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"Quantum biology: Do weird physics effects abound in nature?"
January 28, 2013 4:05 AM   Subscribe

Quantum Biology - Disappearing in one place and reappearing in another. Being in two places at once. Communicating information seemingly faster than the speed of light. This kind of weird behaviour is commonplace in dark, still laboratories studying the branch of physics called quantum mechanics, but what might it have to do with fresh flowers, migrating birds, and the smell of rotten eggs? More: Quantum smell' idea gains ground Both BBC.
posted by marienbad (59 comments total) 18 users marked this as a favorite

 
"...Prof Vosshall believes the vibrational theory to be no more than fanciful. I like to think of the vibration theory of olfaction and its proponents as unicorns. The rest of us studying olfaction are horses," she told BBC News. "The problem is that proving that a unicorn exists or does not exist is impossible. This debate on the vibration theory or the existence of unicorns will never end, but the very important underlying question of why things smell the way they do will continue to be answered by the horses among us."

That is the theory that I have, and which is mine, and what it is too.
posted by three blind mice at 4:17 AM on January 28, 2013 [5 favorites]


This is covered briefly in this ask-recommended textbook where they talk about valence shells and covalent bonding and how all the electrons cold be on the "other side" of the nucleus due to quantum probablility. It made me wonder if there were other quantum effects in nature - DNA replication and in the early evolutionary days (the swamp of proteins stuff), and viola! teh beeb is on it!
posted by marienbad at 4:19 AM on January 28, 2013


The "quantum smell" idea is probably right. The older idea of olfactory recognition is pretty ridiculous, when you think of it, relying as it does on the assumption that molecular configurations are structural "keys" that just happen to fit into "locks" we all happen to have up our noses.

Smell is at least as subtle as sound, and we already accept vibrational models when we talk about sound. Fourier analysis is appropriate for sound, why not for smell?

Luca Turin is some kind of popular exponent of this. That man has an uncanny sense of smell, as anyone who has read The Emperor of Scent, or his previous appearances at Metafilter, (1, 2, 3, etc.) nose.
posted by twoleftfeet at 4:21 AM on January 28, 2013 [4 favorites]


Axiom one: unicorns exist

QED
posted by thelonius at 4:21 AM on January 28, 2013


Smell is at least as subtle as sound...

Piffle. Let me know when there is a literal language for smell and we'll talk. Using sound.
posted by DU at 4:23 AM on January 28, 2013 [4 favorites]


Piffle. Let me know when there is a literal language for smell and we'll talk. Using sound.

We're unable to emit smells where we can control the intensity and nuance. (Except that one uncle who wants you to pull his finger.)

Smell is more responsible for flavor than your tongue, especially subtle and nuanced tastes.
posted by Slap*Happy at 4:30 AM on January 28, 2013 [2 favorites]


Let me know when there is a literal language for smell and we'll talk. Using sound.

Let's have dinner. I'll cook up a wonderful meal. You can enjoy the sound of it (sizzling, crackling, crunching), but I'm going to enjoy the taste. It may not be a literal language, but you'll know good food when you taste it.
posted by twoleftfeet at 4:31 AM on January 28, 2013 [1 favorite]


My feeling is that it would be weird if quantumn effects didn't abound in nature. Living organisms are constantly pumping protons across membranes (or using a flow of protons to drive molecular machines), shuttling electrons around the place, breaking chemical bonds and extracting energy with remarkably high efficiency, distinguishing between near-identical molecules, etc. Any effect that reliably affects the interactions underlying these processes will be exploited; the evolutionary pressures acting on such fundamental biological functions are too strong for any potential advantage to be left untapped.

Evolution is, to borrow a phrase, too stupid to get confused. It doesn't matter that these things seem complex, couter-intuitive and exotic to us, because there's no mind at work here, just dumb chance in which every possible configuration is pitted against the rest. Our opinion of how difficult it is to understand a particular facet of the universe makes no difference to how that facet functions, or how things that we (think we) do understand interact with it.

Being surprised that complex and difficult-to-study effects are important seems a bit like the drunk guy being surprised that his dropped keys are in the dark gutter, rather than under the pavement where he'd chosen to search because of the better light.

...of course, all this bloviating is just to take my mind off the day when quacks get hold of this paper and use it in defense of the already bizarrely common "quantumn vibrations" in their marketing copy. Because on that day, I fear I won't be able to stop myself from face-palming hard enough to shatter the back of my skull.
posted by metaBugs at 4:50 AM on January 28, 2013 [29 favorites]


Smell is at least as subtle as sound, and we already accept vibrational models when we talk about sound. Fourier analysis is appropriate for sound, why not for smell?


Well, that's a different scale of vibration, you understand, right? We're not talking about air waves as in sound, we're talking about something closer in scale to light waves.

