Short Wave - The Science Of Smell And Memory

Episode Date: November 29, 2019

Why can a smell trigger such a powerful memory? Biological anthropologist Kara Hoover explains what's going on in the brain when we smell, how smell interacts with taste, and why our sense of smell is heightened in the winter. Follow host Maddie Sofia on Twitter @maddie_sofia. Email the show at [e-mail] pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Maddie Safaya here, hope you had a happy Thanksgiving, if that's your thing. So, I don't know about you, but Kara Hoover is absolutely the kind of scientist I would corner at a holiday party. You probably get sick of people asking you what your favorite smell is, huh? Oh, I have so many favorite smells. Yeah, I know I don't get tired of that because I love smells and they change all the time. Kara is a biological anthropologist. at the University of Alaska Fairbanks.

And smell expert. One of my current favorite smells right now is a Joe Malone Cologne Cologne called Gingerbread. It's a holiday scent, and it just smells so delicious. Ooh, a little holiday scent. Yeah, yeah, it came out last year, I think. And I also like rum tobacco. That's another perfume by Comptoire Sud Pacific.

I think it reminds me a little bit of my grandfather's pipe tobacco when I was young. You know that feeling. When a smell catches you and takes you right back, to a place and time. Can I tell you, Cara, I've got a weird one that whenever I smell the smell that comes along with those little, like, fog machines, I have a very, I'm telling you, I have a very vivid memory of that E.T. ride at Disney World, because I was very afraid of E.T. And my mom was like, you know how we're going to solve this?

Put you on that E.T. ride. And now when I smell those machines, I'm like, ah! And I just, that is funny. I never want to see E.T. or his foggy little butt ever again. But I do want to know why smell and memory are so tightly linked. So this episode, Kara Hoover explains. Plus, some amazing way your sense of smell can change, depending on your environment. So smell is considered to be the strongest sense tied to memory.

And that's because signals from all your other senses first have to make a pit stop in the part of your brain called the thalamus, which then send signals to other parts of your brain, like a little relay system. But not smell. Smell signals bypass the relay center and pretty much directly reach the parts of your brain, responsible for emotion and memory. So smell is sent on those pathways before you really have time to think about it. So you're going to be emotionally reacting to a smell, which will then potentially evoke a memory

if you have some kind of stored memory associated with that smell or related smell. Right. So because it just kind of goes directly into that like emotional and memory center. Yeah. Yeah, it triggers the emotions and it triggers the memory. And that's before you actually have time to think about it. Whereas most of the other senses get processed in the frontal lobe, you know, so you're thinking about them, you know, after they've already been sensed, but you don't know that. Well, smell is different. You sense it. And then you think about it. So is part of the reason why it's so strongly tied to memory is because it's also hitting that emotional center. Because I know, like, things that are very emotional, we tend to memory, like to remember a little bit more. Definitely, yeah. And I think that one of the things that I find really interesting when I teach my science of smell class is when I try to make these connections across different parts of the brain and emotional responses to smells, these perceptual pathways and so on, is that stress can operate to enhance your memory of a smell. So when you experience stress, anxiety or fear, you are activating a stress response in the body. And one of the things that happens is an increase in cortisol, which is a

hormone associated with stress. It's a steroid. And cortisol increases your sense of smell. It makes it more sensitive. Gotcha. Okay. So when we're talking about smell and memory at this time of year, it's kind of hard not to think about all the scents that we associate with the holidays. But in fact, like our olfactory system is also working harder at this time in the year, right? Like in the winterish time. Yes. So volatiles, which are airborne odorants. are more active when it's hot and humid. So that means that during hot and humid weather, you're getting a lot of information from the environment

and the olfactory system has to slow down because it's getting too much. It's being overwhelmed. So there are kind of like more smells in the air in the summer. Is that right? Yeah. Yeah. So we've got information overload and we've got to figure out what's important.

In the winter, there's not that many because it's not hot and it's not humid. So there's not as many airborne chemicals for us to bind in our noses. It's called olfactory adaptation when you receive two. too much of a signal, your olfactory receptors shut down and they don't transmit anything anymore. Like when you go into a room and you're like, this smell is like, this really smells like onions. And then you stay in that room for a while and you're like, I don't smell onions anymore. Yeah, and you think the odor is faded. Or if you go away on vacation and you come back to your house, suddenly you smell your house.

