Statistical Sampling of the Olfactory Environment

It appears that a discovery has been made, all over the place and all at once, about how the mixture of air changes the way smells are perceived. 

It's not at all unusual that multiple simultaneous discoveries have appeared, in fact it's the rule not the exception in science. The articles below all seem to have discovered that a turbulent cloud of odor molecules smells different than what I'll call a more homogenous, slow-moving cloud. 

Based on the above image, see the great CFD video illustration of air movement here.

It's like you're getting a more representative sample. When smells occur in your environment, they move as streams and plumes, picture wisps of smoke. If you're about to "sample" a piece of data, it means you're about inhale a cubic foot of air. What are the chances the amount of molecules you need to register an odor will be in that cubic foot? If you were to snapshot the cube before you inhale, you could imagine the airsteams of the odor you're looking for, let's say the scent of a female moth pheromone, twirling through the cube. But if you shook up all the air around you, to get into your breathing space some of the airstreams from outside the space, then you get more chance that the target molecule will make it into your "sample" sniff. From a statistical point of view it does make sense - you're squeezing more airstreams into a smaller space and time.

Study suggests that 'Jedi' rodents remotely move matter using sound to enhance their sense of smell

Oct 2024, phys.org

https://phys.org/news/2024-10-jedi-rodents-remotely.html

Surprise! "This phenomenon has never been observed before, or I believe even suspected, in any animal"

(This is from a bioacoustics researcher btw.)

Scientists have debated the purpose of the ultrasonic vocalizations (USVs) produced by rodents since the discovery of these sounds in the 1950s. This new paper suggests they do it to shake up their surroundings in ways that influence how inhaled particles enter their noses, suggesting that rodents use sound to enhance their sense of smell.

"They're creating new pathways of information by manipulating their environment and controlling the molecular interactions of particles around them."

Rodents explore their environment by stroking surfaces with their whiskers, visually scanning, and incessantly sniffing. Mercado discovered that studies on vocalizations that also monitored sniffing showed that rodents immediately sniffed after producing each USV.

"That could be a coincidence, or it might suggest the two are functionally related," he says. "I knew that techniques for using ultrasound to manipulate particles are used in the field of vibroacoustics and thought immediately that might also work for animals."

Vibroacoustics, or artificially produced ultrasonic vibrations, cause airborne particles to cluster, leading Mercado to suggest that rodents are using USVs to create odor clusters enhancing the reception of pheromones (chemical signals), thus making it easier for the vocalizer to detect and identify friends, strangers, and competitors.

via University at Buffalo: Eduardo Mercado et al, Do rodents smell with sound?, Neuroscience & Biobehavioral Reviews (2024). DOI: 10.1016/j.neubiorev.2024.105908. 

https://dx.doi.org/10.1016/j.neubiorev.2024.105908

Study uncovers how silkworm moth's odor detection may improve robotics

Oct 2024, phys.org

https://techxplore.com/news/2024-10-uncovers-silkworm-moth-odor-robotics.html

They employed high-speed photogrammetry to computationally analyze the aerodynamic consequences of wing motions of the silkworm moth (Bombyx mori).

This insect that no longer flies due to domestication, but does flap its wings when they detect pheromones.

One of the key findings of the study was that B. mori samples the pheromone selectively from the front. The moth scans the space by rotating its body while fanning to locate the pheromone sources. The directional sampling of the pheromone molecules is particularly helpful when searching for an odor source since the moth can determine the direction of the odor plume upon the detection of the pheromone.

This could lead to advancements in robotic odor source localization technologies, where drones equipped with insect antennae for odor detection carefully adjust their orientation and the configuration of their propellers and odor sensors to optimize detection capabilities.

via Chiba University Graduate School of Engineering: Olfactory sampling volume for pheromone capture by wing fanning of silkworm moth: a simulation-based study, Scientific Reports (2024). DOI: 10.1038/s41598-024-67966-y

https://dx.doi.org/10.1038/s41598-024-67966-y

People with no sense of smell found to have abnormal breathing patterns

Oct 2024, phys.org

https://medicalxpress.com/news/2024-10-people-abnormal-patterns.html

The researchers sought to address anecdotal accounts of people who could not smell and began "breathing funny" after contracting COVID-19.

The research team recruited 52 volunteers, 21 of whom were suffering from anosmia, and fitted them with a breathing monitor for 24 hours.

