Question: Why are taste and smell so closely linked with our memory?
Stuart Firestein: The connection between taste, smell and memory is a very curious one. It’s well documented. We’ve all had the experience. There are interesting quirky things about it. Why there is such a connection or how it exactly works is not so well known, but we get hints from the nature of it.
So we’ve all had the experience of course, this so called "Proustian" experience. You know there is a famous passage in Marcel Proust’s "Remembrance of Things Past" in which he tastes a Madeline cookie and a sip of lemon tea and this vivid memory from 40 years earlier, from his childhood 40 years earlier—coming home from church and having this lemon tea and a Madeline cookie at his aunt’s house—just comes back to him and perfectly vivid, as if it were right there in front of him and he writes several pages about that and then goes onto write what, 40 volumes or some crazy thing, about 7 volumes I think it actually is of memory, of memories. So that’s maybe the extreme example, but we’ve all had that experience where we smell something or we taste something and some memory quite vivid comes back, usually from quite some time ago.
Now one of the things we can note about those memories is they’re always emotionally laden somehow or another. You don’t smell something and remember a page of text or an equation or a phone number or something useful like that. You always remember something like grandma’s living room, the first day of school. You know one of the most recognizable smells in America is the smell of crayons, Crayola crayons. So you know that brings right back, you can imagine that smell and you’re right back in school somehow or another. So it’s always something emotional, your first lover or some event like that. So that is one important thing about it. It seems to have an emotional content rather than an informational content if you will, for these memories.
The other is that they are long-lasting. We recall things from many, many years ago and they’re extremely vivid. Now the ones that involve taste—which I remind you again also involve olfaction really—we call them taste aversions because you have the sense that it’s taste and it’s in your mouth, but this is just a trick by the way, your brain is playing on you. If you’ve done the jelly bean experiment you’ll know that the flavor is due to your olfactory system and yet the experience of flavor is unquestionably still in your mouth. This is just some little trick your brain plays on you because it thinks that is where it should taste things. So we call them taste aversions. These are very interesting and we’ve all had this experience too. We eat some food. A few hours later we get sick from it and that’s it. We just can’t even think about eating it again. This is also very, very interesting kind of learning, which is very uncommon.
For one, it’s one-trial learning. You eat something. You get sick from it. You’re done with it. It lasts for an extremely long time, typically years, sometimes the rest of your life. You just don’t want anything to do with whatever it was that made you sick, peanut butter or lobster or whatever it was you know. And most remarkably this memory can be formed with several hours of delay, which is very uncommon. Usually in order to make... and this works for other animals well, not just people. You can induce a taste aversion in a mouse or a rat or a dog or anything. They get them normally, but you can also induce them. And you can do them with hours of delay, so you can taste the food. You can eat the food and then you get sick on it four or five, six hours later and that’s... You could have even eaten things in between that and it doesn’t matter. Your aversion will be to what you tasted then that made you sick. And as I say that is true for other animals as well, so it’s one-trial learning. It’s extremely long-lasting. It’s a very stable, intense memory and it can be formed with significant delay in it.
There is a great instance of this I have to say. A researcher named John Garcia I believe is his name. Several years ago he was... I forget where he was, but at some university in I believe California, in any case in the West. And there was a problem with coyotes predating on sheep, so sheep farmers were up in arms. The coyotes were killing off their sheep and they wanted to go out and shoot all the coyotes, which would have also been a bad idea because it’s part of a whole ecosystem, et cetera, et cetera. So Garcia came up with this idea that maybe he could get the coyotes to leave the sheep alone and he did it by using taste aversion, so he took a few sheep carcasses, dead sheep and he laced them with a chemical called lithium chloride. Now if you eat something with lithium chloride in it you will get dreadfully ill. You’ll get terribly sick, miserable nausea and all the rest of that, but you will not die from it and so these coyote
would come and eat these sheep. Then they’d go back to their burrow and they would spend a miserable night being sick from the sheep and that was it. They just didn’t want anything to do with sheep after that and you had these coyotes that just they’d find something else to eat, whatever it was. I’ll go kill something else, but I’m not messing with sheep anymore, so it was effective actually.
Recorded September 22, 2010
Interviewed by Andrew Dermont