Smell is our most evocative sense, with instant associations with emotions and memories. Cognitive neuroscientist Rachel Herz, PhD, explains why she loves the stink of a skunk, why a blow to the head can kill off your sense of smell, and how you get a new nose every month. Plus… why stores, hotels, and other brands create signature scents.
Phil Stieg: Hello, I’d like to welcome to Dr. Rachel Herz, the world’s leading expert on the psychology of smell. She is an academician at Brown University and Boston College who has published multiple books that analyze the relationship between smell, emotion and memory. Rachel, thank you for being with us today.
Rachel Herz: Thank you, Phil, it’s great to be here.
Phil Stieg: In the preface of your book. You talked about how this early event in your life seems to have affected your life’s work. Can you tell us? It’s kind of a cute story, I guess, but can you tell us about it?
Rachel Herz: Well, it’s also interesting how we always tell our narrative from the present time backwards, so it all makes sense retrospectively. I don’t know that at the time it was really dictating my life’s future work.
But the story is that I love the smell of skunk. And the story has to do with why I love the smell of skunk, since it is a peculiar passion.
The first time I ever experienced the scent, I was in the backseat of the car with a beautiful summer day. I was probably about four or five years old. My parents are in the front seat. All of a sudden, the scent wafted it into the car from the unrolled windows. And my mom, from the front seat said, oh, I love that smell. And I didn’t know what it was. And so I’m sitting there, it’s a beautiful day. I love Mommy. Mommy said she loved that smell. And so I love that smell, too.
Subsequent to that, when I was a little bit older and on the playing grounds with a bunch of other kids, the same scent manifested. And I said, oh, I love that smell. And everyone turned around and went, Gross, you’re so weird. That skunk is disgusting. You’re disgusting, et cetera, et cetera. And then I learned that that was not a popular opinion to have and not to share it widely, but I did not know that that’s what it was. And this really speaks to the fact that we learn our experiences with smell through our associations, through our first encounters, and particularly the emotional meaning that coalesces with that scent. And for me, it was Mommy and beautiful day and all good things.
Phil Stieg: And a scent that she liked. Do you feel that smell is a stronger mechanism for triggering memories than the other senses?
Rachel Herz: So I don’t just feel it, I know it. But just to unpack that a little bit better, it’s not necessarily that you are going to get more memories triggered by smells. Memories triggered by smells are much more emotionally potent, we feel them much more viscerally. They activate the emotional centers of the brain much more acutely, and they also bring us back in time and space to that original event, much more potently. So they’re much more evocative of that original experience.
Phil Stieg: Can you really explain to us in simple anatomical terms whereby an odor actually brings back a memory?
Rachel Herz: So the mechanism of smell is that we have chemicals that are floating out in the air. We inhale through our nostrils. And the first location where these land is in this mucous patch right at the top of our nostrils that we could ostensibly touch if we could stick our finger up high enough because they are directly exposed to the environment. That’s also a unique feature of the sense of smell. And from there, an electrical chemical pattern of activity is produced which then goes into the olfactory bulb. These small structures that are basically at the level of our eyebrow. They’re about the size of a pea or a raisin. And from there immediately are transduced to a part of the brain that’s called the limbic system. And specifically these two interconnected structures, the amygdala and the hippocampus. And the amygdala is specifically involved in processing emotion and emotional memory. And the hippocampus is involved in learning and association. And these conjoined structures is actually where our conscious perception of scent takes place.
The sense of smell is also really amazing because it’s constantly regenerating. Those neurons that are out in your nose are constantly being born and dying and being born and dying, basically because they’re exposed to toxins from the air that we breathe all the time. They get killed off, and then they regenerate. So basically, you’ve got a new nose basically every month.
Phil Stieg: What’s the evolutionary importance of the development of smell regarding the human species?
Rachel Herz: Well, so the basic function of smell is the same across species. It is basically to approach or not to approach or avoid on the basis of what is the meaning of that scent. So if a scent is a signal for danger, you want to avoid it. If it’s a signal for poison, et cetera, you want to avoid it. Things that smell good we want to approach, and things that smell bad, we want to avoid.
Now, what’s different about us and a few other species is what smells good and what smells bad is not innately hardwired. We are generalists as a species, meaning that we can exploit any habitat on this planet. So anything, generally speaking, could potentially end up being food or could end up being something that we want to avoid. Whereas animals that live in very restricted ecological niches, they have exact specific prey, exact specific predators. They’re actually born knowing what the good smells and the bad smells are. But we, as a function of being generalists, have to learn what they are, and we learn very, very quickly. It only takes one experience to get that stamped in. And once we learn it, it kind of can feel as if it’s innate. But our responses are actually based on this prior learning.
