Saturday, 30 November 2013

Olfactory Dreams - Do we perceive smells in our dreams?

Can we experience smell in dreams? Many people would say that they experience a distinct sense of smell when dreaming, myself included. JK Huysmans, a nineteenth century writer and dream diarist recounted vivid dreams where he experienced intense smell and colour sensations, but the scientific basis for claims that smell is possible in dreaming has received little empirical research. In the "Statistics of Dreams" published in American Journal of Psychology (1893), Mary Whiton Calkins analysed the dream diaries of two subjects, recorded over a 6 - 8 week period and found that olfactory sensations appeared very rarely - visual and auditory perceptions are much more common. A later study at Wellesley College by Sarah Weed and Florence Hallam (1896) stated that olfactory perceptions appear in less than 15% of dreams. A further Wellesley College study by Hall and Titchener, published in American Journal of Psychology (1901) cited olfactory dreams, such as one where the dreamer was holding a can emitting vapours which were absorbed into a sponge, and created the sensation of an 'oppressive' and "strong, stifling, choking odour". Another olfactory dream cited in this study was as follows:

"I dreamed of looking off towards Milton and saying that beyond lay the ocean. I immediately got the keenest and most natural smell of wind from the flats and the delicious ocean odour. This gave me such intense pleasure, as it always does, that I awoke."

In Freud's Interpretation of Dreams (1900), he included an account of an olfactory dream:

"Eau de Cologne was held to his nostrils. He found himself in Cairo, in the shop of Johann Maria Farina. This was followed by fantastic adventures which he was not able to recall."

AL Zadra, TA Nieleon and DC Donderi, researchers at the McGill University in Montreal published "Prevalence of auditory, olfactory and gustatory experiences in home dreams" in Perceptual and  Motor Skills (1998). They asked 164 subjects whether they had experienced taste or smell in dreams - 41% of females and 35% of males stated they had. Subjects were asked to record their dreams upon waking, enabling the researchers to gather 3,372 dream records. More than half of these dreams recounted auditory perception, but less than 1% recounted smell. They found that experiencing smell in dreaming was a widespread, but low frequency phenomenon, with huge gender differences - 20.9% of females, compared with just 2% of males recalled experiencing smell in their dreams. 

Since 1950s research, we are aware that external stimuli such as light and sound may occasionally be incorporated into dream content. K Trotter, K Dallas and P Verdone, sleep researchers at Cal State, Sacramento, published "Olfactory stimuli and their effects on REM dreams" in Psychiatry Journal of the University of Ottawa (1988) following experiments where they exposed subjects to a smell for five minutes during the REM stage of sleep. The subjects were woken a minute later and asked to recall their dreams. Around 19% of the subjects recalled a smell perception during their dream - which is consistent with the rate of dream incorporation associated with other forms of external stimuli. One piece of anecdotal evidence from the study claimed:

The subject was presented with a freshly cut lemon while in REM sleep. The resulting dream was: "I dreamed I was in Golden Gate Park. I was walking by some gardenias. They were just opening. All of a sudden I could smell the gardenias, but they smelled like lemons rather than gardenias".

The researchers used both pleasant smells (lemon, peanut butter, roses) and unpleasant smells (dog faeces, match smoke, onions), finding that the pleasant smells were more likely to be incorporated into the subjects dreams - in 27% of cases, compared with 11% for the unpleasant smells. However, the pleasantness of the smell was found to have little effect on the emotional tone of the dream itself - approximately 33% of odour-stimulated dreams were unpleasant. A study of 15 female subjects by German researchers, Stuck and Schredl et al, of the University Hospital Mannheim, "The impact of olfactory stimulation on dreams" (2008) presented at the American Academy of Otalaryngology in Chicago found that unpleasant smells (i.e. hydrogen sulphide, which smells like rotten eggs) produced predominantly negative dream content, whereas pleasant smells (i.e. phenyl ethyl alcohol, which smells like roses) tended to produce positive dream experiences. The researchers also used a neutral substance as a control. After waking the subjects for recording of their dreams, it was discovered that the specific smells did not appear in the dreams (i.e. the rotten egg smell was not incorporated into the dream content as rotten eggs). The olfactory sense is closely related to the brain's limbic system, which is responsible for emotion and behaviour. The brain handles smell stimuli in a very different way to visual or audio sensory information, and so the female subjects of the study recalled dreams about activities linked to smell (i.e. cleaning a toilet or walking through a garden) rather than the particular smells themselves. This research is clearly at odds with the data obtained by the Sacramento teams. What is certain, however, is that the boundary between smells and dreamscapes is porous - and indeed smell can be incorporated into the dream experience, much like other forms of external stimuli.

