“Blood, Sweat and Tears” SAGE Talk

By Robert Bernstein

“The UCSB SAGE Center for the Study of the Mind promotes the study of the relationship between brain, mind and behavior.” We are privileged to have them here for the quality of the speakers they are able to bring.

On February 9 I attended their talk “Blood, Sweat and Tears: Human Social Chemosignaling in Health and Disease” by neuroscientist Noam Sobel of the Weizmann Institute of Science in Israel. That is also the title of his new book. The talk had been on hold for three years, due to COVID. Here are my photos from the occasion.

We think of humans as being very visual as our most refined sense and often think of our sense of smell as not very well developed or important. COVID was certainly a wake-up call of the importance of our sense of smell (olfaction) as millions of Americans lost this sense, at least temporarily.

In fact, the human sense of smell is outstanding. Sobel said that it is better than most terrestrial mammals and better than any machine. Mercaptan is a foul-smelling gas that is added to natural gas so that we can detect its presence. We can detect less than one tenth of one part per trillion! Equivalent to one drop in two Olympic sized pools!

A 1986 cover of National Geographic showed a dog tracking a dead pheasant that had been dragged across the ground. It turns out humans can also track such a subtle fragrance if they bother to try. They just need to put their nose near the ground.

He cited a research paper “Mechanisms of scent-tracking in humans” by Jess Porter (and others, including Sobel). Published in Nature Neuroscience in 2007. They discovered that having two nostrils is important for human tracking ability.

We think of dogs as the prime example of an animal that is olfactory-centered. We see dogs sniff each other. But we also sniff our babies and our partners. But not strangers. Or do we?

He showed some images of famous people meeting and seeming to get in sniffing distance of each other.

But he went on to show another way we sniff each other that is far less obvious. It starts with a handshake!

Shortly after this photo was taken of Angela Merkel shaking Putin’s hand, he noted that Merkel placed her hand near her face. It may be totally unconscious, but this is common behavior, once you know to look for it!

And humans are very good at detecting fragrances transferred by a handshake.

We also sniff ourselves, Sobel claimed. What messages are exchanged? What bodily sources? It is right there in the title of his talk and book: Blood, Sweat and Tears.

Why do we tear up at all? This is actually poorly understood. Darwin wrote about “Suffering and Weeping” in Chapter 6 of his book “The Expression of the Emotions in Man and Animals”.

Also in that book Darwin noted that our facial expression of disgust is the same as if we were spitting something out. We use the same expression for moral disgust.

Sobel cited a study where tears were collected for study. This is not an easy study to do! There was a gender bias as most of the volunteers were women. They were able to collect one milliliter of tears in fifteen minutes.

Tears are odorless to our conscious sense of smell. But sniffing tears has a powerful effect. The study showed a 10-15% drop in male testosterone levels from sniffing tears. But they must be fresh. Frozen and thawed does not work!

Science, especially social science, has had a bit of a “replication crisis” in recent years. Amazingly, this fiendishly difficult research was replicated successfully!

The Taylor Aggression Paradigm is designed to objectively elicit and measure people’s aggression in response to provocation from an opponent. It can take many forms, but all involve competing against an opponent who makes you angry and you have the option of doing something noxious in response.

In the version used in the tears study, it involved the opponent receiving real money and deciding how much to share with you. If he acts like a jerk, you can blast him w a 90dB noise.

The results? Exposure to fresh tears reduced aggression relative to the control of being exposed to pure saline.

The same phenomenon was observed with mice and mice tears. The search was on for what is the specific chemical. The researchers speculated that it was some sort of peptide compound. Peptides are not volatile. The other question is what is the brain mechanism.

Hexadecanal (abbreviated as HEX) is a “social buffering cue”. It is found in all mammals. HEX lowers aggression in men. But increases aggression in women!

This was tested in an fMRI machine and the researchers determined that the Left Angular Gyrus is key. The activation is the same in men and women. So they looked at functional connectivity and got their answer. They saw connectivity with the amygdala that increased in men and decreased in women.

From the abstract of the Science Advances paper by Eva Mishor (and others, including Sobel):
“HEX then modulated functional connectivity between the angular gyrus and a brain network implicated in social appraisal (temporal pole) and aggressive execution (amygdala and orbitofrontal cortex) in a sex-dependent manner consistent with behavior: increasing connectivity in men but decreasing connectivity in women.”

They developed a theory: Males can be aggressive toward their offspring. Whereas females can be aggressive to protect their offspring.

Sobel went on to talk about the “smell of fear”. It really is a thing. They get people to do scary things like jumping from a plane and collect their sweat. Subjects smelling this later have a Galvanic Skin Response as if they are feeling that fear. Fear is literally contagious this way.

Interestingly, people with autism have the opposite response! This could actually be used to diagnose autism.

Sobel finished up with a final question about how odors may relate to reproduction.

He talked about the Margaret Bruce Effect with mice reproduction, published in 1959.

Female mice will self-abort their pregnancies if they smell a male mouse that is not the father of the mouse they are carrying! This happens 80% of the time. Some researchers are theorizing that something similar could be happening with unexplained spontaneous abortions in humans. Particularly the phenomenon Recurrent Pregnancy Loss (RPL). This is defined by two or more failed pregnancies and is considered distinct from infertility.

Sobel then took some questions. I asked about this claim: If a woman goes on or off of birth control pills, her attraction to her partner’s body odor can change. He said that is true. It can be a real problem! A couple might decide to have a child. The woman stops taking the pill and can become less attracted to her partner. There is no good theory for this.

I also asked if there is any idea what specific compound is involved in these different effects with tears and sweat. He said that millions have been spent on trying to find the answer, with no answer found so far. He said it is a very difficult problem to solve.

One woman asked if women have a better sense of smell than men. Sobel said no. This belief is likely due to attention bias. Women may pay more attention to smells. But their actual threshold of perception is no different than for men.

To learn more about the SAGE Center for the Study of the Mind and to see what events are coming up, please visit their web site at https://www.sagecenter.ucsb.edu/


Written by sbrobert

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  1. Sexual attraction, diplomacy… So much may depend on our olfactory sense and we still know very little. I am grateful to Noam Sobel for his tireless research and for sharing it with us.
    Thank you for the kind words, JAZZEE! The SAGE meeting room is usually full to capacity for these talks. I hope their audio-visual-computer system can be repaired so that people will again be able to watch these talks remotely.

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