Friday, February 7, 2025

Olfactory Therapy Sounds Like Aromatherapy



Not sure I can believe all this - because you know as they say, extraordinary claims require extraordinary evidence. 

We're talking about a thing called therapeutic olfactory stimulation, also called olfactory enrichment and olfactory therapy. We start with the first study, which says: 

"Olfactory enrichment can improve the memory of older adults by 226%" 

They took 43 people over 60 years old and exposed them to 7 different odorants a week, one per night, for 2 hours, using an odorant diffuser, and then gave them the Rey Auditory Verbal Learning Test where they saw improved scores, and gave them fMRI scans that showed improved functioning in the left uncinate fasciculus as assessed by mean diffusivity.

I'm not a research scientist working in a lab and writing papers, and so the only thing I see here that's a flag is that the study took place during the covid lockdown, and something about social interaction related to the study could definitely improve brain health, because we know that happens. But that also caused lots of other problems like how they had to remove people from the study because their baseline taken in the office might be so different from follow-ups done remotely. 

They do reference a few other studies that support this idea, so I'll just copy directly:  
...olfactory stimulation during sleep deepens slow-wave sleep (Wolfe and Herzberg, 1996; Goel et al., 2005), which is the most restful portion of the sleep cycle, and people report feeling more vigorous the next day after nighttime olfactory exposure (Goel et al., 2005). Odorants enhance normal sleep, and they also improve abnormal sleep at a magnitude similar to that of sleep medication (Hardy and Kirk-Smith, 1995).

Bottom line is, I think we are eagerly awaiting another study, done not-during a pandemic and with a larger group beyond the 43 people participating here. 

via University of California Irvine Center for the Neurobiology of Learning and Memory: Overnight olfactory enrichment using an odorant diffuser improves memory and modifies the uncinate fasciculus in older adults. Cynthia C. Woo, Blake Miranda, Mithra Sathishkumar, Farideh Dehkordi-Vakil, Michael A. Yassa, Michael Leon. Frontiers in Neuroscience, 2023; 17 DOI: 10.3389/fnins.2023.1200448 [full text available]



But not so fast, we're not done yet. If the results from the above study are found to be credible, that would make the study below a lot more important:

Smell loss is linked to more than 100 diseases in new study
Oct 2024, phys.org

"We now know that pleasant scents can decrease inflammation, potentially pointing to the mechanism by which such scents can improve brain health." The study delves into the methodical tracking of 139 medical conditions associated with both olfactory loss and heightened inflammation, uncovering insights into a shared pathway linking these factors. Olfactory loss, which often precedes conditions such as Alzheimer's and Parkinson's diseases, may serve as an early indicator of disease onset, allowing for more proactive therapeutic approaches.

By showing how olfactory enrichment can mitigate inflammation, this research has laid a foundation for future studies aiming to explore the therapeutic use of scent to address a broader range of medical conditions.

via Charlie Dunlop School of Biological Sciences at University of California Irvine and Oxford Research Centre in the Humanities: Michael Leon et al, Inflammation and olfactory loss are associated with at least 139 medical conditions, Frontiers in Molecular Neuroscience (2024). DOI: 10.3389/fnmol.2024.1455418

Thursday, February 6, 2025

Male vs Female

 

Insects are not like people, because they have antennae instead of noses, and because they use pheromones and we don't. Still, it's always good to remember that when it comes to the chemosensory world, there's always a difference between males and females:

The differing olfactory worlds of female and male silk moths
Jan 2024, phys.org

Male moths live in a completely different olfactory world to their female counterparts. For example, the antennae of male silk moths are highly specialized to detect female sex pheromones like bombykol and bombykal, while females cannot even smell their own pheromones.

Bombykol attracts and bombykal deters, for males.

For females, they can't smell any of that. Instead they smell isovaleric acid and benzaldehyde, which are in silkworm feces, which can be found on mulberry trees, since they are the only trees where silk worms live, and they're also where silk moths want to lay eggs.

via Max Planck Institute for Chemical Ecology and Martin Luther University Halle-Wittenberg: Females smell differently: characteristics and significance of the most common olfactory sensilla of female silkmoths, Proceedings of the Royal Society B: Biological Sciences (2024). DOI: 10.1098/rspb.2023.2578



Study suggests an 'odor sensor' may explain male and female differences in blood pressure
Mar 2024, phys.org

Blood pressure in premenopausal human and mouse females is typically 10 points lower in both diastolic and systolic pressure than in males. Some studies suggest the difference may be caused by sex hormones, but the biological basis for the variation is not entirely clear.

