How Smell, Taste & Pheromone-Like Chemicals Control You

00:00:00.000 | - Welcome to the Huberman Lab Podcast,

00:00:02.280 | where we discuss science and science-based tools

00:00:04.880 | for everyday life.

00:00:05.900 | I'm Andrew Huberman,

00:00:10.120 | and I'm a professor of neurobiology and ophthalmology

00:00:12.680 | at Stanford School of Medicine.

00:00:14.620 | This podcast is separate

00:00:15.680 | from my teaching and research roles at Stanford.

00:00:17.940 | It is, however, part of my desire and effort

00:00:19.960 | to bring zero cost to consumer information about science

00:00:22.880 | and science-related tools to the general public.

00:00:25.580 | In keeping with that theme,

00:00:26.680 | I'd like to thank the sponsors of today's podcast.

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00:02:05.180 | Today's podcast is also brought to us by Inside Tracker.

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00:06:02.880 | This month, we've been talking about the senses,

00:06:05.200 | how we detect things in our environment.

00:06:08.280 | The last episode was all about vision,

00:06:10.680 | how we take light and convert that information

00:06:13.800 | into things that we can perceive,

00:06:15.560 | like colors and faces and motion, things of that sort,

00:06:18.840 | as well as how we use light to change our biology

00:06:21.760 | in ways that are subconscious, that we don't realize,

00:06:24.200 | things like mood and metabolism and levels of alertness.

00:06:28.680 | Today, we're going to talk about chemical sensing.

00:06:31.540 | We're going to talk about the sense of smell,

00:06:34.340 | our ability to detect odors in our environment.

00:06:37.680 | We're also going to talk about taste,

00:06:39.500 | our ability to detect chemicals and make sense of chemicals

00:06:44.060 | that are put in our mouth and into our digestive tract.

00:06:47.760 | And we are going to talk about chemicals

00:06:49.740 | that are made by other human beings

00:06:52.220 | that powerfully modulate the way that we feel,

00:06:54.980 | our hormones, and our health.

00:06:57.460 | Now, that last category are sometimes called pheromones.

00:07:01.060 | However, whether or not pheromones exist in humans

00:07:04.140 | is rather controversial.

00:07:05.560 | There actually hasn't been a clear example

00:07:08.180 | of a true human pheromonal effect.

00:07:10.960 | But what is absolutely clear, what is undeniable,

00:07:14.160 | is that there are chemicals that human beings make

00:07:18.060 | and release in things like tears onto our skin and sweat

00:07:23.060 | and even breath that powerfully modulate

00:07:27.100 | or control the biology of other individuals.

00:07:30.100 | In fact, right now, even if you're completely alone,

00:07:33.680 | your chemical environment internally

00:07:36.380 | is being controlled by external chemicals.

00:07:39.120 | Your nervous system and your hormones and your metabolism

00:07:42.340 | are being modified by things in your environment.

00:07:46.160 | So we're going to talk about those.

00:07:48.040 | It's an absolutely fascinating aspect to our biology.

00:07:51.320 | It's one of our most primordial,

00:07:54.060 | meaning primitive aspects of our biology,

00:07:56.420 | but it's still very active in all of us today.

00:07:59.620 | This episode, believe it or not,

00:08:01.700 | will have a lot of tools, a lot of protocols.

00:08:05.620 | Even though I'm guessing most of you

00:08:07.280 | can probably smell your environment just fine,

00:08:10.180 | that you know what you like to eat and what tastes good

00:08:12.380 | and what doesn't taste good to you,

00:08:14.840 | today's episode is going to talk about tools

00:08:16.740 | that will allow you to actually leverage

00:08:19.500 | these chemical sensing mechanisms,

00:08:21.260 | including how you smell,

00:08:23.580 | not how you smell in the qualitative sense,

00:08:26.180 | but how you smell in the verb sense,

00:08:28.180 | the action of sniffing and smelling

00:08:30.900 | to enhance your sense of smell

00:08:33.380 | and to enhance your sense of taste,

00:08:35.820 | as well, believe it or not, to enhance your cognition,

00:08:38.980 | your ability to learn and remember things.

00:08:41.500 | Everything we're going to talk about, as always,

00:08:43.240 | is grounded in quality peer-reviewed studies

00:08:45.600 | from some excellent laboratories.

00:08:47.460 | I'll provide some resources along the way.

00:08:49.400 | So that means tools and protocols

00:08:51.100 | and also basic information.

00:08:52.360 | You're going to learn a ton of neuroscience

00:08:54.660 | and a lot of biology in general.

00:08:56.800 | And I think what you'll come to realize by the end

00:08:59.140 | is that while we are clearly different

00:09:01.260 | from the other animals,

00:09:02.740 | there are aspects to our biology that are very similar

00:09:06.700 | to that of other animals in very interesting ways.

00:09:10.380 | Before we dive into chemical sensing,

00:09:12.620 | I want to just briefly touch on a few things

00:09:14.580 | from the vision episode.

00:09:16.340 | One is a summary of a protocol.

00:09:18.980 | So I covered 13 protocols last episode.

00:09:21.940 | If you haven't seen that episode, check it out.

00:09:24.020 | Those protocols will allow you to be more alert

00:09:26.540 | and to see better over time if you follow them.

00:09:28.940 | All of them are zero cost.

00:09:30.080 | You can find any and all of them at hubermanlab.com.

00:09:33.320 | There's a link to those videos and tools and protocols.

00:09:36.560 | Everything is timestamped.

00:09:37.920 | The two protocols that I just want to remind everybody of

00:09:42.600 | are the protocol of near-far viewing

00:09:46.760 | that all of us, regardless of age,

00:09:50.060 | should probably spend about five minutes three times a week

00:09:54.480 | doing some near-far viewing exercises.

00:09:56.720 | So that would be bringing a pen or pencil up close

00:09:59.280 | to the point where you're about to cross your eyes

00:10:01.380 | but you don't cross your eyes and then out at some distance

00:10:04.800 | and then look beyond that pen or other object

00:10:08.300 | that you're using off as far as you can into the distance.

00:10:11.100 | It would be great if you could do this on a balcony or deck

00:10:13.220 | and then look way off in the distance

00:10:14.860 | and then bring it back in.

00:10:16.100 | This is going to exercise that accommodation reflex,

00:10:19.040 | the change in the shape of the lens

00:10:20.980 | can help offset a number of things,

00:10:23.300 | including myopia, nearsightedness.

00:10:25.720 | The other one is this incredible study

00:10:28.580 | that showed that two hours a day outside,

00:10:31.620 | even if you're doing other things while you're outside,

00:10:34.140 | can help offset myopia and nearsightedness.

00:10:37.240 | So try and get outside.

00:10:38.660 | It's really the sunlight and the blue light, right?

00:10:40.880 | Everyone's been demonizing blue light out there,

00:10:42.620 | but blue light is great provided it's not super, super bright

00:10:45.740 | and really close to your eyes.

00:10:48.140 | Blue light is terrific if it comes from sunlight.

00:10:51.020 | Two hours a day outside is going to help offset myopia,

00:10:54.180 | nearsightedness.

00:10:55.020 | Now that's a lot of time.

00:10:56.360 | I think most of us are not getting that time,

00:10:58.520 | but since you can do other things like gardening

00:11:00.800 | or reading or walking or running,

00:11:03.140 | if you can get that two hours outside,

00:11:04.740 | your visual system and your brain will benefit.

00:11:08.060 | I also would like to make one brief correction

00:11:11.140 | to something that I said incorrectly

00:11:13.340 | in the previous episode.

00:11:15.080 | At the end of the episode, I talked about lutein

00:11:18.480 | and how lutein may help offset some moderate

00:11:22.740 | to severe age-related macular degeneration.

00:11:25.460 | As well, I talked about how some people are supplementing

00:11:27.560 | with lutein even though they don't have

00:11:29.660 | age-related macular degeneration,

00:11:31.700 | with the idea in mind that it might help

00:11:33.580 | offset some vision loss as they get older.

00:11:36.740 | I said lutein and lutein was the correct thing to say,

00:11:40.280 | but once or twice when I started speaking fast,

00:11:43.940 | I said leucine and not lutein.

00:11:47.440 | I want to emphasize that leucine and amino acid,

00:11:50.700 | very interesting, important for muscle building,

00:11:52.780 | covered in previous episodes,

00:11:54.520 | but lutein, L-U-T-E-I-N,

00:11:59.220 | is the molecule and compound that I was referring to

00:12:01.860 | in terms of supplementing for sake of vision.

00:12:04.500 | So I apologize, please forgive me, I misspoke.

00:12:07.720 | A couple of you caught that right away.

00:12:09.920 | In listening to the episode after it went up,

00:12:11.820 | I realized that I had misspoken.