Phil Stieg: You state in the book that smells evoke emotions, but they also can become emotions. That’s a distinction you need to make for me.
Rachel Herz: What I mean by that is that smells can become a proxy for the experience of emotion itself because they so instantly can evoke emotions once they have been connected to them. So the first time you ever meet a scent, it doesn’t do anything until it becomes connected to something emotionally meaningful. Now, a lot of the time, scents don’t become emotionally connected to something super strong. They’re just kind of generally good. Like I like the smell of coffee or I don’t like the smell of the tar on the street, or something along those lines. However, when a sense is connected to something that’s emotionally potent, like a special person or other source of experiences as a function of that deep interconnection, and because the first response we have to ascend is fundamentally emotional because of the neuroanatomy behind it, it can actually become a proxy for that emotional experience. So you smell something and you instantly feel happy, excited or worried or nostalgic or a whole variety of other emotions without even consciously, necessarily registering why it is you’re feeling that way. So they have the ability to really elicit this sort of basic emotional response very instantaneously.
Phil Stieg: You do an excellent job in your book by getting the reader hooked. In the first chapter, when you start off talking about an individual, Michael Hutchins, who loses the ability to smell and the impact it has on his life. Can you describe that for us?
Rachel Herz: Yeah, sure. So for those of you who don’t know Michael Hutchinson, was the lead singer of the band in excess who is this really popular Australian new wave band. And he actually had sort of one of these kinds of tragic rise to fame, excessive stardom. Everything is wonderful. And then major crash, tragedy and demise and actually literally major crash, tragedy and demise because he was hit while he was riding a bicycle, leaving a club after a show and fell off his bicycle and hit the back of his head and suffered a mild traumatic brain injury. However, this mild traumatic brain injury ended up totally destroying his sense of smell.
The way the sense of smell works is that it’s basically this patch of membrane at the top of your nostrils. But then the sensory neurons are located right there. And the axons of those sensory neurons, which are what goes into the brain, have to pass through this very thin, porous bone that’s at the level of your eyebrow called the cribiform plate. And it passes these sort of axons pass through it. And I like to use the analogy of like a Chia pet. So these axons are passing through and then they bundled together to form the olfactory nerve and so on. What happens is if you get hit hard at basically the level of the eyebrow or at the back of the head, you get that bone moving and that bone moves and it shears off those axons.
Now what happens is when this cribiform plate gets Jarred, those axons have difficulty now getting back into the brain, even though they can regenerate and form and so forth. And typically this happens because the accident or the trauma to the head when this happens causes this curved form plate to start to get inflamed, and that inflammation causes those tiny holes to scar over. So even though the axons are regenerating on the other side, on the side of your nostrils, they can’t get back up into the brain. And that’s why people lose their sense of smell permanently when they get sort of relatively minor accidents that can happen either in a car accident or even hard contact sports like football or soccer, where people are getting hit in the head a lot. And so these issues are what led, in his case, to his losing his sense of smell, Michael Hutchins losing his sense of smell and permanently, and at that point started this downward spiral in his life where everything started falling apart. He went into a major, very serious depression and ended up committing suicide.
Phil Stieg: So that got me hooked. And then right away, you go on to the next subject, which actually kind of surprised me because it’s a subjective issue I would think – the story about Jessica, where it becomes a medical legal issue. Now, I would never give her a lawyer, put it past the lawyer to miss an opportunity, but she lost her smell, and this became a medical legal case. I understand you testify in situations like this.
Rachel Herz: Yes. So I work often as an expert witness in cases of involving the sense of smell, specifically the psychological side of it. And those cases are pretty much divided up between these kind of personal injury lawsuit cases where someone loses their sense of smell in an accident and the insurance company is like, well, who cares? It’s not like you lost vision where the American Medical Association says that’s worth 85% of your life’s worth. This is only according to the American Medical Association, worth between one and 5%. So here’s your tuppence. And now go on your merry way and leave us alone. Otherwise, you seem fine.
And this was the first case where I was ever brought in to say, no, wait a second. This is not just nothing. This actually has affected this person in a very serious way, which has actually changed the entire spectrum of her life. And it was actually as a function of meeting this person that I decided to write the book The Scent of Desire, because I had never sort of seen the other side of the equation so dramatically. And for this woman, everything in her life had turned upside down.
One of the things that was so touching for me is that she said that she had never paid attention to her sense of smell before. She completely took it for granted. She completely ignored it. And here was this person. Now, she was in her late twenties. She had been married for a few years. She had a new career. Everything was moving along forward, and she was planning on having a family. And all kinds of things were moving ahead. And then she has this accident where she ends up losing her sense of smell. And now everything in her life has turned upside down.