Olfactory receptors are found all over the body, in lots of places that are not only in our nose, like in our kidneys for example (and on the surface of our skin but I don't have the science for that, only personal experience). Anyway, they've now found an olfactory receptor lining blood vessel walls of a part of the kidney that releases a blood pressure hormone called renin. 

Olfacotry receptors each have their own gene, so it's easy to look at a population and select people with mutations of this gene, which they did. These people, women, who didn't have the gene also had blood pressure levels just like men. 

via Johns Hopkins University School of Medicine and Queen Mary University of London: Jiaojiao Xu et al, An Evolutionarily Conserved Olfactory Receptor is Required for Sex Differences in Blood Pressure, Science Advances (2024). DOI: 10.1126/sciadv.adk1487.

Wednesday, February 5, 2025

Olfactory Otherness


I have a crazy idea there's a correlation between the rise of anxiety in a population and the decline in body odor due to deodorant and hygiene practices, as well as due to the increased availability of privacy, which is what I'll call the ability for each of us to have our own bedroom when growing up, or to live in an apartment alone as an adult, things that weren't available back in time because of financial constraints. That being said, the studies below do seem to suggest that smell has a stronger effect on our emotional states and our mental health status then we are aware of. 


Research shows that sniffing women's tears reduces aggressive behavior in men
Dec 2023, phys.org

Science strikes again!
  • They use the words "emotional tears" just to clarify. (not all tears are created equal)
  • The men played a two-player game where they were allowed to get revenge on the opponent.
  • Revenge-seeking aggressive behavior during the game dropped more than 40% after the men sniffed women's emotional tears.

via Weizmann Institute of Science: Agron S, de March CA, Weissgross R, Mishor E, Gorodisky L, Weiss T, et al. (2023) A chemical signal in human female tears lowers aggression in males. PLoS Biology (2023). DOI: 10.1371/journal.pbio.3002442



Scents might help depressed individuals, new study says
Feb 2024, phys.org

Scents are more effective than words at bringing back a memory of a specific event and could even be used in the clinical setting to help depressed individuals get out of the negative thought cycles and rewire thought patterns, aiding faster and smoother healing.

"It was surprising to me that nobody thought to look at memory recall in depressed individuals using odor cues before"

Professor Young presented study participants with a series of opaque glass vials containing potent familiar scents—from oranges and ground coffee to shoe polish, and even Vicks VapoRub. After asking participants to smell the vial, Young asked them to recall a specific memory, whether good or bad.

via University of Pittsburgh: Kymberly Young et al, Recall of Autobiographical Memories Following Odor vs Verbal Cues Among Adults With Major Depressive Disorder, JAMA Network Open (2024). DOI: 10.1001/jamanetworkopen.2023.55958

 
Study finds social interactions and olfactory cues prompt contagious itch in mice
Jun 2024, phys.org

Contagious itch only occurs in mice when they observe if a mouse that has been in their proximity is scratching.

Anosmic observer mice, whether itch-naïve or itch-experienced, displayed no contagious itch behavior.

via Tehran University of Medical Sciences: Shayan, M. et al. Social interactions and olfactory cues are required for contagious itch in mice. Scientific Reports(2024). DOI: 10.1038/s41598-024-61078-3.


Research shows young infants use their mother's scent to perceive faces
Jul 2024, phys.org

We tested 50 infants aged from 4 to 12 months, and found that the face-selective EEG response increases and complexified, indicative of improved face perception with development.

As expected, we also found that the benefit of adding the mother's body odor diminishes with age, confirming an inverse relation between the effectiveness of visual perception and its sensitivity to a concurrent odor.

Overall, this demonstrates that visual perception actively relies on odor cues in developing infants until the visual system becomes effective by itself.

What surprised me the most, not only in these studies but also in the previous studies we conducted, is the fact that the mother's odor has such a strong effect on the perception of various unfamiliar faces ... by showing reduced reactions to fearful faces, higher attention toward an unfamiliar woman, and increased interbrain synchrony between the infant and that woman.