I'm sure there are tons of quantum effects in biology. If there is an efficiency to be gained, its almost certain that life has figured out how to use it somewhere.
posted by empath at 4:51 AM on January 28, 2013 [1 favorite]


It may not be a literal language, but you'll know good food when you taste it.

In other words, while a good medium for enjoying food, not nearly as subtle as sound.
posted by DU at 4:57 AM on January 28, 2013


I don't think 'subtlety' has anything to do with whether you can use it for language or not. Language is in the brain, not the ear, as many deaf people can attest.

In any case, explain to me in words the smell of fresh earth after rain.
posted by empath at 5:03 AM on January 28, 2013 [1 favorite]


Most of what the mysteries of smell and the mysteries of how biological systems may or may not take advantage of quantum effects have in common is that they are both mysterious. This does not make a awfully defensible theoretical model. However, there are conflicting reports in the literature about how various model organisms from fruitflies to fish to humans may or may not be able to distinguish between chemically identical compounds that are isotopically distinct by smell. If this is actually the case, then whatever is going on must have at least some quantum component.

Here is the actual paper:
Molecular Vibration-Sensing Component in Human Olfaction
Whether olfaction recognizes odorants by their shape, their molecular vibrations, or both remains an open and controversial question. A convenient way to address it is to test for odor character differences between deuterated and undeuterated odorant isotopomers, since these have identical ground-state conformations but different vibrational modes. In a previous paper (Franco et al. (2011) Proc Natl Acad Sci USA 108:9, 3797-802) we showed that fruit flies can recognize the presence of deuterium in odorants by a vibrational mechanism. Here we address the question of whether humans too can distinguish deuterated and undeuterated odorants. A previous report (Keller and Vosshall (2004) Nat Neurosci 7:4, 337-8) indicated that naive subjects are incapable of distinguishing acetophenone and d-8 acetophenone. Here we confirm and extend those results to trained subjects and gas-chromatography [GC]-pure odorants. However, we also show that subjects easily distinguish deuterated and undeuterated musk odorants purified to GC-pure standard. These results are consistent with a vibrational component in human olfaction.
Most of reasons this model would seem attractive to laypeople are pretty foolish when you have a sense of the tools that our cells would need to be using. Smell is detected using proteins in the G-protein coupled receptor superfamily, which are bianry detectors, on or off - and this would work roughly the same way whether it was detecting purely chemical aspects or something more also. For context here is a critical response to the last paper to get everyone's underwear in a twist:
Olfaction is a chemical sense, not a spectral sense
Franco et al. (1) argued that molecular vibrations contribute to odor detection by Drosophila. They claimed that deuterated odorants have a unique C-D stretch vibration that produces a “deuterium odor character” independent of the “structure and chemical properties of the odorant molecules.” The discrimination of normal and deuterated odorants by flies is a clear and convincing finding, but such isotope effects do not prove that the animals are sensing infrared molecular vibrations using inelastic electron tunneling spectroscopy (IETS) (2).

The ability of humans to discriminate isotopes by smell is not as great as has been suggested (2). One study found no discrimination between normal and deuterated acetophenone (3). Hydrogen and deuterium compounds generally have very similar odors even when they can be distinguished. Notably missing from the Franco et al. article (1) are descriptions of the odors of the compounds in humans.

The vibration theory seems to be based in part on the idea that olfaction functions like “the other spectral senses, vision and hearing” (2). However, there is no continuous odor dimension that would be needed for a truly spectral system. The IETS mechanism (2) has not been observed in any biological system. NADPH cannot generate free electrons as proposed in the model.

The hypothesized correlation between odor similarity and spectral similarity fails in two ways. First, odors can be very different even when infrared spectra are very similar. The infrared spectrum of civetone, a macrocyclic ketone with a musk odor, is practically identical to that of its odorless acyclic analog (4). Odor differences in optical isomers with identical infrared spectra also do not support the vibration theory.

Second, odors can be very similar even when spectra are very different. In the case of isotope substitution reported in the Franco et al. article (1), the great difference between C-H and C-D infrared stretch vibrations (3,000 vs. 2,200 cm−1) would be equivalent to half the entire spectral range in human vision or half an octave in hearing, extremely easy discriminations compared with isotope discriminations by odor. Isotope substitution does not lead to large chemical or odor differences despite large frequency differences. An attempt to establish a quantitative relationship between odor similarity and spectral similarity would likely refute the vibration theory of olfaction.

The depiction of the vibration theory as an alternative to “shape” theory or a “lock-and-key” mechanism is misleading. Odor chemistry involves many factors besides shape. Ethanol and ethanethiol may have roughly similar shapes, but chemically they are as different as roses and skunks. Using vibrations to detect isotopes by odor is biochemically irrelevant because animals have no need to make such distinctions. Olfaction is a chemical sense, not a spectral sense. The relation between odor similarity and chemical similarity is evident when one considers not only shape but other concepts like molecular weight, functional groups, polarity, acidity, basicity, and steric interactions. Whether in humans or flies, odorants bind and activate receptors through a combination of chemical features no different from other types of receptor-based molecular signaling in biology (5).
posted by Blasdelb at 5:07 AM on January 28, 2013 [19 favorites]


The distinction between quantum- and non-quantum effects is just a category that we impose: really everything depends on quantum effects. As for the odor thing, I would be very surprised if Turin isn't mostly right. The lock-and-key model of olfaction implies that there are very many different olfactory sensors, with clever wiring that allows us to simultaneously make sharp distinctions between a huge number of smells while simultaneously placing them in associated families - musky, floral, minty and so forth.

