Speaking of Psychology - Encore - Unlocking the mysteries of smell, our most underappreciated sense, with Pamela Dalton, PhD

Episode Date: December 29, 2021

Many people around the world have lost their sense of smell this past year due to COVID-19. Before the pandemic, scientists had already begun to gain a deeper understanding of how sophisticated our sense of smell is and how it is intertwined with our mental and physical health. Now, the pandemic is giving that research new urgency. Pamela Dalton, PhD, of the Monell Chemical Senses Center, discusses what we know about how our sense of smell works, the connections between smell, emotions and memory, how a rapid smell test could improve COVID-19 screening, how she developed the “world’s worst smell,” and more. Links Pamela Dalton, PhD Monell Chemical Senses Center Music Electronic Ambient Loop by tyops via Freesound.org Learn more about your ad choices. Visit megaphone.fm/adchoices

Speaking of psychology is taking a short winter break, so we're revisiting one of our favorite episodes from the past year. In March, we talked to Pamela Dalton from the Manel Chemical Sciences Center about how scientists are gaining a deeper understanding of human's sophisticated sense of smell and learning more about how intertwined it is with our memories, emotions, and mental and physical health. We also talked about how the COVID-19 pandemic has added new urgency to this research. I hope you enjoy this episode from our archives. Speaking of psychology, we'll be back in January with new weekly episodes. Thank you for listening. Smell has been called our most underappreciated sense. When people think about it, if they think about it at all, many consider it an evolutionary relic, something that is important for animals but not for us humans. We tend to think we aren't

even that good at detecting smells, certainly not as good as our dogs, for instance. About 10 years ago, a The international poll found that more than half of young people said they'd be willing to give up their sense of smell before they'd give up their laptop or cell phone. But in recent years, scientists have begun to learn more about this overlooked sense and how to gain a new understanding of how sophisticated human sense of smell really is, and how it is intertwined with our mental and physical health. Now the COVID-19 pandemic is giving this research new urgency because one common side effect of the virus, even among people with otherwise mild cases, is the loss of or changes in the sense of smell. Some people recover their sense quickly, but for others,

the changes seem to be long-lasting or perhaps even permanent. Why is this happening? And what are the consequences for those who are affected? More broadly, how important is our sense of smell? What are the connections between smell and our emotions? Welcome to Speaking of Psychology, the flagship podcast of the American Psychological Association that examines the links between psychological science and everyday life. I'm Kim Mills. Our guest today is Dr. Pamela Dalton, an experimental psychologist at the Monel Chemical Senses Center in Philadelphia, an independent nonprofit research institute dedicated to studying the senses of taste and smell. Dr. Dalton's research focuses on how our emotions and cognitive processes affect the way that we experience smell,

and how smell affects our emotions and our memories. She's been called a smell ebriety, especially because of her work to identify the worst smell in the world, which we will talk about. How could we not? She's currently leading a research team that's working on a rapid smell-based test called Sentinel to identify cases of COVID-19. Thank you for joining us today, Dr. Dalton. That's my pleasure, Kim. Because COVID-19 is top of mind for most of us these days, can you tell our listeners,

do researchers know why COVID interferes with the sense of smell and is loss of smell a common side effect of other viruses? First of all, a loss of smell. following a virus has been known before, but it has never been as common or as prevalent as it is with the COVID-19 virus. And so we are experiencing a tremendous surge in people, the prevalence of people who are losing their sense of smell, even for a brief period of time. And what it's doing is making them aware of just how important this sensory system is. I've read reports that COVID can cause both anosmia, the loss of smell, or parosmia changes in smell. Can you talk a little bit about the differences between the two and describe what you and other researchers have found?