00:12:13.620 | So lutein for vision, lutein for muscles

00:12:17.340 | and muscle growth and strength, et cetera.

00:12:20.100 | Before we dive into the content of today's episode,

00:12:23.020 | I want to just briefly touch on color vision.

00:12:25.800 | Many of you asked questions about color vision

00:12:28.380 | and color perception, and indeed color perception

00:12:31.600 | is a fascinating aspect of the human visual system.

00:12:35.080 | It's one of the things that makes us unique.

00:12:37.140 | There are certainly other animals out there

00:12:39.360 | that can detect all the colors of the rainbow.

00:12:41.520 | Some can even detect into the infrared

00:12:43.720 | and to the far red that we can't see,

00:12:47.400 | but nonetheless, human color vision,

00:12:49.140 | provided that somebody isn't colorblind,

00:12:51.160 | is really remarkable.

00:12:53.060 | And if you're interested in color vision

00:12:55.160 | or you want to answer questions about art

00:12:58.380 | or about, for instance, why that dress

00:13:00.900 | that showed up online a few years ago

00:13:02.540 | looks blue to you and yellow to somebody else,

00:13:05.160 | all the answers to that are in this terrific book,

00:13:07.960 | which is "What is Color?"

00:13:09.660 | 15 questions and answers on the science of color.

00:13:12.440 | I did not write this book, I wish I had.

00:13:14.820 | The book is by Ariel and Joan Ekstut,

00:13:17.600 | that's E-C-K-S-T-U-T.

00:13:20.380 | So it's "What is Color?"

00:13:21.780 | 50 questions and answers on the science of color.

00:13:25.620 | It's an absolutely fabulous book.

00:13:27.100 | I have no business relationship to them.

00:13:29.200 | I did help them get in contact

00:13:31.300 | with some color vision scientists

00:13:32.860 | when they reached out to me.

00:13:34.300 | And you can know that all the information in the book

00:13:36.260 | was vetted by excellent color vision scientists.

00:13:39.160 | It's a really wonderful and beautiful book.

00:13:41.080 | The illustrations are beautiful.

00:13:42.600 | If you're somebody who's interested in design or art,

00:13:46.280 | or you're just curious about the science of color,

00:13:48.340 | it's a terrific book, I highly recommend it.

00:13:50.400 | If you just look it up online,

00:13:51.840 | there are a variety of places

00:13:53.240 | that will allow you to access the book.

00:13:55.200 | So let's talk about sensing chemicals

00:13:57.400 | and how chemicals control us.

00:13:59.520 | In our environment,

00:14:01.400 | there are a lot of different physical stimuli.

00:14:04.720 | There is light, photons, which are light energy,

00:14:09.000 | and those land on your retinas

00:14:11.520 | and your retinas tell your brain about them

00:14:13.880 | and your brain creates this thing we call vision.

00:14:16.900 | There are sound waves, literally particles

00:14:19.180 | moving through the air and reverberations

00:14:22.200 | that create what we call sound and hearing.

00:14:25.520 | And of course there are mechanical stimuli,

00:14:29.280 | pressure, light touch, scratch, tickle, et cetera,

00:14:34.280 | that lands on our skin or the blowing of a breeze

00:14:37.040 | that deflects the hairs on our skin.

00:14:39.400 | And we can sense mechanical touch, mechanical sensation.

00:14:44.400 | And there are chemicals.

00:14:46.160 | There are things floating around in the environment,

00:14:48.720 | which we call volatile chemicals.

00:14:52.620 | So volatile sounds oftentimes like emotionally volatile,

00:14:55.860 | but it just means that they're floating around out there.

00:14:58.380 | So when you actually smell something,

00:15:01.000 | like let's say you smell a wonderfully smelling rose

00:15:04.960 | or cake, yes, you are inhaling the particles into your nose.

00:15:09.960 | There are literally little particles of those chemicals

00:15:12.280 | are going up into your nose

00:15:14.200 | and being detected by your brain.

00:15:16.840 | Also, if you smell something putrid, disgusting or awful,

00:15:21.760 | use your imagination.

00:15:23.840 | Those particles are going up into your nose

00:15:26.760 | and being detected by neurons that are part of your brain.

00:15:30.540 | Other ways of getting chemicals into our system

00:15:34.400 | is by putting them in our mouth,

00:15:37.440 | by literally taking foods and chewing them

00:15:41.520 | or sucking on them and breaking them down

00:15:43.780 | into their component parts.

00:15:45.400 | And that's one way that we sense chemicals

00:15:47.300 | with this thing, our tongue.

00:15:50.020 | And there are chemicals that can enter

00:15:53.100 | through other mucosal linings and other kind of,

00:15:57.120 | just think damp, sticky linings of your body.

00:16:00.340 | And the main ones would be the eyes.

00:16:02.760 | So you've got your nose, your eyes and your mouth,

00:16:04.860 | but mainly when we have chemicals coming into our system,

00:16:07.600 | it's through our nose or through our mouth.

00:16:10.260 | Although sometimes through our skin,

00:16:12.840 | certain things can go transdermal, not many,

00:16:15.220 | and through our eyes.

00:16:17.060 | So these chemicals, we sometimes bring into our body,

00:16:21.580 | into our biology through deliberate action.

00:16:24.900 | We select a food, we chew that food

00:16:27.760 | and we do it intentionally.

00:16:28.920 | Sometimes they're coming into our body

00:16:31.080 | through non-deliberate action.

00:16:32.820 | We enter an environment and there's smoke

00:16:35.340 | and we smell the smoke and as a consequence, we take action.

00:16:39.260 | Sometimes we are forced to eat something

00:16:41.460 | because somebody tells us we should eat it

00:16:43.260 | or we do it to be polite.

00:16:44.780 | So there are all these ways

00:16:45.600 | that chemicals can make it into our body.

00:16:48.480 | Sometimes however, other people are actively making chemicals

00:16:52.560 | with their body.

00:16:53.720 | Typically this would be with their breath, with their tears,

00:16:58.280 | or possibly, I want to underscore possibly

00:17:01.780 | by making what are called pheromones,

00:17:03.480 | molecules that they release into the environment,

00:17:05.560 | typically through the breath that enter our system

00:17:09.640 | through our nose, our eyes, or our mouth

00:17:12.020 | that fundamentally change our biology.

00:17:15.080 | I will explain how smell and taste

00:17:18.380 | and these pheromone effects work,

00:17:20.780 | but I'll just give an example,

00:17:22.280 | which is a very salient and interesting one

00:17:25.420 | that was published about 10 years ago

00:17:27.420 | in the journal Science.

00:17:28.960 | Science Magazine is one of the three,

00:17:30.780 | what we call apex journals.

00:17:33.040 | There are a lot of journals out there,

00:17:34.360 | but for those of you that want to know,

00:17:35.760 | Science Magazine, Nature Magazine, and Cell

00:17:40.360 | are considered the three top kind of apex journals.

00:17:43.480 | They are the most stringent

00:17:44.940 | in terms of getting papers accepted there,

00:17:47.900 | even reviewed there.

00:17:49.000 | They have about a 95% rejection rate at the front gate,

00:17:53.360 | meaning they don't even review 95%

00:17:55.340 | of what gets sent to them.

00:17:56.640 | Of the things that they do decide to review

00:17:59.120 | then get sent out,

00:18:00.240 | a very small percentage of those get published.

00:18:02.480 | It's very stringent.

00:18:03.760 | This paper came out in Science

00:18:06.440 | showing that humans, men in particular in this study,

00:18:10.300 | have a strong biological response and hormonal response

00:18:14.400 | to the tears of women.

00:18:18.280 | What they did is they had women,

00:18:20.760 | and in this case it was only women for whatever reason,

00:18:23.640 | cry and they collected their tears.

00:18:28.420 | Then those tears were smelled by male subjects

00:18:32.080 | or male subjects got what was essentially the control,

00:18:36.560 | which was the saline.

00:18:38.220 | Men that smelled these tears that were evoked by sadness

00:18:43.000 | had a reduction in their testosterone levels

00:18:46.480 | that was significant.

00:18:48.160 | They also had a reduction in brain areas

00:18:50.720 | that were associated with sexual arousal.

00:18:53.560 | Now, before you run off with your interpretations

00:18:56.320 | about what this means and criticize the study

00:18:58.400 | for any variety of reasons,

00:19:00.360 | let's just take a step back.

00:19:02.160 | I will criticize the study for a variety of reasons.

00:19:04.480 | Two, one is that they only used female tears

00:19:08.220 | and male subjects.

00:19:09.520 | So it would have been nice for them to also use female tears

00:19:13.400 | and female subjects smelling those,

00:19:16.080 | male tears and male subjects smelling those,

00:19:18.760 | male tears and female subjects smelling those and so on.

00:19:22.240 | They didn't do that.

00:19:23.400 | They did have a large number of subjects, so that's good.

