Think of your childhood home. Personally, at 25 years old, it hasn’t been long since I graced the narrow, carpeted halls of the suburban tract house I called home in Fort Wayne, Indiana. Perhaps for some readers it’s been more than a couple decades. In any case, the solidity and depth of detail you are able to conjure regarding how a place or a thing looked becomes fuzzier as time marches on.
Now, here’s another exercise in memory: what if you were to catch a whiff of that particular combination of spices your mom used when she made your favorite food? Or, how might a completely different scent, like detergent, remind of you of the fresh piles of clean laundry that you helped fold? Isn’t it strange that, in a certain way, we remember a place or person better through our sense of smell than through our other senses? Why is it that the distinct fragrance of orange DialⓇ soap takes me back to my warm memories of Mrs. Hathaway’s Kindergarten classroom but might remind someone else of the awful times they were forced to wash behind their ears every night?
This power an olfactory experience has — to instantly transport the mind back to a specific place and time, and stir up such a specific swirl of emotions — has always fascinated me, so I set out to learn as much as I could about how we process this wide world of smells on a physiological level while also learning about Olfactory Memory, or the recollection of smells.
Some of my colleagues here at WonderLab told me about an exhibit the museum featured a few years ago called “Smells Like Nano” created in conjunction with Kevin and Laura Brown of IU’s Chemistry department. The exhibit featured a big blue nose and several different stations, each with a squeeze bottle and a 3D model of the smell’s associated molecule. In each bottle was a cotton ball bearing the scent of things such as mint, almonds, pineapple, and even foul odors such as vomit and rotting flesh. The goal was for visitors to identify each scent while learning some basic chemistry. Their memories of this exhibit were vivid. Many exclaimed: “Smells Like Nano!” while laughing and cringing (rotting flesh?). Exhibits aside, I asked them which smells they remember from grade-school. The first and most popular answer: the smell of fresh, purple-inked pages from the Mimeograph machine. Mmmmmm….mimeograph ink.
The Mechanism of Olfaction
So what was happening physiologically when the students of the 1970’s and 80’s lifted those sheets of paper to their faces and inhaled the sweet, faintly gluey smell of sulfated castor oil? The answer is Olfaction, the science-y term for our sense of smell. The basic mechanism of olfaction seems to be relatively uniform among different animal species, but for the purposes of this discussion, let’s consider human olfaction.
First and foremost, for a smell to be perceived by our noses it has to be in a volatile (gaseous) state, which means that when we bend down to smell a flower, which is obviously a solid, what we’re actually inhaling is its radiated mixture of volatile odorants, or the molecules that give us the sensation of an scent when introduced to our olfactory system. The odorants make their way up into our sinus and collide with what’s called the olfactory epithelium, a smallish, mucus-lined patch of tissue on the roof the nasal cavity.1 On average, the human olfactory epithelium is about 9 cm2, a bit larger than a normal postage stamp. Fun fact: the canine epithelium is much larger, around 170 cm2, the size of a small handkerchief.2 On top of that, most dog breeds have about 30% more ORN’s and can detect a much larger variety of odorants.3 This means that when a dog smells something, it’s as if its mind is entering a world we feeble humans can’t even imagine!
Once an odorant gets trapped in the mucus, it is picked up by the hair-like censors of one of the millions of Olfactory Receptor Neurons (ORN’s), which then fires its unique signal up into the olfactory bulb. On the ends of each of these little hairs are the receptor proteins that are coded to bond with only one specific type of odorant molecule.4 To quote Hank of Crash Course, “just imagine a piano with thousands of keys able to produce millions of unique chords, and you’ll get an idea of how amazing our noses are!”1 These more easily-digestible “chords” are then sent via the olfactory tract, into the olfactory cortex, and then to different parts of the brain, where the real magic happens.
Into the Brain
Though the smell data is utilized in many different parts of the brain, a select few play important roles in the context of olfactory memory. However, in order to talk about olfactory memory, here are a few important terms regarding memory in general.
Explicit memory (a.k.a. Declarative memory) is factual information that is deliberately and consciously encoded into short-term and/or long-term memory, such as “yesterday I had yogurt for breakfast.” Implicit (or Procedural) memory refers to skill-based information that is encoded automatically and without conscious effort, such as how one remembers how to ride a bike or tie their shoes. When it comes to olfactory memory, the Frontal Cortex is where we explicitly remember and label a smell, such as “this is the smell of fresh bread.” Other parts of the brain, namely the Limbic System, are where we process the more implicit, often emotional memories associated with a particular smell.4
When I was a young kid, my mom would have me close my eyes as she quizzed me on the names of each herb or spice she would hold under my nose. Not only was this activity expanding my explicitly-encoded, olfactory database, my brain was automatically tying implicit, emotional memories to those smells. So now when I close my eyes and smell a jar of oregano, my frontal cortex tells me “this is oregano,” but I’m also reminded of the golden years of childhood (not to mention the delight of eating Italian cuisine).
On the other end of the emotional spectrum, olfactory memory is also key to our more animalistic instincts for survival; an animal is more likely to survive and reproduce if it can identify the smokey smell of a nearby forest fire as “DANGER!” or sniff out its mother’s milk before it’s old enough to open its eyes. These primal urges that we associate with certain smells are processed mostly in our Amygdalae (colored red in the accompanying GIF). These two sets of nuclei are heavily involved in the formation of emotional memories, especially those of fear and fight-or-flight. This explains why the uniquely awful smell of burning hair caused me to quickly pull by arm away from the burner the other day when I wasn’t paying attention while cooking breakfast.
Also within the Limbic System are two Hippocampi (the two seahorse-shaped lobes connected to the amygdalae), which play an important role in the formation of new, Episodic memories, or memories of specific, personal experiences. The hippocampus receives most of its olfactory data from the amygdala, which more or less dictates how to file it away as a memory. 4
So what does all of this say about our brains and who we are as humans? Certainly there are other species with better olfactory systems and more specialized anatomy for mechanisms like odor localization and recognition, but I believe learning what science has discovered about our physical selves— such as the connection between what we smell and what we remember — is not only fun and stimulating, but a crucial step to better understanding our equally-important emotional selves.
Tucked into its own cozy nook of the ever-expanding library of our brain is our collection of olfactory memories – some collected from early childhood. So, whether it’s the cleansing scent of dish soap, the warm smell of cinnamon or cloves, the ominous odor of a lit firework fuse, or the comforting fragrance of a loved one’s perfume, your olfactory experiences are ever-present in everyday life.
Which smells from your childhood do you remember most fondly? What other questions do you have about our amazing brains? We’d love to hear your thoughts in the comments section below! Happy smelling!
About the Author
Eric Schepper is a 25 year-old alumnus of Indiana University’s Folklore and Ethnomusicology department, and is currently inhaling the earthy smell of his English breakfast tea. He is a development Intern at WonderLab as well as an ESL teacher for Monroe County Public Library’s VITAL Program. He loves teaching almost as much as he enjoys learning, especially about world cultures, new advances in the sciences, and interesting people.