There’s Nothing Like the Smell of Home

Photo of the metro

About two weeks ago, I arrived very jet-lagged in Paris and couldn’t wait to explore the city. I wanted to take it all in – the sights, the sounds, and the smells. We hit the ground running during our first evening in Paris and rode the metro to the Eiffel Tower. As we waited in the metro station, I realized that I recognized the exact smell of the station. The dusty, metallic smell of the metro brought back many fond and vivid memories during my childhood where I often rode the metro in Toronto. I began to wonder why the smell of the metro brought back such vivid, emotional memories that happened over 10 years ago.

Balls at the museum that emitted smells when you picked them up!

Fast forward to several days ago, I experienced something similar in the Musée du Parfum (perfume museum). It is an amazing museum that is filled with lots of perfume and strong scents that we were able to sniff! One of the scents that stood out to me smelled just like a campfire. Similar to my metro experience, the strong smell of the burning wood brought back many great memories of roasting marshmallows around a bonfire at camp every year.

Fragrant roses at the museum

In the courses that I’ve taken as an NBB major, I have learned about the separate pathways in the brain that are active during olfaction, memory retrieval, and certain emotional responses. Interestingly, I have not yet learned what happens when those pathways interact like when an emotional memory is retrieved from an odor. I wanted to delve deeper and learn more about what is happening when memories and emotions are retrieved from odors.

Olfactory Pathway Diagram

It is already known that olfaction, memory, and emotion are closely linked in the brain. An olfactory signal is transmitted from the primary olfactory cortex to the amygdala and the hippocampus before being sent to higher order olfactory cortices (Shipley and Reyes, 1991). The amygdala is generally associated with emotional responses, while memory processes are closely linked to the hippocampus (Fortin et al., 2004; Cardinal et al., 2002). So, the olfactory signal is relayed through two brain structures that are important for both emotion and memory. 

In 2014, Saive et al. published a study that sought to better understand the interaction between emotion, olfaction, and memory. They tested the hypothesis that emotions invoked by odors facilitate the memory of specific unique events. To do this, they created a model to study memory and mimic real-life situations as best as possible in humans. Participants explored three laboratory episodes, each consisting of three unfamiliar odors (what), positioned at three specific locations (where), within a specific visual environment (which context). Participants explored one episode per day for three days, which they called encoding days. On the 4^th day, called retrieval day, they were tested with distractor odors and the odors that they had previously experienced. The distractor odors were used to make sure that participants were associating the correct smells with their memory. Participants were asked to push a button if they recognized the smell, and then had to choose the specific location that they experienced the odor and the correct visual context. They also rated the odors based on pleasantness to investigate the influence of emotion on memory performance.

This study had several important findings that helped researchers better understand what was going on when participants retrieved memories from specific odors. First, they found that the number of accurately remembered contexts and locations was significantly higher when the odors were more pleasant or more unpleasant than neutral. This suggests that the intensity of the emotion  and the distinctness of the smell (but not pleasantness vs. unpleasantness) enhanced memory retrieval. This is what they expected to see – we are more likely to associate a memory that has emotional context with an odor than a neutral smell that we might experience every day.

Measured response times showed that the more information the participants remembered about an episode (what, where, which context), the faster they answered. Interestingly, the time period between odor recognition and retrieving details about their experience was constant no matter how accurate their retrieval was. Since there was no response time difference observed, researchers suggested that after odor recognition participants immediately recalled the whole episode at once rather than in pieces. Put simply, participants didn’t go step-by-step in their memory to recall where there were or how they were feeling, they instead remembered the entire memory at once. This led the researchers to propose a model to explain the cognitive processes that are involved in this unique memory retrieval. This model states that recognizing an odor and retrieving details about the memory associated with the odor are combined into a simultaneous memory retrieval process that begins as soon as an odor is smelled.

One strength of this study is that it mimicked real-life scenarios in the laboratory as naturally as possible by allowing participants to freely explore contexts with unique odors and ranging emotional valences. This makes the model suggested by the researchers more relevant to life outside of the laboratory and helps us better understand how odor is closely tied to memory recognition. Now I understand why I was able to quickly retrieve memories from so long ago just from a smell. Maybe many years from now, the smell of fresh baked bread will bring back fond memories of the many boulangeries (bakeries) I visited during my time in Paris.

Cheers,

Sarah

Bibliography:

Cardinal, R. N., Parkinson, J. A., Hall, J., & Everitt, B. J. (2002). Emotion and motivation: the role of the amygdala, ventral striatum, and prefrontal cortex. Neuroscience & Biobehavioral Reviews, 26(3), 321-352.

Fortin, N. J., Wright, S. P., & Eichenbaum, H. (2004). Recollection-like memory retrieval in rats is dependent on the hippocampus. Nature, 431(7005), 188-191.

Saive, A. L., Royet, J. P., Ravel, N., Thévenet, M., Garcia, S., & Plailly, J. (2014). A unique memory process modulated by emotion underpins successful odor recognition and episodic retrieval in humans. Frontiers in behavioral neuroscience, 8, 1-11.

Shipley, M., & Reyes, P. (1991). Anatomy of the human olfactory bulb and central olfactory pathways. In The human sense of smell (pp. 29-60). Springer Berlin Heidelberg.

Images:

http://www.cbc.ca/news2/interactives/brain/gfx/smell-pathway.jpg – Olfactory pathway diagram

https://pixabay.com/en/train-subway-tunnel-speed-1836126/ – Metro photo, Creative Commons

Photos at the museum – taken by myself