Speaker 1: Why do you like the taste of something that your
Speaker 1: friend does not. Why new kids not like coffee but
Speaker 1: adults do. Can we consider smell and taste both part
Speaker 1: of something bigger? And what does any of this have
Speaker 1: to do with whether your culture eats spicy foods or
Speaker 1: whether women actually synchronize their menstruation or smelling someone's armpits.
Speaker 1: Welcome to Inner Cosmos with me David Eagleman. I'm a
Speaker 1: neuroscientist and author at Stanford and in these episodes, we
Speaker 1: sail deeply into our three pound universe to understand why
Speaker 1: and how our lives look the way they do. Over
Speaker 1: the last few months, I've received several requests to make
Speaker 1: an episode on the topic of smell and taste and
Speaker 1: flavor and why we like some more than others and
Speaker 1: why are some tastes acquired? So that's what we're gonna
Speaker 1: do today, and we're gonna start with taking a little
Speaker 1: time to appreciate how the stuff works. It hasn't escaped
Speaker 1: my notice that when I talk with people on airplanes,
Speaker 1: everyone seems to have a reasonable understanding of how their
Speaker 1: eyeballs work capturing light photons from the world. But if
Speaker 1: smell or taste comes up there generally seems to be
Speaker 1: less known about how that physically works. In other words,
Speaker 1: when there's an apple pie on the counter across the room,
Speaker 1: how precisely does your brain detect that? And let's say
Speaker 1: you taste some drink with molecules of this shape or
Speaker 1: that shape and you say, oh, that's blueberry flavored or
Speaker 1: oh that's lemon flavored. What is happening in your tongue
Speaker 1: and in your brain? So we're first going to understand
Speaker 1: that how these systems explore the world around us and
Speaker 1: how they work, and then we'll transition into cool questions
Speaker 1: like why did you not like coffee as a kid
Speaker 1: but you do now? Or why do you always choose
Speaker 1: this flavor of ice cream and your friend always chooses
Speaker 1: this other one? And I'll just say this episode is
Speaker 1: quite personal for me because when I was a kid,
Speaker 1: I fell off a roof and smashed my nose very badly,
Speaker 1: and as a result, I've always had a particularly terrible
Speaker 1: sense of smell. And watching people around me be able
Speaker 1: to identify things that a different level than I could
Speaker 1: has always made me very interested in this topic. So
Speaker 1: let's start by thinking about the senses generally, all your
Speaker 1: senses are just specialized detectors for picking up some sort
Speaker 1: of information stream from the world. Vision works by capturing
Speaker 1: and transforming the energy of photons which bound so objects.
Speaker 1: Hearing works by picking up these sensitive mechanical forces. On
Speaker 1: the ear drum. You have air compression waves that wiggle
Speaker 1: this membrane back and forth, and your brain analyzes that data.
Speaker 1: Touch is also a detector of mechanical forces. When you
Speaker 1: touch something, you physically distort these receptors in your skin.
Speaker 1: But taste and smell these are different from the others.
Speaker 1: They have a divergent strategy for picking up on information
Speaker 1: from the world. They work by being exquisitely sensitive molecule detectors.
Speaker 1: So let's start with taste. How does taste work. The
Speaker 1: sensitive taste is called gustation, and we see this in
Speaker 1: the Latin expression de gustibis known s disputandum, which means
Speaker 1: about taste. There is no disputing, or, as it's come
Speaker 1: down to us in English, there is there's no accounting
Speaker 1: for taste. Now, the ancient Romans were fond of this phrase,
Speaker 1: and as we'll see, there is something sufficiently profound about
Speaker 1: this observation that it has stuck with us for a
Speaker 1: couple thousand years. So how does taste Gustachian work biologically?
Speaker 1: Here's how. You have microscopic taste receptors all over your
Speaker 1: tongue and also, by the way, spread even more widely,
Speaker 1: even on your palate and the upper half of your
Speaker 1: esophagus and more. Now, these little taste receptors are embedded
Speaker 1: in the membrane of what we call taste cells, and
Speaker 1: taste cells clump together, about one hundred of them into
Speaker 1: taste buds, and taste buds cluster to form the bumps
Speaker 1: on your tongue that you can see with the naked eye.
