Olfactory Overload

For centuries, smell has been considered the lowest sense. Even Science itself has avoided it. No more; olfaction is experiencing an absolute revolution.

Oh really? Yes. Consider for a moment, the €2.8M price tag on this European olfactory heritage and sensory mining project, called Odeuopa. That's a nice price tag for research on the history of smells.

image credit:  Inception 3A Output 53 - Roelof Pieter - 2015

I review a few hundred articles every week, pulling aside anything I see on olfaction. Some weeks there's a good article, maybe two, sometimes nothing. Much of the time, the article is about a development in hi-tech sensors or electronic noses, or how the East doesn't like "new car smell" and what Western car companies are doing about it... . 

But now, about once a month for seven months in a row, another piece of research surfaces to enrich our understanding of olfactory perception. Not just hype-cycle blurbles, but domain-foundation scientific breakthroughs are redefining how we think about olfaction, and our models of how it works.

The news is that each one of us employs a dynamic, combinatorial chemosensory system. It's capable of adapting in real time to an ever-changing environment, and it's using a combinatorial network of hundreds of genetically-determined olfactory receptors working in unison to identify and interpret any possible combination of odorous chemicals that we could ever be exposed to. 

 

First, a reminder of what it means to be using a "combinatorial" approach to perception. Epistemologically, combinatorics comes from mathematics, but combinatoric optimization and combinatorial dynamical systems are subfields of this domain, usually found in areas like graph theory or network theory. These areas overlap with the "brains" of our early 21st century artificial intelligence machines -- the deep learning neural networks you should be hearing about daily. 

But what does it mean for olfaction to be combinatorial? It means that olfaction is all gestalt. We don't use one type of neuron to smell one type of smell. We use a bunch for each, and they overlap too. In other words, it's a mess.

Some odorants, in theory, could activate (or inhibit) every receptor we have (roughly 400 functional). And it's the combination of all those excitations and inhibitions that create odor identity. That's a lot of combinations. And you would need all of them to identify that one odorant. And if you lost only one, by viral infection for example, that thing would not smell the same. In reality, this is not how it works because it's a lot more complicated, and there are so many exceptions to the rule that it's barely a rule. But it's getting clearer by the day. 

The main point of a combinatorial system is that you can't "map" it (it's a mess, remember?). This is something Science has been trying to do for a long time. Using language as an intermediary, this attempt to map the olfactory dimension started with the Dravnieks dataset, a bunch of odorous molecules mapped to descriptors produced by people who smell those molecules:

Dravnieks A. Atlas of odor character profiles. Philadelphia: ASTM; 1985.

Arctander is also used to organize the aromasphere by way of language: 

Arctander S. Perfume and flavor chemicals (aroma chemicals). Montclair, NJ: Author; 1969.

But then things changed. The DREAM dataset is produced, using huge chemoinformatics datasets for the individual molecules, mapped against equally huge semantic analysis datasets made of a bustling lexicon of odor words. This paper via Leslie Vosshall's lab in Rockefeller University sums it up:

Keller A, Vosshall LB. Olfactory perception of chemically diverse molecules. BMC Neurosci. 2016 Aug 8; 17(1):55. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4977894/

Multidimensional Folds - Lach - 2010

And now onto 2020, a big year for olfaction. Figures so much of this will be overshadowed by a raging global pandemic.

In March, a study from Hebrew University shows us that our olfactory receptors are not just activated but inhibited, and that they can change over time from one to the other. Back in 2006, Wilson and Stevenson's book Learning to Smell investigated this idea of the blank slate. The thing is, optogenetics wasn't invented yet. Well it may have been invented, but they weren't slipping glass fibers into mouse neurons to monitor their activity in real time. We're not looking at the psychology of smell anymore but the actual neurological behaviors of it. 

And they see that the receptors themselves do in fact learn, change, adapt, and even revert back to a previous state. I've repasted this description already elsewhere on this site, because it's such a big deal, but again:

The general profile of excitatory vs. inhibitory responses by mitral cells changed with learning and task demands. In naive animals, most responsive cells (71%) responded by excitation to the odours. Following the learning of the 5-decision boundary task, the ratio of excitatory/inhibitory responses reversed. After learning, the majority (71.4%) of neurons now responded by inhibitory calcium transients to the odours (Fig. 6C,E). The ratio of inhibitory vs. excitatory responses reverted back to normal after retraining the mice on the 1-decision boundary task. Specifically, 73.3% of responsive neurons were again excitatory on day 18.

