Koerth: What do your memories smell like?

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What does a memory smell like?

To my kids, it’s a rain-soaked alley behind Magers & Quinn Booksellers — an odd mixture of musty concrete, petrochemicals and a light soupcon of distant potatoes frying in oil. They couldn’t put their finger on what it reminded them of, exactly, just that it was “important” and made them “feel safe.” (My best guess is that they’re thinking of the year or so in their early childhood when we lived and cooked in the basement, steps away from the family wood shop, during a home renovation.)

For a friend of mine, memory smells like wild onions. On a recent fall walk, I was hit with the thick, pungent scent of the weed fighting back against the violence of a lawn mower. But he was transported to childhood and how the green stems grew around third base at a ballpark, always ready to be plucked and nibbled as a mid-game snack.

From the homey funk of the Malt-O-Meal factory in Northfield to the decidedly less cozy aroma of bacteria processing Duluth’s sewage at the Western Lake Superior Sanitary District, Minnesota’s cities are full of smells that pull us back to specific moments in our lives — who we were and how we felt. And though they’re not always as pleasant as a freshly baked sponge cake, these city smells are no less powerful when it comes to evoking memories.

Why that’s true, though, is still a bit of a mystery, experts told me. We know how smells get to your brain, said Venkatesh Murthy, a professor of molecular and cellular biology at Harvard. “There are always small molecules coming off objects, carried by the wind and the breeze,” he said.

What’s more, each thing we think of as a distinct smell is actually a bunch of different molecules, linking up to different receptors. There could be 50 distinct chemical molecules that your brain has to register together in order to understand that it’s smelling coffee, Murthy said. In fact, his team does studies where it subtracts one molecule at a time until people stop recognizing that coffee scent as coffee.

One of the big questions around scent and memory is how your brain coordinates all those different molecules and receptors into a single idea. Murthy’s favorite theory right now is that your brain is effectively matching patterns of neuron activity to a specific scent. Coffee is coffee because a particular set of brain cells all light up at once in a particular way. The more often that pattern appears, the stronger the links form between those brain cells. When that network is activated, you remember that it’s the coffee network.

Part of what makes this theory cool is that it would kinda mean scent and memory are strongly linked because simply recognizing common smells is a function of remembering and learning. When you smell something, your brain is registering a pattern of molecular signals. It’s pretty easy for other sensory information — what you regularly see or touch when that smell is happening, or even the strong emotions you have — to get linked into the pattern. When Murthy smells jasmine, his brain remembers both that this is the smell of a flower and the nighttime bike rides he took as a child in India, where a strong jasmine scent filled the air.

This is reflected in animal research done by Kurt Fraser, a University of Minnesota assistant professor of psychology. Frazer studies motivation, but his work involves training rats to associate neutral smells with rewards they want to get or punishments they want to avoid. If the rat learns to associate lemon with a zappy electrified floor and vanilla with a highly pleasurable drug, it eventually avoids anything that smells like lemon and seeks out vanilla.

Ultimately, there may not be a ton of difference between Murthy’s jasmine-coated childhood memories and a rat expecting to get a box full of cocaine every time it smells vanilla. Likewise, an alley can bring up feelings older than your earliest clear memories, and a strong onion smell can make you feel like a kid again.