Speaker 1: These are called pipille. Now, I know different listeners are
Speaker 1: doing different things while listening, but if you're able, either
Speaker 1: now or later, go to a mirror or bust out
Speaker 1: your front facing camera on your cell phone and take
Speaker 1: a look at your tongue. You'll notice the surface is
Speaker 1: not smooth. You have all these bumps, these papillae, and
Speaker 1: you'll notice that some of these are bigger bumps. These
Speaker 1: are called fungiform, meaning like a mushroom, and off to
Speaker 1: the sides you have some that look leaf like and
Speaker 1: others way in the back that look pimple. Like, what's
Speaker 1: cool is that you've had this tongue your whole life,
Speaker 1: and it's possible that you've never looked really carefully to
Speaker 1: see what you are made of. But this is all
Speaker 1: part of the joy of self discovery. Okay, So back
Speaker 1: to the structure here, so you can see these papilla
Speaker 1: on your tongue. But what you can't see because it's smaller,
Speaker 1: is that inside the taste buds, the taste cells arrange
Speaker 1: themselves so they're little receptors line a central pore. So architecturally,
Speaker 1: these guys are set up to catch chemicals. That's what
Speaker 1: they're built for. Even if you, the owner, are totally
Speaker 1: unaware of that. You're just walking around and you lick
Speaker 1: the ice cream and you say, oh yeah, that rocky
Speaker 1: Road tastes awesome, and you say, of course I can
Speaker 1: distinguish rocky Road from lemon from vanilla. But how does
Speaker 1: that work. The answer is, we have this miraculous microscopic
Speaker 1: engineering in ourselves. But the story gets even better because
Speaker 1: this whole system can detect and distinguish flavors with extraordinarily
Speaker 1: high specificity. So to understand how it does that, let's
Speaker 1: turn to the food that you put in your mouth.
Speaker 1: Everything that you eat or drink can be understood in
Speaker 1: terms of the molecules that they're made of, and we
Speaker 1: call these tastins Tasteans fall into five basic categories, and
Speaker 1: I know you're already well acquainted with four of them, sweet, salty, bitter,
Speaker 1: and sour. But what's the fifth taste category, which was
Speaker 1: added more recently. I'll give you a second. The fifth
Speaker 1: taste category is called umami. Umami this is a Japanese
Speaker 1: word meaning delicious taste, and we usually describe this flavor
Speaker 1: as savory. So for the sweet category, the standard thing
Speaker 1: we might think about is sucrose. For salty, a prototypical
Speaker 1: stimulus might be sodium chloride, which is table salt. For sour,
Speaker 1: the prototype is citric acid, like from a lemon. For bitter,
Speaker 1: it's quinine. And for umami, that fifth taste category, it's
Speaker 1: msgm MO, a sodium glutamate. Okay, So what happens when
Speaker 1: you put some taste int in your mouth? What happens
Speaker 1: is that the various chemicals, little molecules bind to the
Speaker 1: taste receptors. And even though I told you there are
Speaker 1: five categories, there are about fifty different receptors that we have,
Speaker 1: and there are all kinds of ways that these receptors work. Mechanically.
Speaker 1: Some cells activate when sodium physically flows through a channel
Speaker 1: in the membrane. Other cells activate because the key thing
Speaker 1: in sour compounds, which is hydrogen ions, block certain channels
Speaker 1: in the membrane. In other cases, taste ins bind to
Speaker 1: proteins in the cell membrane and change their shape, which
Speaker 1: leads to a cascade of changes inside the cell. So
Speaker 1: there's a huge variety of ways that these molecules that
Speaker 1: you've just put in your mouth physically get translated into
Speaker 1: signals that shoot off into your brain. So it seems
Speaker 1: like a strange zoo of things that can happen here.
