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We have perfected recording technology for both sounds and images but are still in the stone age when it comes to recording other types of sense perceptions. The sense of smell is probably the third one most of us would want to be able to record after sights and sounds. However, there have been and still are very limited attempts to make this a reality. What obstacles could be keeping this still mostly science-fictious technology from becoming realized and can we contribute to making it happen?
The importance of it: The sense of smell has been romanticized and given great importance in relation to human memory and emotions in famous literary works, such as In Search of The Lost Time by Marcel Proust and Perfume: The Story of a Murderer by Patrick Süskind. But those ideas have not only fictional/experiential but also scientific basis [1,2].This is mostly due to the neuroanatomy of smell perception, namely the olfactory bulb and its relations with the limbic system. This link between memory, emotions, and smell perception makes this sense very important for generating and re-creating meaningful human experiences. This perception is already a sort of trigger for replaying your internal emotional "records", therefore being able to record and replay various scents on demand would contribute to this even more, raising experiential capabilities to another level.
The technology: There are two approaches towards realizing this kind of technology - electrical and chemical. Chemical works by simply analyzing the original molecular composition of a particular scent and trying to recreate it afterwards. The sense of smell in this case is triggered by aromatic molecules, while in the electrical approach it's triggered by electrostimulation of either the scent receptors or parts of the CNS responsible for olfactory perception. Chemical is the one that's usually tried, but there have been attempts to apply the electrical approach also.This Wikipedia article lists the inventions of scent capture and re-creation technology in chronological order.
Electrical approach, if perfected, would be convenient for generating different smells at a fast rate, making it suitable for incorporating into virtual reality gear and similar devices. However, apart from the difficulty to generate smell perception in humans this way, another big problem, at least for the primary stages of its development, is that nobody is prone to sticking electrodes up their nostrils, let alone in their brain. Therefore this approach, just like Neuralink, would be, at least in the beginning, more suitable for restoring the sense of smell in people who have its loss or dysfunction.
Chemical approach is more natural and might work better than electrical, but it has its own complications. Making a record in this case might be easier than replaying it. The former would just need some chromatography-based analysis and then the data about molecular composition could be stored digitally, but in the replaying part, to cover a large enough spectrum of smells the technology would have to synthesize "on the go" or have a pre-available palette of huge numbers of already synthesized molecules and use separate compounds for generating separate smells or make mixtures. In 2006, a prototype created by Japanese scientists only had 96 base compounds to mix and produce various smells, which is far from enough to cover the spectrum. Natural smells might be difficult to re-create because they are often made of many shades of different aromatic compounds. On the other hand, some artificial smells that are put into food or household products are sufficiently reminiscent of natural ones. Natural molecules could also be used in cases where they are not too complicated or expensive to extract, store, etc.
Another complication with the chemical approach in contrast with the electrical one is that molecules of aromatic compounds are present in the air for quite some time after they are released and this would be a problem if the user wanted to perceive many different scents in a rather short time. So an air refreshing function might be necessary, cleaning the air of odors and then releasing new ones. A gradual transition could also be an option to make the experience seem more natural. Also, the smell of the ambient air in which the user is while "listening to the record" should be taken into account. A hermetic camera filled with oxygen or completely odorless air might be used to solve this issue. Depending on what type of situation would be attempted to recreate, the smell producing device could move closer or more away from one's nose. A wearable device might be unpractical or/and unappealing to the user.
But most of those problems with the chemical approach mentioned above are only valid if we want to make a real-time record of changing scents in a changing situation, like a movie or a virtual reality setting or/and want to be able to use the technology in a quick and convenient manner. This might have to wait a bit longer, but just as photography was invented before video recording and was a crucial part in the development of the latter, a record of a single scent at a time seems like a logical thing to start with.
But technological problems may not be the only obstacle. Lack of demand or/and interest for this technology could be another major drawback. Not all people are sensitive to smells and not all give importance to them. Do you see it as being valuable and would you like to contribute to making it happen?
Physical differences in receptors indicate greater accuracy of "electrical approach"
jnikolaDec 04, 2020
Since I was a kid, I was asking everybody how do they see colors. For example, I would ask them what color is the ball I am holding right now and everyone said blue. But I wasn't really convinced that they see the same blue. What if they see it red, but while learning color names, they learned that their red ball is called blue. They will never make a mistake, because all the "red" things they see, they call them "blue". How they really see it, the color that the brain makes by receiving the signals will be the enigma forever. PS It's less likely they see it red, probably just a different blue.
Why am I saying this? Because differences in perception exist in all our senses, including smell.
I surely was surprised by the visual perception differences, but I was literally shocked when I found out that I am the only one smelling the food being a bit too old, or that I am the only one that thinks a certain perfume smells a bit bad. I know people make a memory about the sight or a smell, which greatly influence their later perception of the same or similar odors, but here I want to emphasize the differences on a reception level, which are, I guess, much more complex in the context of smell, compared to the vision. Why?
