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Speaker 1: Why do you like the taste of something that your

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Speaker 1: friend does not. Why new kids not like coffee but

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Speaker 1: adults do. Can we consider smell and taste both part

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Speaker 1: of something bigger? And what does any of this have

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Speaker 1: to do with whether your culture eats spicy foods or

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Speaker 1: whether women actually synchronize their menstruation or smelling someone's armpits.

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Speaker 1: Welcome to Inner Cosmos with me David Eagleman. I'm a

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Speaker 1: neuroscientist and author at Stanford and in these episodes, we

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Speaker 1: sail deeply into our three pound universe to understand why

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Speaker 1: and how our lives look the way they do. Over

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Speaker 1: the last few months, I've received several requests to make

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Speaker 1: an episode on the topic of smell and taste and

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Speaker 1: flavor and why we like some more than others and

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Speaker 1: why are some tastes acquired? So that's what we're gonna

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Speaker 1: do today, and we're gonna start with taking a little

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Speaker 1: time to appreciate how the stuff works. It hasn't escaped

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Speaker 1: my notice that when I talk with people on airplanes,

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Speaker 1: everyone seems to have a reasonable understanding of how their

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Speaker 1: eyeballs work capturing light photons from the world. But if

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Speaker 1: smell or taste comes up there generally seems to be

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Speaker 1: less known about how that physically works. In other words,

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Speaker 1: when there's an apple pie on the counter across the room,

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Speaker 1: how precisely does your brain detect that? And let's say

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Speaker 1: you taste some drink with molecules of this shape or

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Speaker 1: that shape and you say, oh, that's blueberry flavored or

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Speaker 1: oh that's lemon flavored. What is happening in your tongue

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Speaker 1: and in your brain? So we're first going to understand

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Speaker 1: that how these systems explore the world around us and

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Speaker 1: how they work, and then we'll transition into cool questions

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Speaker 1: like why did you not like coffee as a kid

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Speaker 1: but you do now? Or why do you always choose

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Speaker 1: this flavor of ice cream and your friend always chooses

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Speaker 1: this other one? And I'll just say this episode is

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Speaker 1: quite personal for me because when I was a kid,

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Speaker 1: I fell off a roof and smashed my nose very badly,

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Speaker 1: and as a result, I've always had a particularly terrible

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Speaker 1: sense of smell. And watching people around me be able

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Speaker 1: to identify things that a different level than I could

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Speaker 1: has always made me very interested in this topic. So

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Speaker 1: let's start by thinking about the senses generally, all your

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Speaker 1: senses are just specialized detectors for picking up some sort

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Speaker 1: of information stream from the world. Vision works by capturing

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Speaker 1: and transforming the energy of photons which bound so objects.

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Speaker 1: Hearing works by picking up these sensitive mechanical forces. On

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Speaker 1: the ear drum. You have air compression waves that wiggle

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Speaker 1: this membrane back and forth, and your brain analyzes that data.

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Speaker 1: Touch is also a detector of mechanical forces. When you

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Speaker 1: touch something, you physically distort these receptors in your skin.

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Speaker 1: But taste and smell these are different from the others.

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Speaker 1: They have a divergent strategy for picking up on information

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Speaker 1: from the world. They work by being exquisitely sensitive molecule detectors.

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Speaker 1: So let's start with taste. How does taste work. The

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Speaker 1: sensitive taste is called gustation, and we see this in

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Speaker 1: the Latin expression de gustibis known s disputandum, which means

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Speaker 1: about taste. There is no disputing, or, as it's come

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Speaker 1: down to us in English, there is there's no accounting

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Speaker 1: for taste. Now, the ancient Romans were fond of this phrase,

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Speaker 1: and as we'll see, there is something sufficiently profound about

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Speaker 1: this observation that it has stuck with us for a

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Speaker 1: couple thousand years. So how does taste Gustachian work biologically?

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Speaker 1: Here's how. You have microscopic taste receptors all over your

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Speaker 1: tongue and also, by the way, spread even more widely,

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Speaker 1: even on your palate and the upper half of your

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Speaker 1: esophagus and more. Now, these little taste receptors are embedded

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Speaker 1: in the membrane of what we call taste cells, and

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Speaker 1: taste cells clump together, about one hundred of them into

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Speaker 1: taste buds, and taste buds cluster to form the bumps

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Speaker 1: on your tongue that you can see with the naked eye.