Speaker 1: But as long as the signaling is consistent, that's all
Speaker 1: you need. So if you taste cinnamon, you get this
Speaker 1: very weird pattern of activation, and as long as you
Speaker 1: get that same pattern tomorrow, then you can identify that
Speaker 1: as cinnamon again. And this huge variety of these random
Speaker 1: tricks of mother nature gives us a lot of nuance
Speaker 1: and ability to discriminate when we sit down to enjoy
Speaker 1: a meal. So these signals shoot over to the brainstem,
Speaker 1: and then to the thalamus and finally to the core tex,
Speaker 1: a special area that we call the primary gustatory cortex. Okay,
Speaker 1: so how does taste actually get constructed? I told you
Speaker 1: that we have these taste receptors that respond preferentially to
Speaker 1: sweet or salty or something like that. But how do
Speaker 1: we get from something like that to something very specific
Speaker 1: like the taste of chocolate covered peanuts. With time and experience,
Speaker 1: we learn to recognize combinations of flavors, thousands and thousands
Speaker 1: of them. Now how do we get that kind of
Speaker 1: diversity from only fifty receptor types in five categories. Well,
Speaker 1: it's because each of these receptors will also activate in
Speaker 1: response to other types of taste ins if those are
Speaker 1: present and high enough concentrations. And it's not that each
Speaker 1: taste bud talks to one fiber going back into the brain,
Speaker 1: but instead multiple taste buds talk to a single fiber.
Speaker 1: So we can skip the details, but the bottom line
Speaker 1: is that anything you stick in your mouth triggers a
Speaker 1: pattern of taste receptor activation, which then stimulates a specific
Speaker 1: pattern of goostatory cells in the cortex. So this sense
Speaker 1: of taste uses populations of neurons to encode the sensation.
Speaker 1: This is what's called pattern encoding. It's not that chocolate
Speaker 1: covered peanuts activates this neuron. Instead, it activates thousands of neurons.
Speaker 1: This pattern of thousands of neurons maps onto lemon pie,
Speaker 1: and this other pattern over here maps on the bobagaoush,
Speaker 1: and this pattern maps on the anchovies and so on.
Speaker 1: Now what happens if there's damage to this gustatory system.
Speaker 1: It impairs your ability to taste. This is called dysgusia,
Speaker 1: or at the extreme agusia, and this can result from
Speaker 1: all kinds of different problems if it's at the level
Speaker 1: of the taste cells. Happily, these turnover quickly every couple
Speaker 1: of weeks, so damage to the taste cells themselves is
Speaker 1: often reversible. For example, there's a chef named Grant Ashats,
Speaker 1: and he made headlines after being diagnosed with tongue cancer
Speaker 1: and losing his sense of taste as a result of
Speaker 1: radiation treatment. And so he described how with time he
Speaker 1: regained taste sensation one category at a time. Now, people
Speaker 1: sometimes get dysgusia from COVID, and I'll come back to
Speaker 1: that a little later. But you can also get dysgusia
Speaker 1: from damage directly to the cortex, just like we see
Speaker 1: in all the other senses. If you damage the primary
Speaker 1: gustatory cortex, you don't understand basic taste anymore. If the
Speaker 1: damage happens in a higher level area, we move from
Speaker 1: the basic details to more abstract representation. So with damage
Speaker 1: to the secondary goustatory cortex, you can still identify basic tests,
Speaker 1: but you can't do more subtle recognition of food type
Speaker 1: and flavor intensity. Now what's fascinating is that if you
Speaker 1: lose other senses, that can also affect your sense of taste.
Speaker 1: For example, consider how your experience of each bite includes
Speaker 1: touch information in your mouth about texture and temperature, what
Speaker 1: is sometimes called the mouth feel of food. But by
Speaker 1: far the most influential sense on our perception of taste
Speaker 1: is smell. The nuance that we have and our perception
Speaker 1: of taste is cranked up way more from the interplay
Speaker 1: of taste and smell. Just think about what things like
Speaker 1: when you have a head cold. So now we turn
Speaker 1: to act too all about smell and then will come
Speaker 1: to the more general concept of flavor. So our other
Speaker 1: chemical sense smell, known as old faction. Lets us perceive
Speaker 1: airborne chemicals. Now, we humans don't rely on our sense
Speaker 1: of smell as much as we do on other sensory
Speaker 1: windows like vision and hearing. But other cousins of ours
Speaker 1: in the animal kingdom, like dogs and rodents, they capitalize
Speaker 1: on old faction to read the environment around them like
Speaker 1: a book. A dog can tell that a cat wandered
Speaker 1: onto the lawn hours ago, and rats can locate little,
Speaker 1: tiny morsels of food buried underneath layers of cage bedding.
