Instant Genius - Why smell is our most underrated sense

Episode Date: January 10, 2025

It’s commonly thought that when compared to other members of the animal kingdom we humans have a particularly poor sense of smell. But this couldn’t be further from the truth. Modern research has proven that human beings are surprisingly sophisticated sniffers, at least on par with the vast majority of other animals. In this episode, we catch up with Prof Jonas Olofsson, a psychologist based at Stockholm University, to talk about his latest book The Forgotten Sense – The New Science of Smell. He explains what happens when odour molecules enter our nasal passages and are processed by our brains, tells us how our sense of smell is intimately linked to our memories and emotions and answers the question that has been debated across countless dinner tables all over the world: can some people really identify wines just by smelling them? Learn more about your ad choices. Visit podcastchoices.com/adchoices

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I'm Jason Goodyear, commissioning editor at BBC Science Focus. It's commonly thought that when compared to other members of the animal kingdom, we humans have a particularly poor sense of smell. But this couldn't be further from the truth. Modern research has proven that human beings are surprisingly sophisticated sniffers, at least on par with the vast majority of other animals. In this episode, we catch up with Professor Jonas Olofsen, a psychologist based at Stockholm University,

to talk about his latest book, The Forgotten Sense, the New Science of Smell. He explains what happens when odour molecules enter our nasal passages and are processed by our brains, tells us how our sense of smell is intimately linked to our memories and emotions, and answers the question that has been debated across countless dinner tables all over the world. Can some people really identify wines just by smelling them? Welcome to the podcast. Thanks very much for joining us. So in the book, you mention that typically humans or humans, thought to have a poor sense of smell. But that isn't the case at all, is it?

Yeah. So there's been a long-standing notion, at least in the Western world, that the sense of smell is a primitive sense. So already ancient philosophers wrote about this without, obviously, without really doing any experiments. And Aristotle said that the sense of smell was among the worst in the animal kingdom. Women supposedly had a little bit better sense of smell than men, but men were better at using their eyes, and that was a more kind of intellectual sense. And that's like a kind of a gendered stereotype, both related to smell and also related to gender and the relationship between human, non-human animal cognition and perception that has really lasted through the centuries.

And I write in my book about French neurologist called Paul Broca, who wrote about animals as if they could be divided into those who have a good sense of smell or bad sense of smell, or those who are oriented more towards smell versus not. And humans belong to those who did not use their sense of smell very much. But this was before there were any. comparisons, systematic comparisons, and now we have those, and they show a quite different picture. So what do we know about this? In the book, you say that dogs have a better sense of smell than humans, for example, but most other animals are around the same or even worse.

Yeah, of course, it is hard to compare. It's hard to compare the sense of smell and how it is tested relative to a spider monkey or a bat or a cat. But most animals, they like food, and you can train them to find food and treats using their nose. And you can use that to basically teach them how to do a smell test. So you reward them when they find the smell. And so using those types of techniques, researchers have been able to establish sensory thresholds, as they're called, for a variety of non-human animals for a variety of odor molecules

because our sensitivity to one smell doesn't have to say very much about what our sensitivities are for other molecules. So you have to test each species on a bunch of different molecules, basically. And so there was a systematic comparison that was done by Matthias Lasca a professor in

Sweden actually. He aggregated results from a bunch of different studies and compared research on human sense of smell versus non-human animal sense of smell for the same molecule. And when you add those up,

humans are very versatile and very sensitive to many different smells. So if you put them all together, we outperform or are equal to all other animals, with exception of the dog, among those who have been studied. So let's get technical for a minute then. You mentioned their odor molecules. So what happens when an odor goes into our nasal passages and then makes its way into our brains? Yeah, so that is a surprisingly complex process. So there are odor molecules all around us and they have to, for them to become

odors, they have to be of a certain molecular weight so that they are volatile and they can be carried around in the air. They also have to be able to match with a receptor cell, a receptor neuron, in our nasal cavity. So inside of our nostrils, there are two little pockets that contain these odor receptors. At the top of the nasal cavity on each side, there's a an area about the size of a stamp, if anyone remembers what the stamp look like still, that contains about 5 million of these receptor cells in this. So they're very densely packed. When the odor molecule comes up there, it fits with one of these types of receptors.

So we have over 400 of those types. So it's a very multidimensional sense. So we can pick up on hundreds and hundreds of different. molecules. And each odor that we perceive has molecules of different types. They can be dozens of different molecular types that fit with different receptors. And so this interaction with the neuroepithelium, as the receptors are called, that determines ultimately what is a signal that will be transported into the brain. So from our nasal cavities, there are, are small perforations in the base of the skull.

And that's where the axons of these nerve cells go up into the brain, and there they interact with the olfactory bulb. And that's the first part of the brain, the central nervous system, that is being used to process smell. Having said that, why are some smells stronger than others? Is it a case that simply the molecules are in higher concentration? Are these certain receptors more sensitive? Or is it a bit of both?

It's really both. We are very variable. And not just humans, all species have a different kind of sensitivity to different molecules. And it's believed that that has to do with evolutionary pressures. We're pretty good at perceiving molecules that are found in fruits, for example. And that's true for other mammals. And of course, fruit is a major food source.

