nose I remember in my late teens burning a particular candle, scented with lavender and lilac, while listening to the music of Simon & Garfunkel, Jefferson Airplane, Crosby, Stills, Nash & Young, and the then-psychedelic Beatles. To this day, those scents conjure up powerful memories of that wonderful and troubled time, and the potent mix of emotions that defined me, my generation and the age we lived in. There are no words to describe this — when I’m exposed to these smells, in any context, they penetrate immediately into my amygdala and hippocampus, bypassing the brain’s logical circuits and evoking pure, vivid emotion and forgotten memories. I must consciously and physically resist the instant and overwhelming instinct to cry, so overcome am I with the rush of pure feeling, stunning recollection.

When I travel on business, especially when I go overseas for brief visits, I remember little of the minutiae of the cities I taxi through on the way to indistinguishable office boardrooms. But as soon as I arrive and set foot outdoors I know what city I am in, could tell you where I was if I was deaf and blind, by the unique odour that absolutely distinguishes each city. Suddenly I recall the smallest details of parks, restaurants, landmarks I’ve only seen once and which never even registered in my conscious mind. Take away the olfactory clues, and all is once again forgotten.

My research on emotion in animals (see my essay How to Save the World ) has confirmed my intuition that there is a powerful connection between senses (and sensitivity), memory and emotion. The sense of smell intrigues me in particular, because it seems to evoke memory and emotion in a particularly visceral way, and because our culture seems to denigrate it as a base, nasty, inferior sense. To try to understand the boundless pleasure our dog Chelsea gets from incessant sniffing of everything around her, I decided to do some more research into our most mysterious and maligned sense, and its ability to spark emotion and memory, two of the attributes of life that give our existence meaning. Here is what I learned:

  • Most animals learn what foods in nature are safe to eat, and which to avoid, by smelling their mother’s breath
  • People who are depressed are just as able to distinguish different smells as those in normal spirits, but the reaction in the parts of the brain that govern both sensory processing and emotion is significantly muted
  • Richard Feynman, in his book Surely You’re Joking…, explains that man lost much of his innate sense of smell after he stood upright, and describes an experiment that shows that, with a little training, anyone can learn to distinguish blindfolded the hands of a large number of people simply by smelling them once at close range
  • Humans have evolved relatively few scent receptor cells (12M) in their noses compared to rats (100M) and some dogs (220M)
  • Women generally have a much stronger sense of smell than men, though sensitivity varies throughout the menstrual cycle; the leading hypothesis is that this conveys selective procreation advantage as women sense and select as mates men whose antibodies (which emit distinctive smells) complement their own
  • From swabs taken from the underarms of moviegoers leaving the theatre, most women (but few men) were able with minimal training to accurately tell with one sniff whether the movie seen was a comedy, drama, or horror film
  • Memories that are scent-related last much longer and are more intense than those connected with other senses, though recollection of objective facts is no more acute
  • The powerful “odour-memory-emotional recall” connection is called the Proust effect from his description “that sweet aroma released the vast structure of recollection”; a Scientific American study paraphrased this as “scent evokes a powerful and visceral remembrance, a rare experience of simultaneity”
  • Smells are conveyed to the receptors by molecules precisely large enough for detection yet small enough for airborne dispersion
  • Some dogs can smell minute amounts of explosives and other chemicals, and even subcutaneous diseases
  • Smells both convey and alter mood; global expert Dr. Rachel Herz of Brown University says “emotions are abstracted versions of what olfaction tells an organism at a primitive level”
  • Things learned in the presence of a particular odour are more easily recalled a short time later if the odour is reintroduced ; maybe smart students should set up shop in the examination room while they study for exams
  • Smell is 10,000 times more sensitive than taste (measured by ability to detect a proportionally smaller amount), and in the absence of smell, taste acuity is reduced by 75%
  • Smells can bring on varied and profound physiological changes such as a drop in blood sucrose; in other words, aromatherapy works
  • There is no accepted ‘language’ or ‘colour wheel’ of smells in any of Earth’s major cultures
  • The cultural variety of likes and dislikes of certain smells is attributed to associated memories, much as memory influences our personal love for or dislike of certain music (there are other similarities between smells and sounds)
  • A dramatic increase in ability to differentiate smells can be learned fairly quickly
  • The three most popular Western smells are vanilla, lavender and jasmine
  • Some Japanese companies promote workplace creativity and mental energy by broadcasting scents attuned to the human body clock: citrus in the morning, flora in the afternoon, cedar and cypress in the evening; musk, on the other hand, has been shown to lower workplace productivity (it is emotionally distracting)
  • Introverts generally have a more acute sense of smell than extroverts, perhaps their awareness of subliminal danger signals carried in some scents makes them socially cautious
  • Almost any scent can now be extracted, replicated and amplified inexpensively and effectively in laboratories
  • Perfumes, other than the musk family of scents that accentuate natural body odour, were rarely used until two centuries ago, about the same time Western culture demoted the sense of smell to a ‘baser’ sense
  • Arab cultures have highly evolved scent rituals for women, entailing the layering of scents in prescribed sequence, and the after-dinner sampling of multiple scents as perfumes and incense, a social bonding experience in which all women go home smelling the same
  • In some tribal cultures such as the Amazon Desana people, scent is the primary identifier and descriptor of individuals, and tribal language allows precise articulation of each person’s natural personal odour, the odour imparted by the foods he/she eats, the odour imparted by his/her emotional makeup, and the odour imparted by his/her fertility chemistry
  • Every individual, except identical twins, has a highly distinct and unique odour, which most animals can differentiate easily

If you’re interested in the physiology of smell, here’s a good source. And if you prefer your education more entertaining, I highly recommend Tom Robbins’ hilarious  Jitterbug Perfume . As for me, I’m content, in this time when our humanity seems to be in short supply, to learn a little more about what makes us human. And as I put my substantial nose a bit closer to the ground, I’m starting to share Chelsea’s enthusiasm for the sensory delights, and the accompanying memories and emotions, that in our zeal to be separate from the rest of life on Earth, we have lost ‘smell’ of, to our impoverishment.

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  1. Marie Foster says:

    What a great article Dave. Thanks for sharing the information. I did know some of it of course, but much of it was news to me.

  2. beSharp says:

    A little late, but great article. Aromatherapy truly does work (check my home page). It is an ancient and powerful healing method.

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