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  1. #1

    purplebird7's Avatar
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    Default The Secret of Scent - Needs An Epilogue

    I would like an update on the Shape vs Vibration theory as presented in Luca Turin's book, The Secret of Scent.

    Although Linda Buck and Richard Axel received the Nobel Prize in 2004 for their "shape" theory of olfaction, some of their writing was retracted in 2008.

    http://www.nytimes.com/2008/03/07/sc...7retractw.html

    Meanwhilie, it is reported that Luca Turn has been using his "vibration" theory to successfully manufacuture aromachemicals with the firm Flexitral.

    What is the current situation of the thory of olfaction?

  2. #2
    FloatingPoint's Avatar
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    Default Re: The Secret of Scent - Needs An Epilogue

    Quote Originally Posted by purplebird7 View Post
    I would like an update on the Shape vs Vibration theory as presented in Luca Turin's book, The Secret of Scent.

    Although Linda Buck and Richard Axel received the Nobel Prize in 2004 for their "shape" theory of olfaction, some of their writing was retracted in 2008.

    http://www.nytimes.com/2008/03/07/sc...7retractw.html

    Meanwhilie, it is reported that Luca Turn has been using his "vibration" theory to successfully manufacuture aromachemicals with the firm Flexitral.

    What is the current situation of the thory of olfaction?
    Linda Buck was a co-author (not the lead author) of the retracted paper, which likely means she just put her name on it to give a young researcher a career boost. Richard Axel had nothing to do with it. And the retracted paper had nothing to do with the research for which they won the Nobel. Also, the shape theory is not Buck and Axel's per se; it's been around for a long time. They won the prize for discovering the genes that give rise to odorant receptors and describing various details about how the receptors work (http://nobelprize.org/nobel_prizes/m...004/press.html). Their work apparently wasn't a "slam dunk" for the shape theory, but it did give significant support for the shape theory by showing how receptors work combinatorially to cover the large number of different odors that we can distinguish, as opposed to an older model that postulated one receptor per odorant. As the Nobel press release says:

    "Most odours are composed of multiple odorant molecules, and each odorant molecule activates several odorant receptors. This leads to a combinatorial code forming an "odorant pattern" – somewhat like the colours in a patchwork quilt or in a mosaic. This is the basis for our ability to recognize and form memories of approximately 10,000 different odours."

    I'm curious as well to know the current state of the vibrational theory of olfaction. I don't know how reliable or up-to-date it is, but this is the Wikipedia entry on the vibration theory, for what it's worth:

    http://en.wikipedia.org/wiki/Vibration_theory

    From the sound of it, the evidence is mixed and not a lot of experimental research is being done to confirm or deny the vibrational theory, probably because most mainstream researchers still don't take it very seriously. Here is one (fairly) recent study that lends it some support:

    http://www.physorg.com/news89542035.html

    Science moves slowly and rarely answers questions with the kind of certainty people sometimes imagine it to. It will probably be some time before we fully understand how smell works. For the time being though, the scientific establishment is still pretty strongly behind the shape theory.
    "Certainly, virtue is like precious odours, most fragrant when they are incensed, or crushed: for prosperity doth best discover vice; but adversity doth best discover virtue."

    - Francis Bacon

  3. #3
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    Redneck Perfumisto's Avatar
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    Default Re: The Secret of Scent - Needs An Epilogue

    Very interesting stuff, FP. Do you know if there is any support for a combination of the two theories? I get the impression that the cross-terms available by allowing shape (especially chiral ones) to interact with an electronic detection mechanism (or mechanisms) within each receptor could allow all of the facts to be explained. Of course, if vibration is not needed, lop it off with Occam's razor. But some of the facts (and I'm especially thinking the metallocenes) just scream for a non-dead key. You know - like the ones in Fords, that have a chip in the handle. They merge a shaped key and an electronic swipecard to give a gazillion combinations and a non-starting car (or in my case, truck ) should a thief try to mess with it.

    I really don't see these so much as competing theories - more like different explanations of different parts of a single complex story, both having made the (in retrospect) regrettable choice of saying they could explain everything.

