German researchers used specific volatile odorants with a negative or a positive smell ("rotten eggs" versus "roses") to simulate subjects during sleep. They then recorded the subjects' impressions when they were awakened. When using the unpleasant odorant, the emotional coloration of the dream was predominantly negative, while under stimulation with the pleasant stimulus, nearly all dreams had a positive coloration.

Researchers note that only recently information on olfactory function during sleep has become available, and that this is the first valid study that documents the impact of olfactory function on dreams. This study may also open a potential field of therapeutic intervention with nocturnal olfactory stimulation.

Source: EurekAlert (Press Release)