Sense and sensibility: Olfaction and anxiety

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  • Published: Oct 1, 2013
  • Author: David Bradley
  • Channels: MRI Spectroscopy
thumbnail image: Sense and sensibility: Olfaction and anxiety

Smelly

Now, Wen Li, professor of psychology at the University of Wisconsin-Madison Waisman Center and her colleagues have used functional magnetic resonance imaging (fMRI) to prize open the lid of the olfactory black box and to take a sniff, not at how odour evokes emotions, but at how emotions such as anxiety can

The sense of smell has been with us a long time in evolutionary terms, at its most fundamental single-cell life forms have receptors for the detection of external molecules, which one might loosely describe as smell. But, from invertebrates to mammals, olfaction has a primal influence on the brain, which continuously and subconsciously processes the steady stream of data from scent molecules that waft under our noses.

The aroma of freshly baked bread, a lover's hair, sweaty socks or fresh vomit can stir powerful emotions within us, even if we somehow think that our sense of smell is a lesser scent to vision and hearing and even if we imagine other animals are more driven to follow their noses than we are. Odours directly influence the biochemistry in the emotional centres our brains evoking passion or disgust, perhaps rekindling long-forgotten memories or simply reminding you that it is time to do the laundry. The biochemistry of these emotional responses has remained something of a closed "black box" with a tight lid.

Something to sniff at

Now, Wen Li, professor of psychology at the University of Wisconsin-Madison Waisman Center and her colleagues have used functional magnetic resonance imaging (fMRI) to prize open the lid of the olfactory black box and to take a sniff, not at how odour evokes emotions, but at how emotions such as anxiety can "rewire" the brain so that our perception of particular scents changes, perhaps giving the smell of a lover's hair the odour of freshly discarded socks at times of stress.

Writing in the September issue of the Journal of Neuroscience, the team describes how they showed twelve volunteers disturbing images and text related to car crashes and war to induce some degree of anxiety and carried out an fMRI while simultaneously exposing them to what might be described as neutral scents or malodorous aromas. The results suggests that even the pleasantly neutral smells seem to be perceived as malodorous when the volunteers were feeling anxious; they rated the smells during the experiment on a scorecard. This is perhaps fuelling a feedback loop that could heighten their levels of stress. The finding is important, the team says, because it could help them understand the dynamic nature of smell perception and the biology of anxiety as the brain changes under stressful circumstances and reinforces negative sensations and feelings.

Olfactory concern

"After anxiety induction, neutral smells become clearly negative," explains Li, who worked with Madison colleagues Elizabeth Krusemark and Lucas Novak on the project as well as with Darren Gitelman of Northwestern University's Feinberg School of Medicine. "People experiencing an increase in anxiety show a decrease in the perceived pleasantness of odours. It becomes more negative as anxiety increases." She adds that, "The environment smells bad in the context of anxiety. It can become a vicious cycle, making one more susceptible to a clinical state of anxiety as the effects accumulate."

During the fMRI studies, the team showed that two distinct and typically independent circuits of the brain are invoked. One is dedicated to olfactory processing, the other to emotional response. When the volunteers were exposed to anxiety-inducing images and various odours, these two centres apparently become intimately linked. "In typical odour processing, it is usually just the olfactory system that gets activated," explains Li. "But when a person becomes anxious, the emotional system becomes part of the olfactory processing stream." Intriguingly, after the anxiety induction and the imaging process was over, several of the subjects still rated the panel of apparently neutral smells as being malodorous.

Although the two separate systems of the brain are next to each other, in everyday circumstances there is limited "crosstalk" between the two. However, under conditions of induced anxiety, it seems that they behave as if there is a direct connection between them that cuts across the two systems. This finding may have implications in the clinic as it reveals new insights into the biological mechanisms at play during periods of anxiety. "We encounter anxiety and as a result we experience the world more negatively," says Li. "It can potentially lead to a higher level of emotional disturbances with rising ambient sensory stress."

"The next step will be to examine effects in people with clinical anxiety," Li told SpectroscopyNOW. "The ultimate goal would be to integrate sensory training in clinical intervention for anxiety disorders," she adds.

Related Links

J Neurosci, 2013, 33, 587: "From Early Sensory Specialization to Later Perceptual Generalization: Dynamic Temporal Progression in Perceiving Individual Threats"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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