Tag Archives: olfaction

Not Being Able to Smell Really Stinks !

Bonjour, tout le monde! I’m having a wonderful time in Paris. Classes have been in session for almost two weeks now, and my classmates and I are having a great time learning both in and out of the classroom. This afternoon, for example, we visited Le Grand Musée du Parfum (The Grand Perfume Museum).

Front entrance of the museum

Rachel and Alicia smelling some fancy perfumes!

This museum does a wonderful job at explaining the intricacies of all things perfume! On the ground floor we were welcomed with audio guides in English. They were a huge plus because my French knowledge is very elementary. The basement floor had multiple rooms that explained the history of perfume. From medicinal qualities, like 17th century plague doctors using aromatic vinegars to protect themselves against contagions, to ceremonial scents, like ancient Egyptians bathing Cleopatra with sacred oil blends in 1st century BC, this floor had countless historical stories about perfume. The top floor is dedicated to the art of the perfumer. It contains multiple rooms that play video loops of perfumers explaining their artistic vision and how they’re inspired to create new perfumes every day.

Ground level of the museum

The remaining floor is all about sensory immersion. There are several little tests visitors can take to understand the role of olfaction in their day-to-day lives. Interactive “Fragrance Games” as well as a “Sensory Garden” make this floor both entertaining and enjoyable for most. Sadly, I was not very entertained. I wasn’t able to participate in the interactive games, and I didn’t enjoy this floor as much as the others. This is because I have hyposmia.

Hyposmia is a condition that means you can’t detect odors as well as the average person. It’s a milder form of anosmia, or inability to smell. When I was 17 years old, I was in an accident that left me with a fractured skull and a severe traumatic brain injury, or TBI. I’m totally fine now, four years later, except I still have a hard time smelling the world around me. Wondering how a TBI could possibly affect someone’s ability to smell? Let me explain.

Here’s a simplified explanation of olfaction. Your olfactory bulb, the main part of your brain responsible for processing odors, is located at the bottom part of the frontal lobe of your brain. It has many connections to higher brain areas to process smells and associate them with memories and emotions. Your nasal cavity has a mucous membrane that contains odor receptors on olfactory neurons that travel through a bone in your skull called the cribriform plate to communicate with your olfactory bulb.

In a head injury, a “coup” occurs at the site of the impact with the object. So, as shown in the picture, if someone hits the front of their head hard enough against a wall, their brain will suffer from a coup injury at the front of their brain. A “countrecoup” injury occurs at the site opposite the impact. So, in the same example, the person would experience a “countrecoup” injury at the back of their brain. This rough, abrupt movement causes the cribriform plate to sever some or all olfactory neurons, depending on the severity of the impact. This movement breaks the connection to the olfactory bulb, causing anosmia. My neurologist first described the process to me as a cribriform plate being sort of a like a cheese grater with olfactory neurons threaded through it. He told me that when my accident happened, my cribriform plate shredded my olfactory neurons like cheese. Yum! Before leaving the hospital with this delicious yet sad image, my doctor gave me a bit of hope. He told me that olfactory neurons are one of the only ones in the human body that have the natural capability to regenerate! Despite my wishful thinking, it has been four years now since my injury, and I have very little to no perception of smell. So I have to wonder: is it really true? Will I really be able to smell again someday? I did a little PubMed searching, and here’s what I found.

Researchers at Boston University recently did some research to learn more about regenerated olfactory neurons and their ability to function properly. Previous studies have shown that olfactory neurons do, in fact, have the ability to grow back, or regenerate (Schwob, 2002). The more important aspect of regaining smell, though, is where these neurons reconnect to the olfactory bulb.

If neurons don’t reconnect to the right areas of the brain after damage, then your perception of what you’re smelling would be off. The receptors from your nasal cavity have to link up with the exact area of your brain to tell you what you’re smelling. This process is kind of like an operator making sure an incoming call is directed to the right person. You don’t want to be connected to your Aunt Beth if you’re really trying to call your best friend. Similarly, if you smell something like chocolate, that neuron needs to connect to the area in your brain responsible for perceiving the smell of chocolate.

Dr. Cheung and his colleagues recently conducted a study to find out whether or not regenerated olfactory neurons are able to connect to their corresponding area of the brain. In order to do this, they used mice whose olfactory bulbs glow when activated. This allowed researchers to map where in the brain new olfactory neurons reconnected to after damage. They used an odor that is toxic to olfactory neurons to damage one side of the brain of the mice. Then, after a period of time for the mice to recover from the damage, images were taken of their brains after exposure to different odors. These images allowed for researchers to see where the neurons that regenerated during the recovery period connected to the brain.

