https://www.youtube.com/watch?v=paHSFXQfL5EPleasant scents give rise to pleasant dreams, and foul smells turn fantasy to phantasmagoria: so concludes a small, unreplicated and wholly plausible study on odor and dreaming.

Led by Michael Schredl and Boris Stuck – who have shown, respectively, that women are not awakened by the smell of rotten eggs, and that snores do not correlate with nightmares – a team of German researchers tested the effect of odor on the dreams of 15 young adult women, the demographic scientifically shown to have the most sensitive olfactories.

Once deep in REM sleep, they were exposed to ten-second aromatic flushes of phenyl ethyl alcohol, roughly analogous to roses, or hydrogen sulfide, typically found in rotten eggs and a standby of odor-and-dream science. (In a methodological aside, the test apparatuses are formally known as "Sniffin' Sticks.") An odorless chemical was used as a control.

Having sniffed, the women were roused and asked to report. The tone of their dreams consistently tracked with the tenor of the smells – but unlike dreamers who incorporate external sounds, such as an alarm clock radio, the women did not recall having smelled roses or rotten eggs. Instead they experienced a shift in the emotional content of their dreams.

https://www.youtube.com/watch?v=LLna-XxRGXoThis suggests that "olfactory stimuli are processed differently than other sensory modalities on higher brain levels," a fancy way of saying that brains handle smells differently than sound or touch. Several dreams did involve smell-associated activities – cleaning a toilet, eating a kiwi or parsley-stuffed potatoes, being stuck in a stuffy room – but in only one case did a test subject report smelling something: "a grinning Chinese woman [who] also looked disgusted because they (dreamer and Chinese woman) smelled something rotten."

This dream, however, was prompted by the odorless control substance.

The study, announced at the American Academy of Otolaryngology – Head and Neck Surgery annual conference, has not yet been published or replicated. With the help of time-release room fresheners, I intended to try and replicate it myself this weekend; but unless the smell of new Ikea curtains counts as a stimuli, I forgot.

If it does count, I can report that they had no effect whatsoever, and may function as a stylish yet affordable alternative to odorless Sniffin' Sticks. Then again, given the near-apocalypse of the U.S. economy, it's possible that the curtains had an ameliorative effect, comparable to roses; the researchers may wish to test this in future studies of "whether positively toned olfactory stimuli yield a significant shift in the emotional tone of nightmares."

Information processing during sleep: the effect of olfactory stimuli on dream content and dream emotions [unpublished]

Videos: Dream sequences from The Science of Sleep, Tarkovsky's Nostalgia and a Chuck E. Cheese commercial.

Note: A colleague provided an anecdote redolent of the researchers' results.

"My mom once had a dream that she was taking care of a baby, and it started to smell," she recalled. "So she changed the diaper, but the baby was still smelly. She kept washing and washing and washing the baby, but it still smelled. Finally she woke up and realized my dad was farting up the place."

Any other Wired Science readers have smell-and-dream stories to share?

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