Anxiety makes the world smell worse!

Anxiety stinks! Stress may not only make you smell bad, but also the world around you, a new study suggests.
The study shows that when people are anxious, smells they once found neutral become distasteful.
Scientists using powerful new brain imaging technologies have revealed how anxiety or stress can rewire the brain, linking centers of emotion and olfactory processing, to make typically benign smells malodorous.
Researchers led by Wen Li, a professor of psychology at the University of Wisconsin-Madison Waisman Center, said that the brains of human subjects experience anxiety induced by disturbing pictures and text of things like car crashes and war transform neutral odours to distasteful ones, fuelling a feedback loop that could heighten distress and lead to clinical issues like anxiety and depression.

The finding is important because it may help scientists understand the dynamic nature of smell perception and the biology of anxiety as the brain rewires itself under stressful circumstances and reinforces negative sensations and feelings.
"After anxiety induction, neutral smells become clearly negative," said Li.

"People experiencing an increase in anxiety show a decrease in the perceived pleasantness of odours. It becomes more negative as anxiety increases," Li said.
Using behavioural techniques and functional magnetic resonance imaging (fMRI), Li's group looked at the brains of a dozen human subjects with induced anxiety as they processed known neutral odours.
Functional MRI is a technology that enables clinicians and researchers to observe the working brain in action.

In the course of the experiment, researchers 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.
Subsequent to anxiety induction and the imaging process, subjects were asked again to rate the panel of neutral smells, most assigning negative responses to smells they previously rated as neutral.
"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," said Li.
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 study was published in the Journal of Neuroscience.