Although the perception of the vision is mechanically determined by the physical properties of sticks, cones, and the electrical signal conversion/transmission, perception of the smell relies on more than 400 different types of specialized sensor proteins, followed by yet undetermined electrical conversion and signal procession. A molecule of an odor that entered our nose can trigger several olfactory proteins, which must make it hard for the brain to recognize the patterns of a smell and intensity .
Researchers recently questioned 332 people to rate the intensity and pleasantness of 70 common odors and then sequenced and identified differences in more than 400 olfactory receptor genes. Then they related all the differences found with the odor perception and found out that a single receptor change was enough to affect the individual's perception of an odor. They also found out that less-functional receptor OR11A1 resulted in changes in odor intensity perception of a 2-ethylfenchol .
The impact
What does it mean for the future of a smell recording? If the odors start to be recorded and shared, the differences in the individual reception of the odors could result in a different perception of a smell much more if the technology is based on the chemical approach. Although it feels more natural and works better to use chemicals, electrical impulses could result in higher precision/accuracy by avoiding the physical differences in the receptors of each individual.
[1]C. Trimmer, A. Keller, N. R. Murphy, L. L. Snyder, J. R. Willer, M. H. Nagai, N. Katsanis, L. B. Vosshall, H. Matsunami, J. D. Mainland. Genetic variation across the human olfactory receptor repertoire alters odor perception. Proceedings of the National Academy of Sciences, 2019; 201804106 DOI: 10.1073/pnas.1804106115
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Povilas S4 years ago
Thanks for your contribution and pointing out this issue:) There are few important things to note here. The same smell perceived differently by different people would be an issue to solve in a context when someone would try to transmit a perception of a particular smell to another person to let them know how exactly they perceive it. This is not really what smell recording is about. That’s more of a technologically achieved telepathy you are talking about. There would be differences in perception of recorded smells just like there are differences in naturally perceived smells. Smell recording is about preserving scents so that one could experience them later, just instead of using solvents and other chemical means, the technology would be more sophisticated and could be used in a more quick and convenient manner. Just like you’d pluck petals of a particular species of wild rose and dry them or make rose water in order to preserve the fragrance and later give it for your friend to smell. It wouldn’t mean that your friend and you would perceive the smell in the same manner, but that’s not what this is about. Different people might perceive colors of the same picture differently, but photo technology is about making pictures, not letting people perceive them in the same way.
Also, electrical approach might seem more precise and subjectivity-removing at first, but when you think about it better, it’s actually even more complicated. In order to achieve precision, you’d have to stimulate each of hundreds of receptors individually and maybe even more than that, because I believe the same receptor might send different bioelectrical signals. That is very hard to achieve technologically. Of course, it’s not that precision with the chemical approach is easy to achieve, but in the case of electrical approach, you’d have to do a double job, because you’d have to correlate the electrical signals with particular smells and therefore with particular chemicals because those are what activates the receptors in the natural process. I mean how would you achieve the correlation between particular smells and particular electrical signals otherwise? By trying random impulses and questioning what the person is perceiving? The latter would be super abstract and subjective. To record the smell, chemical molecules would have to be involved anyway and then they’d have to be somehow correlated with the signals, by building a large database perhaps. So subjectivity that was present in the chemical approach would stay, I mean I don’t see how electrical approach bypasses it.
As I said, what you’re talking about seems more to me like the transfer of subjective perception (which was already processed by CNS) to another person, which would be a cool thing to have, no doubt, but that’s a bit of a separate topic and a separate technology.
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jnikola4 years ago
Povilas S I understand what you are talking about and I agree that the problem I was pointing out is about perception, but there is a reason for it. Although it is not the topic of the discussion, I will use visual perception as a tool to explain my flow of thoughts.
The general opinion and the main problem in visual perception is that what we see is not simply a mechanically translated retinal stimuli. I think that it could be the same with smell. When the light enters the eye, the photosensitive retinal cells receive and transduce the signal to retinal ganglion cells, and further to optic nerves and the visual cortex of the occipital lobe. That means that before any neural processing of the image (cross-talk between emotions, memories, visual cortex, and others), which I think you consider as perception, there are multiple layers where small differences in chemical or later, electrical signals can cause differences. Although it is not so well investigated as the vision, the smell could function in a similar way. And exactly because it is not explored enough, I just supposed these small differences in signal transduction could play a significant role in personal smell perception. and be diminished by using the electrical approach.
So, what I think about are some lower levels of perception, which could actually be called signal processing, not perception. By using the term "perception", I could cause a misunderstanding and I´m sorry about that.