via Hebrew University: Flexible Representations of Odour Categories in the Mouse Olfactory Bulb. Elena Kudryavitskaya, Eran Marom, David Pash, Adi Mizrahi. Hebrew University of Jerusalem. Mar 24 2020. BioRxiv. doi: https://doi.org/10.1101/2020.03.21.002006

https://www.biorxiv.org/content/10.1101/2020.03.21.002006v1.article-info

April. When you hear the phrase "more than the sum of its parts," that's codeword for things combinatorial. This one doesn't use the optogenetics described above, but an imaging technique called SCAPE microscopy:

Making sense of scents - 3-D videos reveal how the nose detects odor combinations

Apr 2020, phys.org

https://phys.org/news/2020-04-scents-d-videos-reveal-nose.html

Using a cutting-edge 3-D imaging method called SCAPE microscopy, the Columbia team monitored how thousands of different cells in the nose of a mouse responded to different odors—and mixtures of those odors. They found that the information that the nose sends to the brain about a mixture of scents is more than just the sum of its parts.

...

The researchers expected to see that the cells activated by mixtures of odors would be equivalent to adding together responses to individual odors. In fact, they found that in some cases an odor can actually turn off a cell's response to another odor in a mixture [previously known via violet ionones]; in other cases, a first odor could amplify a cell's response to a second odor.

...

The team's data challenged the traditional view that the brain makes sense of a mixture of scents by figuring out all of the individual components. It confirmed what perfumers have long known: combining different scents can create a certain experience on its own, essentially becoming an entirely new scent that can provide a completely different experience.

via Stuart Firestein's lab at Columbia University: L. Xu el al., "Widespread receptor-driven modulation in peripheral olfactory coding," Science (2020). https://science.sciencemag.org/cgi/doi/10.1126/science.aaz5390

Multidimensional - Oliver Panthsdown - 2008

Skipping May, June shows us "synthetic olfactory perception" which is exactly what it sounds like.

Researchers at New York University's Langone Health Center simulated olfactory perception with a synthetic electronic odor signal. In laymen's terms, mouse noses were tricked into thinking they smelled something when it was actually just an electrical signal. This is kind of like the way you can open someone's skull and zap certain parts of their brain, and they will feel tingles in corresponding parts of their body, even though you're not touching those parts of their body (don't try this at home though).

There are also some interesting results from this study that support the mostly-uncontroversial yet definitely misunderstood theory of information processing in the olfactory bulb, which is that the detection of odor-representations is more of a combinatorial process, and less of a one-to-one system of odor molecules and neuron receptors. And, this combinatorial perception theory is a primary reason as to why we cannot comprehensively organize olfactory experience into subsets or primary odors. (And the reason for writing a book about the language of smell.)

via NYU Langone: Manipulating synthetic optogenetic odors reveals the coding logic of olfactory perception. Edmund Chong, Christopher Wilson, Shy Shoham, Stefano Panzeri, Dmitry Rinberg. Science 19, Jun 2020, Vol. 368, Issue 6497, eaba2357. DOI: 10.1126/science.aba2357

Later on, in July, Harvard Medical School releases a similar study, showing "flexible cortical representations in odor space" here:

via Harvard Medical School: Stan L. Pashkovski et al, Structure and flexibility in cortical representations of odor space, Nature (2020). DOI: 10.1038/s41586-020-2451-1. http://dx.doi.org/10.1038/s41586-020-2451-1 [alt link] https://www.newsbreak.com/news/1593236184136/structure-and-flexibility-in-cortical-representations-of-odour-space

Sum-of-its-parts strikes again, July. 

Engineering and philosophy combine for an emerging understanding of smell

Jul 2020, phys.org

https://medicalxpress.com/news/2020-07-philosophy-combine-emerging.html

Shi Nung Ching of the Preston M. Green Department of Electrical & Systems Engineering, and doctoral student Sruti Mallik developed computational models of neural circuits that mimic the sensory act of smelling. They found the models also manifest certain properties analogous to those observed in olfactory sensory processing in insect brains.

