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Information processing during sleep: the effect of olfactory stimuli on dream content and dream emotions.

Michael Schredl, Desislava Atanasova, Karl Hörmann, Joachim T Maurer, Thomas Hummel, Boris A Stuck

Journal of Sleep Research June 22, 2009 DOI: 10.1111/j.1365-2869.2009.00737.x (opens in new tab)

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AI-extracted from the abstract
Characteristics Experimental within-subject study using intranasal chemosensory stimulation during REM sleep Peer reviewed
Sample size 15
Population Healthy, normosmic (normal sense of smell) adult volunteers
Topics Dreaming
Keywords Humans Polysomnography Emotions Mental processes Dreams Cues Arousal Smell Sleep, rem Female Young adult
Key findings Olfactory stimuli delivered during REM sleep significantly changed dream emotional tone: the pleasant rose odour (phenyl ethyl alcohol) yielded more positively toned dreams, while the unpleasant rotten-egg odour (hydrogen sulphide) yielded more negatively toned dreams. No direct incorporations, in which the dreamer smells something, were reported. The authors conclude that olfactory information is processed during sleep and that dream emotional tone depends on the hedonic quality of the odour.

Abstract

Research has shown that external stimuli presented during sleep can affect dream content, thus reflecting information processing of the sleeping brain. Olfactory stimuli should have a stronger effect on dream emotions because their processing is linked directly to the limbic system. Because selective olfactory stimulation does not increase arousal activity, intense olfactory stimulation is therefore a prime paradigm for studying information processing during sleep. Fifteen healthy, normosmic volunteers were studied by intranasal chemosensory stimulation during rapid eye movement sleep based on air-dilution olfactometry. For olfactory stimulation, hydrogen sulphide (smell of rotten eggs) and phenyl ethyl alcohol (smell of roses) was used and compared with a control condition without stimulation. The olfactory stimuli affected significantly the emotional content of dreams: the positively toned stimulus yielded more positively toned dreams, whereas the negative stimulus was followed by more negatively toned dreams. Direct incorporations, i.e. the dreamer is smelling something, were not found. The findings indicate that information processing of olfactory stimuli is present in sleep and that the emotional tone of dreams can be influenced significantly depending upon the hedonic characteristic of the stimulus used. It would be interesting to conduct learning experiments (associating specific odours with declarative material) to study whether this declarative material is incorporated into subsequent dreams if the corresponding odour cue is presented during sleep. It would also be interesting to study the effect of positively toned olfactory stimuli on nightmares.

Comparable studies

Other experimental studies on dreaming, most cited first.

Study Year Design Participants
Lucid Dreaming Verified by Volitional Communication during Rem Sleep Selected subjects proficient in lucid dreaming 1981 Experimental study n = 5
Incorporation of concern- and nonconcern-related verbal stimuli into dream content. Seven male subjects studied during sleep Stages 2 and REM 1981 Experimental study n = 7
Lucid Dreaming and Alpha Activity: A Preliminary Report Good dream recallers 1982 Experimental study n = 10
Lucid dreaming during NREM sleep: Two case reports 2012 Sleep laboratory study
The Dream Catcher experiment: blinded analyses failed to detect markers of dreaming consciousness in EEG spectral power. Human participants during sleep 2020 Experimental study with blinded classification n = 9

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