00:19:25.700 | That adds power to the study.

00:19:28.060 | And they did have to collect these tears

00:19:31.240 | by having the women watch what was essentially a sad scene

00:19:34.500 | from a movie.

00:19:35.380 | They actually recruited subjects that had a high propensity

00:19:37.920 | for crying at sad movies, which was not all women.

00:19:41.560 | It turns out that the people that they recruited

00:19:43.080 | for the study were people who said,

00:19:44.740 | "Yes, I tend to cry when I see sad things in movies."

00:19:48.380 | What they were really trying to do is just get tears

00:19:50.820 | that were authentically cried in response to sadness

00:19:55.200 | as opposed to putting some irritant in the eye

00:19:58.320 | and collecting tears that were evoked by something else

00:20:02.180 | like just having the eyes irritated.

00:20:04.740 | Nonetheless, what this study illustrates

00:20:08.340 | is that there are chemicals in tears that are evoking

00:20:12.880 | or changing the biology of other individuals.

00:20:16.500 | Now, most of us don't think about sniffing

00:20:18.700 | or smelling other people's tears,

00:20:20.900 | but you can imagine how in close couples

00:20:24.080 | or in family members or even close friendships, et cetera,

00:20:27.680 | that we are often in close proximity

00:20:29.740 | to other people's tears.

00:20:31.560 | Now, I didn't select this study as an example

00:20:34.100 | because I want to focus on the effects of tears

00:20:36.820 | on hormones per se,

00:20:38.200 | although I do find the results really interesting.

00:20:40.820 | I chose it because I wanted to just emphasize

00:20:44.340 | or underscore the fact that chemicals that are made

00:20:47.340 | by other individuals are powerfully modulating

00:20:50.740 | our internal state.

00:20:52.720 | And that's something that most of us don't appreciate.

00:20:56.280 | I think most of us can appreciate the fact

00:20:58.420 | that if we smell something putrid, we tend to retract,

00:21:01.060 | or if we smell something delicious, we tend to lean into it.

00:21:04.720 | But there are all these ways in which chemicals

00:21:06.740 | are affecting our biology,

00:21:08.300 | and interpersonal communication using chemicals

00:21:12.620 | is not something that we hear that often about,

00:21:15.520 | but it's super interesting.

00:21:16.860 | So let's talk about smell and what smell is

00:21:19.340 | and how it works.

00:21:20.320 | I'm going to make this very basic,

00:21:21.900 | but I am going to touch on some of the core elements

00:21:24.060 | of the neurobiology.

00:21:25.520 | So here's how smell works.

00:21:27.660 | Smell starts with sniffing.

00:21:30.560 | Now that may come as no surprise,

00:21:32.200 | but no volatile chemicals can enter our nose

00:21:36.180 | unless we inhale them.

00:21:37.640 | If our nose is occluded or if we're actively exhaling,

00:21:41.900 | it's much more difficult for smells to enter our nose,

00:21:45.240 | which is why people cover their nose

00:21:46.660 | when something smells bad.

00:21:49.380 | Now, the way that these volatile odors

00:21:52.420 | come into the nose is interesting.

00:21:54.140 | The nose has a mucosal lining, mucus,

00:21:57.480 | that is designed to trap things,

00:21:59.160 | to actually bring things in and get stuck there.

00:22:02.180 | At the base of your brain,

00:22:04.500 | so you could actually imagine this or if you wanted,

00:22:07.380 | you could touch the roof of your mouth,

00:22:09.100 | but right above your mouth,

00:22:11.140 | about two centimeters is your olfactory bulb.

00:22:14.500 | The olfactory bulb is a collection of neurons,

00:22:16.620 | and those neurons actually extend out of the skull,

00:22:20.380 | out of your skull, into your nose, into the mucosal lining.

00:22:24.720 | So what this means in kind of a literal sense

00:22:27.340 | is that you have neurons that extend their little dendrites

00:22:31.900 | and axonoid-like things, their little processes,

00:22:34.260 | as we call them, out into the mucus,

00:22:37.300 | and they respond to different odorant compounds.

00:22:41.140 | Now, the olfactory neurons also send a branch

00:22:44.420 | deeper into the brain, and they split off

00:22:47.260 | into three different paths.

00:22:50.900 | So one path is for what we call innate odor responses.

00:22:55.900 | So you have some hardwired aspects

00:22:59.220 | to the way that you smell the world

00:23:01.100 | that were there from the day you were born

00:23:03.100 | and that will be there until the day you die.

00:23:05.860 | These are the pathways and the neurons

00:23:09.100 | that respond to things like smoke,

00:23:12.180 | which, as you can imagine, there's a highly adaptive function

00:23:15.440 | to being able to detect burning things,

00:23:17.700 | because burning things generally means lack of safety

00:23:20.820 | or impending threat of some kind.

00:23:22.940 | It calls for action, and indeed these neurons

00:23:26.980 | project to a central area of the brain called the amygdala,

00:23:30.180 | which is often discussed in terms of fear,

00:23:32.060 | but it's really fear and threat detection.

00:23:34.940 | So some compounds, some chemicals in your environment,

00:23:37.620 | when you smell them, unless you're trained to overcome them,

00:23:40.880 | because you're a firefighter,

00:23:42.720 | you will naturally have a heightened level of alertness,

00:23:46.920 | you will sense threat, and if you're in sleep even,

00:23:50.640 | it will wake you up, all right?

00:23:52.280 | So that's a good thing, it's kind of an emergency system.

00:23:55.140 | You also have neurons in your nose

00:23:57.680 | that respond to odorants or combinations of odorants

00:24:01.040 | that evoke a sense of desire

00:24:04.080 | and what we call appetitive behaviors, approach behaviors,

00:24:07.480 | that make you want to move toward something.

00:24:09.660 | So when you smell a delicious cookie

00:24:12.660 | or some dish that's really savory that you really like,

00:24:17.380 | or a wonderful orange, and you say, "Mm,"

00:24:21.860 | or it feels delicious or it smells delicious,

00:24:25.300 | that's because of these innate pathway,

00:24:27.180 | these pathways that require no learning whatsoever.

00:24:30.620 | Now, some of the pathways from the nose,

00:24:33.220 | these olfactory neurons into the brain,

00:24:35.180 | are involved in learned associations with odors.

00:24:39.240 | Many people have this experience

00:24:42.920 | that they can remember the smell of their grandmother's home

00:24:47.920 | or their grandmother's hands even,

00:24:51.080 | or the smell of particular items baking

00:24:54.520 | or on the stove in a particular environment.

00:24:58.820 | Typically, these memories tend to be

00:25:00.660 | of a kind of nurturing sort, of feeling safe and protected,

00:25:04.460 | but one of the reasons why olfaction, smell,

00:25:08.340 | is so closely tied to memory

00:25:10.260 | is because olfaction is the most ancient sense that we have,

00:25:14.200 | or I should say chemical sensing

00:25:16.060 | is among the most primitive and ancient senses that we have,

00:25:19.340 | probably almost certainly evolved

00:25:21.060 | before vision and before hearing.

00:25:24.100 | But when we come into the world,

00:25:26.980 | because we're still learning about the statistics of life,

00:25:29.980 | about who's friendly and who's not friendly

00:25:32.360 | and where's a fun place to be

00:25:33.800 | and where's a boring place to be,

00:25:35.840 | that all takes a long time to learn,

00:25:37.560 | but the olfactory system seems to imprint,

00:25:40.680 | seems to lay down memories very early

00:25:43.860 | and to create these very powerful associations.

00:25:47.340 | And if you think about it long enough and hard enough,

00:25:51.100 | many of you can probably realize

00:25:54.120 | that there are certain smells that evoke a memory

00:25:57.500 | of a particular place or person or context.

00:26:00.760 | And that's because you also have pathways out of the nose

00:26:03.840 | that are not for innate behaviors

00:26:05.700 | like cringing or repulsion or gagging

00:26:10.700 | or for that appetitive mmm sensation,

00:26:13.360 | but that just remind you of a place or a thing or a context.

00:26:17.400 | Could be flowers in spring,

00:26:19.240 | could be grandmother's home and cookies.

00:26:22.100 | This is a very common occurrence

00:26:24.580 | and it's a very common occurrence

00:26:25.900 | because this generally exists in all of us.

00:26:28.300 | So we have pathway for innate responses

00:26:31.680 | and a pathway for learned responses.

00:26:33.580 | And then we have this other pathway

00:26:36.060 | and in humans, it's a little bit controversial

00:26:38.080 | as to whether or not it sits truly separate

00:26:40.380 | from the standard olfactory system

00:26:42.860 | or whether or not it's its own system embedded in there,

00:26:46.420 | but that they call the accessory olfactory pathway.

00:26:50.420 | Accessory olfactory pathway is what in other animals

00:26:53.660 | is responsible for true pheromone effects.

