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The Mysterious World of Smell
Posted By Mark Sisson On April 27, 2011 @ 10:01 am In Personal Improvement | 90 Comments
What can you smell around you right now? Food? Coffee? Copier ink? Soil? Cleaners or chemicals? An office mate’s cologne from twenty feet away? It’s true we apprehend the world primarily through pictures and sound unlike, say, our canine  friends. If we lose our sense of sight or hearing, we embark upon a physically, emotionally, and socially challenging journey of adaptation. If we lose our sense of smell, it’s strange and unfortunate, but life goes on pretty much the same as it always did. Nonetheless, smell still pervades our interaction with the world (and each other) in ways we don’t appreciate or even fully understand.
Think for a minute: what are the scents that inhabit your memory? Which smells somehow transport you to another time, place, and (perhaps) emotional state? Is it the smell of saw dust from your father’s workshop, of spices in your grandmother’s kitchen, of backyard “camp” fires in summer, of a perfume worn by your mother or partner? (For me, there’s something about white onions – a vestige from family dinners while I was growing up.) More than simple sight or sound perhaps, smell evokes deep-seated memories with a stunning emotional clarity. A long forgotten scent suddenly wafting in our direction can leave us momentarily disoriented in a poignant revisiting of associated pain or nostalgia. Scents can initiate such powerful recollections that experts are now studying and designing treatment for the smell-related triggers of PTSD .
The biology of smell is multifaceted and, to a surprising extent, unsettled. When we’re exposed to a scent, molecules travel through the nasal passages and either link up with correspondingly shaped receptors (the lock and key theory) or trigger receptors based on their vibrational frequency (swipe card theory). But there’s more. Jonah Lehrer, author of Proust Was a Neuroscientist , offers a theory (in yet another debate) on why the sense of smell is so emotionally loaded  – for better or worse: “One possibility…is that the olfactory cortex has a direct neural link to the hippocampus. In contrast, all of our other senses (sight, touch and hearing) are first processed somewhere else – they go to the thalamus – and only then make their way to our memory center. ” From the memory center, it’s on to the emotional centers in the brain – and the corresponding sentimental fallout.
In the midst of new research, smell remains perhaps the most underappreciated of the senses. Having allegedly “traded” a stronger sniffer for full color vision over the course of later evolution, it’s not the key survival strategy for our species that it is for others. We have far fewer olfactory receptor genes than, say, a mouse (350 and 1100 respectively). To boot, some sixty percent of ours are inactive  anyway. Some experts, however, have recently proposed that we’re not so smell-deficient as we think . With an upright posture and the corresponding loss of “filters” animals lower to the ground used, these researchers argue, we got along pretty well with fewer receptors and more advanced retronasal (back of the mouth) olfaction.
Although it might not be the dominant sense, smell appears to be the most resilient. An Australian study showed that olfactory function remains remarkably steady  as we age as long as we’re in good health, don’t smoke, and aren’t taking certain medications like those aimed at lowering blood pressure and cholesterol. (Hmmmm….is smell an endangered sense in our medical culture?) In fact, loss of smell is an essential early indicator of neurological conditions like Parkinson’s and Alzheimer’s . The nose knows after all.
Beyond the basic biology, however, is a whole realm of behavioral impact. In recent years, marketers have begun exploiting our natural propensity to feel good and stay longer in stores that smell good. (Their definition of good being subjective, I’d add.) Anyone selling a house is advised to bake cookies or pie prior to open houses or showings. A good scent can be enough to inspire us to linger here or there, but what if the scent is so subtle that we don’t even know we’re actually smelling anything?
Much of what we smell operates on a subliminal level. We may not consciously identify or even notice a scent, but it can nonetheless have substantial impact in surprising ways. One study (PDF ) suggests that an odor exposure can be enough to shape our opinion of people around us – provided, in fact, we don’t know it’s there. Participants in one study sniffed bottles with extremely faint scents (sweat, lemon, and a neutral scent, specifically). Those who couldn’t consciously perceive a diluted sweat scent in the respective bottles went on to rate the likability of people in photographs less favorably. Those who perceived the scent were able to discount it from their subsequent assessment of the photos.
