Anxiety causes a slew of unpleasant symptoms that all of us have experienced to greater or lesser degrees. Sweating, rapid heartbeat, churning stomach, and fear – these are just a few symptoms of an anxious mind. One lesser known symptom is that when we’re anxious, things don't smell quite right.
A new study explored this odd effect by focusing on the role of stress in rewiring the brain. Two brain circuits that don’t typically “talk” to each other—one linked to our sense of smell and another linked to emotional processing—can become cross-wired when we experience stress-induced anxiety. The result is that stressful experiences transform normally neutral odors into bad ones.
Researchers first asked a group of subjects to rate several smells, all of which were inoffensive neutral odors. The subjects were then hooked up to a functional magnetic resonance imaging machine (fMRI) while they watched a series of disturbing images, like car crashes and graphic war scenes, accompanied by equally disturbing text messages.
After the fMRI, the subjects were exposed to the same set of smells and asked to rate them again. This time, the majority of subjects changed their rating of the smells from neutral to offensive.
"After anxiety induction, neutral smells become clearly negative," explains Wen Li, a professor of psychology at the University of Wisconsin-Madison Waisman Center, who led the study. "People experiencing an increase in anxiety show a decrease in the perceived pleasantness of odors. It becomes more negative as anxiety increases."
The fMRI brain scan—which allowed the researchers to watch what was happening in the subjects’ brains in real time—suggests that stress-induced anxiety from watching the disturbing images and reading the messages triggered a cross-wiring between the smell and emotion brain circuits.
"In typical odor processing, it is usually just the olfactory system that gets activated," says Li. "But when a person becomes anxious, the emotional system becomes part of the olfactory processing stream."
The researchers think that this effect accumulates over time. The more anxiety we experience, the more the cross-wiring between these two brain circuits strengthens – resulting in more and more otherwise neutral smells turning into bad ones. The vicious cycle triggered by this effect is that the smells themselves contribute to more anxiety.
According to Li, "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."
This isn’t the first study, by far, to examine the link between emotions and sense of smell. Journals are full of research explaining why, for example, we think of the holiday season when we smell pine cones, or remember family gatherings when we smell cookies baking. But it is one of the first to explore the specific role of anxiety in causing a bridge between these brain circuits, and that understanding may help psychologists untangle the bundle of anxiety triggers in people diagnosed with anxiety disorders.
The study was published in the Journal of Neuroscience.