00:26:56.980 | We will talk about true pheromone effects,

00:26:59.100 | but for example, in rodents and in some primates,

00:27:04.100 | including mandrills, if you've ever seen mandrills,

00:27:06.860 | they have these like big beak noses things,

00:27:09.000 | you may have seen them at the zoo,

00:27:09.940 | look them up if you haven't seen them already,

00:27:11.520 | M-A-N-D-R-I-L-S, mandrills,

00:27:15.140 | there are strong pheromone effects.

00:27:17.300 | Some of those include things like

00:27:20.120 | if you take a pregnant female rodent or mandril,

00:27:24.860 | you take away the father that created those fetuses or fetus

00:27:29.860 | and you introduce the scent of the urine

00:27:36.060 | or the fur of a novel male,

00:27:39.840 | she will spontaneously abort or miscarry those fetuses.

00:27:43.820 | It's a very powerful effect.

00:27:45.420 | In humans, it's still controversial

00:27:48.340 | whether or not anything like that can happen,

00:27:50.420 | but it's a very powerful pheromonal effect in other animals.

00:27:53.560 | Another example of a pheromone effect

00:27:56.020 | is called the Vandenberg effect,

00:27:57.520 | named after the person who discovered this effect,

00:28:00.100 | where you take a female of a given species

00:28:04.220 | that has not entered puberty,

00:28:06.160 | you expose her to the scent or the urine

00:28:10.020 | from a sexually competent, meaning post-pubertal male,

00:28:14.820 | and she spontaneously goes into puberty earlier.

00:28:18.740 | So something about the scent triggers something

00:28:20.980 | through this accessory olfactory system,

00:28:23.160 | this is a true pheromonal effect,

00:28:24.820 | and creates ovulation and menstruation,

00:28:28.820 | or in rodents, it's an estrous cycle, not a menstrual cycle.

00:28:32.340 | So this is not to say

00:28:35.340 | that the exact same things happen in humans.

00:28:37.220 | In humans, as I mentioned earlier,

00:28:39.060 | there are chemical sensing between individuals

00:28:41.460 | that may be independent of the nose,

00:28:44.500 | and we will talk about those,

00:28:46.200 | but those are basically the three paths

00:28:48.300 | by which smells, odors, impact us.

00:28:51.820 | So I want to talk about the act of smelling,

00:28:54.940 | and if you are not somebody who's very interested in smell,

00:28:58.800 | but you are somebody who's interested

00:29:00.360 | in making your brain work better,

00:29:02.180 | learning faster, remembering more things,

00:29:04.800 | this next little segment is for you,

00:29:06.980 | because it turns out that how you smell,

00:29:09.740 | meaning the act of smelling, not how good or bad you smell,

00:29:12.760 | but the act of smelling, sniffing and inhalation,

00:29:17.680 | powerfully impacts how your brain functions

00:29:20.200 | and what you can learn and what you can't learn.

00:29:22.920 | Breathing generally consists of two actions,

00:29:25.700 | inhaling and exhaling, and we have the option, of course,

00:29:28.980 | to do that through our nose or our mouth.

00:29:32.220 | I've talked on previous episodes

00:29:33.660 | about the fact that there are great advantages

00:29:36.420 | to being a nasal breather,

00:29:38.260 | and there are great disadvantages to being a mouth breather.

00:29:42.200 | There are excellent books and data on this.

00:29:45.180 | There's the recent book, "Breath" by James Nestor,

00:29:47.720 | which is an excellent book that describes

00:29:50.360 | some of the positive effects of nasal breathing

00:29:52.540 | as well as other breathing practices.

00:29:54.480 | There's also the book, "Jaws" by my colleagues,

00:29:57.140 | Paul Ehrlich and Sandra Kahn, with a forward by Jared Diamond

00:30:01.000 | and an introduction by Robert Sapolsky from Stanford.

00:30:05.000 | So that's a book, "Chock-a-block" with heavy hitter authors

00:30:08.500 | that describes how being a nasal breather

00:30:11.720 | is beneficial for jaw structure,

00:30:14.180 | for immune system function, et cetera.

00:30:17.660 | Breathing in through your nose, sniffing,

00:30:21.380 | actually has positive effects on the way

00:30:24.060 | that you can acquire and remember information.

00:30:27.040 | Noam Sobel's group, originally at UC Berkeley

00:30:31.360 | and then at the Weizmann Institute,

00:30:33.740 | has published a number of papers

00:30:36.640 | that I'd like to discuss today.

00:30:38.540 | One of them, "Human Non-Olfactory Cognition Phase-Locked

00:30:43.000 | with Inhalation."

00:30:43.840 | This was published in "Nature Human Behavior,"

00:30:45.640 | an excellent journal.

00:30:47.780 | It showed that the act of inhaling

00:30:51.000 | has a couple of interesting and powerful consequences.

00:30:55.340 | First of all, as we inhale, the brain increases in arousal.

00:31:00.340 | Our level of alertness and attention increases

00:31:03.920 | when we inhale as compared to when we exhale.

00:31:07.100 | Now, of course, with every inhale, there's an exhale.

00:31:10.020 | You could probably double up on your inhales

00:31:11.900 | if you're doing size or some of the physiological size.

00:31:14.220 | I've talked about these before.

00:31:15.060 | It's a double inhales followed by an exhale,

00:31:17.940 | something like that.

00:31:18.820 | Or if you're speaking, you're going to change your cadence

00:31:21.260 | and ratio of inhales and exhales.

00:31:22.620 | But typically, we inhale, then we exhale.

00:31:26.320 | As we inhale, what this paper shows

00:31:29.500 | is that the level of alertness goes up in the brain.

00:31:33.980 | And this makes sense because as the most primitive

00:31:37.260 | and primordial sense by which we interact

00:31:40.460 | with our environment and bring chemicals into our system

00:31:44.420 | and detect our environment, inhaling is a cue

00:31:49.420 | for the rest of the brain to essentially to pay attention

00:31:52.940 | to what's happening, not just to the odors.

00:31:55.500 | As the name of this paper suggests,

00:31:57.900 | human non-olfactory cognition, phase locked with inhalation.

00:32:02.860 | What that means is that the act of inhaling itself

00:32:07.060 | wakes up the brain.

00:32:08.180 | It's not about what you're perceiving

00:32:10.260 | or what you're smelling.

00:32:12.340 | And indeed, sniffing as an action, inhaling as an action

00:32:16.660 | has a powerful effect on your ability to be alert,

00:32:20.660 | your ability to attend, to focus,

00:32:23.260 | and your ability to remember information.

00:32:26.020 | When we exhale, the brain goes through a subtle

00:32:30.220 | but nonetheless significant dip in level of arousal

00:32:34.060 | and ability to learn.

00:32:35.820 | So what does this mean?

00:32:37.260 | How should you use this knowledge?

00:32:39.420 | Well, you could imagine, and I think this would be

00:32:42.500 | beneficial for most people, to focus on nasal breathing

00:32:46.780 | while doing any kind of focused work

00:32:49.220 | that doesn't require that you speak or eat

00:32:51.420 | or ingest something.

00:32:52.520 | There is a separate paper published

00:32:54.920 | in the Journal of Neuroscience that showed that indeed,

00:32:57.900 | if subjects, human subjects, are restricted

00:33:00.560 | to breathing through their nose, they learn better

00:33:04.140 | than if they have the option of breathing

00:33:06.260 | through their mouth or a combination of their nose and mouth.

00:33:09.580 | These are significant effects in humans

00:33:11.400 | using modern techniques from excellent groups.

00:33:14.380 | So sniffing itself is a powerful modulator

00:33:18.160 | of our cognition and our ability to learn.

00:33:22.100 | You can imagine all sorts of ways

00:33:23.280 | that you might apply that as a tool.

00:33:25.180 | And I suggest that you play with it a bit,

00:33:27.340 | that if you're having a hard time staying awake and alert,

00:33:30.420 | you're having a hard time remembering information,

00:33:32.420 | you feel like you have a kind of attention deficit,

00:33:34.500 | nonclinical, of course, nasal breathing ought to help,

00:33:37.980 | extending or making your inhales more intense ought to help.

00:33:42.980 | Now, this isn't really about chemical sensing per se,

00:33:45.900 | but here's where it gets interesting and exciting.

00:33:48.980 | If you are somebody who doesn't have

00:33:50.580 | a very good sense of smell,

00:33:53.000 | or you're somebody who simply wants to get better

00:33:55.320 | at smelling and tasting things,

00:33:58.220 | you can actually practice sniffing.

00:34:00.860 | I know that sounds ridiculous,

00:34:02.100 | but it turns out that simply sniffing nothing,

00:34:05.520 | so doing something like this,

00:34:06.920 | [inhales deeply]

00:34:08.560 | I guess the microphone sort of has a smell.