On the other part, I completely agree the electrical approach is much more difficult in terms of receptor stimulation. What I thought about skipping by using the electrical approach was exactly that small step from the stimulus reception to conversion into an electrical signal, that could eliminate some variabilities. It doesn´t necessarily need to be measured in the nose, but anywhere in the olfactory signal transduction system (e.g. olfactory nerve). It would definitely require the development of a method to measure the electric signal after the chemical signal reception and conversion, which is the biggest challenge. It would also require a correlation of electrical patterns with certain molecules/chemicals, in addition to the molecules-smells correlations needed for both approaches. Let´s hope science can solve that soon.
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List of odorless materials to build the equipment
Shubhankar KulkarniDec 15, 2020
Most materials have some kind of smell - even plastic, iron, steel, glass, and other inert materials. When you use any of these materials to build the smell-recording equipment, the smell of these materials itself might get trapped in the system. Any smell you record will be tainted with the smell of the equipment material. We, therefore, need to have a list of materials that do not smell/ release any kind of odor.
Moreover, the material should be such that no odor molecules attach to it. That might again ruin the smells that you want to preserve/ record.
If you know any such material that does not release odor, mention it in the comments here with links to supporting studies.
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Povilas S4 years ago
Good point. All materials are evaporating at a higher or lower rate, but to determine which ones "don't smell" I think we have to consider the biology of smell perception, namely the smell receptors, some materials, even if they are in the vaporized form won't react with the receptors, therefore, they won't produce smell perception.
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Shubhankar Kulkarni4 years ago
Povilas S Right. I am assuming all natural smells will stimulate the receptors since humans were in contact with them at some point during the evolution. My best guess would be some synthetic material. But like I mentioned in the suggestion, I could not think of any synthetic material that does not have a smell.
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Povilas S4 years ago
Shubhankar Kulkarni I think many materials that we might associate with some smell are actually not triggering the perception themselves, it's rather some other, mostly organic materials that accumulate on the surface of those primary materials. It could be products of oxidation processes or the metabolites of microorganisms, etc. The most smell-inert material I can think of is glass. If it smells then I can't tell how. Maybe a powdered glass would smell, that's likely, but we barely encounter it in that form and it would also be dangerous to inhale. But ordinary glass surfaces, if they smell of something then I think it's because of something that's gathered on the surface. And this might also be true with metals, they seem to smell but this might be because of metals being reducing agents and reacting with air to form oxides. Unless we know what molecules trigger the receptors we can't say what we smell.
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Photochrom equivalent for smells
Povilas SDec 04, 2020
This project by an English designer done as her MA work is a feasible and elegant way for approaching the realization of a simple scent record-making and re-creation. The "recording" part is based on a headspace technology, that consists of an air-sucking device which then passes the air with captured aromatic molecules through an absorbing material. And for the analysis and re-creation, you need a lab to bring the sample to. Just like you needed a lab for photochromic pictures to make them. The problem with this is that no existing labs would be very prone to making an analysis, let alone the recreation of a molecular sample for a random person unless you'd pay them enough money, which will obviously not be worth it. But if the infrastructure for the technology got well established and this would become a common thing with many people using it, already existing labs could make separate sections for this and generate additional income or specific labs for just that purpose (like photochrom shops) could get established. A record re-creation process could also become much more swift this way.
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Scent preservation as scent recording
Povilas SDec 04, 2020
Even in the single "scentographic" record scenario, the re-creation process might be too complicated. Imagine you've done the analysis and have the molecular composition stating percentages of different compounds of the scent you want to re-create. You'd have to get those compounds one way or another and mix them in respective quantities. To be able to recreate a wide variety of scents you'd have to have a huge number of compounds, which might not be feasible to achieve. What if instead efforts would be put in better preserving the original scent so that the sample itself could serve as a record?
The main problem with this is that the concentrations of the aromatic compounds collected from the air around a certain object or even more so in the case of collecting fragrant atmospheric air are very small. But they could be increased by prolonging the time in which the air is sucked, the intensity of the airflow, the sensitivity of the absorbing substrate, etc. This might not work in all situations, but, for example, when the scent of a summer night in the meadow full of wildflowers is aimed to be preserved, the air sucking machine could be left outside for a few hours and the yield on an absorbing substrate could be sufficient to recreate the experience if preserved and smelled later.
The absorbing substrate should probably be thin and have a large surface area to collect greater amount of volatile compounds and then the aromatic molecules could be detached from the substrate (by heating, washing, etc.) and made into a concentrate or forced into a smaller area on the same collecting substrate and then preserved in a proper way by whatever conditions necessary. To increase the smell sensitivity, before smelling the preserved sample, the person and/or the environment could be specially prepared. A camera filled with odorless air could work for that. Scent perception sensitivity can be increased just like any other sense - by depriving of triggers for some time. So sitting in such a camera or wearing a mask and breathing the air from a special container for some time before introducing the smell of the sample might work.
Povilas S Dec 04, 2020
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