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Speaker 1: These are called pipille. Now, I know different listeners are

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Speaker 1: doing different things while listening, but if you're able, either

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Speaker 1: now or later, go to a mirror or bust out

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Speaker 1: your front facing camera on your cell phone and take

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Speaker 1: a look at your tongue. You'll notice the surface is

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Speaker 1: not smooth. You have all these bumps, these papillae, and

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Speaker 1: you'll notice that some of these are bigger bumps. These

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Speaker 1: are called fungiform, meaning like a mushroom, and off to

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Speaker 1: the sides you have some that look leaf like and

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Speaker 1: others way in the back that look pimple. Like, what's

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Speaker 1: cool is that you've had this tongue your whole life,

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Speaker 1: and it's possible that you've never looked really carefully to

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Speaker 1: see what you are made of. But this is all

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Speaker 1: part of the joy of self discovery. Okay, So back

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Speaker 1: to the structure here, so you can see these papilla

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Speaker 1: on your tongue. But what you can't see because it's smaller,

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Speaker 1: is that inside the taste buds, the taste cells arrange

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Speaker 1: themselves so they're little receptors line a central pore. So architecturally,

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Speaker 1: these guys are set up to catch chemicals. That's what

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Speaker 1: they're built for. Even if you, the owner, are totally

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Speaker 1: unaware of that. You're just walking around and you lick

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Speaker 1: the ice cream and you say, oh yeah, that rocky

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Speaker 1: Road tastes awesome, and you say, of course I can

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Speaker 1: distinguish rocky Road from lemon from vanilla. But how does

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Speaker 1: that work. The answer is, we have this miraculous microscopic

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Speaker 1: engineering in ourselves. But the story gets even better because

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Speaker 1: this whole system can detect and distinguish flavors with extraordinarily

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Speaker 1: high specificity. So to understand how it does that, let's

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Speaker 1: turn to the food that you put in your mouth.

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Speaker 1: Everything that you eat or drink can be understood in

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Speaker 1: terms of the molecules that they're made of, and we

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Speaker 1: call these tastins Tasteans fall into five basic categories, and

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Speaker 1: I know you're already well acquainted with four of them, sweet, salty, bitter,

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Speaker 1: and sour. But what's the fifth taste category, which was

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Speaker 1: added more recently. I'll give you a second. The fifth

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Speaker 1: taste category is called umami. Umami this is a Japanese

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Speaker 1: word meaning delicious taste, and we usually describe this flavor

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Speaker 1: as savory. So for the sweet category, the standard thing

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Speaker 1: we might think about is sucrose. For salty, a prototypical

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Speaker 1: stimulus might be sodium chloride, which is table salt. For sour,

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Speaker 1: the prototype is citric acid, like from a lemon. For bitter,

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Speaker 1: it's quinine. And for umami, that fifth taste category, it's

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Speaker 1: msgm MO, a sodium glutamate. Okay, So what happens when

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Speaker 1: you put some taste int in your mouth? What happens

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Speaker 1: is that the various chemicals, little molecules bind to the

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Speaker 1: taste receptors. And even though I told you there are

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Speaker 1: five categories, there are about fifty different receptors that we have,

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Speaker 1: and there are all kinds of ways that these receptors work. Mechanically.

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Speaker 1: Some cells activate when sodium physically flows through a channel

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Speaker 1: in the membrane. Other cells activate because the key thing

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Speaker 1: in sour compounds, which is hydrogen ions, block certain channels

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Speaker 1: in the membrane. In other cases, taste ins bind to

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Speaker 1: proteins in the cell membrane and change their shape, which

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Speaker 1: leads to a cascade of changes inside the cell. So

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Speaker 1: there's a huge variety of ways that these molecules that

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Speaker 1: you've just put in your mouth physically get translated into

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Speaker 1: signals that shoot off into your brain. So it seems

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Speaker 1: like a strange zoo of things that can happen here.

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Speaker 1: But as long as the signaling is consistent, that's all

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Speaker 1: you need. So if you taste cinnamon, you get this

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Speaker 1: very weird pattern of activation, and as long as you

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Speaker 1: get that same pattern tomorrow, then you can identify that

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Speaker 1: as cinnamon again. And this huge variety of these random

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Speaker 1: tricks of mother nature gives us a lot of nuance

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Speaker 1: and ability to discriminate when we sit down to enjoy

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Speaker 1: a meal. So these signals shoot over to the brainstem,

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Speaker 1: and then to the thalamus and finally to the core tex,

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Speaker 1: a special area that we call the primary gustatory cortex. Okay,

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Speaker 1: so how does taste actually get constructed? I told you

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Speaker 1: that we have these taste receptors that respond preferentially to

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Speaker 1: sweet or salty or something like that. But how do

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Speaker 1: we get from something like that to something very specific

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Speaker 1: like the taste of chocolate covered peanuts. With time and experience,

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Speaker 1: we learn to recognize combinations of flavors, thousands and thousands

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Speaker 1: of them. Now how do we get that kind of

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Speaker 1: diversity from only fifty receptor types in five categories. Well,

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Speaker 1: it's because each of these receptors will also activate in

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Speaker 1: response to other types of taste ins if those are

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Speaker 1: present and high enough concentrations. And it's not that each

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Speaker 1: taste bud talks to one fiber going back into the brain,

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Speaker 1: but instead multiple taste buds talk to a single fiber.

