Saturday, March 1, 2014

Research: Smell something funny? You might be STRESSED: Neutral scents become unpleasant when you're under pressure

smellsYou might be aware of your heart pounding and even your hands shaking in times of extreme stress.

And now scientists have found that scents smelling unusual can also be an indicator of anxiety.

Humans’ sense of smell is affected when we are anxious, with stress re-wiring the brain so that scents don’t smell right, according to a new study.

Previously neutral smells become unpleasant and the greater the stress, the larger the change in smell, scientists claim.

Wen Li, a professor of psychology at the University of Wisconsin-Madison, used brain imaging to reveal how anxiety or stress can rewire the brain, linking centres of emotion and smell-processing to make typically benign smells foul stenches.

For the study, published in the Journal of Neuroscience, subjects were made anxious by showing them disturbing pictures and text of subjects like car crashes and war.

The study found that this transformed neutral odours to distasteful ones, which the scientists explained could fuel a feedback loop heightening distress and leading to clinical issues like anxiety and depression.

‘After anxiety induction, neutral smells become clearly negative,’ professor Li said.

‘People experiencing an increase in anxiety show a decrease in the perceived pleasantness of odours. It becomes more negative as anxiety increases.’

Stress transforms neutral odours into distasteful ones, which could fuel a feedback loop heightening distress and leading to depression

Stress transforms neutral odours into distasteful ones, which could fuel a feedback loop heightening distress and leading to depression

Using behavioural techniques and functional magnetic resonance imaging (fMRI), Professor Li's team looked at the brains of 12 human subjects with induced anxiety as they processed known neutral odours.

Before entering the fMRI scanner where participants were shown a series of disturbing pictures and text, subjects were exposed to and rated a panel of neutral smells.

In the course of the experiment, the scientists observed that two distinct and typically independent circuits of the brain - one dedicated to olfactory processing, the other to emotion - become intimately intertwined under conditions of anxiety.

After anxiety induction and the imaging process, subjects were asked again to rate the panel of neutral smells, and most assigned negative responses to smells they previously rated as neutral.
Professor Li said: ‘In typical odour processing, it is usually just the olfactory system that gets activated, but when a person becomes anxious, the emotional system becomes part of the olfactory processing stream.’

Although those two systems of the brain are right next to each other, under normal circumstances there is limited crosstalk between the two.

However, under conditions of induced anxiety, the Wisconsin team observed the emergence of a unified network cutting across the two systems.

The results could be used to uncover the biological mechanisms at play during periods of anxiety.

Professor Li said: ‘We encounter anxiety and as a result we experience the world more negatively.

‘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.

‘It can potentially lead to a higher level of emotional disturbances with rising ambient sensory stress.’


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