There’s been a big change in how scientists approach the topic of human body odor. For years it was a chemist’s game—all about analyzing sweat to isolate the stinky molecules. Dermatologists and bacteriologists were also at the table: they identified the metabolic pathways by which skin bacteria transform odorless fresh sweat into heavy duty BO. For the most part research focused on the physical production of BO.
I hope to post about some of these new wave BO studies over the next few weeks.
I’ll start here with an experiment by a multidisciplinary team of German researchers at Christian Albrechts University in Kiel. One of the authors is Bettina Pause who taught at CAU for many years. Since 2005 she has been a Professor of Biological Psychology and Social Psychology at the Heinrich Heine University in Düsseldorf. I’ve followed her work for years; it is rigorous, inventive, and always interesting.
The title of her new paper grabbed my attention: “Induction of empathy by the smell of anxiety.”
The researchers used a standard cotton-pads-in-the-armpits method to collect sweat from male and female donors. Anxiety sweat was collected from German university students just before and during an oral examination; a passing grade is required for graduation, hence the anxiety. Exercise sweat—the control stimulus—was collected from other students who rode an exercise bike for a similar length of time.
The various types of BO (from men and women, the anxious and the exercising) were delivered to the noses of yet other students as they lay in a MRI magnet that imaged metabolic activity in their brain. These smellers also rated the stimuli for intensity, familiarity and pleasantness. (This quick summary doesn’t do justice to the elegant procedures and cool technologies used by the CAU team. Read the paper for the details.)
The test subjects rated the BO smells as not particularly strong, neither pleasant nor unpleasant, and not particularly familiar. Ratings of anxiety sweat and exercise sweat were statistically indistinguishable. So we’re not talking about knock-your-socks-off levels of BO, but about faint levels of relatively unobjectionable scent. In fact, on half the presentations no odor was consciously detected at all.
Despite being indistinguishable and barely discernable, the anxiety sweat and exercise sweat triggered responses in many brain areas. When the CAU imaging team subtracted the responses of exercise sweat from those of anxiety sweat, they could locate brain areas selectively activated by the odor of human anxiety. This cluster of brain areas, identified in the image at the top of this post, includes the insula, the precuneus, the fusiform gyrus and the cingulate gyrus.
Wha-wha-what? OK, this is some hard-core neuroanatomy. Long story short, these are not brain areas usually active during the processing of smells. Instead, according to Pause and colleagues, these areas are active when we decode social emotions from face and body signals, when we think about the emotional state of other people, and when we make empathic judgments that distinguish between self and non-self.
To the CAU team, this means that anxiety BO activates brain resources associated with social emotions and empathy—an interesting and reasonable speculation. But wait, there’s more! They characterize this response as “an automatic contagion of the feeling” of empathy. “In other words,” they conclude, “smelling the feelings of others could be termed an incorporation of the chemical expressions and thus the feelings of others.”
Here I think the CAU team gets a little ahead of its data. Even if the insula, precuneus, etc. really are mediators of social emotional processing, empathy, and so forth, there’s no direct evidence in this experiment that smelling anxiety sweat changes how people evaluate themselves, other people, or empathy-related social situations in general.
Perhaps having anxiety sweat pumped up your nose unconsciously activates empathy processing centers deep in your old monkey-brain. But does it have any effect at all on how you feel about the nervous guy sitting next to you on the subway? Or how you treat the tense looking person you meet at a party?
This is a provocative study, but I’m going to need more direct evidence—a change in behavior or mental processing, for example—before I hop on board the Empathy Express.