I have discovered that the sense of smell, like the other senses, is engaged differently by the calendar.

For instance, if I am walking in the spring, my first scent will most likely be growing things: grass, trees, and flowers the most likely sources. But walk out the same door in the fall, and the scent will be decaying and dead things, particularly the leaves of the trees: having served their growing season’s purpose, they slowly die, then drift down to the ground to be blown away or collected and disposed of.

This same concept applies to man-made objects, and in my neighborhood, happens every Thursday. That’s the day when our roll-away waste containers are lined up like soldiers, one, two, or three abreast, standing at attention (some at-ease) at the end of the driveway. Throughout the day, the garbage trucks come by to grab, dump, and replace the empty containers back in the driveway. So on Thursdays, any walk down the sidewalk of the neighborhood is inviting your nose to be a collector of the last week’s life, now trash. Even through the plastic trash bags and mostly-closed lids, the odors can be pervasive. Decaying food is often the main component, but for those families with little ones, the odor of food comes in a different scent! By the design of the collection machinery, the lids of empty containers remain open – to air out, but also to announce to any passerby the strongest odors of what was formerly occupying the container.

And it is at this moment that your nose knows – not only what was in the container a short while ago, but what that scent brings to your memories.

According to science, the sense of smell is closely linked with memory, probably more so than any of our other senses.  Those with full olfactory function may be able to think of smells that evoke particular memories; the scent of an orchard in blossom conjuring up recollections of a childhood picnic, for example.  This can often happen spontaneously, with a smell acting as a trigger in recalling a long-forgotten event or experience.

Given the time of year, try this the next time you are walking through Target or an office supply store: Pick up a box of crayons, open the top, and take a deep breath. Most likely, you will be transported from the store aisle to elementary school, with memories of your new box of crayons comforting the uncertainty of a new classroom full of friends yet to be made.

So how does your nose know?

According to the National Institutes of Health, your sense of smell – like your sense of taste – is part of your chemosensory system, or the chemical senses.

Your ability to smell comes from specialized sensory cells, called olfactory sensory neurons, which are found in a small patch of tissue high inside the nose. These cells connect directly to the brain. Each olfactory neuron has one odor receptor. Microscopic molecules released by substances around us—whether it’s coffee brewing or pine trees in a forest—stimulate these receptors. Once the neurons detect the molecules, they send messages to your brain, which identifies the smell. There are more smells in the environment than there are receptors, and any given molecule may stimulate a combination of receptors, creating a unique representation in the brain. These representations are registered by the brain as a particular smell.

Smells reach the olfactory sensory neurons through two pathways. The first pathway is through your nostrils. The second pathway is through a channel that connects the roof of the throat to the nose. Chewing food releases aromas that access the olfactory sensory neurons through the second channel. If the channel is blocked, such as when your nose is stuffed up by a cold or flu, odors can’t reach the sensory cells that are stimulated by smells. As a result, you lose much of your ability to enjoy a food’s flavor. In this way, your senses of smell and taste work closely together.

Without the olfactory sensory neurons, familiar flavors such as chocolate or oranges would be hard to distinguish. Without smell, foods tend to taste bland and have little or no flavor. Some people who go to the doctor because they think they’ve lost their sense of taste are surprised to learn that they’ve lost their sense of smell instead.

Your sense of smell is also influenced by something called the common chemical sense. This sense involves thousands of nerve endings, especially on the moist surfaces of the eyes, nose, mouth, and throat. These nerve endings help you sense irritating substances—such as the tear-inducing power of an onion—or the refreshing coolness of menthol.

And so all day, every day, you are confronted with a smorgasbord of smells. Your five million olfactory cells can sniff out one molecule of odor-causing substance in one part per trillion of air. And you take about 23,000 breaths per day processing about 440 cubic feet of scent-laden air.

But most people have a very limited vocabulary for describing aromatic experience: “It stinks” or “That smells good” are the most common references. If you want to pay attention with your nose, aim to increase your discrimination of and appreciation for smell by expanding your olfactory vocabulary.

Make “Smells” a Theme for a Day

Record what you smell and how it affects you through the course of a day. Seek out unusual or intense aromas. Linger in the cheese department of your favorite gourmet store. Drive to the country and walk through a barnyard. Inhale the aroma of all the herbs and spices in your kitchen. How does smell affect your moods? Your memory? Aim to find and record specific examples of aromas affecting your emotion or recall.

How to Think Like Leonardo da Vinci, Michael J. Gelb

By prompting yourself to focus explicitly on scents and odors, you will most likely find yourself remembering the past while also developing a new appreciation for what your nose knows.

inspired by Alexandra Horowitz’s On Looking

and Rob Walker’s The Art of Noticing