We detect color with a very few (three plus one) types of receptors that respond differently to light of different frequencies. If a light activates one group of receptors weakly and another strongly we say that the light is orange (or purple, or whatever) and we can associate it with other, similar shades of light. If we had hundreds of receptors, each of which only responded to its own frequency, would we be able to do this? I think we would just have names for each hue we can recognise, and no general theory of color at all.

Smell is obviously more complex than color, but we do recognise general families of odor, which implies that it isn't true that one smell has one receptor. But once we accept that a particular smell must trigger more than one receptor, or trigger the same receptor differently, we have moved away from the chemical lock-and-key mechanism that lies behind classic odor theory. I'm very glad to see confirmation for Turin's ideas, and I hope this leads to the ultimate demonstration: a scent designed on computer and whose qualities are predicted before it is synthesised.
posted by Joe in Australia at 5:10 AM on January 28, 2013 [2 favorites]


I think smell is far more subtle than sound. Most big animals rely more on smell than sound when making life or death decisions that don't involve immediate reactions. Human beings have lost some of our sensitivity to smell in favor of a sensitivity to sound and vision, but that doesn't mean that smell is less complex. Smell doesn't have the advantage of a direct localizability. You can pinpoint an event communicated by vision or sound ("over there, just behind that tree") but you can't be as accurate with smell. Nonetheless, a sensitivity to smell is probably a better feature to have for organisms that don't have to react to immediate threats. You're probably better smelling a food source from a distance than trying to see or hear it.

I'm told that ants have a very good sense of smell. We know that dogs have a better sense of smell than we do. It makes sense, if your primary need is to gravitate towards food sources.
posted by twoleftfeet at 5:11 AM on January 28, 2013


To be honest, I'm annoyed by all of this, but in large part for non-scientific reasons. This kind of research unfortunately goes a long way towards encouraging the crazies with lines of reasoning like, SCIENTISTS WERE WRONG ABOUT QUANTUM STUFF I DON'T UNDERSTAND IN BIOLOGY! THEREFORE MY HOMEOPATHY/TELEKENESIS/POWER-OF-POSITIVE-THINING-WOO/LASER-REIKII-MASTERY BULLSHIT HAS BEEN PROVEN CORRECT!
posted by Blasdelb at 5:13 AM on January 28, 2013 [10 favorites]


the lock-and-key model of olfaction implies that there are very many different olfactory sensors, with clever wiring that allows us to simultaneously make sharp distinctions between a huge number of smells while simultaneously placing them in associated families - musky, floral, minty and so forth.

There are a great many different olfactory sensors. As much as 3% of the human genome is just for scent receptors.

It's not as simple as a lock and key model, anyway.
posted by empath at 5:13 AM on January 28, 2013 [3 favorites]


Something I didn't know until just recently, the sun works because of quantum tunnelling, which is kind of like the birthday paradox with respect to the number of atoms in the sun combined with the very small chance of the tunneling occurring.
posted by odinsdream at 5:21 AM on January 28, 2013 [1 favorite]


If this is true it gives literal meaning to the metaphor "I smell a rat."

Smell, like gravity, is one of those still enigmatic things with which every person has an intimate, first hand acquaintance, but that science cannot simply or fully fully explain without resorting to the hand-waving magic of quantum mechanics.

I pity the people of the future who will have all the answers.
posted by three blind mice at 5:23 AM on January 28, 2013


See that's the thing. Terribly written articles like this give the impression that quantum mechanics is 'hand-waving magic'. It's not. That's the way the world really is. It's not magic. We can understand it, predict it, manipulate it, make it do what we want. Every time you watch a 3-d movie, you're using technology that depends on quantum mechanics to work. The computer your typing on depends on (or had to be engineered to work around) quantum mechanical effects. The articles you read in the popular press are full of hand-waving, but the actual science is not.

There is no reason that the universe had to be easy to understand, but it is, more or less, understandable. You just need to spend 10 years studying the math, first.
posted by empath at 5:29 AM on January 28, 2013 [7 favorites]


I don't think 'subtlety' has anything to do with whether you can use it for language or not.

Yes and no. You can obviously use a binary system for language and there's not much subtlety there. OTOH, humans can both detect and emit/create smells and yet no language has ever evolved there that I'm aware of. So if by "subtle" we mean "complex enough to carry information from mind to mind" then no, smell is apparently not subtle.

