A Whiff of the Past: How Smell Awakens Memories We Thought We'd Forgotten

Jamie sat beside the large library window, surrounded by students with their heads buried in books, seemingly oblivious to everything around them. Before him lay a mountain of biology notes, but his attention had wandered far beyond the pages.

Outside, the sky had opened up. Rain poured onto the fresh grass, darkening the heaps of sand scattered across the ground. After more than ten months without a single rainfall, the earth was finally receiving its long-awaited shower.

A slight opening beneath the window frame allowed a cool breeze to slip through, carrying with it something strangely familiar.

And then it hit him.

The smell of rain-soaked earth.

He knew that smell.

Suddenly, the library seemed to fade away.

He was back in the city where he had grown up. The familiar streets where he once cycled on errands, his family's garden, the scent of damp soil rising from the ground, and the gentle chuckles of his parents sharing a cup of tea. Scenes from a childhood that had long slipped into the background came rushing back, as though the years between then and now had momentarily vanished.

For a fleeting moment, the past felt almost within reach.

He hadn't been thinking about those streets or the garden. He hadn't tried to remember any of it. Yet somehow, a single scent had brought it all back with startling clarity.

But how can smell unlock memories that had remained untouched for years?

When Memories Show Up Uninvited

Scientists have a name for those moments when memories suddenly pop into your head without warning: involuntary autobiographical memories. Interestingly, memories triggered by smells often feel more emotional than memories prompted by sights or sounds. This is often associative, meaning that a memory is triggered by something in the present that shares a distinct similarity with an experience.

In simple terms, this could mean remembering walking into your mother’s closet at the age of six and noticing her favourite perfume. This may seem like a very ordinary event, one that is likely to be forgotten over time. However, ten years later, you hurriedly jump on a bus, and the lady sitting across from you happens to be wearing that same perfume. Suddenly, the memory of walking into your mother's closet comes rushing back, even though there was no deliberate attempt to remember it.

This cannot be entirely equated with mind-wandering. While mind-wandering involves the mind drifting away from what is happening in the present, involuntary autobiographical memory involves the spontaneous recollection of a personal experience without consciously trying to remember it. Although both can occur together, they are not the same.

But here's something else to think about. Just because a memory feels incredibly real doesn't necessarily mean every detail happened exactly as we remember it. Remember our earlier discussion about false memories? Well, our brains can sometimes fill in missing details or even convince us of things that never happened!

So, while a familiar smell might bring the past rushing back, it doesn't necessarily mean we're remembering every detail correctly.

Sounds Fascinating, But Is There Proof?

Well, there is! While this has probably happened to you or someone you know, a few curious scientists decided to take a closer look.

In 1935, psychologist Donald Laird had a curious thought. What if our noses could do more than just smell? What if they could bring back memories we hadn't thought about in years? To find out, he asked 254 people to share moments when a smell unexpectedly reminded them of the past.

Many described vivid memories, but one account was particularly interesting. A man whose father worked at a sawmill explained how the smell of sawdust brought back remarkably clear pictures of his childhood. He could deliberately try to remember the people and objects from those days, but it was the smell that brought the entire scene back to life, almost as though he were experiencing it all over again.

This suggested something fascinating: smells might not just remind us of past events. They could make those memories feel remarkably vivid and real.

Years later, in 1999, Aggleton and Waskett decided to put the nose to another test. This time, at the Jorvik Viking Centre in York, a museum filled with the sights, sounds and smells of Viking life. They invited former visitors to answer questions about their trip while exposed to either the original museum scents, unfamiliar scents or no smells at all.

After a short break, the smells were switched in two groups, and everyone answered the questions again.

And guess what? Those who went from unfamiliar smells to the original Viking scents remembered significantly more details! The other groups showed no such significant improvement.

But how are smell and memory linked?

The Science Behind the Sudden Flashbacks

Past research has suggested that there is a special neural connectivity between the olfactory cortex, amygdala and hippocampus that is related to the connection between smell, emotion and memory. In 2004, Herz and colleagues decided to peek inside the brain. Using functional magnetic resonance imaging (fMRI) scans, they studied a group of women exposed to scents linked to personal memories. They found greater activity in brain areas involved in emotions and memory, including the amygdala and hippocampus regions, than when the memories were prompted by corresponding visual cues.

So perhaps our noses have been keeping little reminders of the past all along, just waiting for the right smell to bring them back.

What’s special about the nose?

Firstly, the nose is pretty cool, and it probably doesn't get enough credit for what it does!

A human has 400 types of functional odour receptors, which means you can potentially distinguish an astonishing variety of smells. But that's not all; the nose is situated in a special place. So just like how nutrients have to pass through the blood to different organs, similarly, sensory information from your eyes, skin and ears has to pass through the thalamus before reaching the cerebral cortex. Think of the thalamus as a bouncer standing at the door, deciding which information gets passed along.

Smell plays by a different set of rules. While information from most senses stops at the thalamus before reaching higher brain regions, smell takes a more direct route to brain areas closely connected to the limbic system. These include regions associated with the amygdala and hippocampus, which play important roles in emotions and memories. In fact, the olfactory system shares close anatomical connections with these limbic structures. So, it's almost as though odours know exactly which door to knock on!

That’s a lot of science, so how does it help?

Just as you may be curious about the relevance of all this, Morrison and his colleagues had a question of their own. Could a smell become so closely linked to a frightening experience that simply smelling it again would bring back the fear?

To find out, they introduced mice to certain smells while giving them mild electric shocks to their feet. After a while, something interesting happened. The mice began to fear those smells, even when there were no shocks!

But that wasn't all. The researchers discovered that the mice had developed more smell-detecting neurons sensitive to those particular odours, along with larger glomeruli, tiny structures involved in processing smell signals.

Now came another question. Could the mice learn not to be afraid?

So, the researchers repeatedly exposed them to the same smells, only this time without the shocks.

And guess what? The mice gradually became less afraid!

Now, think about what this could mean for people living with post-traumatic stress disorder (PTSD), where a familiar smell can sometimes bring back frightening memories. Could understanding how the brain learns and unlearns these associations help researchers develop better treatments?

Of course, what happens in mice may not work in quite the same way in humans, but it raises some fascinating possibilities for understanding how smells become linked to our experiences.

And perhaps that's what makes our sense of smell so remarkable. A familiar scent can bring back the warmth of childhood, the comfort of someone we love, or even a moment we'd rather forget.

So, the next time a familiar smell suddenly takes you somewhere you haven't been in years, remember Jamie and that rainy afternoon in the library.

Sometimes, all it takes to revisit the past is a single breath.

Image disclosure:All illustrations featured in this article were created using generative artificial intelligence (AI).