Whenever I smell mothballs, I’m sent tumbling back in time. Suddenly, I’m back in my grandparent’s cabin in Maine, where I spent many summers growing up — and where the distinct, musty aroma of mothballs wafted out of the hallway closet. If I catch even a whiff today, I’m instantly whisked away back to that hallway, filled with a deep sense of comfort and security.
It seems like a given that smell is closely linked to memory. (You might be recalling your own odor-triggered recollections right now.) In fact, many studies have found a connection between smells, emotions and powerful memories. Neuroscientists have even used fMRI brain scans to show that odors evoke strong memories and emotions due to the brain regions responsible for processing them.
In short, the nose knows more than we think. Here’s what researchers have revealed about how smell, memory and emotion are intertwined.
What Parts of the Brain Control Smell?
Scholars and scientists have been picking at the link between olfaction and emotional memory for well over a century. And while that connection is becoming better understood, our understanding of it is still fairly primitive, says Venkatesh Murthy, a neuroscientist at Harvard University whose lab explores the neural basis of odor-guided behaviors in animals.
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Still, the architecture of the brain itself may offer some clues. Smells are processed by the olfactory bulb, a structure located in the front of the brain, before being sent on a direct route to the limbic system — which includes the amygdala and the hippocampus, the regions that regulate emotion and memory. These privileged connections between the olfactory system and the limbic system may help explain why odor, in particular, can evoke stronger emotional memories than our other senses.
“When we think of [the regions responsible for processing] memory and emotion, they just happen to be physically or geographically close to the parts of the brain involved in smell,” says Murthy. “One attractive idea is that maybe it’s the proximity of these connections; it takes fewer stations to get directly [from smell to emotion and memory.]”
Emerging research appears to back this up, too. Scientists used neuroimaging and intracranial electrophysiology — where electrodes are placed directly on an exposed participant's brain to record its electrical activity — to show that the connection between the hippocampus and olfactory system is stronger than our other sensory systems, according to a study published in Progress in Neurobiology in 2021.
What Types of Memory Involve Smell?
Not all types of memory are created equal. Working memory, or short-term memory, refers to our ability to retain small bits of current information in our minds — like when you’re thinking of a phone number while plugging it into your contacts list. Semantic memory, on the other hand, refers to our general knowledge of the world, like facts and abstract concepts.
But it’s episodic memory, or memories of specific events from a first-person perspective, that’s most closely linked to our sense of smell. In other words, odor-triggered memories tend to be autobiographical, and deeply tied to the person experiencing them.
“A lot of the power for odors to evoke particular memories comes from a particular life experience that an individual person has had,” says Theresa L. White, a professor of psychology at Le Moyne College who studies learning, memory and sensory psychology. “Doing research with odors is so variable, because people have had a variety of experiences.”
How Does Taste Impact Smell?
What’s more, these memories can also encompass things that we tend to associate with our sense of taste. (Try pinching your nose the next time you sink your teeth into a particularly flavor food.) French novelist Marcel Proust’s literary musings on memory were famously triggered not by a specific odor, but by a nibble of a madeleine cake and a sip of tea.
“Rather than thinking about pure odors, if you think about foods, you know that people have widely-varying palates,” says White. “A lot of what comes from flavor is the sense of smell.”
Read More: Why Does Our Sense of Taste Change As We Get Older?
Murthy agrees, noting that what we think of as “taste,” or flavor, is a combination of our senses of taste and smell. That’s because when we take a bite out of something, the molecules from the food that we’re eating are broken down and sent to the nasal epithelium and olfactory bulb for processing.
“When you’re eating, a huge amount of the sense that you’re getting is actually smell, because the chewing volatilizes those things and they go into the back of your mouth and eventually the nose,” adds Murthy.
Why Does Smell Trigger Memory?
Let’s recap: A growing body of research has found connections between odors and powerful, emotionally-charged memories. Scientists think that memory and smell may be more closely linked than other senses because the brain’s layout enables quick connections between the olfactory system and the limbic system, where emotion and memory are processed.
What’s more, researchers think that memories triggered by smells tend to be associated with unusual scents, or scents from long ago that we don’t often think about — like, in my case, the musky aroma of mothballs. When that happens, it can feel like we’re re-experiencing those emotions for the first time.
“When we notice something that we haven’t smelled in a particularly long time, it can drag us back to that episodic memory, and connect us to it,” says White.
For White, the smell of gardenias takes her right back to childhood, when she had gardenia bushes in front of her house and her aunt’s house as a little girl.
“I can remember being out there with my aunt and clipping them, and literally smelling them until they went brown,” she says. “It takes you back to that time, and to something early in life.”
“I think that’s one of the reasons smells stand out to people,” adds White. “The memories they uncover aren’t ones that we think about very often. Most people are caught by surprise at falling back into that.”
Read More: What Happens in Your Brain When You Make Memories?