Thus, it seems like the mother's body odor reassures the infant and promotes their interest when they encounter novel people. In other words, this primary social odor that infants learn already in the womb seems to encourage prosocial cognitions and behaviors.

via Society for Research in Child Development, Development of Olfactory Communication & Cognition  Lab in the Center for Taste, Smell and Feeding Sciences at Université de Bourgogne, University of Hamburg, Université de Lyon, Institut Universitaire de France, Université de Lorraine, Centre Hospitalier de Nancy, and Centre National de la Recherche Scientifique CNRS: Olfactory-to-visual facilitation in the infant brain declines gradually from 4 to 12 months, Child Development (2024). DOI: 10.1111/cdev.14124


Smell of human stress can affect dogs' emotions, leading them to make more pessimistic choices
Jul 2024, phys.org

Dogs experience emotional contagion from the smell of human stress.

The researchers recruited 18 dog-owner partnerships to take part in a series of trials with different human smells present. During the trials, dogs were trained that when a food bowl was placed in one location, it contained a treat, but when placed in another location, it was empty. Once a dog learned the difference between these bowl locations, they were faster to approach the location with a treat, which reflected 'optimism', while a slow approach indicated 'pessimism'.

These trials were repeated while each dog was exposed to either no odor or the odors of sweat and breath samples from humans in either a stressed or relaxed state. The stress smell made dogs slower to approach the ambiguous bowl.

via University of Bristol Veterinary School: Parr-Cortes, Zoe ; Muller, Carsten T ; Talas, Laszlo et al, The odour of an unfamiliar stressed or relaxed person affects dogs' responses to a cognitive bias test, Scientific Reports (2024). DOI: 10.1038/s41598-024-66147-1


Emotional body odors may enhance the effect of mindfulness therapy
Nov 2024, phys.org

48 women with symptoms of social anxiety and 30 women with depression were divided into three different groups exposed to either happiness body odor, fear body odor, or clean air, then tasked with performing mindfulness exercises over two consecutive days.

"The results were quite surprising as we observed an enhanced symptom reduction for individuals with social anxiety that received chemosignals, regardless of whether they came from fear or happiness body odors. This may indicate that it is not the emotion itself that leads to the improved effect, but perhaps rather that chemosignals convey a kind of 'human presence.'"

Two nuanced results: 1. Exposure to fear body odor resulted in lower heart rate variability indicating a less relaxed state even though this was not reflected in the self-reported anxiety ratings, and 2. No differences were seen for the group with depressive symptoms, only anxiety.

via Karolinska Institutet and National Center for Suicide Research and Prevention: Cinzia Cecchetto et al, Sniffing out a solution: How emotional body odors can improve mindfulness therapy for social anxiety, Journal of Affective Disorders (2024). DOI: 10.1016/j.jad.2024.10.088

Tuesday, February 4, 2025

Fragrance Generators



Text generators and image generators and even video generators have been hitting the streets and hitting our screens for a while now, but let's not forget the molecule generators, maybe we could call them chemical generators and make it real confusing (they're generating possible chemicals, like the formula for a chemical not yet known by science, not actual chemicals; that's for a different robot). 

Perfume engineering uses trial-and-error to find new fragrant chemicals. That's how we do everything before we know how to do it. It's very inefficient. So now we're trying to use machine learning to take at least some of the guessing out of all this. And it works, sort of. 

Machine learning gives us new molecules to work with, but it doesn't tell us how to combine those molecules with others. It can't predict the perceived intensity of the just-discovered but not-yet-created molecule.

Molecules yes, perception no.

Perfumes have no copyright protections; they are protected by the inability for people to guess the composition. You can get the molecules right, but not the amounts relative to each other; changing the ratio of even two molecules from 10:1 to 10:3 is enough to mess up the overall effect.

So this effort is to predict the overall effect of a bunch of molecules mixed toegther, not just one but a bunch together. They train a neural net using molecules and words. I can't really tell which word-dataset they're using, because it seems to be proprietary, and based on Teixeira et al's 2014 Perfumery Radar 2.0 (https://sci-hub.se/10.1021/ie403968w).


Using AI to replicate odors and validating them via experimental quantification of perfume perception
Mar 2024, phys.org

via Norwegian University of Science and Technology: Bruno C. L. Rodrigues et al, Molecule Generation and Optimization for Efficient Fragrance Creation, arXiv (2024). DOI: 10.48550/arxiv.2402.12134



I'm skeptical because the list is so short, but it might be as simple as this: citrus, fruity, green, floral, herbaceous, musk, oriental, and woody; and based on the rationale that this small group represents 75% of the odor space (Teixeira 2010). 