And then after a while, you don't smell your house again. Right, right. So that's one of the classic examples. So it's the same thing. If there's an absence of odor, we become more sensitive because we're trying to pick up these environmental cues that might be useful. Right, right. I didn't realize that like our sense of smell. could ramp up. I kind of intuitively notice that I'd stop smelling things once I'm in the room with

them for a little bit. But that's kind of awesome. Yeah. And so if the odor is faint, our olfactory system becomes more sensitive and it tries to gather up as much as it can. So it's not the same as something like vision or hearing, which is fixed. They function the way they function all the time. You can't upscale your hearing when the volume's too low. So in the Sophia family, in my family, the holidays are all about eating as much as physically possible to the point of discomfort. And is it true that we smell differently when we're like hungry versus when we're full? Yeah, there's some really interesting evolutionary information on that. So, you know, and also people who are working in obesity research are interested in the sense of smell and how it stimulates appetite or decreases appetite.

And most of this research suggests that food smells become less appetizing when you're full. But we're so divorced from listening to our biological signals when it comes to food consumption that I'm, You know, even if that's actually true, people say it's less appealing. That doesn't mean to actually stop eating. I was going to say, that's probably for the best. But now I'm like, I don't know that I listen to those signals. You know, the signal is there are more mashed potatoes here. Yeah, and it was good.

And you want to keep eating it because, you know, it makes you happy. Right, right. Okay. So I read that mammals can kind of smell while they're chewing and eating like it's a continual process. Can you talk to me a little bit about that? Yeah. So we think about smelling is when we inhale. and that's one type of smelling.

But we also have a second type of smelling when we're chewing and air gets pushed up into the nose and back down into the mouth. And that's a secondary sense of smell, which is one of the reasons why we think of things that we like as tasting good, but in fact they smell good or, in fact, it's the combination of taste and smell, which is flavor. And that's one of the reasons why a lot of professional wine tasers actually chew the wine so they can get that retranasal olfaction and fully experienced. the flavor sensation, which is smell and taste together. Right, right. Okay, so rapid fire. Tell me some of your favorite facts about the sense of smell. So one of the fun facts that I think is really neat about the sense of smell is that our noses have two nostrils that are separated and one is working at a time.

What? They alternate. Yeah. So it's kind of funny when you have a cold, sometimes you're stuffed on one side and your sense of smell seems to be coming and going. And that's why, because when it's on the clog side, you can't smell anything. and when it's on the good side, you can. Mind blown. Next fact, please. Olfactory receptors are located throughout our bodies, and they serve different functions,

and we haven't been able to figure out what all of those functions are. But it could be that the sense of smell is used in guiding the sperm to the egg. What? There's olfactory receptors located in the prostate, and maybe they have a function in protecting against cancer. There's olfactory receptors in our kidneys. They're all over the place. They're in our skin. We don't really know what a lot of them are doing in those places yet. What a day. Okay. So what is like one of the biggest myths that you consistently hear about smell?

Oh, that we only can smell 10,000 smells. We got more than that? Yeah, we can smell an infinite number of odors and no one really has quantified it. That 10,000 smells was debunked in Avery Gilbert's book, What the Nose knows. And he finally tracked down the origin of it. Some engineer was trying to count. calculated, came up with this figure, and then it just gets recited over and over and over again. So basically, we're not giving our noses enough credit, is what you're telling you. No, we're not. And that's the other myth that our sense of smell is not important, that as soon as we stood upright and removed ourselves from the ground, smelling was no longer important. That's not really true either. And a lot of people also say that, you know, when vision came along in primate, certainly, that smell became less important. But just because you stand upright doesn't mean you're

not still in a smellcape. You're just in a different small scape. And it's not as if our sense of smell diminished just because we relied on vision more. Right. And in fact, there have been studies showing that people who are blind don't have a better sense of smell. They're just probably more aware of it. They remember it more because it's important to them. Yeah, I've definitely heard that too. Yeah, there've been a couple studies in the last two years. One just came out about two months ago. So the evidence does show that your senses don't work harder and better. You just use them better, I think. Interesting. Interesting. Okay. So, oh, I know. Yeah, I have got another fun fact. Yes. Do it again?

Females have the same roughly size scale to body, olfactory bulbs as males. Okay. But we have like two or three times the number of neurons that men have. That tracks. Keep going on. Yeah. And so that means that we're, you know, more sensitive to smells. Wow. Yeah, there's a lot of weird stuff going on when it comes to sex differences in our ability to smell with females being the more interesting of the sexes. I find that to be the case just generally speaking, don't you?

Yes, I do. Okay, Kara Hoover, Associate Professor in the Department of Anthropology at the University of Alaska Fairbanks. Smell you later. Oh, yeah, smile you later. I've been waiting to do that all day. All right. I mean, I practiced it a couple times. Thanks again to Kara Hoover.

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