00:34:10.460 | I guess my pen doesn't have a smell.

00:34:12.500 | [inhales deeply]

00:34:14.040 | Turns out that doing a series of inhales,

00:34:16.660 | and of course each one is followed by an exhale,

00:34:18.820 | 10 or 15 times, and then smelling an object

00:34:22.700 | like an orange or another item of food,

00:34:26.020 | or even the skin of somebody else,

00:34:27.960 | will lead to an increase in your ability to perceive

00:34:32.340 | those odors.

00:34:33.900 | Now, there are probably two reasons for that.

00:34:36.440 | One reason is that the brain systems of detecting things

00:34:39.480 | are waking up as a mere consequence of inhaling.

00:34:42.400 | So this is sort of the olfactory equivalent

00:34:45.440 | of opening your eyes wider in order to see, more or less.

00:34:50.120 | Last episode, I talked about how opening your eyes wider

00:34:52.080 | actually increases your level of alertness.

00:34:54.060 | It's not just that your level of alertness

00:34:55.680 | causes your eyes to be open wider.

00:34:58.000 | Opening your eyes wider can actually increase

00:34:59.560 | your level of alertness.

00:35:00.760 | Well, it turns out that breathing more deeply

00:35:02.340 | through the nose wakes up your brain,

00:35:04.660 | and it creates a heightened sensitivity

00:35:08.440 | of the neurons that relate to smell.

00:35:11.840 | And there's a close crossover,

00:35:13.980 | I'm sure you know this, between smell and taste.

00:35:16.240 | If any of you have ever had a cold,

00:35:18.120 | or for whatever reason you've lost your sense of smell,

00:35:21.040 | you become what they call anosmic,

00:35:22.580 | your sense of taste suffers also.

00:35:24.520 | We'll talk a little bit more about why that is

00:35:26.340 | in a few minutes.

00:35:27.520 | But as a first protocol,

00:35:28.920 | I'd really like all of you to consider

00:35:31.620 | becoming nasal breathers while you're trying to learn,

00:35:34.560 | while you're trying to listen,

00:35:36.080 | while you're trying to wake up your brain in any way

00:35:39.680 | and learn and retain information.

00:35:42.600 | This is a powerful tool.

00:35:44.880 | Now, there are other ways to wake up your brain more as well.

00:35:47.960 | For instance, the use of smelling salts.

00:35:50.440 | I'm not recommending that you do this necessarily,

00:35:52.420 | but there are excellent peer-reviewed data

00:35:55.220 | showing that indeed, if you use smelling salts,

00:35:58.860 | which are mostly of the sort that include ammonia,

00:36:02.740 | ammonia is a very toxic scent,

00:36:05.840 | but it's toxic in a way that triggers this innate pathway,

00:36:10.140 | the pathway from the nose to the amygdala

00:36:12.120 | and wakes up the brain and body in a major way.

00:36:14.720 | This is why they use smelling salts when people pass out.

00:36:17.040 | This is why fighters used to use,

00:36:19.680 | or maybe sometimes still use,

00:36:21.780 | smelling salts in order to heighten their level of alertness.

00:36:24.200 | This is why power lifters will inhale smelling salts.

00:36:28.160 | They work because they trigger the fear

00:36:31.600 | and kind of overall arousal systems of the brain.

00:36:34.280 | This is why I think most people

00:36:35.280 | probably shouldn't use ammonia or smelling salts

00:36:37.440 | to try and wake up, but they really do work.

00:36:40.120 | If you've ever smelled smelling salts,

00:36:41.580 | and I have, I tried this, they give you a serious jolt.

00:36:45.680 | It's like six espresso

00:36:47.520 | infused into your bloodstream all at once.

00:36:49.380 | You are wide awake immediately.

00:36:51.640 | And you feel a heightened sense of kind of desire to move

00:36:54.820 | because you release adrenaline into your body.

00:36:57.240 | Now, inhaling through your nose

00:36:58.740 | and doing nasal breathing is not going to do that.

00:37:00.760 | It's going to be a more subtle version

00:37:02.760 | of waking up your system, of alerting your brain overall.

00:37:07.640 | And for those of you that are interested

00:37:10.260 | in having a richer, a more deep connection

00:37:14.200 | to the things that you smell and taste,

00:37:16.260 | including other individuals perhaps, not just food,

00:37:21.060 | practicing or enhancing your sense of sniffing,

00:37:23.400 | your ability to sniff

00:37:24.480 | might sound like a kind of ridiculous protocol,

00:37:26.480 | but it's actually a kind of fun

00:37:28.380 | and cool experiment that you can do.

00:37:29.640 | You just do the simple experiment of taking,

00:37:32.060 | for instance, an orange, you smell it,

00:37:34.120 | try and gauge your level of perception

00:37:36.920 | of how orangish it smells or lemony, lemon-ish, lemony?

00:37:41.320 | I don't know, is it lemon-ish or lemony?

00:37:43.780 | Lemony, it smells.

00:37:45.560 | Then set it away.

00:37:48.160 | Do 10 or 15 inhales.

00:37:51.400 | Followed by exhales, of course, or just through the nose.

00:37:54.620 | Not going to do all 10 or 15.

00:37:55.980 | And then smell it again.

00:37:57.220 | And you'll notice that your perception of that smell,

00:37:59.340 | the kind of richness of that smell

00:38:01.760 | will be significantly increased.

00:38:03.780 | And that's, again, for two reasons.

00:38:05.380 | One, the brain is in a position to respond to it better.

00:38:09.260 | Your brain has been aroused by the mere act of sniffing,

00:38:12.380 | but also the neurons that respond to that lemon odor,

00:38:16.160 | that lemony or odor are going to respond better.

00:38:19.860 | So you can actually have a heightened experience

00:38:22.560 | of something.

00:38:23.400 | And that, of course, will also be true for the taste system.

00:38:26.000 | You also can really train your sense of smell

00:38:28.640 | to get much, much better.

00:38:30.480 | When Noam Sobel's group was at Berkeley,

00:38:32.140 | I happened to be a graduate student around that time.

00:38:34.740 | And every once in a while, I'd look outside

00:38:37.300 | and there would be people crawling around on the grass

00:38:40.700 | with goggles on, gloves on, and these hoods on,

00:38:43.940 | with earmuffs, and they looked ridiculous.

00:38:47.440 | But what they were doing is they were actually learning

00:38:49.520 | to follow scent trails.

00:38:51.880 | So in the world of dogs, you have sight hounds

00:38:54.320 | that use their eyes in order to navigate and find things.

00:38:57.680 | And you have scent hounds that use their nose.

00:38:59.440 | And the scent hounds are remarkable.

00:39:00.840 | They can be trained to detect a scent.

00:39:02.880 | These are the sniffing, you know, the bomb sniffing

00:39:05.240 | and the drug sniffing dogs in airports.

00:39:08.240 | There are now dogs, actually,

00:39:09.560 | that can sniff out COVID infections

00:39:12.480 | with a very high degree of accuracy.

00:39:14.160 | They can be trained to that.

00:39:15.400 | There's something about the COVID and similar infections

00:39:19.480 | that the body produces probably in the immune response,

00:39:22.080 | some odors, and the dogs are, I think, as high as 90%,

00:39:25.360 | in some cases, maybe even 95% accuracy, just remarkable.

00:39:29.100 | There are theories that dogs can sniff out cancer.

00:39:31.840 | This stuff all exceeds statistical significance.

00:39:34.800 | It's still a little bit mysterious in some ways,

00:39:36.760 | but you may not ever achieve the olfactory capabilities

00:39:41.760 | of a scent hound, but what Noam Sobel's lab did

00:39:46.360 | is they had people completely eliminate their visual

00:39:49.800 | experience by having them wear dark glasses or goggles.

00:39:53.160 | So they couldn't see, they couldn't hear,

00:39:54.560 | they couldn't sense anything with their sense of touch.

00:39:56.640 | They had thick gloves on, but they had these masks on

00:39:59.800 | where just their nasal passages were open.

00:40:02.120 | And people could, in a fairly short amount of time,

00:40:05.880 | learn to follow a chocolate scent trail on the ground,

00:40:09.860 | which is not something that most people want to do.

00:40:12.520 | But what they showed using brain imaging, et cetera,

00:40:15.160 | in subsequent studies is that the human brain,

00:40:19.320 | you can learn to really enhance your sense of smell

00:40:23.060 | and become very astute in distinguishing whether or not

00:40:26.720 | one particular odor or combinations of odors is such

00:40:30.580 | that it's less than or more than a different odor,

00:40:34.260 | for instance.

00:40:35.140 | Now, why would you want to do this?

00:40:36.240 | Well, if you like to eat as much as I do,

00:40:39.400 | one of the things that can really enhance your sense

00:40:41.840 | of pleasure from the experience of ingesting food

00:40:45.620 | is to enhance your sense of smell.