Speaker 1: So here's the interesting bit. Although humans and dogs and
Speaker 1: rats we all rely on smell to different degrees, it
Speaker 1: all works in our brains the same way the floating
Speaker 1: chemical signals. These are called odorans, and you walk around
Speaker 1: all day vacuuming these in mostly through your nose a
Speaker 1: little through your mouth. Once these molecules have entered the
Speaker 1: giant vessel of your nasal cavity, they get sucked over
Speaker 1: to the main sensory organ, which is called the old
Speaker 1: factory epithelium, and that's at the back of that big
Speaker 1: space inside your nose. In humans, this structure is less
Speaker 1: than ten square centimeters, which is about the size of
Speaker 1: a half dollar coin. Compare that to dogs whose epithelium
Speaker 1: is seventeen times larger. Now, the old factory epithelium is
Speaker 1: covered with a layer of mucus, and that's how the
Speaker 1: molecules stick and come into contact with the little feelers
Speaker 1: of the receptor cells, called the dendrites. Okay, but how
Speaker 1: do we distinguish different smells like chlorine from lavender from
Speaker 1: wood burning at a campfire, given that these are all
Speaker 1: just molecules of different shapes. Well. A lot of the
Speaker 1: groundbreaking work in this field was done by Richard Axel
Speaker 1: and Linda Buck who discovered a huge number of old
Speaker 1: factory receptor genes in rats, about one thousand of them,
Speaker 1: and by the way, they won the two thousand and
Speaker 1: four Nobel Prize for that. Turns out, these old factory
Speaker 1: receptor genes are the largest gene family in the rodent genome.
Speaker 1: We humans also have that same gene family, but only
Speaker 1: about four hundred of these genes are still functional in US.
Speaker 1: So these receptors started becoming discovered in nineteen ninety one,
Speaker 1: not that long ago, and at first the guess was
Speaker 1: that maybe each receptor encodes an odor, But the way
Speaker 1: it turns out is that each odorant molecule has its
Speaker 1: particular shape, and it binds to several different receptor types,
Speaker 1: and a single receptor type responds to lots of different
Speaker 1: odorants that all happened to share some particular shape feature. So,
Speaker 1: just like the sense of taste, you have pattern encoding.
Speaker 1: This whole random looking population of neurons represents the scent
Speaker 1: of freshly cut grass, and this other group over here
Speaker 1: represents mint, and this other population represents hot chocolate and
Speaker 1: so on. Now, before I go on what's going on
Speaker 1: with COVID and smell. A lot of people end up
Speaker 1: with what's called a noosmia, which is a lack of
Speaker 1: smell and inability to smell. There's a growing literature on this,
Speaker 1: and the answer to why it happens isn't fully agreed on.
Speaker 1: But you can see how with the huge variety of
Speaker 1: molecular mechanisms underlying smell, it's not hard for a virus
Speaker 1: to throw a wrench in the machinery, in other words,
Speaker 1: to temporarily tweak things so that the signals the brain
Speaker 1: are used to have now been changed. Okay, so back
Speaker 1: to how smell works. From these receptors and the epithelium,
Speaker 1: the signals shoot to the olfactory bulb and from there
Speaker 1: to the primary olfactory cortex. From this part of the cortex,
Speaker 1: information zooms out to a network of other areas that
Speaker 1: are involved in higher order abstractions like familiarity and edibleness.
Speaker 1: And again we see that the primary sensory cortex represents
Speaker 1: the basic data and then higher level cortical processing becomes
Speaker 1: more abstract from there. So we have this sophisticated machinery
Speaker 1: to pick up on floating chemical signals in the world.