    Also, I see the use of non-trained subjects to differentiate fragrances as being of dubious benefit - if not like using fetal chihuahuas to see if dogs can really track foxes. I suppose if chihuahuas are giving out the grant money it makes sense, but really - I'd rather have bloodhounds. To me it smacks of phony objectivity. Would there be any reason to use non-trained subjects, provided that it was a double-blind experiment? Yes, I can see it if the point of what you are doing has anything to do with finding out what non-trained subjects can do. But if the question you are asking is any function of "can human receptors do this - yes or no?", in order to answer the most fundamental questions of mechanism, then by George, I'd think you'd want the most sensitive and linguistically wired receptors you could lay your hands on.

    Or maybe I'm too much of an old dog and a paper chemist to do lab science anymore. Damn whippersnappers. Where'd they put my oxygen now?

  4. #4

    narcus's Avatar
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    Default Re: The Secret of Scent - Needs An Epilogue

    Turin intended to be back at London University. When I heard that, my first idea was that he may be picking up the threads, and perhaps do more research now. I think it would be best to ask him directly.
    'Il mondo dei profumi è un universo senza limiti: una fraganza puo rievocare sensazioni, luoghi, persone o ancora condurre in uno spazio di nuove dimensioni emozionali' L. V.

  5. #5
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    Default Re: The Secret of Scent - Needs An Epilogue

    Quote Originally Posted by narcus View Post
    Turin intended to be back at London University. When I heard that, my first idea was that he may be picking up the threads, and perhaps do more research now. I think it would be best to ask him directly.
    Thanks, narcus - I may do that. I may bone up on it a bit more first, and I definitely would like to look at some of the original literature (unfortunately, it's not exactly work-related, so I can't burn up the usual resources). I've hesitated going beyond the first bit of Burr's book, in part because I'd rather not mess with my objectivity, and I know that Burr's writing sold me on Hermès. I was thinking to save the book for later.
    * * * *

  6. #6
    FloatingPoint's Avatar
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    Default Re: The Secret of Scent - Needs An Epilogue

    Quote Originally Posted by Redneck Perfumisto View Post
    Very interesting stuff, FP. Do you know if there is any support for a combination of the two theories? I get the impression that the cross-terms available by allowing shape (especially chiral ones) to interact with an electronic detection mechanism (or mechanisms) within each receptor could allow all of the facts to be explained. Of course, if vibration is not needed, lop it off with Occam's razor. But some of the facts (and I'm especially thinking the metallocenes) just scream for a non-dead key. You know - like the ones in Fords, that have a chip in the handle. They merge a shaped key and an electronic swipecard to give a gazillion combinations and a non-starting car (or in my case, truck ) should a thief try to mess with it.

    I really don't see these so much as competing theories - more like different explanations of different parts of a single complex story, both having made the (in retrospect) regrettable choice of saying they could explain everything.

    Also, I see the use of non-trained subjects to differentiate fragrances as being of dubious benefit - if not like using fetal chihuahuas to see if dogs can really track foxes. I suppose if chihuahuas are giving out the grant money it makes sense, but really - I'd rather have bloodhounds. To me it smacks of phony objectivity. Would there be any reason to use non-trained subjects, provided that it was a double-blind experiment? Yes, I can see it if the point of what you are doing has anything to do with finding out what non-trained subjects can do. But if the question you are asking is any function of "can human receptors do this - yes or no?", in order to answer the most fundamental questions of mechanism, then by George, I'd think you'd want the most sensitive and linguistically wired receptors you could lay your hands on.

    Or maybe I'm too much of an old dog and a paper chemist to do lab science anymore. Damn whippersnappers. Where'd they put my oxygen now?
    I don't possess the expertise to comment on the issue with any kind of authority--I was simply marshaling the information available to me for purplebird7's benefit. So take whatever I say with a huge grain of salt. But it seems to me that both Turin and the establishment agree that shape is part of the picture--the question is whether shape alone suffices (there are some observed phenomena it doesn't seem to explain), whether vibration is the correct theory to explain those discrepancies (there could conceivably be other explanations), and whether inelastic electron tunneling is the mechanism by which it happens. The UCL study suggests that inelastic electron tunneling is possible *in theory*, but it hasn't demonstrated that that's what's going on in our noses.