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Speaker 1: So we can skip the details, but the bottom line

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Speaker 1: is that anything you stick in your mouth triggers a

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Speaker 1: pattern of taste receptor activation, which then stimulates a specific

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Speaker 1: pattern of goostatory cells in the cortex. So this sense

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Speaker 1: of taste uses populations of neurons to encode the sensation.

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Speaker 1: This is what's called pattern encoding. It's not that chocolate

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Speaker 1: covered peanuts activates this neuron. Instead, it activates thousands of neurons.

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Speaker 1: This pattern of thousands of neurons maps onto lemon pie,

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Speaker 1: and this other pattern over here maps on the bobagaoush,

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Speaker 1: and this pattern maps on the anchovies and so on.

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Speaker 1: Now what happens if there's damage to this gustatory system.

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Speaker 1: It impairs your ability to taste. This is called dysgusia,

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Speaker 1: or at the extreme agusia, and this can result from

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Speaker 1: all kinds of different problems if it's at the level

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Speaker 1: of the taste cells. Happily, these turnover quickly every couple

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Speaker 1: of weeks, so damage to the taste cells themselves is

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Speaker 1: often reversible. For example, there's a chef named Grant Ashats,

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Speaker 1: and he made headlines after being diagnosed with tongue cancer

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Speaker 1: and losing his sense of taste as a result of

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Speaker 1: radiation treatment. And so he described how with time he

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Speaker 1: regained taste sensation one category at a time. Now, people

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Speaker 1: sometimes get dysgusia from COVID, and I'll come back to

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Speaker 1: that a little later. But you can also get dysgusia

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Speaker 1: from damage directly to the cortex, just like we see

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Speaker 1: in all the other senses. If you damage the primary

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Speaker 1: gustatory cortex, you don't understand basic taste anymore. If the

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Speaker 1: damage happens in a higher level area, we move from

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Speaker 1: the basic details to more abstract representation. So with damage

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Speaker 1: to the secondary goustatory cortex, you can still identify basic tests,

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Speaker 1: but you can't do more subtle recognition of food type

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Speaker 1: and flavor intensity. Now what's fascinating is that if you

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Speaker 1: lose other senses, that can also affect your sense of taste.

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Speaker 1: For example, consider how your experience of each bite includes

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Speaker 1: touch information in your mouth about texture and temperature, what

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Speaker 1: is sometimes called the mouth feel of food. But by

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Speaker 1: far the most influential sense on our perception of taste

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Speaker 1: is smell. The nuance that we have and our perception

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Speaker 1: of taste is cranked up way more from the interplay

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Speaker 1: of taste and smell. Just think about what things like

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Speaker 1: when you have a head cold. So now we turn

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Speaker 1: to act too all about smell and then will come

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Speaker 1: to the more general concept of flavor. So our other

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Speaker 1: chemical sense smell, known as old faction. Lets us perceive

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Speaker 1: airborne chemicals. Now, we humans don't rely on our sense

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Speaker 1: of smell as much as we do on other sensory

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Speaker 1: windows like vision and hearing. But other cousins of ours

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Speaker 1: in the animal kingdom, like dogs and rodents, they capitalize

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Speaker 1: on old faction to read the environment around them like

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Speaker 1: a book. A dog can tell that a cat wandered

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Speaker 1: onto the lawn hours ago, and rats can locate little,

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Speaker 1: tiny morsels of food buried underneath layers of cage bedding.

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Speaker 1: So here's the interesting bit. Although humans and dogs and

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Speaker 1: rats we all rely on smell to different degrees, it

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Speaker 1: all works in our brains the same way the floating

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Speaker 1: chemical signals. These are called odorans, and you walk around

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Speaker 1: all day vacuuming these in mostly through your nose a

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Speaker 1: little through your mouth. Once these molecules have entered the

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Speaker 1: giant vessel of your nasal cavity, they get sucked over

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Speaker 1: to the main sensory organ, which is called the old

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Speaker 1: factory epithelium, and that's at the back of that big

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Speaker 1: space inside your nose. In humans, this structure is less

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Speaker 1: than ten square centimeters, which is about the size of

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Speaker 1: a half dollar coin. Compare that to dogs whose epithelium

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Speaker 1: is seventeen times larger. Now, the old factory epithelium is

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Speaker 1: covered with a layer of mucus, and that's how the

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Speaker 1: molecules stick and come into contact with the little feelers

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Speaker 1: of the receptor cells, called the dendrites. Okay, but how

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Speaker 1: do we distinguish different smells like chlorine from lavender from

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Speaker 1: wood burning at a campfire, given that these are all

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Speaker 1: just molecules of different shapes. Well. A lot of the

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Speaker 1: groundbreaking work in this field was done by Richard Axel

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Speaker 1: and Linda Buck who discovered a huge number of old

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Speaker 1: factory receptor genes in rats, about one thousand of them,

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Speaker 1: and by the way, they won the two thousand and

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Speaker 1: four Nobel Prize for that. Turns out, these old factory

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Speaker 1: receptor genes are the largest gene family in the rodent genome.