Speaker 1: So what do animals do with this? Well, obviously they
Speaker 1: identify things in the world like foods or toxins, but
Speaker 1: it goes beyond that. A lot of animals smell to
Speaker 1: understand not only what but where. They navigate space by
Speaker 1: smelling their way around. So think of a puppy finding
Speaker 1: its mother's nipple via smell, or lobsters locating their prey,
Speaker 1: or moths finding their lovers. All of these are done
Speaker 1: with smell, and this is also a large part of
Speaker 1: how pigeons find their way home or salmon return to
Speaker 1: their stream of origin. They create an olfactory map that
Speaker 1: links specific smells with locations during their travels. But it's
Speaker 1: not only about long distance stuff. Animals can navigate close
Speaker 1: space by smell. They can actually figure out which way
Speaker 1: to turn. Now, how could that work? Well, you probably
Speaker 1: know the brain can localize a sound by comparing the
Speaker 1: signal hitting the two ears, and the side where the
Speaker 1: signal arrives first tells you the side where the sound
Speaker 1: came from. Amazingly, the same strategy is used to find
Speaker 1: the source of a smell. You exploit the inter nostril
Speaker 1: time differences which nostril the odor got to first, And
Speaker 1: it's been shown this is how sharks aside which way
Speaker 1: to turn when they're following a plume of smell, and
Speaker 1: it's not as one might have intuited by the concentration difference.
Speaker 1: So this is a general strategy across senses. If you're
Speaker 1: trying to locate something, you can exploit the timing across
Speaker 1: two channels that are in slightly different places, like your
Speaker 1: two ears or your two nostrils. Okay, so where are
Speaker 1: we now. We've looked at how taste works by chemicals
Speaker 1: binding to receptors in and around the tongue, and we've
Speaker 1: seen how smell is about floating molecules binding to receptors
Speaker 1: at the back of the nasal cavity, and in both
Speaker 1: cases the brain is using pattern encoding. Think of this
Speaker 1: like the way that you strike multiple piano keys to
Speaker 1: make a cord. If you play these neurons, that's eucalyptus,
Speaker 1: This cord of neurons is peppermint, That chord is burnt toast,
Speaker 1: and so on. But the really interesting thing about taste
Speaker 1: and smell is how interactive they are, and a lot
Speaker 1: of times they really can't be separated. It's not always
Speaker 1: useful to think about taste and smell as independent senses,
Speaker 1: so some people talk about this as a composite flavor sense.
Speaker 1: As an example, certain odors like vanilla are consistently said
Speaker 1: to smell sweet, even though sweetness belongs to the domain
Speaker 1: of taste, and according to one study, sweet is the
Speaker 1: most common description of odor. Or we might say that
Speaker 1: something smells spicy or something smells sour, even though these
Speaker 1: are taste words, and food companies understand the interaction of
Speaker 1: smell and taste, so what they'll do is enhance the
Speaker 1: sweetness of a product by adding a sweet smelling odor.
Speaker 1: The same trick of adding a sweet odor can also
Speaker 1: reduce the perceived sourness of something that's acidic, so smell
Speaker 1: and taste are entangled. I mentioned earlier that foods lose
Speaker 1: their flavor when you have a cold because a plugged
Speaker 1: nose affects your sense of smell, and without smell, there's
Speaker 1: little flavor. So as a result of damaging my sense
Speaker 1: of smell when I was a kid, I've always had
Speaker 1: very little discrimination when it comes to food, which is
Speaker 1: not bad. I don't mind eating food that's boring or
Speaker 1: a little off. For food that's very spicy that my
Speaker 1: super taste or friends just can't handle, I'm fine with
Speaker 1: it all. None of the taste particularly stands out for
Speaker 1: me because I just don't experience that much smell. Okay,
Speaker 1: so we've been talking about the interaction between the senses,
Speaker 1: but I just want to return to smell in particular,
Speaker 1: because a discussion about noses would not be complete without
Speaker 1: talking about pheromones. What is a pheromone. It's a chemical
Speaker 1: that's broadcast by an animal to transmit information like identity
Speaker 1: and gender, and it can trigger behaviors in other members
Speaker 1: of the same species. So, for example, pheromones are given
Speaker 1: off by queen bees to halt the sexual development of
Speaker 1: the other females and trigger them to become workers. And
Speaker 1: what we generally see is that drifting molecules can carry
Speaker 1: a high density of information. In other cases, for example,
Speaker 1: pheromones carry information about a prospective mate, like their virility,
Speaker 1: or their genetics, or their age or their fitness. The
Speaker 1: effect of pheromones on sexual behavior has been studied a
Speaker 1: lot in the laboratory. So, for example, female mice are
Speaker 1: presented with a choice of males. It turns out that
Speaker 1: a female's choice of mate is not random, or it's
Speaker 1: not based on visible attributes. Instead, the choice results from
Speaker 1: the relationship between her genetics and that of her suitor.