Yes, we can smell cool things like food and rain. If that's what you mean by "subtle" then yes, smell is subtle. I guess we need to define what it means for two things to be "as subtle as" each other. But I bet that definition won't be transmitted via a smell.
posted by DU at 5:33 AM on January 28, 2013


"He's had some peripheral support, but... people don't want to line up behind Luca," Prof Jacob said. "It's scientific suicide."

Columbia University's Richard Axel, whose work on mapping the genes and receptors of our sense of smell garnered the 2004 Nobel prize for physiology, said the kinds of experiments revealed this week would not resolve the debate - only a microscopic look at the receptors in the nose would finally show what is at work.


Look, until someone invents some kind of look-closer-to-things machine that lets us see the little-things-as-big-things, we're never going to figure this out.
posted by odinsdream at 5:34 AM on January 28, 2013 [4 favorites]


If we had hundreds of receptors, each of which only responded to its own frequency, would we be able to do this?

But isn't this how we do sound? My understanding was that the basilar membrane has a continuously varying resonant frequency, with sensors placed along its length, each one devoted specifically to a particular frequency in the audible band.
posted by escabeche at 5:35 AM on January 28, 2013


In one of the parts of Nietzsche that people ignore, where he's raving about how great science is and how you shouldn't even be allowed to study philosophy until you study some chemistry or physics rigorously for a few years, there is a a great passage about how badly philosophy, in its Platonic disdain for the senses, has underestimated the nose.
posted by thelonius at 5:41 AM on January 28, 2013 [5 favorites]


In any case, explain to me in words the smell of fresh earth after rain

So not petrichor then?
posted by Mrs. Pterodactyl at 5:48 AM on January 28, 2013 [4 favorites]


I'm going to keep trying to make the case that smell is more subtle than sound or vision, an argument that can't reasonably be made by the usual logical and diagrammatic tools of sound and vision. So I'll try to make the case that human beings, supreme controllers of sound and vision, are subliminally controlled by smell.

The scientific evidence is well known, involving sweaty t-shirts and mate selection, and it points towards a recognition that we humans, for all our fancy language and image-making skills, are usually just layering activity on top a deeper level communicated through our noses.

You chose your husband or your wife because of their sparkling personality or their sexy body or their wealth or their intellect or their social status or... No! You chose to mate with that person because they smelled right. Potential partners with conflicting genetic profiles subliminally smell bad, and we don't notice that decision because we are sound- and vision-conscious more than smell-conscious. But it is so.
posted by twoleftfeet at 5:52 AM on January 28, 2013 [2 favorites]


Yes, we can smell cool things like food and rain.

Oh I've smelled fire and I've smelled rain
Smelled sunny days that I thought would never end
Smelled lonely times when I could not find a friend
But I always thought that I'd smell you one more time again
posted by saturday_morning at 5:55 AM on January 28, 2013 [1 favorite]


I don't know about smell, but it's certainly believed that quantum effects are involved in mechanisms like photosynthesis.
posted by adrianhon at 6:35 AM on January 28, 2013 [3 favorites]


> Every time you watch a 3-d movie, you're using technology that depends on quantum mechanics to work.

In fact, any time time you see anything at all you are relying on photoisomerization, a quantum mechanical mechanism that enables vision.

In plants and bacteria, networks of photosynthetic pigments permit quantum mechanical energy transfer cascades that are responsible for the robust quantum biology of photosynthesis.

Birds and newts have evolved sensors with QM properties that enable them to "see" magnetic fields.

Quantum sensing abounds in biology. It might not be responsible for the sense of smell (Blasdelb's comment is a pretty strong counterargument), but quantum effects, in and of themselves, are not an unusual component of biophysical mechanisms.
posted by Westringia F. at 6:36 AM on January 28, 2013 [6 favorites]


Blasdelb has already gone into this in quite a lot of detail, but I would like to mention that there is a vast body of empirical evidence supporting the "shape" theory of olfaction and we actually know a great deal about the chemistry of olfactory receptors and the ways in which scent chemicalw can create conformational changes in the membranes of the sensor neurons in which they are embedded, thus opening the sodium channels of those neurons and causing them to fire.

The basic mechanism is pretty well understood, remarkably comprehensible by the standards of molecular bio (although the "lock and key" metaphor is a little misleading, and it is important to remember that it is only a mechanical analogy for an electrochemical reality) and backed up by a heck of a lot of empirical support at just about every step of the process.

There are many things in biology that are poorly understood, including some things about smell, though my impression is that those things are mostly on the central processing end rather than the detection end. As far as the mechanism by which chemoreceptors (olfaction neurons) operate, we really do have a nice, well-supported model that is as complete and as clean as anything ever is in molecular biology these days. There is not a great deal of actual debate in the scientific community here, to my knowledge.
posted by Scientist at 6:45 AM on January 28, 2013 [4 favorites]


A very cool subject. here is an absolutely fantastic lecture that reviews a few case studies in (possible) quantum biological effects, including smell. The discussion on photosynthesis is one of the coolest things I know.
posted by Buckt at 6:48 AM on January 28, 2013 [3 favorites]


But... but... "Woo!"

