Have you ever smelled something so familiar that it felt like you were transported back through time into one of your earlier memories? Have freshly baked cookies, your grandmother’s chili sauce, or a specific brand of sunscreen after a long winter actually affected the way you feel?

It turns out that science can explain this link between important memories and the smells associated with them. By studying the activity in our brains, scientists may even have an explanation why your uncle tries to tell you the same five stories about his childhood during the holidays each year.

Researchers have long known that episodic memories – the memories you have of particular events – are made up of the combined information from all of your senses (sights, sounds, smells, tastes, and touch). But trying to understand how this sensory information becomes a memory, or how it affects the way you are able to remember an event, is more complicated.

By looking at the structure of the brain, researchers have found that olfactory (smell) information takes a different path through the brain than input from the other senses. Most sensory information has to first go through a region called the thalamus before being interpreted by the other specialized parts of the brain. The thalamus receives input from many sources and then directs it to the right part of the brain. Scientists often consider this the step when a person becomes consciously aware of something.

When it comes to smells, the olfactory information actually passes through the olfactory memory and processing parts of the brain first. That means that we are actually processing the content and memory of a smell before we are consciously figuring out what that smell is.

This smell center of the brain, the olfactory cortex, is also strongly connected with two other areas of the brain: the limbic system and the amygdala. Both of these areas play strong roles in the emotional components of how memories are created and retrieved.

To understand the possible effect of this connection, one group of researchers exposed people to specific smells at the same time as emotionally intense videos. A week later the volunteers were given cues of either sounds, images, or smells from the earlier experience and asked to recall as many details as they could. The people who were reminded of the smell from the week before actually recalled more details about the emotional experience than the people who were given visual or auditory triggers.

Another group of researchers asked volunteers to create a story in their minds to form a link either between two images or an image and a particular smell. The scientists scanned the brains of the volunteers during the process of forming these connections and later when the people were asked to recall the story that they had created for themselves. They found that the part of the olfactory cortex that was activated when the volunteers were exposed to the smell the first time was activated again during the memory – even if the smell was not actually there.

But what does this mean for the smells we are exposed to and the things we remember every day?

A group of researchers in Sweden asked 72 people between the ages of 65 and 80 to describe the memories that came to mind after being exposed to a certain trigger. These triggers were 20 smells, 20 smells with names, or just the names of those 20 smells.

The researchers kept track of how many memories were brought up with each type of trigger, how old the people were at the time of these memories, how pleasant they felt, and how much they felt like they had been transported back in time.

Though the triggers with the names of smells led to the recall of more memories, the people who had been exposed just to smells not only felt more pleasant and felt more like they had been transported back in time, but also recalled memories from younger ages than the people in the other groups. In fact, more than twice as many of the memories were from under the age of ten when smells were one of the triggers.

Think about this in the context of all of the smells that are unique to the holiday season. Depending on where you are from or what holidays you celebrate, these might be burning candles, evergreen trees, cinnamon, crispy latkes, mulled wine, fresh tamales, or even meat on the grill if you live in the southern hemisphere. Whatever the holiday, when we are flooded with the smells of the season the olfactory cortex and our episodic memories may be transporting us back to memories from our childhoods.

So think about that the next time your grandmother wants to tell you about the first time she had gingerbread as a child. You could explain to her how that smell has made a journey through the olfactory parts of the brain, linked up with the thalamus, and probably even brought in the emotion centers of the brain just to bring on that strong sense of nostalgia. Or you could just listen to the story.

Further Reading

Davachi L and Shohamy D (2014) Thanks for the Memories …. Front Young Minds. 2:23. doi: 10.3389/frym.2014.00023

Gottfried J.A., Smith A.P., Rugg M.D., & Dolan R.J. (2004) Remembrance of odors past: human olfactory cortex in cross-modal recognition memory. Neuron. 42:4 doi: 10.1016/S0896-6273(04)00270-3

Jagust W (2014) Dad Can Do Time Travel … But Grandpa Can't!. Front Young Minds. 2:18. doi: 10.3389/frym.2014.00018

Toffoloa, M.B.J, Smeetsa, M.A.M., & van den Houta, M.A. (2012) Proust revisited: Odours as triggers of aversive memories. Cognition and Emotion. 26:1 doi: 10.1080/02699931.2011.555475

Weir, K. (2011) Scents and sensibility. Monitor on Psychology. 42:2

Willander, J. & Larsson, M. (2007) Olfaction and emotion: The case of autobiographical memory. Memory & Cognition. 35:7 doi: 10.3758/BF03193499

Images

http://commons.wikimedia.org/wiki/Category:Thalamus#mediaviewer/File:Thalamus.jpg

https://www.flickr.com/photos/95632040@N00/3356909594