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Speaker 1: We humans also have that same gene family, but only

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Speaker 1: about four hundred of these genes are still functional in US.

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Speaker 1: So these receptors started becoming discovered in nineteen ninety one,

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Speaker 1: not that long ago, and at first the guess was

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Speaker 1: that maybe each receptor encodes an odor, But the way

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Speaker 1: it turns out is that each odorant molecule has its

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Speaker 1: particular shape, and it binds to several different receptor types,

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Speaker 1: and a single receptor type responds to lots of different

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Speaker 1: odorants that all happened to share some particular shape feature. So,

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Speaker 1: just like the sense of taste, you have pattern encoding.

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Speaker 1: This whole random looking population of neurons represents the scent

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Speaker 1: of freshly cut grass, and this other group over here

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Speaker 1: represents mint, and this other population represents hot chocolate and

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Speaker 1: so on. Now, before I go on what's going on

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Speaker 1: with COVID and smell. A lot of people end up

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Speaker 1: with what's called a noosmia, which is a lack of

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Speaker 1: smell and inability to smell. There's a growing literature on this,

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Speaker 1: and the answer to why it happens isn't fully agreed on.

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Speaker 1: But you can see how with the huge variety of

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Speaker 1: molecular mechanisms underlying smell, it's not hard for a virus

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Speaker 1: to throw a wrench in the machinery, in other words,

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Speaker 1: to temporarily tweak things so that the signals the brain

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Speaker 1: are used to have now been changed. Okay, so back

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Speaker 1: to how smell works. From these receptors and the epithelium,

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Speaker 1: the signals shoot to the olfactory bulb and from there

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Speaker 1: to the primary olfactory cortex. From this part of the cortex,

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Speaker 1: information zooms out to a network of other areas that

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Speaker 1: are involved in higher order abstractions like familiarity and edibleness.

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Speaker 1: And again we see that the primary sensory cortex represents

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Speaker 1: the basic data and then higher level cortical processing becomes

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Speaker 1: more abstract from there. So we have this sophisticated machinery

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Speaker 1: to pick up on floating chemical signals in the world.

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Speaker 1: So what do animals do with this? Well, obviously they

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Speaker 1: identify things in the world like foods or toxins, but

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Speaker 1: it goes beyond that. A lot of animals smell to

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Speaker 1: understand not only what but where. They navigate space by

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Speaker 1: smelling their way around. So think of a puppy finding

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Speaker 1: its mother's nipple via smell, or lobsters locating their prey,

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Speaker 1: or moths finding their lovers. All of these are done

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Speaker 1: with smell, and this is also a large part of

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Speaker 1: how pigeons find their way home or salmon return to

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Speaker 1: their stream of origin. They create an olfactory map that

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Speaker 1: links specific smells with locations during their travels. But it's

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Speaker 1: not only about long distance stuff. Animals can navigate close

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Speaker 1: space by smell. They can actually figure out which way

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Speaker 1: to turn. Now, how could that work? Well, you probably

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Speaker 1: know the brain can localize a sound by comparing the

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Speaker 1: signal hitting the two ears, and the side where the

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Speaker 1: signal arrives first tells you the side where the sound

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Speaker 1: came from. Amazingly, the same strategy is used to find

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Speaker 1: the source of a smell. You exploit the inter nostril

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Speaker 1: time differences which nostril the odor got to first, And

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Speaker 1: it's been shown this is how sharks aside which way

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Speaker 1: to turn when they're following a plume of smell, and

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Speaker 1: it's not as one might have intuited by the concentration difference.