Speaker 1: The trick is how she accesses that data. So mammals
Speaker 1: have a set of immune system genes that we summarize
Speaker 1: as the major histocompatibility complex or MHC, and following the
Speaker 1: strategy of keeping the gene pool well stirred, the female
Speaker 1: mouse will choose the mates whose MHC genes are the
Speaker 1: most different from hers. But how do the female mice,
Speaker 1: who are almost blind, figure out who is like them
Speaker 1: and who is unlike them? And the answer is inside
Speaker 1: their noses. There's a little organ called the vomeronasal organ
Speaker 1: and this detects the pheromones, which serve as little genetic
Speaker 1: calling cards. So these chemicals are carrying deep and important information. Now,
Speaker 1: the discovery of pheromones across mammals opens up the possibility
Speaker 1: that humans communicate unconsciously using olfaction in pheromones. And as
Speaker 1: it turns out, some receptors in your nose are identical
Speaker 1: to the receptors that mice use for pheromonal signaling. Now,
Speaker 1: it's not yet clear whether there our pheromonal systems are
Speaker 1: actually operational, but several groups have presented behavioral evidence that
Speaker 1: supports the possibility. So in one study, males wore t
Speaker 1: shirts for several days, allowing their sweat to soak into
Speaker 1: the cotton. Then females smelled the armpits of the shirts
Speaker 1: and selected the body odor that they preferred the most. Now, strikingly,
Speaker 1: and just as you might expect from the mice studies,
Speaker 1: the females favored the males with MHCs that were different
Speaker 1: from their own. So, although we're not consciously aware of
Speaker 1: our pheromonal signals, they might influence our attraction judgments. Beyond
Speaker 1: mate selection, pheromones also seem to offer some other kinds
Speaker 1: of data in humans. One study demonstrated that newborns prefer
Speaker 1: pads that have been brushed against their mother's breast over
Speaker 1: clean pads, presumably because of pheromones, and generally a mother
Speaker 1: and an infant can recognize one another based on smell.
Speaker 1: Humans can also recognize their parents and siblings based on scent,
Speaker 1: which is proposed to aid in incest avoidance. And beyond family,
Speaker 1: it's been shown that when a female sniffs the armpit
Speaker 1: sweat of another woman, the length of her menstrual cycle
Speaker 1: can change. By the way, side note, it's commonly believed
Speaker 1: that women who live together synchronize their menstrual cycles, but
Speaker 1: I just want to clarify that that claim is actually unsupported.
Speaker 1: There have been large scale studies on this and they
Speaker 1: demonstrate that synchronization doesn't happen, but you can get statistical
Speaker 1: fluctuations that give the illusion of synchrony. So although people
Speaker 1: thought this was true in the nineteen seventies, subsequent research
Speaker 1: has failed to replicate that finding. So pheromones convey some
Speaker 1: information in humans, but I'd say the amount they influence
Speaker 1: our behavior is still not totally clear. Human cognition is
Speaker 1: profoundly more complex than mouse cognition, and it's possible that
Speaker 1: pheromones have diminished to a pretty minor role, like legacy
Speaker 1: software that's left on a computer system that has been
Speaker 1: continuously updated. So I want to return now to the
Speaker 1: Latin phrase that I mentioned at the beginning, the gustabus
Speaker 1: known s disputantum or there's no accounting for taste? Why
Speaker 1: do some of us like some tastes and others don't?