Yes. Well, certainly it seems that anosmia, which is the complete loss of ability to smell, is the most dramatic manifestation of a virus, including COVID. It seems like it's turning a light switch off. From one minute, you're tasting and smelling, and the next minute, that olfactory sense is completely gone. And, of course, that affects not only your ability to smell, but your appreciation of flavor. So if you're drinking or eating something, it's going to taste or have the flavor of something completely different

once smell is gone. At that point, however, it turns out that people are not always aware, of changes in their sense of smell unless it is completely gone. And so studies that have actually measured people's ability to smell objectively, as opposed to ask for self-report, have found that there are many more people who have an alteration. So, for example, there is a condition called hyposmia, which is a decrease in your sensitivity, which most people may not be aware of unless they were tested.

But it turns out that a really high percentage of people that contract COVID do have either anosmia or hyposmia when tested. Parasmia, on the other hand, is a different condition. It's the ability to smell, but it's the distortion of what things smell like. So your favorite cup of coffee suddenly smells like gasoline or your chocolate energy bar smells a lot like your dog's purse. poop, which is really very disturbing. However, we think this is actually what happens potentially in the process of recovery of smell when you have lost your sense of smell and the odor system, the olfactory system, is regenerating. And there's still a lot to be learned about this condition. It's been very prevalent in COVID, unlike prior viral disorders.

And so we're really, unfortunately, having a great opportunity to study it and perhaps understand it in a way we never had the opportunity to do so before. Now, I mentioned in my introduction that smell is an underappreciated sense and that people don't realize how important it is until they lose it. How does the loss of smell or changes in their sense of smell affect people? What are the mental, physical, and emotional results of losing your sense of smell? It's really interesting because people are not aware until they lose it about how much it informs their ability to know where they are in time and space, their environment. It's sort of the backdrop of everywhere we go and everyone we interact with.

It's a piece of the fabric of our lives that we just don't appreciate until it's been cut away. So, for example, people talk about feeling disconnected. People talk about feeling disoriented or lost. They hug a loved one and they feel like there's an important piece of the emotional response that's missing. A recognition of who it is that they didn't even realize was encoded as part of their, their representation of that person until it was missing. On the Manel Center website, there's a section about how parents can talk to children

about the loss of smell. I know children are not as susceptible to COVID as adults, but those who do get it, is the loss of smell as common among children as it is in adults? Quite honestly, Kim, we don't know yet. And that's something that we're trying to learn with our sentinel test,

because as you mentioned in your introduction, we're developing a very easy-to-use rapid smell test that we think could be suitable for children. I worked on the National Institutes of Health Toolbox odor ID test a number of years ago, and the goal there was to be able to test children as young as three years old in order to be able to assess their ability to smell.

And this was, irregardless of virus, just sort of understanding the natural ability to smell the same way you would test a child's hearing or their vision, because it is an important sensory system. And so we don't really know what the prevalence is among children, but we do know that children may experience their worlds very differently if they lose their sense of smell, and they may not have the language to communicate what that feels like.

Probably prior to viral disorders and post-viral olfactory dysfunction, the most common way for children to lose their sense of smell of smell would be following a head injury, a sports-related head injury or something like that. And so that was really the only cases where we actually had a sense of prevalence. And there, it turned out that the sense of smell was actually pretty, how quickly it returned or whether you lost it, actually was pretty indicative of how serious the head injury was. Post-virally, we're really still learning. I'm intrigued by the idea you mentioned a little while ago,

of the fact that you can measure how acute people's sense of smell is and if it changes over time. I mean, we're all used to taking eye tests. We take hearing tests. You know, there are things that I think are sort of baselines that everybody agrees. The E is facing left or right. We know how many decibels that sound is. It's coming into our right ear. But how do you measure the degree of taste that someone is experiencing?