There are less common descriptors such as leather, gourmand, aldehydic, balsamic, and herbal which are used only twice. One dimensional descriptors are tobacco, modern chypre, floral oriental, soft oriental, mossy woods, dry woods, and mint, among others. Some molecules didn't come with their own notes, so Good Scents was used as a reference.

Here's a list of the lexica for odor descriptions mentioned in the Perfumery Radar text - Calkin and Jellinek, Jaubert, Roudnitska, Edwards' Fragrance Wheel, Zarzo and Stanton, Boelens-Haring and Thiboud. Apart from these, each fragrance company or perfumer has their own that they've developed over the years. The Perfumery Radar 2.0 itself uses a base layer with eight olfactory families, and two additional layers: an outer layer with seven descriptors and an inner layer with 17 descriptors. 

And here's the info from their table on the most used descriptors by fragrance companies: floral, woody, citrus, fruity, green, oriental, chypre, aromatic, fouger̀e, musk, spicy, ambery, marine; used in different ways by Givaudan, Osmoz, International Flavors & Fragrances, Symrise, Frutarom, MANE, Societ́é Franca̧ise des Parfumeurs (SFP), The Fragrance Foundation, Avon, Fragrantica, LaLoff.

They talk about the difference between using common words for olfactory perception and the more limited set of words used by expert perfumers, which is an important part of constructing these lexica, and also that each fragrance house maps the olfactory space in its own way. 

via Chemical Engineering Department of the Norwegian University of Science and
Technology, Laboratories of Separation and Reaction Engineering and of Catalysis
and Materials and of Chemical Engineering at University of Porto, and SIA Murins Startups in Latvia:  BC Rodriguex et al. Molecule Generation and Optimization for Efficient Fragrance Creation.  

Monday, February 3, 2025

Brother of E-Nose

 

This is about not your Grandma's electronic nose, but other versions that have been showing up:

Researchers develop biomimetic olfactory chips to enable advanced gas sensing and odor detection
Mar 2024, phys.org

Most electronic noses work electrochemically, but this one is biomimetic, so that's new.

"In the future, with the development of suitable bio-compatible materials, we hope that the biomimetic olfactory chip can also be placed on the human body to allow us to smell an odor that normally cannot be smelled. It can also monitor the abnormalities in volatile organic molecules in our breath and emitted by our skin, to warn us on potential diseases, reaching further potential of biomimetic engineering," said Prof. Fan.

via Hong Kong University of Science and Technology: Chen Wang et al, Biomimetic olfactory chips based on large-scale monolithically integrated nanotube sensor arrays, Nature Electronics (2024). DOI: 10.1038/s41928-023-01107-7



Combining human olfactory receptors with artificial organic synapses and a neural network to sniff out cancer
May 2024, phys.org

The device has three parts. a nanodisk containing modified human olfactory receptors grown using E. coli bacteria, a device that simulates neural synapses, and an artificial neural network trained on four specific fatty acids that are known to be present in breath samples of people with certain types of gastric cancers.

The research team plans to continue their work by adding more receptors.

(Only 400 receptors to go!)

via Seoul National University: Hyun Woo Song et al, A pattern recognition artificial olfactory system based on human olfactory receptors and organic synaptic devices, Science Advances (2024). DOI: 10.1126/sciadv.adl2882


Artificial 'nose' can sniff out damaged fruit and spoiled meat
Oct 2024, phys.org

Ah yes - The Antenna Nose:

"Other electronic noses can have several hundred sensors, often each coated with different materials. This makes them both very power-intensive to operate and expensive to manufacture. They also entail high material consumption. In contrast, the antenna sensor consists of only one antenna with one type of coating."

The antenna transmits radio signals at a range of different frequencies into the surroundings. It then analyzes how they are reflected back. The way the signals behave changes based on the gases present, and because the antenna transmits signals at multiple frequencies, the changes create unique patterns that can be linked to specific volatile organic compounds - even isomer compounds that "look" very similar to even the most sophisticated E-noses.

via Department of Manufacturing and Civil Engineering at Norwegian University of Science and Technology: Yu Dang et al, Facile E-nose based on single antenna and graphene oxide for sensing volatile organic compound gases with ultrahigh selectivity and accuracy, Sensors and Actuators B: Chemical (2024). DOI: 10.1016/j.snb.2024.136409


Tiny electronic nose rivals animal scent detection
Nov 2024, phys.org

They measure the timing and frequency of odor bursts in highly chaotic air movements of odor plumes to guess the size and spread of the odor plume.