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Speaker 1: So this is a general strategy across senses. If you're

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Speaker 1: trying to locate something, you can exploit the timing across

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Speaker 1: two channels that are in slightly different places, like your

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Speaker 1: two ears or your two nostrils. Okay, so where are

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Speaker 1: we now. We've looked at how taste works by chemicals

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Speaker 1: binding to receptors in and around the tongue, and we've

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Speaker 1: seen how smell is about floating molecules binding to receptors

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Speaker 1: at the back of the nasal cavity, and in both

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Speaker 1: cases the brain is using pattern encoding. Think of this

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Speaker 1: like the way that you strike multiple piano keys to

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Speaker 1: make a cord. If you play these neurons, that's eucalyptus,

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Speaker 1: This cord of neurons is peppermint, That chord is burnt toast,

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Speaker 1: and so on. But the really interesting thing about taste

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Speaker 1: and smell is how interactive they are, and a lot

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Speaker 1: of times they really can't be separated. It's not always

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Speaker 1: useful to think about taste and smell as independent senses,

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Speaker 1: so some people talk about this as a composite flavor sense.

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Speaker 1: As an example, certain odors like vanilla are consistently said

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Speaker 1: to smell sweet, even though sweetness belongs to the domain

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Speaker 1: of taste, and according to one study, sweet is the

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Speaker 1: most common description of odor. Or we might say that

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Speaker 1: something smells spicy or something smells sour, even though these

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Speaker 1: are taste words, and food companies understand the interaction of

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Speaker 1: smell and taste, so what they'll do is enhance the

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Speaker 1: sweetness of a product by adding a sweet smelling odor.

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Speaker 1: The same trick of adding a sweet odor can also

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Speaker 1: reduce the perceived sourness of something that's acidic, so smell

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Speaker 1: and taste are entangled. I mentioned earlier that foods lose

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Speaker 1: their flavor when you have a cold because a plugged

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Speaker 1: nose affects your sense of smell, and without smell, there's

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Speaker 1: little flavor. So as a result of damaging my sense

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Speaker 1: of smell when I was a kid, I've always had

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Speaker 1: very little discrimination when it comes to food, which is

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Speaker 1: not bad. I don't mind eating food that's boring or

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Speaker 1: a little off. For food that's very spicy that my

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Speaker 1: super taste or friends just can't handle, I'm fine with

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Speaker 1: it all. None of the taste particularly stands out for

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Speaker 1: me because I just don't experience that much smell. Okay,

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Speaker 1: so we've been talking about the interaction between the senses,

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Speaker 1: but I just want to return to smell in particular,

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Speaker 1: because a discussion about noses would not be complete without

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Speaker 1: talking about pheromones. What is a pheromone. It's a chemical

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Speaker 1: that's broadcast by an animal to transmit information like identity

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Speaker 1: and gender, and it can trigger behaviors in other members

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Speaker 1: of the same species. So, for example, pheromones are given

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Speaker 1: off by queen bees to halt the sexual development of

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Speaker 1: the other females and trigger them to become workers. And

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Speaker 1: what we generally see is that drifting molecules can carry

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Speaker 1: a high density of information. In other cases, for example,

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Speaker 1: pheromones carry information about a prospective mate, like their virility,

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Speaker 1: or their genetics, or their age or their fitness. The

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Speaker 1: effect of pheromones on sexual behavior has been studied a

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Speaker 1: lot in the laboratory. So, for example, female mice are

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Speaker 1: presented with a choice of males. It turns out that

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Speaker 1: a female's choice of mate is not random, or it's

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Speaker 1: not based on visible attributes. Instead, the choice results from

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Speaker 1: the relationship between her genetics and that of her suitor.

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Speaker 1: The trick is how she accesses that data. So mammals

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Speaker 1: have a set of immune system genes that we summarize

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Speaker 1: as the major histocompatibility complex or MHC, and following the

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Speaker 1: strategy of keeping the gene pool well stirred, the female

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Speaker 1: mouse will choose the mates whose MHC genes are the

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Speaker 1: most different from hers. But how do the female mice,

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Speaker 1: who are almost blind, figure out who is like them

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Speaker 1: and who is unlike them? And the answer is inside

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Speaker 1: their noses. There's a little organ called the vomeronasal organ

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Speaker 1: and this detects the pheromones, which serve as little genetic

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Speaker 1: calling cards. So these chemicals are carrying deep and important information. Now,

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Speaker 1: the discovery of pheromones across mammals opens up the possibility

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Speaker 1: that humans communicate unconsciously using olfaction in pheromones. And as

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Speaker 1: it turns out, some receptors in your nose are identical

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Speaker 1: to the receptors that mice use for pheromonal signaling. Now,

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Speaker 1: it's not yet clear whether there our pheromonal systems are

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Speaker 1: actually operational, but several groups have presented behavioral evidence that

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Speaker 1: supports the possibility. So in one study, males wore t

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Speaker 1: shirts for several days, allowing their sweat to soak into

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Speaker 1: the cotton. Then females smelled the armpits of the shirts

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Speaker 1: and selected the body odor that they preferred the most. Now, strikingly,

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Speaker 1: and just as you might expect from the mice studies,

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Speaker 1: the females favored the males with MHCs that were different

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Speaker 1: from their own. So, although we're not consciously aware of

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Speaker 1: our pheromonal signals, they might influence our attraction judgments. Beyond

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Speaker 1: mate selection, pheromones also seem to offer some other kinds

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Speaker 1: of data in humans. One study demonstrated that newborns prefer

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Speaker 1: pads that have been brushed against their mother's breast over

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Speaker 1: clean pads, presumably because of pheromones, and generally a mother

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Speaker 1: and an infant can recognize one another based on smell.