In the laboratory in a research setting, you would probably measure what their threshold is for detection, presenting them the same way you would decrease the size of the letters on an eye chart or you would decrease the decibels, you would decrease the concentration of a chemical and you would ask them at what point they could detect. And there are different ways to do that. That takes a lot of time. It's quite involved. It would be done, especially for clinical purposes, if someone came in and said, I lost my sense of smell and you would want to evaluate that. But in a rapid screening test, there are other ways to get at that information quickly. And then if you find a problem, you can refer someone for that more involved

kind of testing. But it basically follows the same sensory changes that you would use. It's a field called psychophysics that is used in vision and hearing as well. It's just done with odorants instead of letters or sounds. Most patient sense of smell does seem to come back, I understand, but for those who have long-lasting effects, is there hope or there treatments that you can use to help people regain their sense of smell? And can you train yourself to smell again? There is some hope. It turns out that at least with COVID, most people do recover their sense of smell. Sometimes even in a week or two following the initial other symptoms or their positive diagnosis. Some take up to two to three to three.

three months and during that period of time, their ability to smell might fluctuate. They'll smell something and then it'll go away and then one day they'll have a good sense of smell the next day not. Unfortunately, it looks like about maybe 10% of people who have been diagnosed with COVID and who have lost their sense of smell, it persists for longer. Now, in other post-viral olfactory disorders, if you follow people out long enough, it looks like you can still recover even up to two to three years after you've lost it. You may not recover completely. You may not be back to where you started, but you might have enough of a functioning sense of smell to navigate your world and to enjoy food again. So we are trying to sort of jump

start that process. And that's one thing that olfactory training is intended to be used for. that instead of avoiding smelling things because you can't smell, you actually stimulate your system with four or five different odorants that you smell religiously every day, a couple of times a day. Sometimes you think about what the odor smelled like when you could remember it. Sometimes you look at a picture. There's different ways to do it. But the idea is the more you stimulate the olfactory system, the more you might actually regrow or regenerate the capacity that you. you had before. So does that mean that there are cells that are lost that can grow back? Is that what's happening physically? It depends on the virus. Some viruses appear to actually affect the

receptors themselves. It appears that in COVID, in a study that was done by Dr. Bob Data at Harvard, that what gets disrupted by the virus are the supporting cells, the ones that actually work to produce and feed the olfactory receptors. And so once that base gets disrupted, then you have olfactor receptors that turn over. Elfactory receptors have a short lifespan. They regenerate continuously throughout life. But if the architecture isn't there to help them regenerate, then you're going to have a loss. And so that's the current main hypothesis of how COVID is disrupting the olfactory system. Once the virus is no longer affecting those supporting cells, they may regenerate, and then the olfactory receptors can start regrowing their connections

to be able to allow us to experience what is smell again. So you're working on an NIH-funded initiative to develop a rapid smell test to identify COVID cases. Can you talk about that? And why would a smell test be better than the test that we have right now? Well, we can't say that it's better than an actual diagnostic test, like a nasal swab or an antigen test or saliva test. But it certainly seems to be better than the symptom screening that people are doing or the temperature screening that people are doing in order to return to the workplace or go into a building or a restaurant.

I mean, every restaurant I go to in Philadelphia takes my temperature before I go in. Yet we know from thousands and hundreds of thousands of instances that this is a very unlikely way to pick up a positive COVID test case. And so given that there have been studies done by this international group of researchers of which many people at Monell are apart, but worldwide, we know that the sense of smell, the loss of sense of smell is actually more predictive than a fever, especially. in the early stages of COVID infection, when you might not have a fever yet or you might not have any other symptoms, but you might be infectious. You might be capable of transmitting

the virus to someone else. And so for that reason, we think it has more value as a screening test. Now, of course, it can be paired with fever temperature screening and symptom screening as well. But we think it will be, in the long run, as a suite of assessments, a better way to identify people who may have COVID, but who are otherwise asymptomatic. What might this look like? I mean, we know what these swabs are, and we've seen the guns that they point at your head to take your temperature, but how will they test your smell? Well, what we have is a card. It's a single card about five by seven, and there are three patches on it. Each one of them is sort of a glue, but only one of them has an odor embedded in