We found it could accurately identify odors in bursts as short as 50 milliseconds. Even more, it could decode patterns between odors switching up to 40 times per second, which is similar to what mice can do when they perform source-separation tasks. This means our device can "smell" at speeds that match those of animals.

They used metal-oxide gas sensors as well as temperature and humidity sensors, improved with high-end electronics and custom-designed algorithms that can sample and control these sensors fast and precisely. 

"We also discovered that rapidly switching the temperature of the sensors back and forth between 150°C and 400°C about 20 times per second produced quick, distinctive data patterns that made it easier to identify specific smells. This approach allowed our device to pick up odors with remarkable speed and accuracy."

via Biocomputation Group, University of Hertfordshire and International Centre for Neuromorphic Systems at Western Sydney University: Nik Dennler et al, High-speed odor sensing using miniaturized electronic nose, Science Advances (2024). DOI: 10.1126/sciadv.adp1764


Nanopore-based 'artificial tongue' can determine chemical makeup of alcoholic drinks
Dec 2024, phys.org

"A single-molecule sensor for rapid analysis of alcoholic beverages" uses a mycobacterium modified with a pore just a few nanometers in diameter.

via Nanjing University: Pingping Fan et al, Nanopore signatures of major alcoholic beverages, Matter (2024). DOI: 10.1016/j.matt.2024.11.025


Friday, July 12, 2024

Nose Diving


The year 2020 was momentous. There was a global pandemic that killed millions of people and brought the world to a standstill for about a year. So most of us completely missed the release of Harold McGee's book, which is absolutely, with no hesitation, and nothing to even compare it to, the greatest and most important book ever written on the topic of smell. 

This person, Harold McGee, is already very well known for his 1984 book On Food and Cooking, which made him a legend of the culinary world. On Food is considered a Bible, if not the Bible, of cooking. He was the first person to look at food and cooking as a scientist. But he's not a scientist. He's not a chef either. He's just a really, really good writer.

When I heard that he was writing another book, this time about smells, I had to make sure it was the same person - this can't be true, not him. Personal note - I also wrote a book about smells, in 2015. I tried really hard to make sense out of the way we talk about the things we smell. I failed. But if there was ever a person that could do what I wanted to do, it was him. I read On Food back around 2010 when two of my closest friends were both going to cooking school. In fact, I had just finished reading it a second time circa 2020, thinking maybe I had learned enough about chemistry in the intervening years to help me digest the more technical parts of this seminal work. 

After I learned of his forthcoming book, but before it was released, I had hopes, but they weren't too high. Smell is too hard. There's just too much there to make sense of it, and for a lot of reasons, we're almost hardwired to NOT make sense of it. I thought it would be more like a primer, a survey, and introduction, a teaser. He certainly can't do to smell what he did to food and cooking. Nobody can. 

Then I read the book. It took me two years; I read every single word, including the notes, and some parts I read twice. But it didn't take long for me to realize what he had done. He wrote the most important book on smell ever written. I know it sounds like hyperbole, but it's not. The last time I checked, which was about 2015ish, there were about 30 books in the Library of Congress on the topic of smell. There were 300 books on perfume bottles, and 30 books on smell. People just don't write about it.

To say that McGee wrote the most important smell book ever is not an exaggeration; but the other side of the truth is that there aren't many books to compare it to. And of all the books that are written about smells, none of them tackle the language of smell (except my attempt, Hidden Scents). Ann-Sophie Barwich does a pretty good job with her 2020 book on the philosophy of smell, but even she avoids some of the messiest parts of olfactory perception, that being the language we use to talk about smells. (Here's my review)

I will cut short my praise and leave one final note, mostly out of personal interest - a fragrance friendly organization called The Perfumed Plume nominated this book Nose Dive alongside a coffeetable compendium by Gestalten called The Essence: Discovering the World of Scent, Perfume and Fragrance for the 2020 Fragrance Book of the Year. I wrote a couple chapters for The Essence. Needless to say, Nose Dive won. Actually, in the end, the pandemic won, because mostly nobody anywhere was paying attention to any of this at the time.



