Author Archives: Kimi Chan

The Nose Knows

Hi Friends!

There are so many scents in Paris that I can talk about, ranging from lovely floral fragrances to freshly baked baguettes in patisseries. My olfactory (another word for smell) senses are overwhelmed with all the new odors that I’m exposed to! Last week, during a class excursion, we went to the Fragonard Fragrance Museum. We got to tour the museum and learn about the history of fragrance. Apparently back in ancient times, they used fragrance to preserve the dead so that the people could mourn the bodies during ceremonies. It’s bizarre to think how much the usage of fragrance has changed since the beginning of time! Now the perfume industry is all about making yourself appear attractive. When I was at Fragonard, my favorite perfume scents were floral mixed with fruity. It was an exciting experience to find the perfect perfume for myself (and my family) and it was extremely fun to try to distinguish all the different scents. I learned from one of my classes here that the human olfactory system can distinguish more than a trillion olfactory stimuli (Bushdid, 2014). One trillion?! That’s a ton of different smells!

I got these three perfumes at the Fragonard Museum for me and my family! Hopefully we all smell nice 🙂

Even though there are many pleasant scents here, I also found some that are cringe-worthy. For example, I noticed that many Europeans smoke cigarettes and the streets are constantly polluted with people smoking. Cute bistros will have tables outside where people smoke, which makes my dining experience quite unpleasant when I’m eating in a haze of smoke. I guess I am never really exposed to this much smoking in the states, so I spent the first couple of weeks here adjusting to the smell of cigarettes. After thinking about all these pleasant and unpleasant smells, I started to wonder…how does this relate to neuroscience? Surely my field of study can explain how my olfactory senses adjust to unpleasant smells!

Typical tables outside of a French bistro. This is my favorite one called Bistrot d’Edmond!

In a study done by Ferdenzi et al. in 2014, the researchers found that repeated exposure to odors induces “affective habituation” of perception and sniffing. “Affective habituation” was a phenomenon described by Cain and Johnson in 1978 that states repeated exposure to a scent shifts odor pleasantness ratings toward neutrality. In other words, this theory says that we will start to like a pleasant smell less and feel more neutral to it if we are exposed to it repeatedly. Cain and Johnson’s “affective habituation” phenomenon happens with unpleasant smells, too. Previous studies, however, only focused on self-reported ratings and did not investigate variations of physiological responses among individuals. Thus, Ferdenzi et al. aimed to analyze both self-reported ratings and changes in sniffing patterns to pleasant and unpleasant smells.

Ferdenzi et al. first recruited twenty-six young adults at a French university (what a coincidence this study was done in France!). The researchers split these people up into two groups – the “likers” and the “dislikers” when presented with an odor such as chocolate. They kept track of these groups and repeated this step with 8 different odors through a nasal mask. The “olfactometer” was connected to a nasal mask and measured how much each person breathed, which calculated the levels of sniffing. Lastly, study participants were instructed to rank how pleasant each smell was on a computer.

This picture shows the experimental device and how study participants would wear a nasal mask in order to smell the odor and rank its pleasantness.

This picture shows the experimental device and how study participants would wear a nasal mask in order to smell the odor and rank its pleasantness.

Ferdenzi et al. found that pleasantness significantly decreased with time in “likers” while unpleasantness tended to decrease with time in “dislikers.” Increase in sniffing also correlated to a shift in greater pleasantness ratings, meaning that people would sniff more when they were repeatedly presented with an unpleasant smell. In general, their findings support the “affective habituation” hypothesis both at the self-reported level and at the olfactomotor level. This is interesting because I find this to be congruent with my life experiences. I notice that I find an unpleasant smell less aversive when I’m repeatedly exposed to it. However, I wonder if 26 young adults is a representative sample of the general population. I wish they had more test subjects and an equal amount of males and females in this study so that the researchers can have a more comprehensive analysis. Previous research has shown that females have better odor identification abilities than males (Doty et al., 1985). I wonder what the results would have been if they had an equal number of males and females.

I now understand why I am becoming more immune to the strong smell of cigarettes here in Paris. Affective habituation and neuroscience can definitely help explain this weird phenomenon! Maybe one day I’ll get accustomed to the pungent smell of body odor on the metro (ha ha!). Let’s just hope that people will wear deodorants on hot days so that I don’t have to deal with smelling and feeling body sweat on the train (eek!). I hope you enjoyed this blog post about smell and neuroscience. Sending love from Paris! 🙂



Bushdid C, Magnasco MO, Vosshall LB, Keller A (2014) Humans Can Discriminate More than 1 Trillion Olfactory Stimuli. Science 343: 1370-1372.

Cain WS, Johnson F Jr (1978) Lability of odor pleasantness: influence of mere exposure. Perception 7(4):459-65.

Doty R, Applebaum S, Zusho H, Settle R (1985) Sex differences in odor identification ability: A cross-cultural analysis. Neuropsychologia 23(5)667-672.

Ferdenzi C, Poncelet J, Rouby C, and Bensafi M (2014) Repeated exposure to odors induces affective habituation of perception and sniffing. Front Behav Neurosci 8:119.

Mirror, Mirror on the Wall, Where is the Bestest Dessert of Them All?

Whenever I travel to somewhere new, I always love exploring their authentic cuisine first. Of course, when I told my friends and family that I was going to Paris for study abroad, everyone told me about all the delicious food the French have to offer. Baguettes, éclairs, escargot, et cetera…you name them. Thus, two weeks ago when I arrived in Paris for the first time, I began my hunt for the perfect dessert!