Researchers found that their sensory system model developed emergent properties—properties that are more than the sum of their parts, so to speak—similar to properties seen in an insect's antennal lobe, which is important for its sense of smell.

via Washington University in St Louis: Sruti Mallik et al. Neural Circuit Dynamics for Sensory Detection, The Journal of Neuroscience (2020). DOI: 10.1523/JNEUROSCI.2185-19.2020

http://dx.doi.org/10.1523/JNEUROSCI.2185-19.2020

Astral Fragments - Stacy Young - 2016

Onto August. They're looking at the rat hippocampus; because that's the place where memories are stored, and it's hardwired into the olfactory system, the limbic system. They're showing that the brain identifies things differently over time. In a way, saying that there is no objective reality, only subjective multitudes:

via the University of Technology Sydney: Laura A. Bradfield et al. Goal-directed actions transiently depend on dorsal hippocampus, Nature Neuroscience (2020). DOI: 10.1038/s41593-020-0693-8

http://dx.doi.org/10.1038/s41593-020-0693-8

September, "sum of parts" again:

Nose's response to odors more than just a simple sum of parts

Sep 2020, phys.org

https://medicalxpress.com/news/2020-09-nose-response-odors-simple-sum.html

"New research from Kyushu University shows that a much more complex process is occurring, with some responses being enhanced and others inhibited depending on the odors present."

via Kyushu University: Shigenori Inagaki et al, Widespread Inhibition, Antagonism, and Synergy in Mouse Olfactory Sensory Neurons In Vivo, Cell Reports (2020). DOI: 10.1016

October shows us that you can teach yourself to smell better. I am compelled to remind the reader that olfactory receptor cells are the only part of your brain that pokes outside the body, making them very vulnerable. This also makes them a great point of entry for viruses invading the body, but it's also the reason why these cells regenerate profusely throughout most of our lives. And that's a reason why you can train yourself to smell better. 

These scientists basically stopped sending odors in the air to one nostril, and found that neurogenesis slowed down (use it or lose it). The idea is that as these cells re-grow, they may be changing the cell types in order to adapt to a changing environment. This is called stimulation-dependent neurogenesis, and although it's still up in the air as to how it all works, get in on the ground floor:

Study finds odor-sensing neuron regeneration process is adaptive

Oct 2020, phys.org

https://medicalxpress.com/news/2020-10-odor-sensing-neuron-regeneration.html

via University of Colorado Anschutz Medical Campus: Carl J. van der Linden et al, Olfactory Stimulation Regulates the Birth of Neurons That Express Specific Odorant Receptors, Cell Reports (2020). DOI: 10.1016/j.celrep.2020.108210

November now. Not olfaction specifically, but memory, which is closely related. The common theory has been that each memory gets its own neuron, but now an alternative model is ascending, and it looks more like the same group of neurons store all memories.

All the data we have on this stuff comes from fMRI. But fMRI can't see individual neurons. If we look at the neurons one at a time, we see something very different happening. 

This is certainly an idea to get familiar with. It should also fill you with wonder at what else we will figure out with rapidly-advancing neuro-tech:

Human intelligence just got less mysterious, neuroscientist says

Nov 2020, phys.org

https://medicalxpress.com/news/2020-11-human-intelligence-mysterious-neuroscientist.html

via the University of Leicester: Rey HG, Gori B, Chaure FJ, Collavini S, Blenkmann AO, Seoane P, Seoane E, Kochen S, Quian Quiroga R. Single Neuron Coding of Identity in the Human Hippocampal Formation. Current Biology : Cb. PMID 32142694 DOI: 10.1016/j.cub.2020.01.035 

Neuroplasticity and Olfactory Existentialism

 

New study reveals how the brain organizes information about odors

Jul 2020, phy.org

 

A study by neurobiologists at Harvard Medical School now provides new insights into the mystery of scent. Reporting in Nature on July 1, the researchers describe for the first time how relationships between different odors are encoded in the olfactory cortex, the region of brain responsible for processing smell.

 

The sense of smell allows animals to identify the chemical nature of the world around them. Sensory neurons in the nose detect odor molecules and relay signals to the olfactory bulb, a structure in the forebrain where initial odor processing occurs. The olfactory bulb primarily transmits information to the piriform cortex, the main structure of the olfactory cortex, for more comprehensive processing. [But] Often, subtle chemical changes—a few carbon atoms here or oxygen atoms there—can lead to significant differences in smell perception.

 

They use a database of physical and chemical features of tons of molecules, probably from the Dragon dataset, which is a relatively new set of thousands of chemical identities based on molar mass, chemical formula, chirality, boiling point, etc.

 

Then they choose three different synthetic odors, each one made of a group of different molecules, and each group having either very diverse features, intermediate, or minimal diversity. The minimally-diverse "odor" group could be made of molecules differing by only one carbon atom, for example.