(^cool illustrations explaining how smells work via biology)

Nose Dive: A Field Guide to the World's Smells
Harold McGee, Penguin, 2020

--see below a note on punctuation "*"
--"osmcosm" (the universe of smells) pxi
--"original volatiles" are birds because volatile means "to fly" pxii
--"The smell of a person's body ... is the body with the flesh removed" -Sartre pxx; meaning the smell is the vaporous molecules, not the substance of the flesh
--"minerality", mineral, mine - smell of moist stones, used in wine-tasting but not the smell of actual minerals which come from inside the earth where it smells like sulfur p23-24
--First, on Earth, life ran on iron and sulfur, then oxygen. Today, some of us, our cells, still run on iron and sulfur, and so oxygen is toxic p25
--"sulfidic" p37
--"catty" cat ketone p80-81
--skin aldehydes Japanese kareishu, nonenal p112
--Essay: Olfactory Comfort in Close Relationships: You aren't the only one who does it, by Donald McBurney, 2014 p125
--The confusion is the very nature of plants and in the way we perceive smells. Plants deposit countless different molecules in their wood and leaves and flowers and fruits because they can. The smell of any particular item is a composite of many different volatiles, of which perhaps a dozen or two predominate. So several different molecules can remind us of the same item. And then on our end, we encounter many of the same molecules in different plants: so one molecule can remind us of several different items. In fact, that's part of the interest of paying close attention to flavor. When we do, we notice echoes and rhymes in many different things. p142
--Plant Metabolic Highways, see charts on page 150 and 152
--on terpenes, again, because we are usually exposed to many of them all at once and from the same source, we *encode* them ambiguously, and so when we try to *decode* them, we get mixed up. p164
--"Plants are profligate chemists" p186
--stinking goosefoot has a "fishy, ammonia-like smell due to an unusual stockpiling of trimethylamine - hence vulvaria, "vulva-like," for the supposedly similar smell of female genitalia (see p116) p203
--The creosote bush, Spanish name hedionilla, from heder, "to stink" (hedione?) p204
--On Flowers and Smell: volatile and pigment molecules share biochemical resources, so that more color means less scent, in part because some scent volatiles are also plant hormones that shorten vase life p211
--Corn salad or mâche, small spinach-like rosette, called lamb's lettuce, a mix of John Milton's garden of Eden and valerian; unlike any other salad green p247
--cilantro - similar culantro, in the celery family, popular in Southern Asia and Mexico, despised elsewhere, described as soapy. "This difference in taste is likely due to genetic differences in sensitivity to the volatiles, cultural differences in exposure to them, and also t their unusual nature. They're neither terpinoids nor benzoids, the usual herb volatiles, so they don't immediately suggest aromatic plants, instead, these aldehydes are commonly encountered in everyday life as breakdown fragments of a the long-chain lipids in soaps and cosmetics: materials that are inedible and distasteful. They're also emitted by various insects, including stinkbugs." p258
--Harold McGee is one of the few people who can start out as a layperson, but through the process of writing, rises to the level of scientist, but while maintaining his lay-language. His writing is so effortless to read, and yet so crystal clear in what it's trying to say, that you are immediately smarter by the end of the sentence. He also has the determination, and the ability, to follow every one of the paradoxes and conundrums the plague the field of olfaction, like the way he describes the Cilantro Problem [above] Part geneticist, part cultural anthropologist, food chemist, flavor chemist, and finally entomologist. Oh, etymologist too, sure.
--This "field guide" takes you to a global grocer featuring every odiferous organism possible, neatly arranged (so neatly arranged) in rows and stands, and all available for us to smell them, albeit only by the words we call them and the names of their molecules. (p266)
--He states that while trying to do his research, "Surprisingly, I haven't found any published studies of raw corn kernels or grits or flour." p276 Note that he has found studies on about a thousand other things, so it's not like he doesn't know what he's doing. Just weird. (And I'm looking at you Big Corn, all that glyphosate, biofuel, whatever. Remove the research remove the competition.)
--methyl sulfyanylhexanol is in passionfruit and underarm sweat p301
--citron is so terpentine-y that Greeks associated it with cedar and juniper p320
--"strawberry furanone" = "pineapple ketone" p331
--Finishing the fruit chapter with Durian: Most plant volatiles are defensive warnings and weapons, but by controlling our exposure to them, we manage to enjoy the sensation they stimulate - so much so that we volunteer to protect them ourselves. p335