The research team found that those volunteers with anosmia did have slightly different than normal breathing patterns. People without the condition, they note, have small inhalation peaks, which prior research suggests coincides with a suspected change in smell. People without the ability to smell had no such peaks.

via The Azrieli National Institute for Human Brain Imaging and Research: Lior Gorodisky et al, Humans without a sense of smell breathe differently, Nature Communications (2024). DOI: 10.1038/s41467-024-52650-6

https://dx.doi.org/10.1038/s41467-024-52650-6

Signal to Noise for the Win

A new model for how the brain perceives unique odors

Oct 2021, phys.org

https://medicalxpress.com/news/2021-11-brain-unique-odors.html

So here is a scientist, a physicist by name, with an interest in the information-processing abilities of biological, and neurological systems. It didn't take him long, I would imagine, to realize that olfaction is a prime model for complex information-processing systems; it was the first sense, used by the first bacteria to detect chemicals in the primordial soup, later used by animals to make a big, complex mammal brain. If you want to look at how information processing happens in biological systems, this would be the ideal place to look.

But first, you have to throw into the garbage everything you know about olfaction already, which should be easy for a computational information scientist. What they did here was to look far out, all the way out -- beyond molecules and their myriad physico-chemical characteristics, of which the molecules themselves number in the billions; beyond genetics and their 30% variation across the global population; beyond cultural effects that are almost too surreal to quantify for methodical research purposes, like where Americans prefer peppermint since it's associated with candy, yet older folks from England don't like mint since it's associated with pain-relief products of their era, or the easier comparison of preference for durian fruit or Époisses de Bourgogne cheese.

Too messy, said the computational information scientist. And so they put it all in the blender, all those variables together. And they called it noise. Boil it all down, cancel it all out, all that dirty data of molecules and genes and cultural and personal association. Throw it all in the same bin, and call it noise. That's what they did.

Actually, they didn't call it noise, they called it "context" --

 "If you experience odors in a similar context, even if they were initially rather different in the responses they evoked in the nose, they begin to be represented by similar neural responses so they become the same in your head," Balasubramanian says.

-medicalexpress

The researchers found that their simplified model could be used to reproduce the same types of results seen in olfaction experiments. It's something that Balasubramanian did not expect to see, as he thought that such a complex process would require "learning and plasticity" in order to adapt and change neural synapses to modify the brain's representation of smells. "We may have found a general strategy of using certain kinds of randomized signals to entrain those effects," he says about their results. "It doesn't have to be just olfaction; it can be elsewhere, too." -medicalexpress

Did you see that? "It doesn't have to be olfaction; it can be elsewhere too." Olfactively-piqued, computational information neuroscientist, where have you been? Proving that the nose-brain is the neural model par excellence, while showing us how it actually works, both at the same time.

*If you want to know more about why olfaction is the ideal model for growing an artificial brain from scratch, it's a constant theme in Hidden Scents.

via University of Pennsylvania: Gaia Tavoni et al, Cortical feedback and gating in odor discrimination and generalization, PLOS Computational Biology (2021). DOI: 10.1371/journal.pcbi.1009479

http://dx.doi.org/10.1371/journal.pcbi.1009479

Post Script:

This study shouldn't be mentioned without this other study, where they taught an artificial network how to smell, via Massachusetts Institute of Technology's McGovern Institute for Brain Research: Peter Y. Wang et al, Evolving the olfactory system with machine learning, Neuron (2021). DOI: 10.1016/j.neuron.2021.09.010. http://dx.doi.org/10.1016/j.neuron.2021.09.010

Post Post Script:

Might as well put this here, since it has to go somewhere -- what happens when you take an information scientist and give them an olfactory science problem? This is what happens. They come up with an answer that is so simple it just makes you look stupid. This is an example, although not a true example, of the other half of the coming dark ages. After a global pandemic, it's inevitable to experience a kind of dark ages, where lots of people died, but way more people got sick, and also a lot of people retired. That's a post-pandemic-pandemic of institutional knowledge loss, like a collective long covid brain fog on our culture -- we forget how to do stuff, because the guy who did it for the past 30 years isn't doing it anymore. That guy either died, got too sick to work, or retired for a million other reasons, of which many of them could be pandemic-related. And there's lots of those guys (and even more of them gals). Who knows what that will look like for us today or tomorrow, but it's happening as we speak, and years from now we might notice, we might even call it the great forgetting. The flip side to the dark ages is the renaissance, which comes from all the new people in new roles and at new jobs. These people are coming in new, with nobody around to teach them how to do things "right," and although that makes for a bumpy road ahead, it also gets you things like this discovery, one of the hardest problems of olfaction taken on by someone who has not much at all to do with olfaction (although he should, because olfaction has been an information science problem all along).