Either way, I think it's fascinating how the backlash against woolly-headed nonsense so often makes it hard to discuss the actual science.
posted by saulgoodman at 6:48 AM on January 28, 2013


pretty sure this is just demons.
posted by elizardbits at 6:58 AM on January 28, 2013


All I know is that I love Daniel Dennett's comparison of our sense of smell to our vision: he says that, were our vision to be as inaccurate as our sense of smell, every time a bird flew across the sky we might describe the sky as having "gone all birdy" for a moment. Oh but sorry, yeah, no science to add to this discussion. Carry on.
posted by Mooseli at 7:05 AM on January 28, 2013


OTOH, humans can both detect and emit/create smells and yet no language has ever evolved there that I'm aware of.

White lily and white lilac look nearly identical, but have different meanings in the Victorian language of flowers.

I guess we need to define what it means for two things to be "as subtle as" each other. But I bet that definition won't be transmitted via a smell.

The dig at the end only makes sense if you still believe your definition of subtlety to be correct. Don't be coy.
posted by LogicalDash at 7:11 AM on January 28, 2013


LASER-REIKII-MASTERY is the name of my new five-piece John Cage cover band. Sure, we only play 4:33, but homeopathic theory guarantees that even this greatly attenuated dose of Cage's work will produce the full effect in the audience of his entire repertoire.
posted by b1tr0t at 7:27 AM on January 28, 2013 [6 favorites]


Sure, we only play 4:33

No comment.
posted by twoleftfeet at 8:17 AM on January 28, 2013


So, to summarize the consensus of this thread, smell is too quantized for quantum.
posted by Buckt at 8:21 AM on January 28, 2013 [1 favorite]


In any case, explain to me in words the smell of fresh earth after rain.

Mostly, geosmin.
posted by en forme de poire at 8:25 AM on January 28, 2013 [1 favorite]


Also this statement from the beginning of the first article, "It is still a tentative, even speculative discipline, but what scientists are learning from it might just spark revolutions in the development of new drugs, computers and perfumes - or even help in the fight against cancer," pretty much showcases everything that is wrong with science reporting these days, in my opinion.

QUANTUM SMELL CURES CANCER, NEWS AT ELEVEN!
posted by Scientist at 8:50 AM on January 28, 2013 [1 favorite]


were our vision to be as inaccurate as our sense of smell,

Innacurate, or subtle?

If smell conveys more information than vision, one would almost expect it to deliver more ambiguous/nuanced (and therefor harder to interpret and easily summarize) results.
posted by saulgoodman at 9:05 AM on January 28, 2013


Also, it's fascinating how every single discussion of a scientific subject is now absolutely dominated by discussion of the sorry state of science journalism--particularly when an emerging scientific view seems to challenge or otherwise modify previously established models or assumptions.

We haven't had a new scientific discovery that managed to make it through the media gauntlet and become firmly settled in the public consciousness as a new consensus view in something like 30 years, I suspect.
posted by saulgoodman at 9:10 AM on January 28, 2013


It occurs to me that the lock-and-key metaphor might make more sense if you think of it something like this:

The membrane of the neuron is a wall. There are doors in the wall (sodium channels) but they are all closed and locked with magnetic bolts. All the locks are the same, but there are many doors. On the outside of the wall there is a crowd of clamoring people (sodium ions) and they are pushing against the doors but can't get through. They are there all the time, whether the chemical is present or not.

The when the scent chemical arrives, it is carrying a magnetic key. This key not only is of the right shape to fit into the lock in one door, but also has the right magnetic field to allow it to physically pull aside the bolts that are keeping the door closed. When the bolts are pulled aside, the crowd of people begins to rush through the doorway (which quickly shuts and re-locks itself).

If enough doors were unlocked and enough people are able to get through, their clamoring will be heard by an interneuron (I am stopping the analogy here) which will pass the message down to the brain that there is a bunch of shouting going on down at Sensory Neuron 358b(ii) and the brain will interpret this as a particular scent based on basically the ID code of the particular neuron that was firing. It will then "say" something like "Hmm, Sensory Neuron 358b(ii) is associated with beta-methyl mercaptan, which smells awful and is poisonous. If I start getting a lot of messages from that neuron and the other beta-methyl mercaptan sensors, I will probably have to do something about it."

Meanwhile the original sensor neuron is resetting itself, pushing all the clamoring people back outside and relocking the doors and back inside again. This is a little bit more tortuous analogy than just saying "lock and key, man" but I think it helps if one understands more of the overall process.