They found that when comparing the unaffected hemisphere of the brain and the recovered one, similar areas of the olfactory bulb were activated in response to multiple odors. This means that when neurons in the damaged hemisphere regenerated, they were able to connect to their respective areas of the olfactory bulb. However, they also found that more significant damage limits the renewing ability of olfactory nerves. Severely damaging the olfactory neurons and the nasal tissue they originate in caused scarring of this tissue. Because of this, there was almost no activation in the damaged hemisphere in response to odorants even after a full recovery period. This means that in severely damaged brains, not only did regenerated neurons not find their way back to their targeted areas of the olfactory bulb, most of them didn’t regenerate at all (Cheung et al., 2014).

My new friends helped me pick out a new perfume!

I really appreciated the way this study was conducted. Instead of being satisfied with their results in the first part of their study, Cheung and his colleagues went one step further to see if severe damage would have a greater effect on neuron pathway restoration. I would like to have seen them try a method of physically damaging the neurons, like severing them, in one group as well as chemically damaging them. I wonder if the physical damage would produce results that are more similar to the severely damaged group.

So, would the damage to my olfactory neurons from my TBI be classified as severe? Will my olfactory neurons ever regenerate and find their rightful place connected to my olfactory bulb? Or is the only reason I can detect smell even a little bit due to only a few of my olfactory neurons regenerating? Unfortunately, I can’t answer any of these questions with one hundred percent certainty. Hopefully further research in this area will help me with these answers. Until then, I guess I’ll just stick to visually interactive museums instead of smelly ones and continue to let my friends help me pick out perfume.

Despite not being able to participate in the fun games on the first floor, I had a really great time at Le Grand Musée du Parfum! If you’re ever in Paris, you should totally visit.

Le Grand Musée du Parfum’s location in Paris


Cheung MC, Jang W, Schwob JE, Wachowiak M (2014) Functional recovery of odor representations in regenerated sensory inputs to the olfactory bulb. Frontiers in Neural Circuits. 7: 1-16.

Schwob JE (2002) Neural regeneration and the peripheral olfactory system. Anat. Rec. 269: 33-49.

Pictures from the museum were taken by myself.

Pictures illustrating coup/countercoup injuries and the olfactory bulb were taken from Creative Commons.

Map section was taken from GoogleMaps.

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 4th 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.




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 Reviews26(3), 321-352.

Fortin, N. J., Wright, S. P., & Eichenbaum, H. (2004). Recollection-like memory retrieval in rats is dependent on the hippocampus. Nature431(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 neuroscience8, 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.


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

Making Memories One Sniff at a Time

Earlier this week we visited Le Grand Musée du Parfum, or for those of you who don’t speak French, the grand perfume museum (kind of easy to guess). Before arriving, I didn’t know what to expect besides that we would smell a whole lot of perfume. I was right, the building was filled with a variety of fragrances waiting to be sniffed, but this was not the only thing the museum contained. We walked through a maze of rooms displaying all sorts of information about perfume, starting with a historical journey of the origins from ancient Egypt to the Roman Empire and all the way to present time. Following the history was a sensory immersion exhibit (my personal favorite being a neuroscientist) that explained how our sense of smell works and contained olfactory games and fragrant riddles. Lastly, the museum had an exhibit dedicated to the art of the perfumer, where they had a collection of raw materials, natural and synthetic, most commonly used by perfumers. By the end of the museum my odor receptors were exhausted.

smelling one of the perfumer’s raw materials

My favorite room of the museum was the jardin des senteurs, or garden of the scents. We were told to walk up to these large white flowers, close ours eyes, breathe in the odor, try to guess what scent we were smelling and see if it triggered any memories. I did exactly this and took a big whiff of the first odor. Immediately I could recognize the smell of a campfire and a memory was triggered. I pictured myself sitting around a fire with my dad and sister and we were roasting marshmallows, an activity I love to do! I opened my eyes and was surprised and fascinated at the same time by this result. I quickly moved on to the next flower, closed my eyes, and sniffed. I was instantly at my grandma’s house on Christmas morning and an aroma floated through the air. It was cinnamon! I was reminded of the freshly baked cinnamon cookies we made around the holidays.