 

Another way to think about these chemical combinations -- some are grouped close together in chemospace and some are spread out, where chemospace is a map of all the features in the dataset. It's like facespace, made of thousands of faces and mapping all the features against each other; eventually you will find the "eignenface" right smack in the middle of the map. These are both examples of an n-dimensional information space, where n is the number of features listed in the dataset. If your understanding of dimensionality stops at the common physical world of three-, then you will need to stretch for this one.

 

Mice then get exposed to each of these "odors" while their neural activity is observed using multiphoton microscopy. They found that low-diversity molecule-groups, ones that were very similar to each other in their chemical characteristics, were associated with clustered neuron patterns. For the inverse, an odor made of very different chemicals would excite neurons all over the place (chemospace x neuronspace). They also found that in general, certain chemical features could be matched with recognizable neuron activity patterns.

 

This sounds as if there is some universal olfactory attributes in the chemical compendium.

 

BUT, they also found that if they repeatedly presented the mice with any two chemicals paired together, then the corresponding neural patterns would become more strongly correlated, and despite how different those two chemicals were.

 

"The brain can rearrange itself."

 

And again, and in other words, olfaction is confusing:

 

"Part of the reason why things like lemon and lime smell alike, he added, is likely because animals of the same species have similar genomes and therefore similarities in smell perception. But each individual has personalized perceptions as well.

 

"The plasticity of the cortex may help explain why smell is on one hand invariant between individuals, and yet customizable depending on our unique experiences."

-Sandeep Robert Datta, associate professor of neurobiology in the Blavatnik Institute at HMS

 

(He also says the phrase "virtual olfactory world" in reference to a future that sounds very exciting, although still very far away.)

 

There's another study here which looks pretty similar. They offer a reiteration of this new explanation for how smells are perceived, and it sounds like this -- we all share a similar smell-space due to our shared genome. This is manifest in the olfactory bulb, and in the way that it codes individual odor molecules based on their physical and chemical properties.

 

They ask "Can distant odours be grouped together if their context is learned to be the same?" And that answer, because of studies like these, is becoming clearer by the day -- yes.

 

In fact, this is the basis of how olfaction works, why it works, and what it's supposed to be doing for us. The common association between chemical properties and neural activity is just a given. It's in that second layer, and over the course of a lifetime of being exposed to different combinations of chemicals, that our brain generates the end results, olfactory perception, which by its nature must be subjective, and because of the transient, vacillating and boundless parameter space of our ontogenetic chemical exposome. (Chemosome?) They call this pairing of chemical milieu and existential moment an odor "contingency," and they say these contingencies are what rewrite the higher olfactive network space.

 

Random fact: "The mouse initiates the trial by touching the lickometer." Yes, the lickometer.

 

Both of these are true; Yes there is a static, predetermined program that senses chemicals in the air in mostly the same way for all people (excepting genetic variation, which can be up to 30%). But there is another network layer found in the olfactory cortex where we all diverge from each other, and this next layer is based on our autobiography, for lack of a better word. Who we are and the decisions we make are changing this second layer with every new encounter.

 

Back to the study, their statement "Our results indicate that representations of categories emerge dynamically by mitral cells in a way that fits not only task demands but also categorical logic" is another way of saying that we can train our nosebrain to interpret any smell in any way we want. And again, "Once learned, these tasks allowed us to assign the same odour stimuli to different category schemes. If mitral cells activity reflect the learning rules, odour representations would change in a way that follows categorical information."

 

The point here is that our olfactory perception network is constantly changing, and that's why it's so hard to pin it down. And that's what it's supposed to do -- it's supposed to help us respond to our environment; but our environment is constantly changing. Society and culture, for example, can cause major shifts in both the chemical soup that surrounds us and in the way we semi-autonomously assign meaning to odor objects. See mint and analgesics in the postwar population of England, or licorice for the same age group, or the smell of "new car" in the East vs West.

 

Body odor, and especially the odor of others who do not eat the same food as you, or follow the same culturally inculcated hygiene rituals as you, will definitely smell "foreign" to you. Until you become more acquainted, of course, at which point it slowly becomes part of your identity also. You do not begin to smell that way, but because your olfactory translation machine no longer flags a smell as "foreign" if it's been around your neighborhood for the past ten years, or if it's been in your own bed for example. The brain can rearrange itself. 

 

So, smells are both objective and subjective. There is a common denominator to the perception of odor molecules, but depending on the infinite variations of exposure that accumulate over a lifetime, that common denominator is shredded, stretched, skewed and refit to match your personal experience in the olfactory multiverse.