the glue, and it's covered by a little plastic screen. that you lift up, so you don't have to scratch it. Many smell tests are scratch and sniff. And while they're very good in a controlled environment, the intensity of the odor depends on how you scratch it. You have to have something to scratch it with. And so we were thinking practically about somebody going into an office where there might be 400 people entering, you know, at 8.30 in the morning,

something that could be done very quickly. So you lift the screen on each of these three patches. And first of all, you scan the QR code with a smartphone. And that brings you to a little survey on your phone. You lift the patches, you smell each one, and you tell us which one has the strongest odor. Because the glue has a little bit of odor. We're trying to work on that.

Then you tell us how strong it is. And that's another really important indicator of COVID, because you may not lose your sense of smell completely, but something that smell, let's say, on a zero to a hundred scale yesterday, as an 80, all of a sudden smells like a 20 to you. Something has changed, right? And so then the final question is, what does it smell like? And your smartphone shows you four pictures with labels,

and you have to decide which one it is. So basically, we're trying to test all three different functions, of the way we use our sense of smell in one rapid test. And this can be done within two minutes for the first time you've used it and probably less than a minute on subsequent times. So the throughput is pretty rapid. And we're hopeful that people that are using it will find it to be equally as convenient.

There's been a lot written about dogs that can sniff out cancer and other diseases. And a couple of years ago, there was a spate of news stories about a woman in Scotland who could, could tell whether someone had Parkinson's disease by smelling their t-shirts. How much does science know at this point about the smell of particular diseases and how might that knowledge help in diagnosis and treatment? We think it's very important. Back before there were diagnostic tests for a lot of diseases, it was very common for physicians

to come and smell a patient. And actually, there are so, certain things like certain ear infections in a child give off a particular odor. They're, you know, there are, of course, people who are in diabetic ketoacidosis have a very particular sort of fruity, appellee scent to them, which is an important way to distinguish them from someone who's otherwise intoxicated or inebriated, right? Because they won't smell like that. Right, right. So moving on to that, science.

like my late colleague at the Monell Center, Dr. George Pretti, was using sense of smell and the volatiles that people emitted to diagnose other diseases. He was working with a group at the University of Pennsylvania at the Working Dog Center to diagnose early stage ovarian cancer, which, as you may know, is something that usually does not get diagnosed until late stages. It turns out that inflammation from infection does produce

does produce an odor in our bodies that anyone, even naive individuals, can discriminate. The question is, can you now get more specific? What is the nature of the infection? Is it viral? Is it bacterial? And one of my colleagues at the Monell Center, Bruce Kimball, just recently got a foundation grant to actually study that. So there's a lot of work going on in the diagnostic area of using smell, or at least using the chemical emissions from our bodies under different disease states.

Now, right now it's being done with dogs, but the hope is to use the dogs to be able to isolate what are the actual chemical signals and then build like an electronic nose or a sensor that can be used so that you don't have to bring a dog into an examining room and have, you know, during your physical exam and have him sniff different parts of your body. But quite honestly, if that's going to tell me something about my health, I'm all for it. That's okay, yeah. It's okay. You know, it kind of works both ways.

I had a vet a couple of years ago who wanted to decide whether my dog needed oral surgery and smelled her mouth. That was an important diagnostic tool for her. She was not trained in the U.S., but, you know, she was right. The dog needed oral surgery. Exactly, exactly. So, yes, that's a really, really developing area of research. and I think it holds a tremendous promise, and it's really one of the pillars of the Monell Center's strategic plan

is to build on that. Let's talk about Spell a little more generally. How well do scientists understand how our olfactory system works compared with, say, our visual or auditory systems? What are the big questions that are unanswered? Well, we learned a lot going back around 15, 18 years ago, when the smell receptor, the ability to smell, the receptor was actually cloned and identified.