00:40:47.520 | And if you don't have a great sense of smell,

00:40:50.240 | or if you have a sense of smell that's really so good

00:40:53.040 | that it's always picking up bad odors,

00:40:55.160 | we'll talk about that in a minute,

00:40:57.240 | well then you might want to tune up your sense of smell

00:41:01.700 | by doing this practice of 10 or 15 breaths,

00:41:04.840 | excuse me, sniffs, not breaths, sniffs,

00:41:07.660 | and then interacting with some food item or thing

00:41:10.740 | that you're interested in smelling more of.

00:41:12.440 | So these could be the ingredients that you're cooking with.

00:41:14.260 | I really encourage you to try and really smell them.

00:41:16.640 | You sometimes hear this as kind of a mindfulness practice,

00:41:18.900 | like, ooh, really smell the food, really taste the food.

00:41:22.200 | And we always hear about that as kind of a mindfulness

00:41:24.660 | and presence thing,

00:41:25.800 | but you actually can increase the sensitivity

00:41:28.040 | of your olfactory and your taste system by doing this.

00:41:30.880 | And it has long-term effects.

00:41:33.120 | That's what's so interesting.

00:41:34.280 | This isn't the kind of thing that you have to do

00:41:35.620 | every time you eat.

00:41:36.620 | You don't have to be the weirdo in the restaurant

00:41:38.160 | that's like picking up the radish

00:41:39.800 | and like jamming it up your nostrils.

00:41:41.480 | Please don't do that.

00:41:42.660 | You don't have to necessarily smell everything,

00:41:44.740 | although it's nice sometimes to smell the food

00:41:47.780 | that you're about to eat and as you eat it,

00:41:49.620 | but it has long-term effects in terms of your ability

00:41:52.500 | to distinguish and discriminate different types of odors.

00:41:56.580 | And these don't even have to be very pungent foods,

00:41:58.840 | it turns out.

00:41:59.680 | The studies show that it doesn't have to be

00:42:01.200 | some really stinky cheese.

00:42:02.860 | There are cheese shops that I've walked into

00:42:04.800 | where like, I just basically gag, I can't handle it.

00:42:07.040 | I just can't be in there.

00:42:08.280 | It just overwhelms me.

00:42:09.880 | Other people, they love that smell.

00:42:11.860 | So you have to tune it to your interest and experience,

00:42:14.340 | but I think even for you Fasters out there,

00:42:17.160 | everybody eats at some point.

00:42:19.360 | Everybody ingests chemicals through their mouth.

00:42:21.980 | And one of the ways that you can powerfully increase

00:42:25.160 | your relationship to that experience

00:42:27.200 | and make it much more positive

00:42:29.520 | is through just the occasional practice

00:42:31.740 | of 10 or 15 sniffs of nothing,

00:42:35.180 | which almost sounds ridiculous, like how could that be?

00:42:37.900 | But now you understand why.

00:42:39.160 | It's because of the way that the sniffing action

00:42:41.060 | increases the alertness of the brain,

00:42:43.040 | as well as increasing the sensitivity of the system.

00:42:46.440 | No other system that I'm aware of in our body

00:42:49.960 | is as amenable to these kinds of behavioral training shifts

00:42:54.260 | and allow them to happen so quickly.

00:42:56.040 | I would love to be able to tell you

00:42:57.660 | that just doing 10 or 15 near-far exercises with a pen

00:43:01.080 | or going outside for 10 or 15 seconds each morning

00:43:04.400 | is going to completely change the way that you see the world

00:43:06.840 | but it actually isn't the case.

00:43:08.240 | You actually, it requires more training,

00:43:10.020 | a little bit more effort in the visual system.

00:43:11.960 | In the olfactory system, in your smell system,

00:43:14.320 | and in your taste system,

00:43:15.620 | just the tiniest bit of training and attention

00:43:18.440 | and sniffing, inhaling,

00:43:20.940 | can radically change your relationship to food

00:43:23.660 | such that you actually start to feel very different

00:43:27.040 | as a consequence of ingesting those foods,

00:43:28.920 | as well as becoming more discerning about which foods you like

00:43:33.100 | and which ones you don't like.

00:43:34.320 | And we're going to talk about that

00:43:35.280 | because there's a really wonderful thing that happens

00:43:37.760 | when you start developing a sensitive palate

00:43:40.000 | and a sensitive sense of smell

00:43:43.120 | in a way that allows you to guide your eating

00:43:46.500 | and smelling decisions

00:43:47.940 | and maybe even interpersonal decisions

00:43:49.580 | about who you spend time with or mate with or whatever

00:43:52.880 | in a way that is really in line with your biology.

00:43:56.080 | In fact, how well we can smell and taste things

00:43:59.300 | is actually a very strong indication of our brain health.

00:44:03.480 | Now, that's not to say that if you have a poor sense of smell

00:44:05.960 | or a poor sense of taste that you're somehow brain damaged

00:44:08.720 | or you're going to have dementia,

00:44:11.520 | although sometimes early signs of dementia

00:44:14.640 | or loss of neurons in other regions of the brain

00:44:17.160 | related to, say, Parkinson's,

00:44:18.680 | can show up first as a loss of sense of smell.

00:44:21.760 | Again, it's not causal.

00:44:25.240 | And it's certainly not the case

00:44:26.680 | that every time you have a sudden loss of smell

00:44:28.820 | that there's necessarily brain damage.

00:44:30.280 | I want to be very clear about that.

00:44:32.000 | But they are often correlated.

00:44:34.240 | There's also a lot of interest right now

00:44:37.100 | in loss of sense of smell

00:44:38.480 | because one of the early detection signs of COVID-19

00:44:41.560 | was a loss of sense of smell.

00:44:43.440 | So I just briefly want to talk about loss of sense of smell

00:44:46.640 | and regaining sense of smell and taste

00:44:49.320 | because these have powerful implications for overall health

00:44:53.180 | and in fact can indicate something about brain damage

00:44:56.800 | and can even inform how quickly we might be recovering

00:44:59.720 | from something like a concussion.

00:45:02.080 | So our olfactory neurons,

00:45:03.960 | these neurons in our nose that detect odors,

00:45:07.460 | are really unique among other brain neurons

00:45:10.800 | because they get replenished throughout life.

00:45:14.720 | They don't just regenerate, but they get replenished.

00:45:18.560 | So regeneration is when something is damaged and it regrows.

00:45:23.060 | These neurons are constantly turning over

00:45:25.400 | throughout our lifespan.

00:45:26.280 | They're constantly being replenished.

00:45:27.840 | They're dying off and they're being replaced by new ones.

00:45:31.340 | This is an amazing aspect of our brain

00:45:34.000 | that's basically unique to these neurons.

00:45:36.440 | There's one other region of the brain

00:45:37.680 | where there's a little bit of this maybe,

00:45:39.720 | but these olfactory neurons,

00:45:42.360 | about every three or four weeks, they die.

00:45:45.440 | And when they die, they're replaced by new ones

00:45:48.800 | that come from a different region of the brain,

00:45:51.100 | a region called the subventricular zone.

00:45:53.800 | The name isn't as important as the phenomenon,

00:45:57.500 | but these neurons are born in the ventricle,

00:45:59.880 | the area of your brain that's a hole that contains,

00:46:02.060 | it's not an empty hole,

00:46:03.080 | it's a hole basically that contains cerebral spinal fluid.

00:46:06.000 | Well, there's a little subventricular zone.

00:46:08.040 | There's a little zone below, sub, the ventricles,

00:46:11.400 | and that zone, if you are exercising regularly,

00:46:15.400 | if your dopamine levels are high enough,

00:46:18.100 | those little cells there are like stem cells.

00:46:23.340 | They are stem cells and they spit out

00:46:25.360 | what are called little neuroblasts,

00:46:27.280 | those little neuroblasts migrate

00:46:29.520 | into the front of your brain and then shimmy.

00:46:32.920 | They kind of move through

00:46:33.760 | what's called the rostral migratory stream.

00:46:35.820 | They kind of shimmy along and land

00:46:38.060 | back in your olfactory bulb, settle down,

00:46:40.500 | and extend little wires into your olfactory mucosa.

00:46:43.840 | This is an ongoing process of what we call neurogenesis

00:46:47.120 | or the birth of new neurons.

00:46:49.180 | Now, this is really interesting

00:46:52.080 | because other neurons in your cortex, in your retina,

00:46:56.360 | in your cerebellum, they do not do this.

00:46:58.480 | They are not continually replenished throughout life,

00:47:01.320 | but these neurons, these olfactory neurons are,

00:47:03.640 | they are special.

00:47:04.840 | And there are a number of things

00:47:07.720 | that seem to increase the amount

00:47:09.820 | of olfactory neuron neurogenesis.

