According to researchers, this can fuel a feedback loop that may heighten distress and lead to issues like anxiety and depression.
A research team led by Dr. Wen Li, a professor of psychology at the University of Wisconsin-Madison, say their findings 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, who conducted the study with UW-Madison colleagues Elizabeth Krusemark and Lucas Novak, and Darren Gitelman, M.D., of Northwestern University’s Feinberg School of Medicine.
“People experiencing an increase in anxiety show a decrease in the perceived pleasantness of odors. It becomes more negative as anxiety increases.”
Using behavioral techniques and functional magnetic resonance imaging (fMRI), Li’s team looked at the brains of a dozen people with induced anxiety as they processed neutral odors.
Before entering the MRI where screens cycled through a series of disturbing pictures and text, the subjects were exposed to and asked to rate a variety of neutral smells.
Once they were out of the MRI, they were asked to rate the neutral smells again. This time, most of the subjects assigned negative responses to smells they previously rated as neutral, the researchers reported.
In the course of the experiment, the researchers observed that two distinct and typically independent circuits of the brain — one dedicated to olfactory processing, the other to emotion — become intertwined under conditions of anxiety.
“In typical odor processing, it is usually just the olfactory system that gets activated,” Li said. “But when a person becomes anxious, the emotional system becomes part of the olfactory processing stream.”
Although the two systems of the brain are right next to each other, under normal circumstances there is limited crosstalk between the two, he said. However, under conditions of induced anxiety, the researchers observed the emergence of a unified network cutting across the two systems.
“We encounter anxiety and, as a result, we experience the world more negatively,” Li said.
“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.”
The study was published in the Journal of Neuroscience.
Contact: University of Wisconsin-Madison