She has lost the desire to be intimate with her husband. She does not want to have children now because she’s first of all worried that she’ll be a bad mother because she won’t be able to smell when there’s, like the cookies are burning in the oven or the nappy needs to be changed. But also more profoundly that she won’t bond with her baby because she can’t smell her baby. She was no longer capable of doing this high-level sort of analytical aspects that her job demanded, because actually there’s a very strong connection between spatial and analytical abilities and your sense of smell because of the hippocampus, that part of the brain is also involved in spatial memory and spatial mapping and so on. People who lose their sense of smell actually tend to get into problems with that.
And her whole quality of life had completely fallen apart. She became paranoid. She didn’t want to socialize. She was worried about body odor, I mean, just about everything you can imagine. And she was so stunned by the degree to which this loss could be so devastating that I mean, of course I wanted to help her, but it was just that she presented such an intense case of everything that can go wrong when you lose a sense of smell. And she had no idea that this was involved. So I came in to basically explain to the insurance company, no, wait a second. This is not 1% of this person’s quality of life and life’s worth. This is huge.
Phil Stieg: Clearly altered her life going forward – a devastating story.
Narrator: At the beginning of the pandemic, public health officials quickly recognized that the loss of the sense of smell was a major indicator of the onset of Covid-19. But what does it mean to have so many people suddenly become Anosmiacs?
In the summer of 2020 a research team in the UK evaluated feedback from 9,000 members of a Facebook group. They wanted to gauge the psychological impact of these widespread occurrences of “Anosmia”, or the absence of the sense of smell.
They wanted to gauge the psychological impact of these widespread occurrences of “Anosmia”, or the absence of the sense of smell. They described Anosmia as an “invisible disease”. As one participant put it:
Reenactment of quote from study:
“When I tell someone I have lost both taste and smell, they react as though it were something minor. It’s 2 of the 5 senses!! People seem to show very little interest or sympathy. I realize it’s not as horrible as going deaf or blind. But I would just expect more than a blase´ response…”
Narrator: Understandably, anosmia alters ones relationship to food. Some participants reported a loss of appetite as food had lost all of its sensual appeal, while others found themselves constantly overeating, stuffing themselves with highly textured, overly spiced food in a frenzied effort to stimulate some feeling of satisfaction.
Covid-19 can also cause other smell-altering conditions, like phantosmia, meaning non-existent or “phantom” smells. Patients have described a constant smell of burnt toast, or being surrounded by the smell of marijuana — but without the experience of getting high.
Most disturbing may be the condition of “parosmia” – the distortion of once familiar smells. People with Covid-related Parosmia often described the smell of their food with words like “sickly metallic cat food” … “dirty fish tank” … or “fruity sewage”. Ironically, sewage itself was frequently described as becoming less repulsive, or, as one participant it – “Poo now smells better than coffee.”
Thankfully, for 90 to 95 percent of Covid patients, Anosmia is temporary and resolves in a few weeks, or sometimes months. But for that unlucky 5 to 10 percent whose “Long Covid” symptoms drag on, we just don’t know yet how long it will be before they can safely … wake up and smell the coffee.
Phil Stieg: In my profession, a lot of people come in with tumors in the region of the olfactory bulb. And actually, the thing that they seem to miss most postoperatively after the tumors out is the altered sense of taste that they have.
Rachel Herz: Well, actually, there’s a whole chapter on the book on taste, and explains the connection between smell and taste and what produces what actually is the experience of flavor. So, for example, the sense of taste, which is also a chemical sense, is really only picking up the perception of salty, sour, sweet and bitter. And we can also put in umami if you want to. But everything else that we experience when it comes to food is due to aroma and the aroma that’s being released from food as we chew in our mouth. And those aroma molecules are actually getting up into the nose through an open airway system between the mouth and the nose, which is also why if you have a cold and your nose is blocked, food doesn’t seem to taste right because the mucus is blocking that passage. So, for instance, the taste of bacon is just salt. It is the aroma of all the bacon molecules that give us the flavor of bacon.
So there’s a huge component of it that’s smell based. And when people lose their sense of smell, they just say taste because it’s an illusion, because it’s happening inside your mouth, but really it’s happening in your nose. And fundamentally, it’s happening in your brain because your brain is knitting together those two sensations.
Phil Stieg: Do you think that people that have no sense of smell have fewer memories?