Then there are the “social chemosignals.” Researchers have recently discovered that humans can “smell” fear sadness in those around them . What’s more is we in turn respond to these subliminal perceptions. The unconscious smell of a woman’s tears reduces a man’s sexual desire and instigates a reduction in testosterone (PDF ).
The pheromone question continues to puzzle researchers, but the results suggest there’s plenty of truth to mine. Researchers have tested the impact of 4,16-androstadien-3-one (an androgen steroid) on women’s perception of speed dating partners (PDF ). Women thought more of the men they met after having been exposed to androstadienone. (I’m sure someone is working on bottling this now.) Add to this equation the particular hormonal profile of where a woman’s at in the menstrual cycle  (or in pregnancy), and you’re suddenly looking at one heck of a richly complicated picture.
In recent years, the birth control pill has come under fire for altering women’s preferences in a partner’s smell. Researchers asked women to select which of ten male body odor samples they preferred both before and after starting hormonal contraception . The majority of Pill users changed their preferences, a phenomenon experts say relates to their artificially altered hormonal state. Although humans, like other mammals, have distinct, genetically set odor identities, the key in these experiments was major histocompatibility complex (MHC) genes, which play a role in immune response. Experts say women naturally look for partners with different MHC genes than they have, but the Pill changes those preferences to a partner with the same MHC profile.
All of this got me thinking about how much time and money we spend in our contemporary culture masking natural scents in favor of artificially concocted formulas. We spray our rooms and ourselves beyond any natural recognition. Who, can anyone tell me, has ever been attracted to a flower or a pine tree? Does this really set anyone at ease? We take medications that fundamentally alter our biochemical perception of those around us or sabotage our sense of smell altogether. We consider scented deodorants a hygiene product and cologne a fashion accessory. In reality, maybe it’s messing with Sasquatch. We seem to enjoy that enterprise as a whole these days.
Potential moral of the story: we’re more subject to the biochemical subtleties of our evolutionary origins and its selection patterns than we’re often comfortable believing. (This is the case in so much of life, isn’t it?) We discount the complexity of our senses, of our evolutionarily designed physiological fabric. At best, it dampens our experience of life. At worst, it gets us in hot water.
Here’s a modest proposal: how about doing away with the sensory games? Embrace your inner animal, your evolutionary shadow in all its biochemical complexity. Revel in the sensory diversity of past memory and present day. Smell whatever you have blooming in the garden right now. Smell your spouse. Smell your kids. Smell that seasoned roast you have in the oven for dinner tonight. Isn’t life better in full sensory dimension? It’s a Primal thing of course.
Thanks for reading today, folks. Shoot me your thoughts on today’s musings in the comment board. Have a great day.
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 designing treatment for the smell-related triggers of PTSD: http://www.haaretz.com/news/israeli-scientists-look-to-smell-therapy-to-treat-trauma-1.4637
 Proust Was a Neuroscientist: http://www.amazon.com/gp/product/0618620109/ref=as_li_ss_tl?ie=UTF8&tag=marsdaiapp07-20&linkCode=as2&camp=217145&creative=399349&creativeASIN=0618620109
 why the sense of smell is so emotionally loaded: http://scienceblogs.com/cortex/2009/11/smell_and_memory.php
 sixty percent of ours are inactive: http://chemse.oxfordjournals.org/content/30/suppl_1/i3.full
 we’re not so smell-deficient as we think: http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.0020146
 olfactory function remains remarkably steady: http://www3.griffith.edu.au/03/ertiki/tiki-read_article.php?articleId=7701
 early indicator of neurological conditions like Parkinson’s and Alzheimer’s: http://archpsyc.ama-assn.org/cgi/content/abstract/64/7/802
 PDF: http://faculty.wcas.northwestern.edu/~paller/PsychSci07.pdf
 humans can “smell” fear sadness in those around them: http://pss.sagepub.com/content/20/2/177
 PDF: http://faculty.washington.edu/beecher/Gelstein_et_al_2011.pdf
 PDF: http://alittlelab.stir.ac.uk/pubs/Saxton_08_androstadienone_preference_H&B.pdf
 hormonal profile of where a woman’s at in the menstrual cycle: http://www.ncbi.nlm.nih.gov/pubmed/11564447
 male body odor samples they preferred both before and after starting hormonal contraception: http://www.livescience.com/2781-pill-women-pick-bad-mates.html
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