What is important here is that the scent chemicals are actually chemically binding with the membrane of the sensor in a way that causes the sensor's membrane to change shape and physically pull open nearby sodium channels, allowing sodium ions to re-enter the neuron and depolarize it, signaling an interneuron (via neurotransmitters, which operate between all neurons in your body in a manner nearly identical to that of scent molecules at an olfactory receptor -- another piece of support for the current model of smell) that something is going on at a particular sensor neuron. This then goes to the brain, which interprets it by identifying which sensor or group of sensors was firing, and where the decision to organize a response (if any) is made.

It's a remarkably elegant process by the standards of biochemistry, which is often not nearly so nice about providing a simple and easy-to-follow causality chain. In this case though we really do have most of the steps worked out and are even able to directly observe many parts of the process as they happen. It is not very mysterious and quantum interactions (except inasmuch as all chemistry involves quantum interactions between atoms) don't have to come into it.
posted by Scientist at 9:14 AM on January 28, 2013 [4 favorites]


Also, the whole argument about whether smell is more subtle than hearing or vision is kind of silly, if you ask me. I mean, ask that question of a dog or a shark. Sense is relative, and different animals have very different umwelts and just because smell arguably isn't a huge part of the human sensory world does not mean that it is not the dominant channel of sensory experience in many animals, where it is a far more subtle and complicated phenomenon in every way, relative to the human experience of olfaction.

The human emphasis on sight and hearing as the dominant senses is an accident of our primate heritage (and they are in fact not at all the most common dominant senses among animals) not evidence of the inherent superiority of photons or pressure waves over chemicals as a way of gathering information about the environment.
posted by Scientist at 9:20 AM on January 28, 2013 [3 favorites]


> Mostly, geosmin.

Borked link; was it meant to be this?
posted by Westringia F. at 9:51 AM on January 28, 2013


That's the way the world really is. It's not magic. We can understand it, predict it, manipulate it, make it do what we want.

"I think I can safely say that nobody understands quantum mechanics." --Richard Feynman.

I remember reading a quote by Feynman to the effect that all it takes is consideration of the double-slit experiment to come to this realization. Do we really "understand" wave-particle duality just because we are able to apply Schrodinger's equation? Chomsky is always saying that we gave up on intuitive understanding of science after Newton (which I don't really understand because Newton's laws seem fairly intuitive to me).

This then goes to the brain, which interprets it by identifying which sensor or group of sensors was firing, and where the decision to organize a response (if any) is made.

There are many things in biology that are poorly understood, including some things about smell, though my impression is that those things are mostly on the central processing end rather than the detection end.


Okay, I'm going to jump on my hobbyhorse. What is completely missing from this, it seems to me, is an explanation for the actual sensory experience, of the "smell of fresh earth after rain " for example, itself. There's nothing in this explanation that explains why there should be any experiencing happening at all. I presume the idea is that "central processing" creates, or is itself, conscious.

Maybe that is true (to my idiotic mind it seems it may be nonsense), but if we have a useful theory for how "information processing" causes or is conscious experience, then we should be able to predict new experiences, such as a new primary color. If the the understanding is that the experience of color actually happens in the color "globs" in the visual cortex, not in the retina, let's say, then the prediction could be that with exactly the same wiring in the eye, you could "rewire" the visual cortex to create completely different colors, or more simply to start with, just cross-wire the opponent color signals such that R,G,B are all reversed - and stop signs start looking blue instead of red for example. An adequate theory of conscious sensory experience should require explanatory power to predict new experiences, not just attempt to describe what we think is happening now.

I have the sense that a few thousand years from now, scientists reading this would say "21st century neuroscience is not even wrong."
posted by Golden Eternity at 9:52 AM on January 28, 2013


> The problem is that proving that a unicorn exists or does not exist is impossible.

Somebody hasn't heard about the Zells.
posted by bukvich at 10:18 AM on January 28, 2013


> If the the understanding is that the experience of color actually happens in the color "globs" in the visual cortex, not in the retina, let's say, then the prediction could be that with exactly the same wiring in the eye, you could "rewire" the visual cortex to create completely different colors ...

Hmm.... There are haptic devices like BrainPort that let people "see" using a tactile sense. This review article (via the wikipedia page on sensory substitution) states that there's evidence for visual cortex activation using tactile & auditory stimulation, which suggests that we can rewire the sensory experience in some way. (I suppose it feels something like an experience of vision created by a non-visual stimulus, but I have no clue....)

In any case, how we perceive a stimulus is a separate question from how we (physically/chemically) detect it, and it's the detection, NOT the perception/experience, that the "quantum smell" hypothesis is trying to address.
posted by Westringia F. at 10:36 AM on January 28, 2013 [1 favorite]


twoleftfeet: Let me know when there is a literal language for smell and we'll talk. Using sound.