    Re trained versus untrained experimental subjects, I'm not sure I agree that it makes that much of a difference. I would be far more concerned about sample size. The business of attaching verbal descriptors to odors is notoriously tricky, even for trained subjects. Just look at the wild disparities in the "notes" that people write up for fragrances on this site, to say nothing of the vast differences in the visceral like/dislike reactions that people have (and it's not as if trained perfumers and chemists all like the same odors, either). Olfaction is not just a matter of what's going on in the odor receptors, there's also a great deal of cognitive neural processing involved, and clearly at some point or points, whether it be in the odor receptors themselves or in the processing of the signals they send, there are significant individual differences related not just to training but to people's respective genotypes and gene expression. We know that some people are anosmic to certain aromachemicals--who's to say that we all even perceive the ones we *can* smell the same? Already we're at the threshold of epistemology.

    One potential problem with trained subjects is that they've been *taught* to attach certain verbal descriptors to certain familiar aromachemicals, which could inadvertently, and paradoxically, be biasing their perceptions. All of which renders these small studies, both for and against vibrational theory, kind of suspect in my book. Ideally we would want an experimental verification of olfactory theory that bypasses subjective verbal descriptors entirely, possibly through things like brain imaging studies and material evidence of inelastic electron tunneling in live G-protein-coupled receptors.

    It's such an exciting area of research that I'm surprised more people aren't working on it; in fact, sometimes it seems like it's dead in the water. One thing's for certain, though: the only way the vibration theory is going to make any headway is if Turin himself pushes for more and larger experimental studies, or designs them himself. For whatever reason, he hasn't been doing much of that the last few years.
    "Certainly, virtue is like precious odours, most fragrant when they are incensed, or crushed: for prosperity doth best discover vice; but adversity doth best discover virtue."

    - Francis Bacon

  7. #7

    Default Re: The Secret of Scent - Needs An Epilogue

    would like an update on the Shape vs Vibration theory as presented in Luca Turin's book, The Secret of Scent.

    Although Linda Buck and Richard Axel received the Nobel Prize in 2004 for their "shape" theory of olfaction, some of their writing was retracted in 2008.

    http://www.nytimes.com/2008/03/07/sc...7retractw.html
    For starters, the term "shape theory" is so very simplistic as to be misleading in any but the most superficial discussion. The theory for which Axel and Buck received a Nobel Prize should be called the "odorant receptor" theory:
    http://nobelprize.org/nobel_prizes/m...004/press.html

    Second, the paper that was retracted was not important to the work for which the Nobel prize was awarded.

    Meanwhilie, it is reported that Luca Turn has been using his "vibration" theory to successfully manufacuture aromachemicals with the firm Flexitral.
    Dr. Turin has made that claim. Who else? Since he does not publish this work in the scientific literature there is no way to verify this. The half dozen products from Flexitral could have been arrived at by educated guesses and trial and error just as IFF, Firmenich, Givaudan etc. do.

    What is the current situation of the thory of olfaction?
    I have not seen any challenge to the odorant receptor binding work such as done by Axel and Buck.
    All these moments will be lost in time, like tears in rain.

  8. #8
    FloatingPoint's Avatar
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    Default Re: The Secret of Scent - Needs An Epilogue

    For anyone who's interested, here's a pretty comprehensive (and technical) overview of the state of olfactory research circa 2002:

    http://www.leffingwell.com/olfaction.htm
    "Certainly, virtue is like precious odours, most fragrant when they are incensed, or crushed: for prosperity doth best discover vice; but adversity doth best discover virtue."

    - Francis Bacon

  9. #9
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    Redneck Perfumisto's Avatar
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    Default Re: The Secret of Scent - Needs An Epilogue

    Quote Originally Posted by FloatingPoint View Post
    For anyone who's interested, here's a pretty comprehensive (and technical) overview of the state of olfactory research circa 2002:

    http://www.leffingwell.com/olfaction.htm
    Wow! That's a pretty amazing site. Thanks for the link.

    I see your points about the complication of trained subjects. Looks like a tough field for measurement in general. The aspect of teaching to particular aroma chemicals seems like a very valid objection.

    Thanks to everybody for taking the time to answer in such detail!

    -Red
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