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Speaker 1: Humans can also recognize their parents and siblings based on scent,

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Speaker 1: which is proposed to aid in incest avoidance. And beyond family,

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Speaker 1: it's been shown that when a female sniffs the armpit

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Speaker 1: sweat of another woman, the length of her menstrual cycle

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Speaker 1: can change. By the way, side note, it's commonly believed

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Speaker 1: that women who live together synchronize their menstrual cycles, but

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Speaker 1: I just want to clarify that that claim is actually unsupported.

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Speaker 1: There have been large scale studies on this and they

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Speaker 1: demonstrate that synchronization doesn't happen, but you can get statistical

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Speaker 1: fluctuations that give the illusion of synchrony. So although people

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Speaker 1: thought this was true in the nineteen seventies, subsequent research

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Speaker 1: has failed to replicate that finding. So pheromones convey some

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Speaker 1: information in humans, but I'd say the amount they influence

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Speaker 1: our behavior is still not totally clear. Human cognition is

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Speaker 1: profoundly more complex than mouse cognition, and it's possible that

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Speaker 1: pheromones have diminished to a pretty minor role, like legacy

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Speaker 1: software that's left on a computer system that has been

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Speaker 1: continuously updated. So I want to return now to the

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Speaker 1: Latin phrase that I mentioned at the beginning, the gustabus

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Speaker 1: known s disputantum or there's no accounting for taste? Why

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Speaker 1: do some of us like some tastes and others don't?

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Speaker 1: For example, I like Brussels sprouts and my wife doesn't.

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Speaker 1: Why do people like different things? Whill As it turns out,

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Speaker 1: there are lots of reasons for starters. There are genetic actors.

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Speaker 1: Take the issue of taste sensitivity. You have genetic differences

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Speaker 1: that determine how sensitive you are to certain tastes. As

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Speaker 1: an example, there's a gene called TAS two R thirty eight,

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Speaker 1: and whatever sequence you have in that gene that determines

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Speaker 1: your sensitivity to bitter things like broccoli or coffee. If

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Speaker 1: you have a heightened sensitivity to bitterness, you're probably not

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Speaker 1: gonna like those flavors. So that's one example of many,

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Speaker 1: But this goes further. Some people are known as super tasters,

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Speaker 1: and they just have more taste buds, and as a result,

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Speaker 1: they're more sensitive to lots of flavors, especially bitterness and sweetness,

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Speaker 1: so they find certain foods just too intense, while people

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Speaker 1: at the other end of the spectrum with fewer taste buds,

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Speaker 1: sometimes called non tasters, prefer more robust flavors because they

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Speaker 1: need that to get the same punch. But that's not all.

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Speaker 1: Your particular tastes are also about your early experiences. Your

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Speaker 1: taste preferences begin to develop even before birth from your

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Speaker 1: mother's diet, which passes into the amniotic fluid and influences

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Speaker 1: your preferences. The general story is that repeated exposure to

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Speaker 1: particular tastes leads to a preference for those flavors. In

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Speaker 1: other words, the foods that you're exposed to early on

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Speaker 1: shape your lifelong tastes. If you're raised in a culture

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Speaker 1: where spicy foods are common, you're more likely to develop

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Speaker 1: a preference for spicy flavors. What one culture considers a delicacy,

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Speaker 1: another might find totally unappealing. But you learn these cultural

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Speaker 1: preferences from your family traditions and your social groups. By

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Speaker 1: the way, on the flip side of preferences, you can

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Speaker 1: also develop an aversion to some foods given some negative

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Speaker 1: experience that you had, like getting sick after eating it once.

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Speaker 1: This is called a conditioned response. And on this topic

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Speaker 1: of individual preferences, I'll also just mention that these can

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Speaker 1: change even by the hour. You might crave particular flavors

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Speaker 1: at particular times because your body is signaling a need

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Speaker 1: for specific nutrients in the same way that you want

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Speaker 1: water when you're thirsty. If you're craving salty foods, you

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Speaker 1: might be responding to a need for sodium. So there

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Speaker 1: are a lot of factors that combine to create your

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Speaker 1: highly individual taste preferences. Your biological makeup, your upbringing, your experience.

