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The dreamers continued sleeping for another minute until the scientists woke them up and asked them to describe their dreams and rate the experience as emotionally negative or positive.
Each subject was interviewed three times: Once after a rose-infused dream, once after smelling the sulfuric scent of rotten eggs, and once after no odor was administered.
The results showed that smelling roses gave nearly all dreams a pleasant tint, whereas the rotten eggs colored dreams negatively.
The control group generally did not report any change in their dreams, although one control dreamer said she and a grinning woman were both disgusted by the smell of something rotten.
Smell of Sleep
Tore Nielson, director of the Dream and Nightmare Laboratory at Montreal's Sacré-Coeur Hospital, commended the research for its technically sophisticated techniques, although he said the structure of the experiment could have been stronger.
Nielson, who was not involved in the study, said he's intrigued that the odors influenced dreams indirectly through emotions, rather than through the direct incorporation of smells.
"This indirect effect may offer a clue to processes of dream formation, i.e., that emotion is the first step in a dream's representation of an important external event," he said in an email.
However, he added, "since the authors waited only one minute between stimulus and awakening, we cannot be sure whether more specific representations of the smells may not eventually have appeared in the dreams."
Neil Bhattacharyya, an ear, nose, and throat surgeon at Brigham and Women's Hospital in Boston, Massachusetts, said the study is interesting and novel.
"We know there's a link between smell and memory," said Bhattacharyya, who was not involved with the study, "and now there seems to be a link between smell and the sleep centers of the brain."
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