Dr. Boris Stuck is a German researcher who has two different areas of interest ? he studies sleep and also the sense of smell (scientists call this olfaction). Several years ago, he decided to combine his two interests and see if smells affected sleep or the dreams people have when they're sleeping. He says there's been very little research on this combination.

The first thing Stuck did was to find people who would be willing to sleep in the lab at the University of Heidelberg, where he works. While they were sleeping, someone sat at the subjects' bedside.When monitors indicated that the person had entered the phase of sleep where dreaming occurs, he or his colleagues exposed the subjects alternately to the smell of roses and the smell of rotten eggs.

We expected that those subjects may incorporate the stimulus in their dream, because we knew from other research? that if you just give them some kind of noise or sound, or whatever, very often this is incorporated into the dream, it becomes then part of the dream content, Stuck says.

Stuck says he expected this to happen for the sense of smell as well.

But it didn't actually, so no matter what you use, people hardly ever dream about smelling, Stuck reports. Nobody told us they were dreaming about roses or something like that. This didn't happen.

But Stuck did find something unexpected. He found that the smells had an impact on the emotional content of the dreams.

If you use positive stimulus, nearly all the subjects reported that the dream they had was predominantly positive, emotionally positive, Stuck says. For his research, the rose smell was the positive stimulus.

And if you use the negative smell, the rotten eggs, nearly all the subjects reported that the dream they had was more negative, there were more negative emotions, Stuck says.

And Stuck says the emotional effect was surprisingly strong ? it was something experienced by almost all the subjects.

He says this kind of phenomenon might be used to help people who have suffered trauma ? or who have recurrent nightmares ? to overcome their difficulties with sleep. He says he'll be exploring these ideas further in future research.

Stuck presented his research this week at the annual meeting of the American Academy of Otolaryngology ? Head and Neck Surgery Foundation in Chicago.