Richard Stevenson and Trevor Case conducted a 2004 questionnaire study, "Olfactory Dreams: Phenomenology, Relationship to Volition Imagery and Odor Indentification" published in Imagination, Cognition and Personality (2005). They asked 284 subjects to answer questions about smell perceptions in dreams. They found that 26.4% of the subjects had olfactory dreams. When the dream content was analysed, around 50% of smell perceptions were found to be food-related, with bacon being the most common food smell recorded. Additionally, 21% of the olfactory dreams were associated with smoke or burning smells and another 21% involved body or animal odours. Similar to the waking world, smell sensations in dreams were briefer, but more emotionally-charged than visual perceptions. A second survey study by Gilbert, Crouch and Kemp on visual and olfactory mental imagery ability, published in Journal of Mental Imagery found multiple links between smell ability in waking states and dream states. Olfactory dreamers were found to experience both visual and olfactory senses more vividly than non-olfactory dreamers, and secondly, persons with more vivid mental imagery for smells experience more vivid smell dreams. It was also found in a follow-up study that olfactory dreamers tend to perform better in identifying specific odours in waking smell tests.

For a very useful literature review on olfactory dreaming, I would direct you to read Weitz, Croy, Seo, Negoias and Hummel, "Studies on Olfactory Dreaming" in Chemosensory Perception (2010). This paper produced arguments and counter-arguments and empirical data on the topic, as well as providing a very useful overview of all the main research studies on the topic of smell perceptions in dreaming.

Another theory of olfactory dreaming is that you do not 'smell' an odour in a dream, but rather, due to the emotive, highly evocative nature of smell-memories (i.e. the fact that smelling a certain perfume out of context, but which you associate closely with another person, can bring to mind vivid memories), the brain is able to trigger an olfactory memory (much like it can trigger other memories while in the dream state) leading the dreamer to believe they are able to smell in the dream. Indeed, smell is the sense which is said to be most closely linked with emotional memory.

Some oneironauts claim that one way of testing whether you can experience smell in dreams is to use Smell Induced Lucid Dreaming techniques. Smell is different from our other senses, where information is processed by the thalamus before being sent to the primary regions responsible for handling the sense perception. When visual information hits the photo-receptors in the eyes, the data is processed by the thalamus before being sent to the optical lobe; with auditory information, the data is sent to the primary auditory centres after being received by the eardrum and processed by the thalamus. A similar process occurs for touch and taste. However, smell is a more 'primitive' sense which bypasses the thalamic switchboard, travelling straight from the nose to the cortical areas of the brain responsible for conscious thought. Professor Tim Jacob, an expert in taste and smell at Cardiff University states: "Smell is the only sense which does not 'sleep'. Information continues to reach the limbic system of the brain and that includes the hippocampus or memory area and the amygdala that is involved wtih emotional response. Other senses have to pass through the 'gate'of the thalamus, which is closed when we sleep."

Therefore SMILD may be an effective lucid dream induction technique as the smell sensation is not routed away from conscious recognition by the thalamus. However, smell is habituated to, very rapidly - fading from conscious awareness very quickly even when still present in our immediate environment. Therefore, in order to be a successful lucidity trigger, the scent employed for this purpose would need to be sprayed into the sleeping environment on a timer system, rather than relying on a single scent being placed in the room at the start of sleep. Essentially, the best way to do this, would be to time the scent activation with the REM sleep stage, which is quite complex - and perhaps even impossible - to achieve in a normal home environment as opposed to within a fully-equipped dream laboratory, but which mirrors the standard method used by dream/sleep researchers in the studies outlined above.

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