Friday, February 10, 2023


Sounds like a big deal. Also sounds like a great explanation for the phantom "Iso E Super" anosmia that isn't a full anosmia.

Researchers reveal an added layer of nuance in our sense of smell
Jan 2023,

They've discovered something called a depolarization lock to add to the standard combinatorial coding model used for odor detection, and it turns off the receptors when presented with high concentrations of an odor. 

You might already be familiar with this phenomenon for odors like violet and hydrogen sulfide (H2S). In the case of H2S, this receptor-deactivating behavior can be life-threatening, which is why you're supposed to wear a supplemental gas monitor, in addition to your nose, when entering areas suspected to contain high concentrations of the gas. 

^This write-up does a good job of explaining the fruit fly experiment that led to this discovery, as well as possible reasons why this would be needed for olfaction. 

via UC Santa Barbara: David Tadres et al, Depolarization block in olfactory sensory neurons expands the dimensionality of odor encoding, Science Advances (2022). DOI: 10.1126/sciadv.ade7209

Post Script:
In addition to Iso E Super, Hedione is another perplexing odorant that's in almost every fragrance formulation from floor cleaners to face cream, and yet most people can't actually smell it. Well, you can smell when it's NOT there, but you can't smell when it is. (Old post mentioning Hedione)

And if I'm reading this correctly, it sounds like someone with a hypersensitive nose might be more likely to lose their sensitivity altogether. I seem to have some kind of hyperosmia myself, and yet when I go out to sample perfume, I often can't smell anything at all. Take the same perfume, put it on a strip of paper and leave it on a table in my house for the next 3 weeks, and I will smell the whole bouquet revealed one at a time as the mixture breaks down. The theory being that if you're hypersensitive to a specific odorant, or all odorants for that matter, your "depolarization lock" will kick in at low concentrations. 

Post Post Script:
Hella synonyms for the musky odorant referred to above, in fact so many that I just wanted to list them here: Iso E Super, Tetramethyl acetyloctahydronaphthalenes is a synthetic ketone fragrance also known as octahydrotetramethyl acetophenone (OTNE) and by other commercial trade names such as: Iso E Super, Iso Gamma Super, Anthamber, Amber Fleur, Boisvelone, Iso Ambois, Amberlan, Iso Velvetone, Orbitone, Amberonne. It is a synthetic woody odorant and is used as a fragrance ingredient in perfumes, laundry products and cosmetics.
-Hall, John B. & Sanders, James Milton, "Perfume composition and perfume articles containing one isomer of an octahydrotetramethyl acetonaphthone", issued 1975

Neural Cartography

This first article doesn't sound like the cartography I came here for, but it's in the title so...
Researchers present insight into the neural cartography of smell
Oct 2022,

Honestly I'm unclear as to what this means; the endoplasmic reticulum has some mediating influence on the neural computations that turn olfactory receptor stimulus into the olfactory perception of a specific odorant?

"It is mind-blowing," said Dr. Lomvardas, also a professor of neuroscience and of biochemistry and molecular biophysics at Columbia's Vagelos College of Physicians and Surgeons. "This system found a way to create a genetically encoded, hard-wired means of transforming randomly-chosen receptor identity to a very precise target in the olfactory bulb."

Perhaps, olfactory neurons are not alone in the way endoplasmic reticulum stress organizes their wiring with downstream neurons. "If it turns out that all neurons do this, this discovery could help us understand much more about the brain," said Shayya.

via Mind, Brain and Behavior Zuckerman Institute at Columbia University:  Hani J. Shayya et al, ER stress transforms random olfactory receptor choice into axon targeting precision, Cell (2022). DOI: 10.1016/j.cell.2022.08.025

Here's another article that makes reference to "maps" but isn't actually about navigation...
Mapping the path from smell to perception
Nov 2022,

"The last frontier of sensory neuroscience"

Because previous studies of the olfactory cortex failed to find any logical organization among neurons there, many neuroscientists suspected information about odors was relayed randomly through the brain. But those studies examined connectivity patterns of just a few dozen neurons.

DNA-based brain-mapping technologies charting the way sensory information is routed between olfactory-processing parts of the brain including the olfactory bulb, which receives sensory information from the nose, the primary smell-processing hub called the piriform cortex, and several other brain regions that receive inputs from the olfactory bulb.

via Cold Spring Harbor Laboratory: Yushu Chen et al, High-throughput sequencing of single neuron projections reveals spatial organization in the olfactory cortex, Cell (2022). DOI: 10.1016/j.cell.2022.09.038

And finally, a little something about how we use olfaction to navigate...
Flies smell the motion of odors and use it to navigate, study finds
Nov 2022,

Flies can sense the direction of moving odor packets themselves, not just the wind.

Cool study design: They genetically modified fly antennae to detect light, then created fictive odor packets out of light and watched how the flies responded to these signals in both windless and windy environments.

via QBio Institute at Yale: Nirag Kadakia et al, Odour motion sensing enhances navigation of complex plumes, Nature (2022). DOI: 10.1038/s41586-022-05423-4