--he refers to geosmin as an "olfactory landmark", sort of a way of organizing odor networks. p348
--octenone, a ketone, metallic and bloodlike, generated by reactive metals from keys and coins, etc. p350-351
--When he introduces terms, he often provides disambiguating context: "To students of the fungal kingdom, mushrooms are "fruiting bodies". And he goes on to explain how mushrooms are like fruit. He is a master teacher. p352
--melons, cucumbers and mushrooms all smell like fish, because fish (and oysters etc) were the first to emit these volatiles hundreds of millions of years before melons p382
--merior is terrior but for the sea, like the tastes of oysters p392
--The volatiles of squid, cuttlefish and octopus have "next to nothing" of research p395
--Toxic smell p401 (add to IH notes)
--Vanilla and clove smell like smoke (not vice-versa, like fish and melons), they are similar to guaiacol, and lignin breaks into vanillin and eugenol in fire (and in people) p412-413
--He calls fossil fuels fossil organics, because they instigated so much of our understanding p419
--He doesn't call benzene "aromatic" but "solvent" and "sweet" p421
--"The volatiles of modern materials," a section between the end of the book, in the chapter on Smoke, Asphalt, and Industry, he describes the smells of polystyrene, rubber, Bakelite, carpets, auto tires, 3-D printers, polyethylene water bottles and food wraps. It's probably the craziest chapter, and section, in the whole book. 
-"I smell it as I type paragraph when I sniff through the keyboard of my warm laptop computer." (Bakelite-like circuit boards)
-"One polymer often used in screwdriver handles (celluloste acetate butyrate) is notorious for breaking down into vinegary and cheesy acetic and butyric acids that accumulate in the toolbox."
-"To this day I sniff pre-packages sandwiches before I buy them." p428-499
--In addition to the common tree-wood volatiles, rotos have unique sesquiterpenoids, probably to defend against soil microbes - shyobbunones, acorenone, costols, and zizaenones appear nowhere else in this book. p463
--In India, wild khus roots (like vetiver) are woven into shades and mats that are sprinkled with water to cool and scent the air. p463
--musks - "animal protein machinery" by-products, "not especially unpleasant but they do get our attention, subliminally or overtly. A touch of musk or beaver is a way of asserting the wearer's animal presence by prestigious proxy rather than poor hygiene: a refined means of visceral communication." p465
--synthetic "white musks" are used for a "hot-iron-on-fresh-laundry" quality - the opposite of the original musk's underside-of-wild-mountain-creature quality! The rare, strange, ambivalent animal materials became a stepping stone to the ubiquitous reassurance of domesticity and cleanliness. p475
--Hedione is named in a chart on p475, the molecule methyl dihydrojasmonate, c.1960, smells like fresh, floral, "transparent," "over-ripe lemons"; and was found later in black tea 1974, and jasmine osmanthus, lima sweet orange p475 (?)
--Hedione again: Edward Roudnitska's Eau Savage, "Wild Water" added to an eau de Cologne citrus-herb mix the newly discovered Hedione and its fresh, bright, "transparent" volatility, which soon became a standard ingredient in modern perfumes. (p475?)
--Monko, or listening to smells (Japanese); It can be exhilarating to listen to beautiful or strange aromatics. It's also exhaustingly inward to focus on the invisible and intangible, and rack the memory for precedents or comparables. But it's building a database, and nose and a sensory work. p483 [he's referring then to the smell lexicon as a "database"]
--He doesn't talk about foods until Chapter 18 Cooked Foods. p484
--The combinatorial code of food: Liebniz Institute for Food Systems Biology near Munich, 2014, Peter Schieberle, Thomas Hofmann, and colleagues reviewed several decades of work and reported that only 230 molecules account for the majority of important volatiles in a wide range of foods, and that any given food aroma can be reasonably simulated with about a dozen of these key molecules in specific proportions. This "combinatorial code"; I assume this is the reference: A Dunkel, M Steinhaus, et al. (2014). Nature's chemical signatures in human olfaction: A foodborne perspective for future biotechnology. Angewandte Chem Int Ed 53: 7124-7143 [key food odorants] 
--Thai scented candle dessert - tian op, beeswax, incense, benzoin, frankincense, sandalwood, citrus peels, herbs, spices, essential oils, even musk p493
--Blood - we usually describe the smell as "metallic" because it's similar to the smell left on our fingers when we handle coins, or in the air when we scrub a bare metal pan or sink. But metals themselves aren't volatile: we're actually smelling the fragments created when stray heme iron and other metals help oxygen attack the carbon chains in our cell membranes, skin oils, or dish soap. Polyunsaturated chains, kinked at several points by double bonds between adjacent carbon atoms, are the most successful metallic-smelling. In the case of blood and exposed surfaces of raw meat, the key fragment is a ten-carbon, one-kink aldehyde with an oxygen atom riding its middle:an epoxy decenal (also see octenone, nonenone ,octadienone, hexenone, heptanone, nonenol) p502-503
