How does the way something smells influence the way it tastes? And why are smell memories more emotional than other types of memories? Brown University professor of psychiatry and human behavior Rachel Herz describes the relationship between the smell of food and its taste.
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IRA FLATOW, host:
This is TALK OF THE NATION: SCIENCE FRIDAY. I'm Ira Flatow.
Just finishing up some leftovers here. Hmm. You know, it won't be the day after Thanksgiving without a cold turkey sandwich on wheat bread with a little bit of what do you like? Well, I like to have some mustard on it. That works for me. And I don't eat this any other time of the year. But, you know, with the smell of turkey and gravy and apple pie in the air, I do get a hunkering for leftover turkey.
We know what food does to our waistlines. But what does it do to our brains? How does the smell of food affect you mood and experiences during the holidays? To find out more, we talk to Rachel Herz, professor of psychiatry and human behavior at Brown University Medical School, and author of "Scent of Desire: Discovering our Enigmatic Sense of Smell."
Now, you write that aroma is very important to creating that holiday ambiance from a psychological point of view.
Dr. RACHEL HERZ (Professor, Brown University): Yes. People have a lot of associations to the holidays that are very much to do with smell. Smell is extremely linked to our memories, in particular to our emotional memories. So when we smell the smells of turkey, pumpkin pie, chestnut stuffing and so on, these are conjuring, not only the feelings of, mmm, this is going to be delicious right now, but also bringing us back to our childhood, bringing us back to past holidays, feasts and so forth and really sort of creating an entire emotional ambiance.
FLATOW: Are our olfactory nerves or our nose hooked into the to sort of the memory part of our brain?
Dr. HERZ: Yes, absolutely. Where the sense of smell is processed is directly linked to the part of the brain that processes emotion and memory. And none of our other sensory systems have this unique access to this these structures in the brain. So smell is really unique with respect to being able to trigger memories and specifically memories with a deep emotional quality.
FLATOW: Mm-hmm. And so smell memories are very emotional.
Dr. HERZ: Yes, they are. That's really what makes them different from other kinds of memories. When I actually began my research in this area and was to sort of try to figure out the question of what people meant when they would say things like, smells are the best cues to memory. If you want to bring a memory back, smell is the best thing. And I wondered what that meant. And it turns out it doesn't mean accuracy. So that is to say, when you smell something versus hearing something or seeing something and it reminds you of something from your past, you're not more accurate about the memory when it's a smell that triggers it, but you're much emotionally engaged in the memory and you actually also feel much more brought back in time and place to that original episode.
So your feelings are much more connected to that memory than they are in any other sort of situation. And I think we kind of misconstrue the emotional vividness, as it were, for betterness, in a sense. I mean, maybe being more emotional is also better. But the actual fact of the memory from an accuracy perspective isn't really different.
Dr. HERZ: It's the feeling we get.
FLATOW: How are smell and taste related?
Dr. HERZ: Well, smell and taste are very intimately related. Without a sense of smell, you really only experience salt, sour, sweet and bitter. And this is why if you have a cold things don't seem to taste right. That's because your nose isn't working properly. And when your nose isn't working properly, you aren't getting any of what is truly called flavor. So if you bite into a delicious piece of roast turkey and you didn't have a sense of smell, all you would taste is salt. And it's your nose that brings all the aromas of the Thanksgiving table to you.
FLATOW: So we give meaning to an event by the smell we associate with it, not just by how strong the smell is.
Dr. HERZ: Absolutely. So if you smelled something and the first time you smelled it it was a very good experience, you would like that smell. And if you smell the same thing and it was a bad experience, you wouldn't like it. Actually, our food preferences globally really demonstrate the enormous spectrum of likes and dislikes. Because when it comes down to like I said before it's salt, sour, sweet and bitter is the taste component. But why one culture thinks one food is revolting and another one thinks it's fabulous has to do with the whole flavor quality and texture and other things as well. But it's what we learn about that smell-flavor combination as being good or bad that makes it delicious or not. And it's definitely true that one man's meat is another man's poison.
By contrast, our tastes are hardwired. So a newborn infant, if you put a drop of sugar on her tongue, she will smile. Or if you put something bitter on her tongue, she'll grimace. But smell comes through learning.
FLATOW: So, in different cultures, things may smell differently, in other words being likeable or not.
Dr. HERZ: Absolutely. I mean, a good example from the point of view of sort of large cultural differences is between Asia and Western Europe and North America. Asians think that cheese is really the most disgusting thing. And Westerners think of it as anything usually from a comfort food to a delicacy. And there is a dish that the Japanese have for breakfast typically, called natto, which is fermented soybeans. And I don't know any Westerner that can bring it to their mouth.
(Soundbite of laughter)
Dr. HERZ: So there's nothing nutritionally relevant about one versus the other. It's not - you know, there's nothing from a protein prospective that makes one good or bad. It all has to do with what we think of what food means to us and what food means to us through aroma and flavor.
FLATOW: Can context affect our perception of a smell?
Dr. HERZ: Absolutely. It can be affected in very dramatic ways. I've done some experiments by - where I've just given people a word and then presented them with something to smell. And depending upon what I've told them it is, they can perceive it as totally horrific or completely delicious.
So for instance, in one case, I gave them a smell that was just a chemical combination and I said this is parmesan cheese. And people said, oh, I love this. I would eat it and it's great and so forth. And then, I gave them the exact same chemical combination and I told them this time that it was vomit, and they were completely horrified. They wouldn't go near it. They wouldn't even believe that it was the same smell.
So this is just with - just a simple word can do that. And certainly our eyes play an enormous role in interpreting for us what we think that we're smelling all the time. I mean, for instance, if you are walking down the street and you passed a garbage dumpster and you also smelled something at that same moment, you go, oh, that's not very good. That must be coming from the garbage.
(Soundbite of laughter)
Dr. HERZ: But if you had that exact same smell and you were in a French restaurant and someone was passing around a cheese plate, you'd think, hmm, this is delicious. So what we interpret about a smell and whether we think it's good or bad is very driven by context. Even what we eat at Thanksgiving, if it were in the wrong place, might not be very good at all.
FLATOW: Rachel Herz is a professor in the department of psychiatry and human behavior at the Brown University Medical School. And she's also the author of "The Scent of Desire: Discovering our Enigmatic Sense of Smell." Thank you very much, Dr. Herz.
Dr. HERZ: Thank you, Ira.
FLATOW: That's all the time we have for today. We'll be bringing you lots more from our archives as we celebrate our 20th year on the air. If you have some favorites, sure, something you'd like to hear again, let us know. Greg Smith composed our theme music.
Have a great, safe holiday weekend. I'm Ira Flatow in New York. Transcript provided by NPR, Copyright NPR.