery rehearsal therapy. Recall a recent bad dream, rework it into something positive, and rehearse that image before bed. Giddyup, pterodactyl!