Why Smells Evoke Memories So Vividly

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Brain regions are synchronized as neurons fire at a common frequency.

“Nothing is more memorable than a smell.

One scent can be unexpected, momentary and fleeting, yet conjure up a childhood summer beside a lake in the mountains; another, a moonlit beach; a third, a family dinner of pot roast and sweet potatoes during a myrtle-mad August in a Midwestern town.” ~ Diane Ackerman

Or, in the somewhat less poetic language of science: areas of the brain that are central to long-term memory and the sense of smell are coupled together by brain waves oscillating at 20-40 hertz.

The findings, published in the journal Nature, come from the Kavli Institute for Systems Neuroscience in Norway, where they have been using mice to explore the strong connections between smell and memory (Igarashi et al., 2014).

In their research, the experimenters first had to simulate the laying down of a smell-related memory, like the association we might have between cut grass and a summer long-ago.

So, the mice were taught that certain smells led them to rewards of food.

Then, they needed to see what happened in the mice’s brains when they retrieved the memory.

This is analogous to the moment when the cut grass smell hits our noses and we are instantly transported back a decade.

Kei Igarashi, the study’s lead author explained the results:

“Immediately after the rat is exposed to the smell there is a burst in activity of 20 Hz waves in a specific connection between an area in the entorhinal cortex, lateral entorhinal cortex (LEC), and an area in the hippocampus, distal CA1 (dCA1), while a similar strong response was not observed in other connections.”

The entorhinal cortex is important in linking spatial memory to smell — the mice had to remember where the reward was — and the hippocampus plays an important role in turning short-term memories into long-term memories, as well as spatial navigation.

Synchronising the brain

Not only does the study explore how smell and memory are linked, it is also one of a wave of new studies investigating how different parts of the brain synchronise with each other to create functional networks.

Edvard Moser, director of the Kavli Institute for Systems Neuroscience, explains:

“This is not the first time we observe that the brain uses synchronised wave activity to establish network connections.

Both during encoding and retrieval of declarative memories there is an interaction between these areas mediated through gamma and theta oscillations.

Together, the evidence is now piling up and pointing in the direction of cortical oscillations as a general mechanism for mediating interactions among functionally specialized neurons in distributed brain circuits.”

It’s a lot to think about when you are smelling a rose; but it’s all happening in that moment when you pick up a rose, breathe in, and are taken back in time.

→ Continue reading: Memory and Recall: 10 Amazing Facts You Should Know

Image credit: Amanda Tipton



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About the author


Dr Jeremy Dean is a psychologist and the author of PsyBlog. His latest book is "Making Habits, Breaking Habits: How to Make Changes That Stick". You can follow PsyBlog by email, by RSS feed, on Twitter and Google+.

Published: 30 April 2014

Text: © All rights reserved.

Images: Creative Commons License