The hunger (and thirst) has been real. Every corner lies a cute patisserie filled with glass cases of tempting desserts. Where do I even begin?! During the first week of the program, our class went on an excursion to Pere-Lachaise cemetery, a beautiful (though slightly haunting) place where many famous people like Oscar Wilde and Chopin are buried. Our instructors led a group scavenger hunt and the prize was a box of French macarons! This was the perfect opportunity for me to try my first macaron in Paris! Being the competitive person that I am, I hurriedly found most of the tombstones on the list with my team while the clock was ticking.

Here is a picture of the winning team snacking on a yummy macaron!

Here is a picture of the winning team snacking on a yummy macaron!

Little did I know the stress induced by this race had led me craving for sweets. This made me wonder – why do I always crave chocolate and sweets whenever I’m stressed? So then I decided to do some research and found some neuroscience to explain this occurrence.

In a study done by Macedo and Diez-Garcia in 2014, they found that excessively ingesting sweet substances may decrease the effects of stress in women and impact leptin levels. You might ask – what is leptin and why does it matter? Well, leptin is a hormone that regulates your appetite and controls energy by restoring it to normal levels in the body called homeostasis. At these normal levels, leptin promotes a feeling of reward by acting on the mesolimbic dopaminergic system. The mesolimbic dopaminergic system is a reward system in our brain and is activated when we do things that are pleasurable, such as eating or even abusing drugs.


Here is a diagram of the mesolimbic dopamine “reward” system.

Anyway, leptin levels rise after you eat and stimulate anorexigen neurons, which suppress the appetite. Basically leptin helps you feel full so that you don’t overeat. It has been found that leptin decreases the feeling of reward in the overweight.

The researchers wanted to study how sweet cravings (SC) in women are related to stress and how SC affect leptin levels in the body. They performed this study in 57 women and divided the participants in two groups – “stress-free” and the “stressed.” These women took a survey that asked them if they had a strong desire to eat sweet food over the last three months in order to identify them as a SC participant. The women then had their blood drawn to measure hormone levels and the researchers measured their body composition.

After controlling for a multitude of factors, they found that among the stressed women, 77.42% had SC. They also found that SC women had significantly higher leptin levels. One way to explain this might be because leptin acts on the hypothalamus (area in the brain in charge of hormones) and suppresses the response to sweet food, changing people’s sensitivity to sweet foods (Niki et al., 2010). Therefore Macedo and Diez-Garcia concluded that stressed women are more prone to SC and this condition is associated with increased levels of leptin.

This study has helped me understand why I keep craving for sweets in Paris. After all, coming to a whole new country has been an overwhelming experience, especially since I have to balance schoolwork and explore the beautiful city at the same time. Five weeks is a lot shorter than I anticipated and I want to travel all over Paris but alas, this is a study abroad program so there is work to do! Now I understand how stress has affected my appetite.

Even at the local Monoprix (the French version of Target), I found myself strolling down the aisles of chocolate and buying a couple bars to snack on later. Back home, I never really buy chocolate because it has never been a habit of mine. A scientific review done by Sinha and Jastreboff (2013) claim that acute stress can increase food intake, especially when highly palatable, calorie-dense foods are available. This helps explain why I keep craving for high-calorie sweet things here! Another study researched on the psychoactive effects of chocolate and desire for more chocolate. They found that the sugar and cocoa contents of chocolate are primarily related to the desire to consume more of it (Nasser et al., 2011). This may explain why I usually eat more chocolate if it’s dark than when it’s just white chocolate. Who knew you could tie in food and neuroscience in Paris?!

Before I go, I wanted to finish this blog post with a few pictures of the delicious desserts I have found and also a map of where I’ve traveled.

Other delicious desserts in glass cases all over Paris – they are always so colorful and pretty!

Delicious desserts in glass cases all over Paris – they are always so colorful and pretty!

Éclair heaven in a patisserie near the Accent center where I go for classes every day! My personal favorite is the Speculoos éclair – om nom nom!

Éclair heaven in a patisserie near the Accent center where I go for classes every day. My personal favorite is the Speculoos éclair – om nom nom!

Lastly, a map of all the places I’ve visited for desserts in Paris. Hopefully by the end of this trip, I’ll have red pins all over!

Lastly, a map of all the places I’ve visited for desserts in Paris. Hopefully by the end of this trip, I’ll have red pins all over!

My journey for yummy desserts does not end here! I shall keep you updated on what and where I eat. Bon appetit, readers 🙂

-Kimi Chan


Macedo D, Diez-Garcia R (2014). Sweet craving and ghrelin and leptin levels in women during stress. Appetite. 80:264-270.

Nasser J, Bradley L, Leitzsch J, Chohan O, Fasulo K, Haller J, Jeger K, Szulanczyk B, Del Parigi A (2011). Psychoactive effects of tasting chocolate and desire for more chocolate. Physiology and Behavior. 104(1): 117-121.

Niki M, Jyotaki M, Yoshida R, Ninomiya Y (2010). Reciprocal modulation of sweet taste by leptin and endocannabinoids. Results and Problems in Cell Differentiation. 52: 101-114.

Sinha R, Jastreboff A (2013). Stress as a common risk factor for obesity and addiction. Biological Psychiatry. 73(9): 827-835.