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Speaker 1: These all play their roles in shaping what you find

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Speaker 1: delicious or distasteful. Now there's a related issue which I've

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00:29:45,720 --> 00:29:49,840
Speaker 1: always found fascinating, which is that my kids don't like coffee.

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00:29:50,360 --> 00:29:52,720
Speaker 1: Every once in a while, they'll say, hey, can I

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00:29:52,760 --> 00:29:54,680
Speaker 1: try a sip of that? And I give them a sip,

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00:29:54,720 --> 00:29:59,200
Speaker 1: and they contort their faces and they're truly incredulous that

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00:29:59,400 --> 00:30:03,320
Speaker 1: I and other adults would swill this black liquid. It's

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00:30:03,440 --> 00:30:06,920
Speaker 1: totally aversive to them. And I remember feeling the same

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00:30:06,960 --> 00:30:09,680
Speaker 1: way when I was a kid, But now I love

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00:30:09,880 --> 00:30:12,800
Speaker 1: my daily addiction to coffee, and I'm sure my kids

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00:30:12,800 --> 00:30:15,760
Speaker 1: will someday as well. So this always led me to

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00:30:15,840 --> 00:30:20,880
Speaker 1: be fascinated by the concept of the acquired taste. So

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00:30:20,920 --> 00:30:23,600
Speaker 1: how do we understand this? Well, given what I said

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00:30:23,600 --> 00:30:27,840
Speaker 1: a moment ago, there are obviously social and cultural factors

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00:30:27,880 --> 00:30:32,040
Speaker 1: that play in here. Children observe adults consuming things and

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00:30:32,080 --> 00:30:38,480
Speaker 1: they come to associate that with maturity or desirable social behaviors. Coffee,

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00:30:38,680 --> 00:30:44,920
Speaker 1: in particular, commonly symbolizes adulthood and provides a sense of sophistication,

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00:30:45,120 --> 00:30:48,120
Speaker 1: making it appealing to children as they get older and

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00:30:48,200 --> 00:30:51,760
Speaker 1: more generally, the drive to fit in with social groups

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00:30:51,960 --> 00:30:55,360
Speaker 1: can also influence us to develop a taste for certain

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00:30:55,400 --> 00:31:00,840
Speaker 1: foods and drinks, And there's also the psychological association. Kids

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00:31:00,880 --> 00:31:06,040
Speaker 1: come to associate certain flavors with positive experiences, like a

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00:31:06,520 --> 00:31:09,680
Speaker 1: fun morning routine with the family, and that leads to

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00:31:09,720 --> 00:31:13,959
Speaker 1: a preference for those smells or tastes. And acquired tastes

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00:31:14,000 --> 00:31:18,240
Speaker 1: are about even more than that, because there's also physical

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00:31:18,280 --> 00:31:23,080
Speaker 1: stuff that happens. Children's taste buds are more sensitive and

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00:31:23,120 --> 00:31:26,040
Speaker 1: they tend to prefer sweet flavors. This is thought to

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00:31:26,080 --> 00:31:31,240
Speaker 1: be a biological safeguard to ensure that they consume calorie

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00:31:31,320 --> 00:31:35,600
Speaker 1: rich foods for growth, and bitter flavors like coffee are

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00:31:35,600 --> 00:31:39,920
Speaker 1: thought to be even more unpleasant because bitterness can signal

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00:31:40,040 --> 00:31:45,560
Speaker 1: toxins in nature. But as children grow, their taste buds change,

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00:31:45,640 --> 00:31:49,520
Speaker 1: their desire for sweetness goes down. They become less sensitive

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00:31:49,560 --> 00:31:53,240
Speaker 1: to bitterness, and that makes certain foods and drinks more

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00:31:53,520 --> 00:31:57,680
Speaker 1: palatable over time, like coffee. There's also the issue of

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00:31:58,280 --> 00:32:02,800
Speaker 1: repeated exposure. So a kid might initially dislike a bitter

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00:32:03,000 --> 00:32:07,160
Speaker 1: or strong flavor like coffee, but with repeated tasting, they

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00:32:07,160 --> 00:32:10,720
Speaker 1: get more accustomed to it. This is called taste acculturation

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00:32:11,080 --> 00:32:16,760
Speaker 1: or flavor learning, where exposure to certain flavors gradually diminishes

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00:32:16,800 --> 00:32:20,240
Speaker 1: their negative reactions. And we also acquire a taste for

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00:32:20,280 --> 00:32:23,680
Speaker 1: coffee because we come to predict what it will do

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00:32:23,880 --> 00:32:27,520
Speaker 1: to us, how it will make us feel. And finally,

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00:32:27,880 --> 00:32:32,600
Speaker 1: when we're talking about acquire tastes, we can't ignore cognitive development.