Jardin des Senteurs (garden of the scents)

Engrossed by this activity, I wondered if different areas of the brain were used when forming and retrieving memories of events in the presence and absence of strong odors. I did some googling and found a recent study that investigated the brain areas involved in episodic memory retrieval, or memories of a specific event, depending on the presence of an odor during encoding, the initial learning of new information (Galliot et al., 2013). Participants in the study consisted of thirteen female students between the ages of 20 and 23 (interestingly no males were used because olfactory abilities and brain regions can differ between genders). The experimental task consisted of two stages. In the first stage (encoding), 32 colored pictures of objects or animals were presented on a computer screen and participants were asked to determine if each picture contained more or less than three colors. This ensured the participants examined each picture carefully, but remained unaware the test was related to memory. During this task participants wore a mask with a valve that contained filter paper soaked in either water or vanillin, an olfactory stimulus usually considered pleasant. Half of the participants wore a mask with vanillin odor for the first 16 pictures and the other half wore the water filtered mask. The participants switched masks for the second 16 pictures.

types of memory

Two weeks later, the second stage (recognition) of the experiment was conducted. During this stage, each of the pictures used in the first stage (target) were presented simultaneously with a new picture (distractor). After the presentation of the two pictures, participants were instructed to press either a left or right button according to the side of the computer screen the participant believed was the target picture. For the duration of this task, participants were in an fMRI machine so that the investigators could record their brain activity. They found brain areas known to be strongly associated with episodic memory retrieval, the posterior hippocampal formations and the anterior thalamic nucleus, were activated whether or not an odor was presented in the first stage. However, they did find that learning in the presence of an odor causes activation of additional brain areas during the retrieval task. One of these areas was the orbitofrontal cortex and it has been previously described as the main site of secondary olfactory processing. They also found other areas in the frontal lobe of the brain, the superior, middle, and inferior frontal gyri (the bumps on the brain), were activated more during presentation of images encoded in the presence of the vanillin odor. However, the specific role in olfaction of these three brain areas remains unclear. I was very fascinated by the results that memories made in the presence of odors activated different brain regions during retrieval.

orbitofrontal cortex

The study also found that there was no significant difference between the number of correct responses of the target images between the pictures encoded with the presence of an odor and the pictures encoded without an odor. This finding made me wonder if the researchers had presented the odor during the retrieval stage of the experiment, would it increase the number of correct responses of the target images encoded with the vanillin odor? When I smelled the campfire and cinnamon odors, my memories were triggered instantly, so I would hypothesize if the participants smelled the vanillin during the recognition task, it would enhance their memory and would increase the number of correct target responses for the pictures encoded with the odor.

Now as I walk through the streets of Paris smelling the freshly baked breads and desserts, I will be reminded that the memories I form will cause different areas of my brain to be activated among retrieval.


Galliot E, Comte A, Magnin E, Tatu L, Moulin T, Milot J (2013) Effects of an ambient odor on brain activations during episodic retrieval of objects. Brain Imaging and Behavior 7:213219.

Pictures 1 and 2 were taken by Dr. Kristen Frenzel

Picture 3: http://www.mindauthor.com/psychology/semantic-episodic-memory/

Picture 4:  https://commons.wikimedia.org/wiki/File:MRI_of_orbitofrontal_cortex.jpg

The Good, the Bad, and the Smelly: Which Odor Will You Notice?

On any given day in Paris, I’m hit with so many different odors. The wet grass smell mixed with morning breeze greets me as I exit my dormitory. The man standing outside the door however snatches this pleasant nature aroma from my nose, masking it with copious layers of cologne. As I make my way to the RER, the stench of urine overpowers my senses forcing me to run down the stairs to catch the train even faster. And once on the train, I realize that perhaps the French sweat more than the average human being, because boy, oh boy, is that body odor game strong (I merely postulate – no scientific data supports such an outrageous presumption). As I step out of the Metro and onto the stairs rising up towards Bastille, the stench of last night’s garbage quickly hits me in the face.

Figure 1: The debris on the steps of the Opera Bastille on a Monday Morning.

Figure 1: The debris on the steps of the Opera Bastille on a Monday Morning.

The odor of the musty water thrown on the stairs by the sanitation department clashes with the spills of beer along those stairs underneath the Opera Bastille.

As I continue to make my way onto Rue de Faubourg Saint-Antoine, I realize that no matter the time of day, a good number of Parisians will always be smoking a cigarette somewhere. Fortunately, the aromas of baguettes and café au laits begin to swirl around me as I step into a local boulangerie (bakery). My nose feels at ease even if it’s just for a moment.

Figure 2: A local boulangerie near the Opera Bastille.

Figure 2: A local boulangerie near the Opera Bastille.

But let’s say I woke up at 9:06AM and class begins at 10:00AM, and not only does Dr. Shreckengost start on time, but he forces us tardy ones to pay penance by bringing French goodies the next day – aka, I want to get to class on time.

