Information Processing During Sleep: the Effect of Olfactory Stimuli on Dream Content and Dream Emotions

Chapter 13: After watching the video in Physio about dreams, I found this article on how smells affect dream content and emotions. Personally, I find dreams fascinating and this research presented a new twist that I had not previously considered.
The first question you may ask is "Why are they using olfactory (smell) stimuli?" Since smells (even rather potent ones) can be "processed in a sleeping brain," the manipulation would not wake the participant, thus allowing them to continue dreaming if need be. Unlike other sensations, smell doesn't stimulate the reticular formation, which causes arousal. They knew that the olfactory sensations connect directly to the amygdala and from there the hippocampus. The amygdala controls emotion, so you can see why they believe smell will have an effect on dream emotion. They hypothesize "olfactory stimuli are processed in higher coritcal areas" than other sense stimuli, therefore interacting with dreams. Another hypothesis is good smells will ellict good dream content and bad smells will ellict bad dream content, because the amygdala processes positive and negative emotions.
The participants were 15 females ranging from age 20-28. They chose females, primarily because research shows females have more acute olfactory functions. All were tested apriori to ascertain whether their olfactory functions were "normal." Their sleep stages were recorded and assessed by an EEG. An olfactometer was used to emit smells, such as rotten eggs or roses. An odorless smell was used as a control.
Participants slept for two night in a row. The first night was used to get comfortable with the surroundings, while the second night the participant was awakened during REM sleep by the researcher. The researcher would then ask what they were dreaming about. The participant was asked to rate their dream emotions on a scale from 0, no emotion, to 3, strong emotion, and a postive or negative was used to denote a good or bad emotion.
A repeated measures ANOVA was performed to analyze the data. Contrasting smells were analyzed via dependent samples t-tests. The results concluded that smell is indeed processed by the sleeping brain and does affect the dream emotion, however, they found no correlation to dream content. They supported the claim that smell is processed in "higher brain levels" and the amygdala is the connecting factor between the smells from olfactory bulbs and positive or negative dream emotions.
This was an interesting study for me, because, as I mentioned earlier, I never assumed smell could affect my dreams. As the study revealed, it doesn't necessarily affect the content of dreams but rather the emotion behind them. So next time you have a bad dream, consider if you threw out any rotten eggs the night before...

Schredl, M., Atanasova, D., Hormann, K., Maurer, J.T., Hummel, T., & Stuck, B.A. (2009). Information processing during sleep: the effect of olfactory stimuli on dream content and dream emotions. European Dream Research Society, 18, 285-290. Retrieved from EbscoHost.
doi: 10.1111/j.1365-2869.2009.00737.x

http://ezproxy.utm.edu/login?url=http://search.ebscohost.com/login.aspx?direct=true&db=aph&AN=43669164&site=ehost-live