00:47:12.200 | There is evidence that exercise, blood flow,

00:47:15.760 | can increase olfactory neuron neurogenesis,

00:47:18.260 | although those data are fewer in comparison

00:47:21.800 | to things like social interactions

00:47:24.240 | or actually interacting with odorants of different kinds.

00:47:28.740 | So if you're somebody who doesn't smell things well,

00:47:31.720 | you have a poor sense of smell,

00:47:33.080 | your olfactory system doesn't seem very sensitive,

00:47:35.680 | more sniffing, more smelling is going to be good.

00:47:38.440 | And then the molecule dopamine, this neuromodulator

00:47:41.140 | that is associated with motivation and drive,

00:47:45.520 | and in some cases, if it's very, very high with mania

00:47:48.840 | or if it's very, very low with depression or Parkinson's,

00:47:52.080 | but for most people where dopamine is in essentially

00:47:54.700 | normal ranges, dopamine is also a powerful trigger

00:47:59.240 | of the establishment of these new neurons

00:48:02.080 | and their migration into the olfactory bulb

00:48:04.320 | and your ability to smell.

00:48:05.860 | Now you don't want to confuse correlation with causation.

00:48:09.760 | So if you're not good at smelling,

00:48:11.360 | does that mean you have low dopamine?

00:48:12.760 | No, not necessarily.

00:48:13.920 | If you have low dopamine,

00:48:15.000 | does that mean that you have a poor sense of smell?

00:48:16.820 | No, not necessarily.

00:48:18.360 | Some people who take antidepressants of the sort

00:48:21.560 | that impact the dopamine system strongly like, well, butrin,

00:48:25.800 | will report a sudden, meaning within a couple of days,

00:48:29.200 | increase in their ability to smell particular odors.

00:48:33.480 | And it's a very striking effect.

00:48:35.680 | Some people, when they are in a new relationship,

00:48:38.140 | because dopamine and the hormones testosterone and estrogen

00:48:41.780 | are associated with novelty and the sorts of behaviors

00:48:45.320 | that often are associated with new relationships,

00:48:48.040 | those three molecules, dopamine, testosterone, and estrogen,

00:48:51.460 | kind of work together.

00:48:53.360 | And oftentimes people will say or report

00:48:56.900 | when they're newly in love or in a new relationship

00:48:58.980 | that they're just obsessed with,

00:49:00.840 | or they just so enjoy the scent of another person,

00:49:03.280 | so much so that they like to borrow

00:49:05.940 | the other person's clothing,

00:49:07.160 | or they'll sniff the other person's clothing,

00:49:09.000 | or they can even just, in the absence of the person,

00:49:11.880 | they can imagine their smell and feel a biological response,

00:49:15.600 | something that we'll talk more about.

00:49:17.220 | So these neurons turn over throughout the lifespan.

00:49:19.840 | And as we age, we actually can lose our sense of smell.

00:49:23.360 | And it's likely, I want to underscore likely,

00:49:25.540 | that that loss of sense of smell as we age

00:49:27.220 | is correlated with a loss of other neurons

00:49:29.740 | in the retina, in the ear.

00:49:31.340 | So loss of vision, loss of hearing, loss of smell,

00:49:33.740 | loss of the sense apparati, which are neurons,

00:49:38.260 | is correlated with aging.

00:49:40.420 | So what we've been talking about today

00:49:42.300 | is the ability to sense these odors.

00:49:44.420 | But what I'd like to do is empower you with tools

00:49:46.900 | that will allow you to keep these systems tuned up.

00:49:48.980 | Last time, we talked about tuning up

00:49:50.660 | and keeping your visual system tuned up and healthy,

00:49:53.820 | regardless of age.

00:49:54.900 | Here, we're talking about really enhancing

00:49:57.680 | your olfactory abilities, your taste abilities,

00:50:00.920 | as well by interacting a lot with odors,

00:50:04.940 | preferably positive odors, and sniffing more,

00:50:09.020 | inhaling more, which almost sounds crazy,

00:50:11.380 | but now you understand why.

00:50:13.120 | Even though it might sound crazy,

00:50:14.160 | it's grounded in real mechanistic biology

00:50:16.780 | of how the brain wakes up and responds to these chemicals.

00:50:20.220 | Now, speaking of brain injury, olfactory dysfunction

00:50:23.220 | is a common theme in traumatic brain injury

00:50:25.840 | for the following reason.

00:50:27.060 | These olfactory neurons, as I mentioned,

00:50:29.380 | extend wires into the mucosa of the nose,

00:50:33.260 | but they also extend a wire up into the skull,

00:50:35.940 | and they extend up into the skull

00:50:37.580 | through what's called the cribriform plate.

00:50:39.240 | It's like a Swiss cheese-type plate

00:50:41.620 | where they're going through,

00:50:42.740 | and if you get a head hit, that bone,

00:50:45.920 | the cribriform plate shears those little wires off,

00:50:48.780 | and those neurons die.

00:50:50.960 | Now, eventually, they'll be replaced,

00:50:53.060 | but there's a phenomenon by which concussion

00:50:56.300 | and the severity of concussion

00:50:57.720 | and the recovery from a head injury

00:50:59.660 | can actually be gauged in part, in part, not in whole,

00:51:02.700 | but in part by how well or fully

00:51:06.000 | one recovers their sense of smell.

00:51:08.440 | So if you're somebody that unfortunately

00:51:09.800 | has suffered a concussion,

00:51:11.140 | your sense of smell is one readout

00:51:13.760 | by which you might evaluate

00:51:15.200 | whether or not you're regaining

00:51:16.380 | some of your sensory performance.

00:51:17.980 | Of course, there will be others

00:51:18.900 | like balance and cognition and sleep, et cetera,

00:51:21.280 | but I'd like to refer you to a really nice paper

00:51:23.740 | which is entitled "Olfactory Dysfunction

00:51:27.020 | "in Traumatic Brain Injury, the Role of Neurogenesis."

00:51:29.940 | The first author is Marin, M-A-R-I-N.

00:51:33.420 | The paper was published

00:51:34.500 | in "Current Allergy and Asthma Report."

00:51:37.140 | This is 2020.

00:51:38.040 | I spent some time with this paper.

00:51:39.360 | It's quite good.

00:51:40.200 | It's a review article.

00:51:41.220 | I like reviews if they're peer-reviewed reviews

00:51:44.740 | and in quality journals.

00:51:46.440 | And what they discuss is,

00:51:48.320 | and I'll just read here briefly

00:51:49.500 | 'cause they said it better than I could,

00:51:51.160 | olfactory functioning disturbances are common

00:51:53.040 | following traumatic brain injury, TBI,

00:51:54.920 | and can have a significant impact on the quality of life,

00:51:57.580 | although there's no standard treatment for patients

00:51:59.240 | with the loss of smell.

00:52:02.560 | Now I'm paraphrasing post-injury.

00:52:05.840 | Olfactory training has shown promise for beneficial effects.

00:52:10.840 | Some of this involves,

00:52:12.840 | they go on to tell us the role of dopamine,

00:52:15.560 | dopaminergic signaling, as I mentioned before.

00:52:17.920 | But what does this mean?

00:52:18.880 | This means that if you've had a head injury

00:52:21.920 | or repeated head injuries,

00:52:23.800 | that enhancing your sense of smell is one way

00:52:26.500 | by which you can create new neurons.

00:52:28.760 | And now you know how to enhance your sense of smell

00:52:30.700 | by interacting with things that have an odor very closely

00:52:34.020 | and by essentially inhaling more,

00:52:36.760 | focusing on the inhale to wake up the brain

00:52:39.360 | and to really focus on some of the nuance of those smells.

00:52:42.360 | So you might do, for instance, a smell test

00:52:45.300 | by which you smell something like a lemon,

00:52:47.140 | put it down, do 10 inhales or so, smell again, et cetera.

00:52:50.840 | You might also just take a more active role

00:52:52.840 | in trying to taste and smell your food

00:52:56.440 | and taste and smell various things.

00:52:58.480 | I mean, please don't ingest anything that's poisonous

00:53:00.360 | so that you're not supposed to be ingesting,

00:53:01.880 | but you know what I mean.

00:53:03.060 | Really tuning up this system,

00:53:04.760 | I think is an excellent review.

00:53:06.440 | We're going to do an entire episode

00:53:08.100 | all about the use of the visual system in particular,

00:53:10.560 | but also the olfactory system for treatment

00:53:12.440 | of traumatic brain injury, as well as other methods.

00:53:14.980 | But I wanted to just mention it here

00:53:16.980 | because a number of people asked me about TBI.

00:53:19.400 | And here again, we're in this place

00:53:21.320 | where the senses and our ability to sense these chemicals,

00:53:24.240 | so these two holes in the front of our face, our nostrils,

00:53:27.260 | is a powerful readout and way to control brain function

00:53:31.560 | and nervous system function generally.