Speaker 1: For example, I like Brussels sprouts and my wife doesn't.
Speaker 1: Why do people like different things? Whill As it turns out,
Speaker 1: there are lots of reasons for starters. There are genetic actors.
Speaker 1: Take the issue of taste sensitivity. You have genetic differences
Speaker 1: that determine how sensitive you are to certain tastes. As
Speaker 1: an example, there's a gene called TAS two R thirty eight,
Speaker 1: and whatever sequence you have in that gene that determines
Speaker 1: your sensitivity to bitter things like broccoli or coffee. If
Speaker 1: you have a heightened sensitivity to bitterness, you're probably not
Speaker 1: gonna like those flavors. So that's one example of many,
Speaker 1: But this goes further. Some people are known as super tasters,
Speaker 1: and they just have more taste buds, and as a result,
Speaker 1: they're more sensitive to lots of flavors, especially bitterness and sweetness,
Speaker 1: so they find certain foods just too intense, while people
Speaker 1: at the other end of the spectrum with fewer taste buds,
Speaker 1: sometimes called non tasters, prefer more robust flavors because they
Speaker 1: need that to get the same punch. But that's not all.
Speaker 1: Your particular tastes are also about your early experiences. Your
Speaker 1: taste preferences begin to develop even before birth from your
Speaker 1: mother's diet, which passes into the amniotic fluid and influences
Speaker 1: your preferences. The general story is that repeated exposure to
Speaker 1: particular tastes leads to a preference for those flavors. In
Speaker 1: other words, the foods that you're exposed to early on
Speaker 1: shape your lifelong tastes. If you're raised in a culture
Speaker 1: where spicy foods are common, you're more likely to develop
Speaker 1: a preference for spicy flavors. What one culture considers a delicacy,
Speaker 1: another might find totally unappealing. But you learn these cultural
Speaker 1: preferences from your family traditions and your social groups. By
Speaker 1: the way, on the flip side of preferences, you can
Speaker 1: also develop an aversion to some foods given some negative
Speaker 1: experience that you had, like getting sick after eating it once.
Speaker 1: This is called a conditioned response. And on this topic
Speaker 1: of individual preferences, I'll also just mention that these can
Speaker 1: change even by the hour. You might crave particular flavors
Speaker 1: at particular times because your body is signaling a need
Speaker 1: for specific nutrients in the same way that you want
Speaker 1: water when you're thirsty. If you're craving salty foods, you
Speaker 1: might be responding to a need for sodium. So there
Speaker 1: are a lot of factors that combine to create your
Speaker 1: highly individual taste preferences. Your biological makeup, your upbringing, your experience.
Speaker 1: These all play their roles in shaping what you find
Speaker 1: delicious or distasteful. Now there's a related issue which I've
Speaker 1: always found fascinating, which is that my kids don't like coffee.