--Olfactory Camouflage - force-feeding birds, castrating hogs, and grain-feeding cattle are all venerable versions of a kind of olfactory camouflage, a pre-cooking on the hoof that emphasizes generically fatty smells over the specifically animal and bloody p506; and this is because livery-ness in game meats and grass-fed cattle, because animals that live on open pasture take lots of multi-kinked carbon chains from whole plants, but are otherwise lean, so their metallic fragments are prominent p505
--Cooked fish bouquet - geranium leaf and cooked potato (methional and octadienone) p507
--Distinctly fishy - when fish or shellfish are less fresh or cooked more thoroughly, the long exposure to oxygen or to heat energy breaks their kinked chains mainly into seven- and ten-carbon fragments, - and this is the mix that smells distinctly fishy p507 ["distinctly fishy" just sounds funny]
--Lovage and the "Maggi plant" - many main dishes in the European tradition begin with the preparation of a base of "aromatic" vegetables (onion, carrot, celery) [~p507-512?]
--MMP gene - German flavor chemists in 2009 and 2011 published major volatiles of meat stews. The dominant "gravy-like"note came from onions and leeks being chopped and then heated, for both chemical and heat enzymes to break them into mercaptomethyl pentanol (MMP). ... MMP activates a receptor from Neanderthals which he calls "sweat-adjacent", suggesting this highly sensitive single receptor may have been about human sweat p512-513 
--rancid oils and stale food charts! p537-538
--"sweaty salty feet" - is a close relative of the Brevibactererum that ferments brine-washed Epoisses and Limberger  and makes it orange, also related to salt water sediment and fish p550
--Pseudofermentation - [my term - true pickles vs acid pickles] true pickles are fermented, modern pickles are "manufactured by simple acidification" p552
--The Industrial Approximation of Soy Sauce - soybeans pressure cooked with strong hydrochloric acid, generates an aroma surprisingly similar to the fermented version p558; see chart: fermented vs acid hydrolyzed p559
--smells like vomit - pecorino romano is a sheep's milk cheese coagulated with the protein-and-fat-digesting-enzymes in an extract of lamb stomach, so it's rich in butyric and sweaty fatty acids [smells like vomit] (and when aged, it smells like pineapple, ie ethyl butyrate, from the butyric acid) p568
--Arcaridial is an unusual molecule, found in the rinds of aged mimolette, which develop colonies of mites that leave behind a powder that smells fatty-nutty or "surprisingly good" for spider pheromones p569
--Fruit fly taint - female drosophila carry a wax-floral aldehyde as a pheromone to attract males, and can leave a detectable off-odor in the [wine] glass within minutes p575
--Hefewizen is banana-like p578
--Japanese buckwheat shochu is a rare grain [rice] spirit without long aging p589
--Yeast travel on insects, and came before flowers p591-592
--In the conclusion he says the tables of molecules and notes "only indicate notes that you may perceive in the overall smells of things. They're not prescriptions for what you should perceive. Smell perception simply isn't prescribable, for reasons that would fill another book." p595 [ahem]

NOTE:
*I vacillate between American and British punctuation with the quotations and commas, apologies.

Thursday, March 7, 2024

Hyperdimensional Navigation Syndrome

 

How humans use their sense of smell to find their way
Oct 2023, phys.org

28 participants each entered a virtual three-dimensional smellscape four times. The placement of eight "odor objects" in the environment (smells like orange or banana) always stayed the same. What changed was where participants were placed in the virtual reality arena and which target odor they needed to find.

Results? "Human subjects can actually navigate spaces using their nose in the context of a particular type of virtual reality environment."

"We also demonstrated that this behavior was associated with the emergence of a particular neural signature indicative of what we might call 'cognitive maps.' This neural signature not only appeared in areas traditionally associated with navigation behavior, but also in olfactory-related brain regions."

Their findings suggest that these two sets of brain regions share a common spatial code, something that hadn't previously been known.

via University of Pennsylvania Jay Gottfried's lab: Clara U. Raithel et al, Recruitment of grid-like responses in human entorhinal and piriform cortices by odor landmark-based navigation, Current Biology (2023). DOI: 10.1016/j.cub.2023.06.087