 

And so to answer an age old question in olfactory research -- "Do odors have their own universal identity, or is our nosebrain a blank slate?" -- the answer is, "Yes."

 

 

Notes:

Study 1 - Harvard Medical School

Stan L. Pashkovski et al, Structure and flexibility in cortical representations of odor space, Nature (2020). DOI: 10.1038/s41586-020-2451-1

http://dx.doi.org/10.1038/s41586-020-2451-1

[alt link]

https://www.newsbreak.com/news/1593236184136/structure-and-flexibility-in-cortical-representations-of-odour-space

 

Abstract: The cortex organizes sensory information to enable discrimination and generalization1,2,3,4. As systematic representations of chemical odour space have not yet been described in the olfactory cortex, it remains unclear how odour relationships are encoded to place chemically distinct but similar odours, such as lemon and orange, into perceptual categories, such as citrus5,6,7. Here, by combining chemoinformatics and multiphoton imaging in the mouse, we show that both the piriform cortex and its sensory inputs from the olfactory bulb represent chemical odour relationships through correlated patterns of activity. However, cortical odour codes differ from those in the bulb: cortex more strongly clusters together representations for related odours, selectively rewrites pairwise odour relationships, and better matches odour perception. The bulb-to-cortex transformation depends on the associative network originating within the piriform cortex, and can be reshaped by passive odour experience. Thus, cortex actively builds a structured representation of chemical odour space that highlights odour relationships; this representation is similar across individuals but remains plastic, suggesting a means through which the olfactory system can assign related odour cues to common and yet personalized percepts.

 

Study 2 - Hebrew University

Flexible Representations of Odour Categories in the Mouse Olfactory Bulb. Elena Kudryavitskaya, Eran Marom, David Pash, Adi Mizrahi. Hebrew University of Jerusalem. Mar 24 2020. BioRxiv. doi: https://doi.org/10.1101/2020.03.21.002006

https://www.biorxiv.org/content/10.1101/2020.03.21.002006v1.article-info

 

Summary: The ability to group sensory stimuli into categories is crucial for efficient interaction with a rich and ever-changing environment. In olfaction, basic features of categorical representation of odours were observed as early as in the olfactory bulb (OB). Categorical representation was described in mitral cells (MCs) as sudden transitions in responses to odours that were morphed along a continuum. However, it remains unclear to what extent such response dynamics actually reflects perceptual categories and decisions therein. Here, we tested the role of learning on category formation in the mouse OB, using in vivo two-photon calcium imaging and behaviour. We imaged MCs responses in naïve mice and in awake behaving mice as they learned two tasks with different classification logic. In one task, a 1-decision boundary task, animals learned to classify odour mixtures based on the dominant compound in the mixtures. As expected, categorical representation of close by odours, which was evident already in naïve animals, further increased following learning. In a second task, a multi-decision boundary task, animals learned to classify odours independent of their chemical similarity. BBBBBB Rather, odour discrimination was based on the meaning ascribed to them (either rewarding or not). Following the second task, odour representations by MCs reorganized according to the odour value in the new category. This functional reorganization was also reflected as a shift from predominantly excitatory odour responses to predominantly inhibitory odour responses. BBBBBB Our data shows that odour representations by MCs is flexible, shaped by task demands, and carry category-related information.

*In comparison to the above Harvard paper, for "mitral cells," read olfacotry bulb, and for "two-photon calcium imaging," read multiphoton microscopy.

 

 

Post Script:

Back to the "first layer" mentioned in the above studies, I need to mention what sounds to me like intensity being a big part of the universal "odor coder." It is certainly one of the chemical features in the corresponding dataset; odors tend to present to us in a known window of intensity, and each molecule has a detection threshold for humans measured in parts per million, billion or trillion. I'm not certain this is what's being implied and surely there's more complicated exclusions to it, but even prior research shows that intensity of an odor is a shortcut through a lot of these categorization and dimension-reduction attempts.

 

Next, this is nuts; pretty sure I've never seen this before -- "The general profile of excitatory vs. inhibitory responses by mitral cells changed with learning and task demands. In naive animals, most responsive cells (71%) responded by excitation to the odours (Fig. 6A,B). Following the learning of the 5-decision boundary task, the ratio of excitatory/inhibitory responses reversed. After learning, the majority (71.4%) of neurons now responded by inhibitory calcium transients to the odours (Fig. 6C,E). The ratio of inhibitory vs. excitatory responses reverted back to normal after retraining the mice on the 1-decision boundary task. Specifically, 73.3% of responsive neurons were again excitatory on day 18 (Fig. 6D,E). (The Hebrew U study)

 

So the "second layer," the one that adds the personal, subjective meaning to your odors, is all inhibition. It's dampening the neurons that were originally excited by this odor and based on universal chemical-genetic affinities, but now have to be quieted based on prior outcomes of interactions with it. It doesn't dampen everything, obviously, or else you wouldn't smell it at all (you mean like violets?), but it dampens enough that the overall pattern of the signal that finally does make it through can be dramatically different. You're literally evolving with every breath you take.