So it's perhaps unsurprising that we're very good at sniffing out banana flavors, et cetera. So, yeah, so that has to do with it. But also the amount, the concentrations vary a lot because these odors have to be transported in air and they are diluted constantly. So, yeah, it's really both. The objective properties of the smell determine how we perceive them. but also our innate capacity, which can vary from person to person. So that also adds another level of complexity. And above that, our expectations, our memories, our sensitivities, our emotions,

those play a big part as well. And that's why we have people who are very sensitive to smells. And the more they smell a particular smell, the more symptoms they get headaches, nausea, etc. So it's really also individual. So you write about smeliers or wine tasters in the book. Can they really distinguish the profiles of different wines simply by smell? And can anyone learn how to do that? Yeah, we actually did a study where we sought to find that out and we compared wine tasters to basically a group of students that we have had to train on a type of memory game. So we designed, if you're familiar with the game memory, where you find matching pairs.

We devised such a game, but instead of using pictures, we use tea flavors. So we put them in identical cans and sent people home with these tea cans and had them practice on finding the matching smells for 40 days, and it took them about 10 minutes per day. And after they came back, their ability to discriminate between different odors was as good as the sommelier, so the wine experts. So they improved their ability to differentiate between smells, and they also improved their ability to describe with words what they were smelling. And this effect was not just true for the tea smells, but also for smells that were not in the teas. So it was a generalizable skill enhancement. But there were also some things that wine experts were really good at

that was not trained in this particular intervention. And that's the ability to perceive very faint smells. So the thresholds that we call it, those were not affected by training, but the wine tasters were really excellent at that. So probably they are born with a very sensitive nose to begin with. and that's why they go into that profession. So let's move on to bad smells. In the book, you mentioned famous smelly foods like Jorian fruit

or the Swedish fermented fish, Strumming. Personally, I've smelled both of these things, and they're not for me. But you actually say you like the fermented fish. So what's the difference between us? That's a good question. There is some research suggesting that people who like, the smell that can be found in rotten fish or fish that is beginning to go bad, they have a certain genetic makeup that makes them perceive that aspect of the smell less intense.

So that makes it perhaps more tolerable. And I think a lot of the strong food smells that turn people off, that can be related to them having an especially sensitive nose for those molecules. And that's why a lot of smells get worse if they are very strong. That's a general phenomenon in smell psychology. So there's some individual genetic variation there. And that also explains why within each culture, there are minorities who like these niche foods,

even if the majority doesn't like it. So as I explained in the book, I'm from the part of Sweden where we eat fermented herring. But that doesn't mean that my family is unified in love for the fermented herring. No, half of us eat it and half of us dislike it. So there are cultural factors that are playing in, obviously, but there's also individual factors. Wishing you could be there live for the big game. soaking up the atmosphere of the crowd. But too often, life gets busy.

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name audio creates systems that deliver exceptional sound and unforgettable listening experiences at home. Try it for yourself at a focal powered by name boutique. Visit focal powered by name.com for more information. You also mentioned that even single-celled organisms can have a sense of smell. So that's fascinating. But what can that tell us about the evolution of the sense of smell in the wider animal kingdom? That's a good question.

I think one thing that we understand from the presence of smelling in all the different branches of the animal kingdom is how important it is for survival and for being able to get. get energy to avoid hazardous environments. So those basic functions, I think, are really profound for any animal. And that can be seen in very simple organisms that they move towards a food source and move away from toxic environments. That's pretty much what we are doing also when we perceive the smell of a restaurant down the street and were attracted to its smell. Sticking with food then, how closely are our sense of smell and sense of taste linked?

They are intrinsically linked to the extent that we misattribute smell experiences as being tastes. And that's one of the reason why we have neglected, in my view, the sense of smell and forgotten about its importance. So when we have food and drinks in our mouths, we chew and we swallow, and that pushes odorous air. So odors are released in the mouth, and they are pushed through the esophagus and up in the nasal cavity out through the nose. But through that route, which is called a retronasal olfaction, we perceive many of the nuances that we associate with the flax. food, but for some mysterious reason, that is being psychologically perceived as coming from the mouth and not the nose.

And that's called oral referral. And we don't really know why that is, but smells and tastes and things that happen in our mouths when we're eating and drinking, they tend to be fused together in a unified percept that we perceive as coming from the mouth. why we call it taste. But if you pinch your nose when you're eating, you will find that it doesn't taste, quote-unquote, very much. And that's because the smell is so important that we can't really do without it. Another interesting idea you talk about in the book is that our sense of smell is an emotional time machine. What do you mean by that? So that is actually my colleague and

collaborator here at Stockholm University, Maria Larsson, has researched these autobiographical memory aspects of smell. There are sometimes called Proustian memories because of the famous section of the book with Madeleine and the tea at the start of the book. So the protagonist's childhood unravels from that smell that he perceives. And what research has found is, is that odors are very good at triggering those memories from the childhood. And they are often not just from an earlier part of our lives than if you cue memories with other types of sensory materials, for example, pictures or words.