Let's have dinner. I'll cook up a wonderful meal. You can enjoy the sound of it (sizzling, crackling, crunching), but I'm going to enjoy the taste. It may not be a literal language, but you'll know good food when you taste it.
So... you admit DU is right, and have nothing to add?
posted by IAmBroom at 10:59 AM on January 28, 2013


We detect color with a very few (three plus one) types of receptors that respond differently to light of different frequencies. If a light activates one group of receptors weakly and another strongly we say that the light is orange (or purple, or whatever) and we can associate it with other, similar shades of light. If we had hundreds of receptors, each of which only responded to its own frequency, would we be able to do this? I think we would just have names for each hue we can recognise, and no general theory of color at all.

While this is at first appealing, it doesn't necessarily follow. Our conscious minds wouldn't be able to tell the difference between just a few sensor types and variegated sensors whose outputs were combined right away.

For example, consider location in space instead of color. You've got a few million photoreceptors, each having a receptive field corresponding to a thin cone in space, right? But we don't go around talking about locations in terms of those thin cones. Because location information gets munged together a bunch of different ways by our big beautiful brains, I can say "the cup in front of me and to my left is at about 10 o'clock", and I can recognize that its location is more similar to the location of the phone at 9 o'clock than it is to the lamp at 3 o'clock.
posted by Jpfed at 11:27 AM on January 28, 2013 [2 favorites]


No, DU is incorrect - we have no language to express sound. The closest we have is musical notation, which is imperfect at best - you can't feed sheet music into a scanner and have the computer recreate what the composer intended without human intervention. A computer can't read back what you've written with fidelity to intent and intonation.

We communicate with sound, because it has advantages in range and latency over smell, and we have given up a large portion of our olfactory senses in favor of unobstructed binocular vision... but we still have a sense of smell that offers a spectrum of sensory input that rivals sound. We may not rub our butts on the wall to leave messages for each other, but we can definitely tell more about our immediate environment through smell than sound. Can you hear if there's been an animal in the room? A stranger? If there's mildew on your clothes? Can you hear if something is good to eat? If the water is fresh? If the place is cozy and well kept? Your nose can tell those things, and more.

Stores hire DJ services to set up an ambiance that appeals to their shoppers - but they also hire scent marketing services for the same end.

Do not confuse sound with language - you do not need sound for language.
posted by Slap*Happy at 12:06 PM on January 28, 2013


Slap*Happy: We may not rub our butts on the wall to leave messages for each other, but we can definitely tell more about our immediate environment through smell than sound. Can you hear if there's been an animal in the room? A stranger? If there's mildew on your clothes? Can you hear if something is good to eat? If the water is fresh? If the place is cozy and well kept? Your nose can tell those things, and more.
You're making a lot of false comparisons.

You don't really smell that an animal has been in the room; you smell that animal scent currently is in the room. I can place a box of greasy yak hair under your seat, and when you sit down you might wonder when the yak was in the room last - but none ever was.

A lot of people are waving around fairly whoo-whoo claims of whether sight, or sound, or smell is the most exact/data-rich/informative sense of all. This is all nonsense. Your senses are not created by the organs that do the detection; the rest of "sensing" is done by the brain. Destroy any one of these three parts: sensor, communication nerve, brain processing area - and you remove the sense entirely.

Ergo, the question of which sense conveys the most information is actually fairly easy to determine: which one has the most brain devoted to its processing? Without the final step of extra processing, the information from any bundle of sensing nerves must be blurred together indiscriminately.

I'm unable to find this data, but perhaps there's a neuroscience expert here who can. I suspect the visual cortex is far larger than any other sensory area, myself.
posted by IAmBroom at 12:58 PM on January 28, 2013 [1 favorite]


From the Animal Behavior class I had last week, the visual cortex is indeed the largest part of the primate brain's sensory-processing apparatus, by far. Sound is next, and smell if far behind. This is not the case for most non-primates, however. In most non-primate vertebrates, the olfactory bulbs are by far larger than the visual cortex.
posted by Scientist at 2:15 PM on January 28, 2013 [1 favorite]


And yes, behavioral experimentation does bear out the extension that this is a useful shorthand for how important a particular sense is to a particular species.
posted by Scientist at 2:16 PM on January 28, 2013


I'm a bit of a stranger to olfaction but I did just finish up quite a bit of work on the retina, so a question for anyone that has a general idea:

Are there a series of gated neurons as in retina? Something that links multiple (and ostensibly different) olfactory detectors together to generate a more complex signal?
posted by Slackermagee at 2:22 PM on January 28, 2013


Scientist wrote: I would like to mention that there is a vast body of empirical evidence supporting the "shape" theory of olfaction and we actually know a great deal about the chemistry of olfactory receptors and the ways in which scent chemicalw can create conformational changes in the membranes of the sensor neurons in which they are embedded, thus opening the sodium channels of those neurons and causing them to fire.