I leave my room at 9:20AM (should have left ten minutes ago), and of course this is the one-day that the tram’s ETA is 7 minutes (instead of in it’s normal 2 minute intervals), the RER is especially slow today, and all of the escalators at Chatel-Les Halles have broken down. Anything that could have gone wrong has and I emerge from the Bastille Metro stop at 9:55AM. The normal walking time from Bastille to class takes a solid 7-8 minutes. Like any other normal human being, I bolt across Rue de Faubourg Saint-Antoine sporting sandals and a bouncing backpack. I arrive panting and sweating at 9:59AM. That’s pretty clutch, I’d say.

Figure 3: Rue de Faubourg Saint-Antoine.

Figure 3: Rue de Faubourg Saint-Antoine.

So what’s the point? You’re probably thinking, “Well that’s cool Reema, nobody cares if you got to class on time (except for maybe you and Dr. Shreckengost)”. Hold your horses – there’s always a point to Reema Stories!

The difference is that when I was stressed and pressed to get to class on time, I did not notice the morning breeze or the aromas of the boulangerie (probably because I didn’t actually go inside one). What I did smell was the smoke from all the cigarettes people were smoking that morning. All I could think about was the detrimental effects of the smoke in my lungs and how these effects would slow my running speed down (not that the immediate inhalation of cigarette smoke was going to immediately affect my respiration at the time, but I didn’t think about the logistics while I was running). The only smells amplified that late morning included harmful or fear inducing odors(I don’t want to die from second-hand cigarette smoke).

I wonder why that it is…

Turns out, I’m not the only one who is extra sensitive to particular odors when I’m under stress. In fact, in some extreme cases of anxiety-related disorder, people are super-sensitive to smells associated with traumatic events in their lives.

In a recent study, Cortese et al. lookeds at the different sensitivity of odors in patients with post-traumatic stress disorder (PTSD). PTSD is a mental health condition triggered by terrifying events, whether those events were experienced or witnessed. Patients with PTSD may experience flashbacks, nightmares, and anxiety from thinking about those traumatic experiences. Many PTSD patients report trauma-related odors are particularly potent reminders of these events. A trauma-related odor might mean the smell of burning to a house fire victim or the smell of bombshells in Iraq or Afghanistan to a war veteran. There’s been increasing evidence and research that odors elicit psychological arousal and retrieval of autobiographical memories PTSD patients (Chu and Downes, 2002). Differential Odor Sensitivity in PTSD: Implications for treatment and future research is one of the first sets of studies of a long-term research plan by Cortese et al. where they looked at the behavioral responses to a range of odors with different qualities (traumatic and non-traumatic) in combat veterans with PTSD, veterans without PTSD, and healthy controls. Particularly, they examined the difference in proportion of individuals reporting distress to different categories of odors, specific individual odors, and the specific hedonic (pleasant vs. unpleasant) valence of such odors.

Figure 4: Buzz words to PTSD.

Figure 4: Buzz words to PTSD.

Cortese et al. found that the olfactory system plays a significant role in the identification of biological threats. The researchers saw that combat veterans, as compared to control subjects, had decreased responses to a large number of odors across various categories and hedonic valence. Cortese et al. believe that hyposmia (a decreased ability to detect and smell odors) may explain some of the decrease in susceptibility of positive valence odors. More so, the experimenters found that combat veterans learned to ignore non-life-threatening “distractor” odors (i.e., garbage, feces, raw sewage) and concentrate on life-threatening odors. Previous studies have shown there to be an association between stress-related disorders and attentional bias toward threat (Bryant and Harvey, 1995; Cisler and Koster, 2010).

Cortese et al.’s study is very important to the field of olfaction, to the field of psychology in which PTSD is studied, and to our country’s veterans. Experimenters analyze a detailed list of odors that affect combat veterans – a type of experimentation that had previously never been done before. However, the researchers don’t actively study this “attention bias” that they claim combat veterans may be exhibiting. The experimenters don’t actively conduct any attentional bias surveying and although data may seem to support previous research on attentional bias, it’s a bit of stretch to predict that there’s a correlation.

While my stressful sprints to class do not closely relate in magnitude to the severity of PTSD that troops go through, I find it interesting to know what odors I detect and what odors I ignore depending on what I’m doing and the mood I’m in.

Maybe I’ll notice every odor on my relaxed plane ride home? Only one way to find out!


Work Cited:

Bryant RA, Harvey AG (1995) Processing threatening information in posttraumatic stress disorder. J Abnorm Psychol 104:537-541.

Cisler JM, Koster EH (2010) Mechanisms of attentional biases towards threat in anxiety disorders: an integrative review. Clin Psychol Rev 30:203-216.

Chu S, Downes JJ (2002) Proust nose best: odors are better cues of autobiographical memory. Mem Cognit 30:511-518.

Cortese BM, Leslie K, Uhde T (2015) Differential odor sensitivity in PTSD: Implications for treatment and future research. J Affective Disorders 179:23-30.