I can say that the sense of smell is the last sensory system to give up its secrets to science. It was very elusive for very long period of time. And some of that was the difficulty in actually using scent to test. I mean, it's always been something of a niche science, which was partly what attracted me to it to begin with, is that there were so many unanswered questions. that I found myself not almost knowing which way to turn,

which was a good thing for a young scientist 28 years ago. But now what really is the major outstanding questions is how do all these receptors work together and tell our brain what we're smelling? We know that we can discriminate probably hundreds of thousands of different sense, and we do so with about 400 different types of receptors that combine in different ways to send a signal to our brain that tells us we're smelling

this blend of coffee versus that blend of coffee. I mean, really, fine-grained discriminations. We still don't understand. The visual world and the auditory world work in two or three dimensions. Smell might work in many more dimensions than that, and we're still trying to figure out. So, for example, at this point in time, it's still unknown. If you take a chemical structure that is novel, how will it smell? In the same way that you could look at something on the hue or saturation, you know, the

color wheel and predict what it will look like to someone who has normal color vision. So we're really at the beginning of that. And a lot of my colleagues are really working very hard on that, but it is a very complex system. It's much more complex than vision or hearing. And so it's moving more slowly, but it is moving. I mean, the ultimate goal, of course, is to be able to digitize smell so that we can transmit a smell over our computers the same way we could. But we have to know how to create that spell.

What are the components other than just putting a bunch of different molecules in a box next to your nose and trying to blend them? You know, are there more sophisticated ways of actually digital? digitizing smell the same way we can do with hearing with noises and also visual stimuli. I recently saw a report about a 3D printer that was making meat, and I would imagine that smell would be really important that if the meat doesn't smell like meat and if you cook it and it doesn't smell it right, then you're not going to eat, you know, printed meat.

Exactly, yes. Yeah, I mean, it's the same thing that happens to someone who loses their sense of smell, right? All of a sudden, food becomes unappetizing. And that either leads them to stop eating because nothing works, nothing is pleasurable, and they lose weight, or the other side of the coin, which is where they continue eating because they're looking for that experience that they can't have. So it goes in both directions. So read that some people experience a loss of smell after they use a zinc nasal spray, and yet zinc seems to be really connected to the sense of taste. There's research showing that people with a taste disorder may see some improvement if they take zinc orally.

So how can zinc be bad for smell but good for taste since the two are very intricately connected? Right. Well, they are separate sensory systems in the periphery. You know, the taste buds and the taste receptors and the oral cavity and of which they are, all over our body, but for the purpose of food, we'll talk about the oral cavity, are peripherally distinct, but they do combine in the brain because flavor is the quintessential combination of taste and smell, a little bit of texture as well. Different chemicals are going to have different effects on different types of receptors, and zinc has been touted as a cure for smell loss, And it's also been implicated as something that causes people to at least transiently have a loss of smell.

And so it's currently not recommended as a treatment for smell loss. In other words, inhaling zinc, a sulfate in the nasal spray. But it is something that people have used. It doesn't seem to be very effective and in some cases may actually cause the opposite effect. Of course, many people who were using it were also doing so because they thought it was going to ward off a virus or a cold. And the question remains, without a clear controlled study, would they have lost their sense of smell transiently anyway and attributed it to the zinc? So that's an open question. You've also done research in how smell is intertwined with memory.

And a lot of people, I think, have a intuitive sense of this. we know that certain smells will bring back vivid images of a particular time or place. Why are smell and memory so connected? Well, we think partly because of their anatomical proximity in the brain, that smell is actually part of the limbic system, which is our emotional system, that allows us to experience pleasure, fear, sadness, etc. And also part of the hippocampus, which is where memories, especially emotional memories, are stored. When we smell something, we often don't identify what we're smelling immediately,