But they're also more emotional and often nostalgic in nature. So we still don't know exactly why the Sesso Smel is such an emotional time machine. but we can experience it. Most of us have one or two of these smells that really brings us back. We do know that the sense of smell is highly developed already from birth. So perhaps the cortical systems being very well integrated, the systems for perceiving smells and the systems for encoding new memories, they are very close to each other in the brain,

and they're very strongly connected to each other. So it seems like they are almost part of the same apparatus in the brain. So there is some kind of evolutionary meaning, perhaps, for us to remember smells very well, possibly because of the importance of remembering foods that made us sick, foods that gave us nutrition, et cetera. So the evolutionary significance is maybe reflected in, that. Another idea in this vein is the effect of smell on our mood. What do we know about that? In my view, smell is a very powerful mood enhancer, but it can really depend on the person and their

smell. And so the evidence is quite mixed for how the sense of smell affects our moods. And my message in the book is that it depends to such a great extent on our personal experiences, perhaps even our genetic makeup. That determines our emotional reactions to a smell. That it's very hard to develop a one-size-fits-all kind of olfactory exposure that creates a certain mood effect. It's often talked about as lavender being relaxing and used in aromatherapy. And there are some studies showing such an effect, but it seems to be moderated by whether we are aware of that it is lavender and that it's used as an aromatherapy odor. So the psychological dimension needs to be taken into account.

If you tell people that lavender could be potentially harmful, the reaction will be completely different. So the subjective experience and the subjective expectation really shapes those emotional effects of ambient odors. In the book, you give a list of popular fragrances. Some of them I really like, like Bergamette, for example. But I really don't like the smell of bananas, which scores quite highly over the population.

A lot of people, and perfumers also, tell me this, that people come in in different workshops, having very strong opinions about what they like and don't like. But when they are exposed to those scents, in an anonymous fashion, their preferences seem quite different. So it's possible that, you know, in the right context, that you would actually enjoy that smell. We carry around a lot of kind of expectations and notions about smells that we like and dislike. But yeah, that can change depending on the context and how it's presented to us. So sticking with bananas and this idea of memory, I remember when I was a kid and I was sick, I used to be giving medicine that was

flavoured with this horrible, revolting synthetic banana flavor. I always hated it. Have I possibly made a connection there? Oh, that would explain it. I think for sure. Those types of experiences can last for a long time. I usually ask my students who has a strong kind of flavor aversion. It's usually about a third of the people in the class. And when they are asked to explain how come they have these strong dislikes, it's usually something that goes back to childhood with being forced to eat a food that they didn't like, for example, or medication. Sometimes it's something that they ate when they were sick.

So their bodies remember it as a potential cause of the illness. That's also a very interesting phenomenon that smells and flavors are very much strongly linked to our perception of the internal state of the organism. So sickness is a very kind of aversive association. the body avoids these smells and tastes because that occurred in the same time frame as the disease. Whether or not they were related or not is a different story. So let's move on from sort of pure odors then to the notion of pheromones. So what are they and how do we perceive them?

The pheromones comes from the insect literature and the idea is that there are hormonal-like, odors, basically. So there are hormones, but instead of communicating within the body, they communicate with other members of the same species, so outside of the body. There are pheromones found in many different species. There's a very kind of strong debate about their presence also in mammals and in humans. But the idea is that they communicate some kind of biological message and that message might not reach the level of awareness, but it impacts us. It's been linked to human bonding, sexuality, attraction, things like that. So how about the idea you talk about of making electronic noses? You know, what are they, what does

that mean? And what could we use them for? So there's a lot of engineering-like research in the last two years, and these developments are powered by new AI technologies, of course. And the idea is to pick up on molecules in the air or from different substances and analyzing them in an effective way. And that's a harder problem than you might imagine, because the concentrations are really faint and they're often, or always, they come in combinations with other, things. So it's always like a very, very messy signal and the signal is also very, very complex. So to have machinery to pick up on that chemical signal and also analyzing it and perhaps even

deriving chemical principles that correspond to human perceptual experiences so that you can recreate a certain smell based on the chemical properties using an entirely different set of ingredients. So you can build it from scratch. That is a great challenge for the field right now. So there is a lot of investment being done in that type of research. And you can use that for a multitude of purposes. Anything from kind of surveying a landscape to detect chemical leaks.

to detecting disease from people's breath. I know people working on kind of COVID-related issues with breathalyzer type of technologies for detecting COVID, very smoothly, cancer detection, et cetera. Thank you for listening to this episode of Instant Genius, brought to you from the team behind BBC Science Focus. That was Professor Jonas Alofson. To read more about the topics we've just discussed, check out its latest book, The Forgotten Sense,

The New Science of Smell. If you liked what you just heard, then please do consider subscribing to Instant Genius on your preferred podcast platform. The current issue of BBC Science Focus magazine is out now. Pick up a copy wherever you buy your favourite magazines or download us on your app store of choice. You can also find us on Apple News or online at sciencefocus.com. This podcast is sponsored by Name, Audio and Focal. The texture and emotional depth of music can be lost through digital sources or poor signal. Name Audio believes you can have digital precision with analogue warmth.

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