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A Rose Would Not Smell as Sweet If You Were Agitated

The circuitry that controls emotions and smell is all tangled up in the brain.


When Hamlet’s friend Marcellus intoned that “something is rotten in the state of Denmark,” he was invoking neuroscience as much as political science.

A recent paper in the Journal of Neuroscience describes using functional magnetic resonance imaging, or fMRI, to look at subjects’ brains while having them either look at or read about things like mutilation, death, or warnings like “Anybody is in danger of being abducted” in between experiencing different odors—some pleasant, like coffee and cloves, others foul and fishy. After the subjects—a dozen college students—were properly agitated, their perception turned the nicer smells to distasteful ones, and the more stressed they got, the worse the nice smells smelled.

"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."

It’s no secret that smell is intimately tied up with emotions, and things like real estate agents baking cookies in houses they show is an attempt to have the warm feeling produced by that fragrance transfer to the property. By the same token, it’s also known that emotion, and not just anxiety, can affect smell. (Two of the authors on this latest paper demonstrated in a paper last year how anxious subjects develop a “remarkable” smelling acuity—for bad smells.)

What we’re learning is how physically tied up the two systems—the one that rules emotions and the one that rules smells—are. The new research, led by Wen Li at the University of Wisconsin, noted that while both systems’ circuitry is next to each other in the brain, and when the emotional system starts to deal with anxiety, it interacts with the olfactory system.

While such crosstalk seems like it might be likely, the fMRI allowed the researchers to actually see it taking place. They also learned something a little disturbing that didn’t involve car crashes or dire warnings—an anxious olfactory system starts feeding its bad news into this unified system.

"We encounter anxiety and as a result we experience the world more negatively,” Li was quoted in a release. “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."

These are affects that all people would experience, and not some sort of "synesthesia," in which people routinely hear purple or know that the number four tastes minty fresh. In those cases, it appears that individual’s brains are at least a little structurally different from the norm. The norm would be “alliesthesia,” in which our internal perceptions influence how we think of external ones.

The authors of this paper believe they’ve sussed out something fundamental about the smell-emotion connection:

This rewired, highly integrative neural circuitry thus constitutes the neural mechanism underlying emotion–olfaction synthesis. An important implication is that such dynamic changes could not only mediate anxiety related olfactory alliesthesia (shown here) but also would account for emotion-laden olfaction in general.

Li and various colleagues have been making waves in the world of odor for years, such as how smell helps us determine a person’s likeability (it’s subliminal, so put the perfume away) or how learning affects smelling. "Verbal context strongly influences the perception of odor quality—a rose by any other name would not smell as sweet," the researchers—also apparently fans of the Bard, were quoted at the time. They’ve argued repeatedly that the nose hasn’t gotten the respect it deserves. Yes, they smell a rat.