I don't think even Turin would say that olfaction isn't a chemical process. We're chemical creatures; it must be chemical at some point. But if it were solely a matter of molecular "shape" then we could take an existing scent that is, say, too fragile or too expensive to be used; figure out what part of the "shape" is critical and then produce another molecule that would twiddle the receptors in the same way. But we can't; vast amounts of money (the scent industry serves the manufacturers of perfume and cosmetics and cleaning products and food chemistry and I don't know what) is poured into this, but it's still very much hit-or-miss - and mostly miss. It isn't just snob value that makes parfumeries hunt out exotic items like oudh and ambergris, or steam-distilled essence of lily-of-the-valley. It's because we still don't know how to replicate their effects.
posted by Joe in Australia at 5:07 PM on January 28, 2013 [2 favorites]


In any case, how we perceive a stimulus is a separate question from how we (physically/chemically) detect it, and it's the detection, NOT the perception/experience, that the "quantum smell" hypothesis is trying to address.

yeah, I get that, but the conversation seemed to have gone beyond detection.

This review article (via the wikipedia page on sensory substitution) states that there's evidence for visual cortex activation using tactile & auditory stimulation, which suggests that we can rewire the sensory experience in some way.

Interesting article. Maybe this is because our sense of 3D space relies on the visual cortex. Here's an interesting discussion I came across sort of related to this. Below Arnold Trehub describes his (fascinating imo) retinoid "theory of consciousness:"
The autaptic neurons in the Z-planes of the retinoid system have short-term memory and are assumed to compose a 4D phenomenal space. It is described as a 3D neuronal structure as a matter of convenience (like any other circuit diagram). But since it has dynamics as well as structure, it must be understood as a biophysical mechanism operating in time as well as space (of course, no structure can exist in zero time). The issue of time, especially phenomenal time is tricky. Einstein’s space-time is an abstract formalism that has proven useful in our understanding of the universe. But we must acknowledge that this scientific formalism, like all abstractions, useful or not, is a product of human biology. From a phenomenological perspective our conscious experience of time is difficult to pin down. But in the 4D manifold of the retinoid world, nothing happens instantaneously. Because of the short-term memory properties of the retinoid system, our experiential tour through retinoid space always fuses a representation of what is happening now (strong), before (weaker), and an anticipation of next (weakest). As we attend to various regions of the phenomenal space around us, our heuristic self-locus travels a path through the space-time plenum of the retinoid structure. The formal description of all of this is not a part of the mechanism that generates the description.
Destroy any one of these three parts: sensor, communication nerve, brain processing area - and you remove the sense entirely.

Maybe this is the only sane thing to believe, but I'm not seeing why removing the sensor necessarily removes sensory perception. If a sensor is simply a detector that converts a physical quantity into a signal, the nerves are effectively cables that transmits the signals to and within the brain, and the brain is simply a "processor" of signals, what would happen if you had the identical signals and the identical "processing," but no sensor? If it is theoretically possible to replace the retina with a CCD based artificial retina that wires into the optical nerve endings through some sort of artificial synapses or something, and this produces virtually identical visual experiences, then it seems it would also be possible to remove the retina entirely and transmit signals from a computer directly to the nerves behind the retina - creating visual experience without a sensor. I'm not saying it's possible, or sane, but I'm not seeing how this has been logically proven implausible by modern neuroscience (I get that the eyes may be sensitive to polarization and other things that a CCD camera is not, but assuming it is possible to generate these responses as well). If it turns out that the 'sensor' must exist for sensory experience to exist, I assume this also implies that the physical quantities being sensed must exist, i.e. externalism.
posted by Golden Eternity at 8:20 PM on January 28, 2013


[IAmBroom:] Destroy any one of these three parts: sensor, communication nerve, brain processing area - and you remove the sense entirely.

Golden Eternity: Maybe this is the only sane thing to believe, but I'm not seeing why removing the sensor necessarily removes sensory perception. If a sensor is simply a detector that converts a physical quantity into a signal, the nerves are effectively cables that transmits the signals to and within the brain, and the brain is simply a "processor" of signals, what would happen if you had the identical signals and the identical "processing," but no sensor? If it is theoretically possible to replace the retina with a CCD based artificial retina that wires into the optical nerve endings through some sort of artificial synapses or something, and this produces virtually identical visual experiences,...
You haven't removed the sensor; you've replaced it with a functionally-similar artificial sensor. Thus, you're agreeing with my point: the sense of sight disappears without a sensor, a communication nerve, and the brain processing area.
posted by IAmBroom at 1:01 PM on January 29, 2013


This was supposed to be the part where I removed the sensor:

"then it seems it would also be possible to remove the retina entirely and transmit signals from a computer directly to the nerves behind the retina"
posted by Golden Eternity at 1:04 PM on January 29, 2013


This was supposed to be the part where I removed the sensor:

"then it seems it would also be possible to remove the retina entirely and transmit signals from a computer directly to the nerves behind the retina"

(the idea being you would take the output of the 'frame buffer' of the graphics system and connect it directly to the optical nerves)
posted by Golden Eternity at 1:05 PM on January 29, 2013


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