but what we have is an association between that scent and a person, a place, an experience, a setting. So it's almost the cue that brings us back to that memory in a way that other stimuli may do so, but not at such an emotional level. A colleague of mine, studied this some years ago as well and showed that even though smells weren't better at recalling a memory, when people recall the memory that was associated with smell, they described it in much more emotional terms and probably felt much more emotional at the same time. And so we think that the interconnections in the cortex are what is responsible for that immediate sense of a flood of emotion or a flood of a memory when we smell something, you know, a perfume that our grandmother wore or the scent of a former boyfriend

or, you know, the chalk smell of being in first grade in school when they still use chalkboards. Before COVID came along, one of the things that you were perhaps best known for was some research you did to determine the world's worst smell, an odor that virtually everyone would find repulsive. How did you do that? And of course, the kicker is what is the world's worst smell? Well, we had a lot of fun with that, Kim, actually. It was something that we were interested in from a scientific perspective because unlike taste, smell does not appear to be hardwired,

our versions or preferences. Babies, you know, human babies, mice babies, all mammalian babies, will reject bitter tasting substances at birth, and they will avidly lick their lips to get something sweet. We don't have any real evidence that there are hardwired in native versions or preferences for smell, and so we wondered if there were universal maloders, what would they be?

So we looked at biological odors of biological origin, assuming that everyone would have had experience with that at some point in time. We know, for example, that there are certain kinds of odors associated with foods that are highly preferred in some cultures and repulsed in others. I mean, let's take durian fruit, for example, where the smell of it is, yes. The smell of it is just, you know, to most people in Western cultures, really unpleasant. But if you grew up with that, and quite honestly, it really doesn't smell that same way once it's in your mouth. But you have to overcome that avoidance. So we looked at things like the smell of human waste,

the smell of decomposing flesh, burning organic matter. I collected hair from my hairdresser and burned that and we captured the odors into a matrix. And so we tested a lot of people. And what we were most interested in was people from different cultural backgrounds. And so I had some opportunity,

I was actually working on summer programs in South Africa at the time. And so I took some of my odorants with me down to South Africa and tested people there, both white South Africans and black South Africans to see if there were differences, you know, culturally. We ended up finding a mixture of sense that comprised both organic decomposition, basically sulfur compounds and a little bit of human waste because that's a bit of human waste. because that's a danger signal to most people. I mean, maybe not the smell of your own bathroom, but when you smell unfamiliar human waste,

you really, in most cultures, and this was true, especially in places where there wasn't good sanitation, and I've worked in India on some of these kinds of odors as well as in South Africa, it can be a vector for disease. Now, the odor itself has no health impact, but it is a proxy.

and it's a warning that there's something there that can be dangerous for you. And so when we mix those together, we came up with something that we called stench soup. And it really did revolt everyone who smelled it. Is it available commercially? I mean, if you wanted to use it on somebody you don't particularly like. I am not going here. If somebody wants to reach out to me, that's different. But yes, no, we are not commercially providing that to anyone at this point in time.

But we were interested to at least see that, and you know, I did not have the opportunity to test this on a two-year-old child or a toddler, who we know is sometimes not at all repulsed by the smell of their own diaper or even their brother's diaper, right? So at what point in development does this actually occur? And that's something that, you know, we're still very interested in. It looks like there is a developmental trajectory. The president and director of Monell many years ago, the former director, actually really looked at this. But it turned out to be that around age eight, children started to mimic their parents' preferences and aversion. So there's definitely a learning process that goes on. Well, Dr. Dalton, this has been absolutely amazing.

I've really enjoyed talking with you. I appreciate your taking the time. It's a pleasure. Thank you so much. You can find previous episodes of Speaking of Psychology on our website at www. www. speakingof psychology.org or an Apple, Stitcher, or wherever you get your podcasts, and please leave us a review.

If you have comments or ideas for future podcasts, you can email us at speaking of psychology at APA.org, that's speaking of psychology, all one word, at APA.org. Speaking of psychology is produced by Lee Weinerman. Our sound editor is Chris Condiion. Thank you for listening. For the American Psychological Association, I'm Kim Mills.