 

 

Compulsory Reference to the Greatest Work of Olfactory Philosophy Ever:

Hosek R J & Freeman W J (2001). Osmetic Ontogenesis, or Olfaction Becomes You: The Neurodynamic, Intentional Self and Its Affinities with the Foucaultian/Butlerian Subject. Configurations 9: 509–541.

The Rumpelstiltskin Principle

As the 4,000 year old tale tells, once you have a name for something, you have power over it.

-wiki

This is a generally recognized principle in psychology, and has some implication for our relationship with smell, a sense for which the stimulus we often fail to call by name.

People Smell

I am not a mouthbreather

Smell is a symbol for confusion and fantasy, from the time when the world was different. Yet it remains among us in a way that has not changed much in hundreds of years, at least not for the general population.

The general population doesn’t interact with smell in the same way as the previous entities. In brief, if the most concise form of knowledge aggregation (science) struggles with smells as distinctive from organic chemistry, one can be certain that the average person will be no less fortunate. Smell, in the everyday sense, does not lend itself to contemplations, and tends to avoid language altogether. People do not talk about smells themselves – they may talk about what they mean, or where they came from, but they do not talk about the smell itself.

People do not converse about the constituents of an odor – in the vast majority of cases, a smell would be referred to as a source, not as a molecular profile of potentially interchangeable parts. Beyond that, people do not notice most smells in the first place. Olfaction operates automatically, actively de-noising and investigating every one of the myriad odorants surrounding our fluid vaporsphere, and yet, we rarely notice.

Furthermore, the process of olfaction as a perception is so riddled with byzantine circuits that it leaves itself highly susceptible to cognitive override and subjective distortion. By the time a smell makes it to a person’s conscious awareness, it is far-removed from its universal essence (although some might suggest that such a thing doesn’t exist in the first place).

Smell is, after all, the animal inside us, and so being, spends very little time in the realm of collective discourse (and in spite of enervating our emotional lives to the maximum). It is somewhat of an overstatement, but not by much, if at all, to say that the general population barely knows what smell is, or how it works, and any discussion on the topic proper shifts immediately to its effects on memory and emotions, leaving the objective analysis of odorants a fallow field.

[x] In fact, Don Wilson and Richard Stevenson in their book, Learning to Smell (2006), make the case for human olfaction as a purely learned phenomenon, thus maintaining that universality in smells cannot exist.

Multimodal Crosstalk

Make it stop.

Got an article here in Wired where we learn about how we taste, and about how we sense everything, really. The brain doesn’t see sensory information as sense-specific, it processes everything together. In the article, psychologist Charles Spence relates it to signal processing – the brain has to process all the signals to figure out what’s good and what’s not. And what we get back is not raw sensory input; instead all the signals interfere with each other, distorting and reshaping each other. Changing the color of white wine to red makes people “taste” red wine. Changing the lights in a room makes you “hear” differently. Senses even distort themselves. White noise makes other noises seem further away; it distorts the aural space of the listener (see Beckerman below).

I bring up all of this because, why, our sense of smell is the most obvious candidate for proving the multi-modal sensory processing of our brains. Smells can be Sharp, Sour, or Green. In fact, smell is one sense that we do not experience as its own. All of the words we use to describe smells come from other senses; and it can be argued that we only experience smell by proxy of the other senses. Perhaps it is too primitive of a phenomenon to translate to the cognizant, self-reflective human – it is the first sense, after all, and made its appearance on the Tree of Life with the Vertebrates, and hence with brains (the two go together).

Lost in Translation

Notes:

Your Senses Are Talking Behind Your Back

Brendan Cole, Wired, July 2016

Professor Charles Spence, at Oxford, studies applied cognitive psychology, consumer psychology, sensory marketing, and multisensory perception. And that would make him a man of interest here at Limbic Signal. He also deals a lot with the future of food.

The Sonic Boom: How Sound Transforms the Way We Think, Feel, and Buy. Joel Beckerman. 2014.