Water Chemistry

Thought I could shed some light on a trendy topic here:  water chemistry and baking success.

Everyone knows Brooklyn pizza is the best pizza, and that there is only one place in the world that makes bagels, and it’s New York City. (If you’ve ever had a bagel in Florida, you know what I’m talking about; unless it was literally baked in NY and shipped to FL, which isn’t uncommon.)

We heard recently the claims of a well-meaning group of entrepreneurs that NYC’s water is now available to the rest of the world. The company's claim: They will analyze your local tap water to calibrate a device that will tweak it to be just like New York City’s water.

What does the water taste like and why? Well, it tastes good, according to taste tests. And the reason is because New York City's water comes from natural reservoirs, highly protected from contamination. This allows the water to pick up minerals in the ground that it passes as it makes its way through the water cycle. Also, the ground it passes is low in calcium, which makes things taste bitter (not better, bitter).

Chances are, however, that taste is not the reason why NYC gets so much props for its water. Chances are it's the chemistry of baking, which is a complicated thing, except to say that it's the chemicals, stupid.

The chemicals themselves are thrown into the Maillard arena to break down and transform.  Pyrrolines and pyridines are some of the bread-smelling chemicals created in this culinary laboratory – the “pyro-“ parts of their names indicate their origin in fire.

I just named two chemicals, but baked goods emanate hundreds of chemicals, all dependent not only on the original chemicals present, but on the nature and extent of the heating reactions. Just like the analogy of the butterfly effect, initial conditions can have a drastic effect on results. In a process as complex as the heated Maillard reaction, a slight change in the initial ingredients can have wide-ranging effects on the bun in the oven.

Taste/smell isn’t the only thing that is subject to change here – texture is a big factor as well, and is affected just as much based on initial ingredients.

Is it the case that the same chemicals that make your water taste good also make your bread taste good and also make you bread the perfect combination of fluffy-chewy-crunchy? Maybe not, but in the case of New York City’s water, some have it all.

Post Script

In case you thought NYC had it all, Paris just put bubbly water in it's water fountains. We call that carbonated water.

Hyperosmia and the Elastic Mind

Design and the Elastic Mind, MOMA, 2008. James Auger and Jimmy Loizeau, Design Interactions Dept., Royal College of Art. 

Penicillium Saprophyticus is a kind of mold that comes around in autumn, when the living tissue of the woodlands begins its seasonal decomposition. At the helm of the HMS Entropy are the roaming swarms of saprophytes that live off of dying plants. In small doses their smell can be intoxicating. The haunting smell of crushed leaves in autumn is not without a touch of this mold.

Just as the seasons, weather events bring their own aromatic indicators. The smell when it’s about to snow, river musk on now-dry floodplains after a severe summer flooding, the smell of the beach on the same floodplains after severe hurricane flooding, and plenty of mold during a mismatching of seasonal characteristics – these all announce the ever-changing and rebirthing of an ecosystem. 

Some people smell strongly of civet, some simply have evaporated cat piss all over them, and sometimes it’s hard to tell the difference. Civet, like lots of smells, is good at low doses, but bad when high, and people become desensitized over time. Many perfumes use civet, on purpose, for this reason. Many grandmothers are avoided, for the same. (Blackcurrant buds give off the same smell, and are used in perfumery.)

Furfural mercaptans are strong – coffee, cannabis, skunkpiss. They intermingle, both in molecular presence, and redintegrated perception. In a classroom, one might smell diesel exhaust, barely perceptible, somehow coming through a labyrinth of antiquated air vents.

Then there is the smell of lactose being processed in the body, on a scale from skim milk, through butter, to mozzarella cheese. Poison ivy (which I get every August) smells like something, though I cannot name it – it is the smell of my own body metabolizing urushiol.

Notes:

Where Science and Design Collide, a Few Weird Sights to Behold

John Schwartz, February 26, 2008, nytimes

ART AND SCIENCE: The show “Design and the Elastic Mind,” at the Museum of Modern Art in New York, features items like “Smell +,” left, whose designer, James Auger, said he wanted to underscore the diminished importance the sense of smell had in our lives by creating a device that allowed people to smell each other’s bodily scents before they met.

http://www.nytimes.com/2008/02/26/science/26elas.html

Design and the Elastic Mind

Paola Antonelli, MoMA, 2008

http://www.moma.org/interactives/exhibitions/2008/elasticmind/

James Auger and Jimmy Loizeau

Design Interactions Dept., Royal College of Art, viaMoMA

http://moma.org/exhibitions/2008/elasticmind/#/237