Rachel Herz: Well, so first of all, there are two different types of being. What’s called anosmic, which means that you don’t have a sense of smell. One is acquired anosmia, which is the most common people who had a sense of smell, and either through illness or injury end up losing it, and then the other kind of what’s known as congenital anasmics. And those people are born without a sense of smell, and that’s actually quite rare. But absolutely, both types of people have memories. It’s just that the degree to which a smell can trigger those memories is different. Fortunately, people who are congenitally anosmic really don’t suffer much in terms of the quality-of-life issues that the people who had it and then lost it do. It depends on the individual. for instance, if you are a chef and you lost your sense of smell, it might be different, but it also depends on your own personality how much smell actually is going to influence you and affect you. But people who don’t have the sense of smell, no matter how they don’t have it, still have memories. It’s just the question of whether their memory could be triggered by a smell or not. And if they don’t have a sense of smell, obviously it can’t be.
Phil Stieg: People frequently talk about individuals that are born blind that their other senses become accentuated. Have you studied blind individuals and is their smell more accentuated or their hearing sense?
Rachel Herz: So actually, it seems that from a neuroanatomical perspective or sort of neural organizational perspective, the sense of smell does not become more acute in people who are born blind or deaf or so forth. However, the attention that’s paid to smell and sort of the cognitive real estate, the cognitive processing of smell can become accentuated because people need to rely on the sense more. And actually, any time that we pay attention to smell, whether we have all of our senses operating or not, we recruit more of our brain in the act of smelling. So we actually can smell more and better.
Phil Stieg: Earlier, you talked about the regular turnover of the sensory organ in terms of smell, both from day to day or week to week, and then also in the process of aging. It made me think about a sommelier the wine tester and going for the bouquet. Does that change over time? So even from month to month might have a different appreciation for if I had the same wine in front of me, I’d appreciate a different bouquet because the cells have turned over?
Rachel Herz: That’s a fantastic question. And the answer is I don’t know, but probably actually because the cells are not all turning over exactly at the same time. So you’re going to have some neurons dying off and being replaced at different speeds. And so as a function of that constant sort of gradual shifting that’s taking place, I would actually say most likely that that bouquet is going to be ever so slightly different at given points in time. So not only do we have a unique nose compared to every person because the specific receptors actually that we have that are being expressed in our nostrils are different for every single person, but actually at any given moment in time, our perception of a Rose or a Cabernet may be actually ever so slightly different within our own self.
Phil Stieg; I’ve certainly noticed whenever I walk into Sachs Fifth Avenue, Macy’s or Bloomingdales that on the first floor, they always have the perfume section to kind of get you. But then I was surprised in your book to read about they’re doing it in casinos and they’re doing it in hotels. I think I understand what the goal is, but how are they doing it? Is there a particular scent that’s good for one type of store? And I was even unaware of casinos. Tell me a little bit.
Rachel Herz: Yeah. So this is a part of what’s referred to as scent marketing or even scent branding. What this is basically doing both in the clothing stores or in the hotels or the casinos is creating another layer of the signature of what it is that the brand is. So, for example, Abercrombie and Fitch, that clothing store has a very specific scent if you ever walk into it. And so that scent is part of their brand, you can actually buy that scent. It’s called “Fierce”. They sell it as a fragrance to wear and so forth. But it’s very much iconic and associated to what the brand of Abercrombie and Fitch is. And likewise, hotel chains that want to have a specific sort of connotation that’s not just visual, but that’s actually emotional and associational will use a specific signature scent that’s been created as their own particular unique blend and have that in the lobby so that the people, when they first walk in can have that scent being activated, and then that will be part of the brand. It’s basically part of the signature, part of the logo of the brand. And that kind of reinforces the emotional experience. And usually the lobby is the most opulent and sort of pleasant place that creates a pleasant association. Casinos are doing the same thing from the perspective of essentially a kind of a branding. So you walk into a particular casino and it has that particular scent connection, and you walk into another one. Let’s say if you’re in Las Vegas and it’s going to smell different. Actually, even the airport in Las Vegas has its own signature scent in it. So it’s part of creating the memory connection.
Phil Stieg: That’s cute. It’s funny. As I was reading your book, I kept wandering back. I had an Austin Healey 3000 when I was in College, and I had a particular leather smell in the interior. And I can still smell that sitting here talking with you. I keep looking for another car that has that scent.
Rachel Herz: We had an Austin Marina when I was growing up, and that had a funny smell, too. I think I know what you mean.
Phil Stieg: Dr. Rachel Herz. I don’t think any of us will take the sense of smell or a particular order for granted after this delightful conversation. And I think that the conversation is going to continue and the importance of smell in our emotional and memory lives is going to be discussed much more fully in the future. Thank you so much for being with us.
Rachel Herz: Well, thank you so much for having me it was my pleasure.