Speaker 1: Every once in a while, they'll say, hey, can I
Speaker 1: try a sip of that? And I give them a sip,
Speaker 1: and they contort their faces and they're truly incredulous that
Speaker 1: I and other adults would swill this black liquid. It's
Speaker 1: totally aversive to them. And I remember feeling the same
Speaker 1: way when I was a kid, But now I love
Speaker 1: my daily addiction to coffee, and I'm sure my kids
Speaker 1: will someday as well. So this always led me to
Speaker 1: be fascinated by the concept of the acquired taste. So
Speaker 1: how do we understand this? Well, given what I said
Speaker 1: a moment ago, there are obviously social and cultural factors
Speaker 1: that play in here. Children observe adults consuming things and
Speaker 1: they come to associate that with maturity or desirable social behaviors. Coffee,
Speaker 1: in particular, commonly symbolizes adulthood and provides a sense of sophistication,
Speaker 1: making it appealing to children as they get older and
Speaker 1: more generally, the drive to fit in with social groups
Speaker 1: can also influence us to develop a taste for certain
Speaker 1: foods and drinks, And there's also the psychological association. Kids
Speaker 1: come to associate certain flavors with positive experiences, like a
Speaker 1: fun morning routine with the family, and that leads to
Speaker 1: a preference for those smells or tastes. And acquired tastes
Speaker 1: are about even more than that, because there's also physical
Speaker 1: stuff that happens. Children's taste buds are more sensitive and
Speaker 1: they tend to prefer sweet flavors. This is thought to
Speaker 1: be a biological safeguard to ensure that they consume calorie
Speaker 1: rich foods for growth, and bitter flavors like coffee are
Speaker 1: thought to be even more unpleasant because bitterness can signal
Speaker 1: toxins in nature. But as children grow, their taste buds change,
Speaker 1: their desire for sweetness goes down. They become less sensitive
Speaker 1: to bitterness, and that makes certain foods and drinks more
Speaker 1: palatable over time, like coffee. There's also the issue of
Speaker 1: repeated exposure. So a kid might initially dislike a bitter
Speaker 1: or strong flavor like coffee, but with repeated tasting, they
Speaker 1: get more accustomed to it. This is called taste acculturation
Speaker 1: or flavor learning, where exposure to certain flavors gradually diminishes
Speaker 1: their negative reactions. And we also acquire a taste for
Speaker 1: coffee because we come to predict what it will do
Speaker 1: to us, how it will make us feel. And finally,
Speaker 1: when we're talking about acquire tastes, we can't ignore cognitive development.
Speaker 1: As children mature, they're just more open to trying new
Speaker 1: foods and flavors, and they're growing cognitive abilities help them
Speaker 1: to better appreciate complex flavors, recognizing the nuances and foods
Speaker 1: that they previously just didn't want to try. And so
Speaker 1: when we think about acquired tastes, there are so many
Speaker 1: things underlying this, social issues, developmental issues, and physical issues,
Speaker 1: all the way down to the level of the taste buds.
Speaker 1: So I hope you enjoyed this deep dive into the
Speaker 1: incredible world of taste and smell and how they work biologically. Now,
Speaker 1: I told you we have about fifty different types of
Speaker 1: taste receptors and about four hundred types of olfactory receptors,
Speaker 1: and that high dimensional space is what defines the boundaries
Speaker 1: of what you taste and smell. In other words, everything
Speaker 1: that you could possibly experience in your entire life lives
Speaker 1: inside this space. But other animals have more receptors for
Speaker 1: smell and for taste, many more, as carved by their
Speaker 1: evolutionary needs. So what would it be like to experience
Speaker 1: something well outside the dimensions of human flavor. We are,
Speaker 1: of course, very special species, a runaway species in terms
Speaker 1: of so many of our talents, but we lag behind
Speaker 1: most of the animal kingdom on this one metric of
Speaker 1: chemical sensing. For much of the rest of our cousins,
Speaker 1: smell into some of you, taste is their main window
Speaker 1: for picking up information from the world. So the next
Speaker 1: time you're out walking with your dog, try to think
Speaker 1: about the world as your cane perceives it. You are
Speaker 1: surrounded by a universe of smells. Just try to imagine
Speaker 1: seeing those as colorful plumes rising up all around you.
Speaker 1: And so when the ancient Romans said there was no
Speaker 1: accounting for taste, they were just talking about personal preference.
Speaker 1: But they couldn't have imagined just how vast the worlds
Speaker 1: of taste and smell are when we look beyond humans
Speaker 1: into the much vaster realm of all the animals and
Speaker 1: their noses tailored by evolution. So the next time that
Speaker 1: you enjoy a delicious meal, or smell a great floral bouquet,
Speaker 1: or walk alongside your dog, just remember that you're only
Speaker 1: scratching the surface of a much larger sensory cosmos. Go
Speaker 1: to Eagleman dot com slash podcast for more information and
Speaker 1: to find further reading. Send me an email at podcast
Speaker 1: at eagleman dot com with questions or discussion and check
Speaker 1: out Subscribe to Inner Cosmos on YouTube for videos of
Speaker 1: each episode and to leave comments. Until next time. I'm
Speaker 1: David Eagleman and this is inner cosmos,