Thursday, October 13, 2022

Headlines in the Smell World

Scientists thought they knew how the nose 'knows,' but new research suggests otherwise
Aug 2022,

I'm not doing a great job following this development, a reversal rather -- there's apparently some reconsideration that needs to be given to the way odorous molecules activate their respective olfactory receptors. Smell is the most understudied of all our senses, so it should be less of a surprise that one of the foundationary hypotheses of olfactory science needs some fine-tuning: 

G protein signal amplification is actually very low—so low that the probability of an odorant receptor activating just one G protein would be perhaps only 1 in 10,000. Yau said that, as such, the activation level "is very weak."

On a sidenote, what really stands out to me from this article is that the rhodopsin in the photosensitive cells on your retina (and all over your body in fact) are so sensitive they can detect a single photon of light. One single photon. And I thought our nose was sensitive. (It is, but for chemicals; the eye, and the photoreceptors in it, are for detecting the electromagnetic radiation beaming through our solar system.)

via Johns Hopkins University School of Medicine: Rong-Chang Li et al, Low signaling efficiency from receptor to effector in olfactory transduction: A quantified ligand-triggered GPCR pathway, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2121225119

Friends at first sniff: People drawn to others who smell like them
Jun 2022,

The researchers found that the odor signatures of "click friends" were statistically more closely matched than odors between non-friends.
This study was done using the T-shirt test, an old trusty in smell science. 

I can't figure out which is more interesting here. The word "click friends" is pretty cool, never heard it. But this one is good: "Nonhuman terrestrial mammals constantly sniff themselves and each other and, based on this, decide who is friend or foe," wrote a group of researchers led by Inbal Ravreby at Weizmann Institute of Science in Israel.

"I don't sniff myself; I am not an animal; gross" as you completely obliviously brush your hair away from your face, or scratch your temple. The study that proved our absolute inability to avoid smelling our own hands (and the hands of everyone we meet, by way of our own hands that shook theirs) found that BEFORE the study even started, while people were still in the waiting room, they had their hand ready next to their nose 22% of the time! (see older post and the article itself). Filthy animals!

via Weizmann Institute of Science in Israel: Inbal Ravreby et al, There is chemistry in social chemistry, Science Advances (2022). DOI: 10.1126/sciadv.abn0154

People who consider olfaction important and actively sniff other's odors have stronger sexual desire
Aug 2022,

This study is based on questionnaires given to Chinese college students, and recall that there is a general understanding in the smell world that Asian people tend to not have the same scent-emitting glands as non-Asians; in other words, the deodorant market doesn't work very well in China. After their initial findings however, they started over and sent the same questionnaires to college students in both the U.S. and in India, and after all that:

  • Students who reported giving high value to olfaction or who actively sniffed other people also reported having a stronger sexual desire than others who responded.
  • Women tended to place more emphasis on smell than men, and reported lower levels of sexual desire in general.
  • Men in India reported stronger sexual desire than those in China and the U.S., and they also reported placing more importance on olfaction.  

A final thought -- culture in some ways can be a stronger mediator for olfactory perception than biology or genetics. Science like this is great, but it's only s very small piece of the full picture. I'm thinking of how the Marshmallow Test fell apart in a recent study because they considered that Japanese kids are conditioned to wait for everyone to be ready to eat at the dinnertable, and U.S. kids are not. 

via Southern Medical University in China and Technische Universität Dresden in Germany: Zi-lin Li et al, Sniffing of Body Odors and Individual Significance of Olfaction Are Associated with Sexual Desire: A Cross-Cultural Study in China, India, and the USA, Archives of Sexual Behavior (2022). DOI: 10.1007/s10508-022-02398-1

Rapid loss of smell predicts dementia and smaller brain areas linked to Alzheimer's
Jul 2022,
(But how about their sexual desire??)

via University of Chicago Medicine: Rapid olfactory decline during aging predicts dementia and GMV loss in AD brain regions, Alzheimer s & Dementia (2022). DOI: 10.1002/alz.12717

New study reveals where memory fragments are stored
Jul 2022,

This is about memory recall, the way we access memories stored in our brains, and it certainly does change the olfactory science, since we tend to consider olfaction as being deeply connected to our autobiographical memory via the hippocampus, which it is, but this suggests there are more olfactory details being stored in the prefrontal cortex than we thought:

While the overall experience is stored in the hippocampus, the brain structure long considered the seat of memory, the individual details are parsed and stored elsewhere, in the prefrontal cortex. This separation ensures that, in the future, exposure to any individual cue is sufficient to activate the prefrontal cortex, which then accesses the hippocampus for recall of the whole memory.

via Laboratory of Neural Dynamics and Cognition at Rockefeller University and Weill Cornell Medicine: Priyamvada Rajasethupathy, Prefrontal feature representations drive memory recall, Nature (2022). DOI: 10.1038/s41586-022-04936-2

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