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00:32:32,720 --> 00:32:36,240
Speaker 1: As children mature, they're just more open to trying new

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00:32:36,280 --> 00:32:39,960
Speaker 1: foods and flavors, and they're growing cognitive abilities help them

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00:32:39,960 --> 00:32:45,920
Speaker 1: to better appreciate complex flavors, recognizing the nuances and foods

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00:32:45,920 --> 00:32:48,560
Speaker 1: that they previously just didn't want to try. And so

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00:32:48,760 --> 00:32:52,640
Speaker 1: when we think about acquired tastes, there are so many

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00:32:52,640 --> 00:32:57,720
Speaker 1: things underlying this, social issues, developmental issues, and physical issues,

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00:32:58,120 --> 00:33:01,080
Speaker 1: all the way down to the level of the taste buds.

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00:33:01,440 --> 00:33:04,040
Speaker 1: So I hope you enjoyed this deep dive into the

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00:33:04,080 --> 00:33:08,840
Speaker 1: incredible world of taste and smell and how they work biologically. Now,

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00:33:08,920 --> 00:33:11,400
Speaker 1: I told you we have about fifty different types of

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00:33:11,440 --> 00:33:15,040
Speaker 1: taste receptors and about four hundred types of olfactory receptors,

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00:33:15,760 --> 00:33:20,200
Speaker 1: and that high dimensional space is what defines the boundaries

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00:33:20,200 --> 00:33:23,680
Speaker 1: of what you taste and smell. In other words, everything

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00:33:24,040 --> 00:33:27,760
Speaker 1: that you could possibly experience in your entire life lives

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00:33:27,800 --> 00:33:33,040
Speaker 1: inside this space. But other animals have more receptors for

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00:33:33,200 --> 00:33:36,600
Speaker 1: smell and for taste, many more, as carved by their

487
00:33:36,880 --> 00:33:41,040
Speaker 1: evolutionary needs. So what would it be like to experience

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00:33:41,120 --> 00:33:46,800
Speaker 1: something well outside the dimensions of human flavor. We are,

489
00:33:46,920 --> 00:33:50,360
Speaker 1: of course, very special species, a runaway species in terms

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00:33:50,360 --> 00:33:53,760
Speaker 1: of so many of our talents, but we lag behind

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00:33:54,120 --> 00:33:56,720
Speaker 1: most of the animal kingdom on this one metric of

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00:33:56,840 --> 00:34:00,560
Speaker 1: chemical sensing. For much of the rest of our cousins,

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00:34:01,200 --> 00:34:04,920
Speaker 1: smell into some of you, taste is their main window

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00:34:05,400 --> 00:34:09,120
Speaker 1: for picking up information from the world. So the next

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00:34:09,160 --> 00:34:12,239
Speaker 1: time you're out walking with your dog, try to think

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00:34:12,239 --> 00:34:15,879
Speaker 1: about the world as your cane perceives it. You are

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00:34:15,920 --> 00:34:20,239
Speaker 1: surrounded by a universe of smells. Just try to imagine

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00:34:20,360 --> 00:34:25,279
Speaker 1: seeing those as colorful plumes rising up all around you.

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00:34:26,640 --> 00:34:29,239
Speaker 1: And so when the ancient Romans said there was no

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00:34:29,320 --> 00:34:33,440
Speaker 1: accounting for taste, they were just talking about personal preference.

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00:34:33,560 --> 00:34:38,080
Speaker 1: But they couldn't have imagined just how vast the worlds

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00:34:38,160 --> 00:34:41,880
Speaker 1: of taste and smell are when we look beyond humans

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00:34:42,200 --> 00:34:45,400
Speaker 1: into the much vaster realm of all the animals and

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00:34:45,440 --> 00:34:49,480
Speaker 1: their noses tailored by evolution. So the next time that

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00:34:49,560 --> 00:34:54,200
Speaker 1: you enjoy a delicious meal, or smell a great floral bouquet,

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00:34:54,400 --> 00:34:59,120
Speaker 1: or walk alongside your dog, just remember that you're only

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00:34:59,200 --> 00:35:09,239
Speaker 1: scratching the surface of a much larger sensory cosmos. Go

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00:35:09,280 --> 00:35:12,320
Speaker 1: to Eagleman dot com slash podcast for more information and

509
00:35:12,360 --> 00:35:16,680
Speaker 1: to find further reading. Send me an email at podcast

510
00:35:16,760 --> 00:35:20,640
Speaker 1: at eagleman dot com with questions or discussion and check

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00:35:20,680 --> 00:35:23,759
Speaker 1: out Subscribe to Inner Cosmos on YouTube for videos of

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00:35:23,800 --> 00:35:28,080
Speaker 1: each episode and to leave comments. Until next time. I'm

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Speaker 1: David Eagleman and this is inner cosmos,