00:53:33.440 | Just a quick note about the use of smelling salts.

00:53:36.080 | I have a feeling that some of you may be interested in that

00:53:38.660 | and its application.

00:53:39.600 | If you are interested in that,

00:53:41.320 | I recommend you go to the scientific literature first,

00:53:44.380 | rather than straight to some vendor

00:53:47.120 | or to the, what do they call it these days?

00:53:49.800 | Costello bro science.

00:53:51.680 | He says bro science, the bro science.

00:53:54.360 | You can go to this paper,

00:53:55.600 | which is excellent and is real science,

00:53:57.400 | which is acute effects of ammonia inhalants

00:53:59.380 | on strength and power performance in trained men.

00:54:01.920 | It's a randomized control trial.

00:54:03.480 | It was published in the Journal of Strength

00:54:04.760 | and Conditioning Research in 2018,

00:54:07.520 | and it should be very easy to find.

00:54:09.080 | I will provide a link to the so-called PubMed ID,

00:54:11.800 | which is a string of numbers,

00:54:13.900 | and we'll put that in the caption

00:54:14.920 | if you want to go straight to that article.

00:54:16.360 | It does show a significant, what they call,

00:54:19.200 | this is what the words they use,

00:54:20.400 | literally in quotes, psyching up effect

00:54:22.400 | through the use of these ammonia inhalants

00:54:26.560 | and a significant increase in maximal force

00:54:30.440 | in force development in a variety of different movements.

00:54:34.360 | So for those of you that are interested

00:54:35.840 | in ammonia inhalants, so-called smelling salts,

00:54:39.280 | that might be a good reference.

00:54:41.200 | The other thing I wanted to talk about

00:54:42.320 | with reference to odors is this myth,

00:54:44.960 | which is that we don't actually smell things in our dreams,

00:54:48.720 | that we don't have a sense of smell.

00:54:50.560 | That's pure fiction.

00:54:52.640 | I don't know who came up with that.

00:54:54.360 | It's very clear that we are capable

00:54:56.900 | of smelling things in our sleep.

00:54:59.440 | However, when we are in REM sleep, rapid eye movement sleep,

00:55:03.200 | which is the sleep that predominates

00:55:04.800 | toward the second half of the night,

00:55:06.680 | our ability to wake up in response to odors is diminished.

00:55:12.520 | It's not absent, but it's diminished.

00:55:14.440 | If smoke comes into the room,

00:55:16.560 | we will likely wake up if the concentration of smoke

00:55:19.160 | is high enough, regardless of the stage of sleep we're in.

00:55:22.020 | But in REM sleep, we tend to be less likely

00:55:25.280 | to smell, to sniff.

00:55:28.000 | And that actually was measured in a number of studies

00:55:30.600 | that sniffing in sleep is possible.

00:55:33.560 | So if you put an odor like a lemon

00:55:35.320 | underneath someone's nostrils

00:55:36.600 | in the early portion of the night, they will smell.

00:55:40.320 | And they will later, they will sniff, excuse me,

00:55:43.000 | whether or not they smell or not,

00:55:43.860 | I guess depends on them and when they showered last,

00:55:45.880 | but they will definitely sniff.

00:55:47.560 | And they will report later,

00:55:49.880 | especially if you wake them up soon after,

00:55:51.840 | that they had a dream or a percept

00:55:54.980 | of the scent of a lemon, for instance.

00:55:57.900 | Later in the night, it's harder for that relationship

00:56:00.420 | to be established.

00:56:01.260 | It's likely that because of some of the paralysis associated

00:56:03.780 | with rapid eye movement, sleep,

00:56:05.440 | which is a healthy paralysis, so-called sleepatonia,

00:56:08.500 | you don't want to act out your dreams in REM sleep,

00:56:10.980 | that there is a less active tendency to sniff.

00:56:14.860 | And actually this has real clinical implications.

00:56:17.820 | The ability to sniff in response

00:56:20.980 | to the introduction of an odor is actually one way

00:56:25.340 | in which clinicians assess whether or not somebody's brain

00:56:28.900 | is so-called brain dead.

00:56:31.000 | That's not a nice term, but brain dead,

00:56:32.580 | or whether or not they have the capacity to recover

00:56:35.900 | from things like coma and other states

00:56:38.500 | of deep unconsciousness,

00:56:40.220 | or I guess you could call it subconsciousness.

00:56:42.620 | So what will happen is if someone has an injury

00:56:45.380 | and they're essentially out cold,

00:56:48.040 | the production of a sniffing reflex

00:56:51.900 | or a sniffing response to say a lemon

00:56:54.740 | or some other odor presented below the nostrils

00:56:57.040 | is considered a sign that the brain is capable

00:56:59.540 | of waking up.

00:57:00.860 | Now that's not always the case, but it's one indication.

00:57:03.740 | So just like you could use mechanosensation,

00:57:07.040 | so a toe pinch, for instance,

00:57:09.720 | or scraping the bottom of somebody's bare foot

00:57:12.200 | to see if they're conscious or shining light in their eyes.

00:57:15.800 | These are all things that you've seen in movies

00:57:17.120 | and television, or maybe you've seen in real life as well.

00:57:20.420 | Well, odors and chemical sensing is another way

00:57:23.100 | by which you can assess whether or not the brain

00:57:24.880 | is capable of arousal.

00:57:26.980 | And actually olfactory stimulation

00:57:29.240 | is one of the more prominent ones

00:57:31.060 | that's being used in various clinics.

00:57:33.420 | As a last point about specific odors and compounds

00:57:37.080 | that can increase arousal and alertness,

00:57:39.420 | and this was simply through sniffing them,

00:57:41.300 | not through ingesting them.

00:57:42.840 | There are data, believe it or not,

00:57:44.740 | there are good data on peppermint

00:57:47.300 | and the smell of peppermint.

00:57:49.300 | Minty type sense, whether you like them or not,

00:57:53.480 | will increase attention,

00:57:55.700 | and they can create the same sort of arousal response,

00:57:59.260 | although not as intensely or as dramatically

00:58:01.840 | as ammonia salts can, for instance.

00:58:04.260 | By the way, please don't go sniff real ammonia.

00:58:06.500 | You could actually damage your olfactory epithelium

00:58:08.660 | if you do that too close to the ammonia.

00:58:10.660 | If you're going to use smelling salts,

00:58:11.700 | be sure you work with someone

00:58:13.440 | or you know what you're getting and how you're using this.

00:58:15.940 | You can damage your olfactory pathway

00:58:18.420 | in ways that are pretty severe.

00:58:19.500 | You can also damage your vision.

00:58:21.060 | If you've ever teared up because you inhaled something

00:58:23.180 | that was really noxious, that is not a good thing.

00:58:27.140 | Doesn't mean you necessarily cause damage,

00:58:28.820 | but it means that you have irritated the mucosal lining

00:58:32.780 | and possibly even the surfaces of your eyes,

00:58:35.480 | so please be very, very careful.

00:58:38.120 | Scents like peppermint, like these ammonia smelling salts,

00:58:42.320 | the reason they wake you up

00:58:43.520 | is because they trigger specific olfactory neurons

00:58:46.660 | that communicate with the specific centers of the brain,

00:58:49.020 | namely the amygdala and associated neural circuitry

00:58:51.380 | and pathways that trigger alertness of the same sort

00:58:54.680 | that a cold shower or an ice bath or a sudden surprise

00:58:58.700 | or a stressful text message would evoke.

00:59:01.300 | Remember, the systems of your body

00:59:04.240 | that produce arousal and alertness and attention

00:59:07.260 | and that cue you for optimal learning, AKA focus,

00:59:10.520 | those are very general mechanisms.

00:59:12.060 | They involve very basic molecules

00:59:13.980 | like adrenaline and epinephrine,

00:59:15.380 | same thing actually, adrenaline and epinephrine.

00:59:18.320 | The number of stimuli,

00:59:20.180 | whether it's peppermint or ammonia or a loud blast,

00:59:23.780 | the number of stimuli that can evoke that adrenaline response

00:59:28.200 | and that wake-up response are near infinite,

00:59:31.580 | and that's the beauty of your nervous system.

00:59:33.580 | It was designed to take any variety of different stimuli,

00:59:37.060 | place them into categories,

00:59:38.700 | and then evoke different categories

00:59:40.940 | of very general responses.

00:59:43.080 | Now you know a lot about olfaction

00:59:44.600 | and how the sense of smell works.

00:59:46.020 | Here's another experiment that you can do.

00:59:48.780 | I'll ask you right now.

00:59:50.680 | Do you like, hate, or are you indifferent

00:59:54.860 | to the smell of microwave popcorn?

00:59:57.140 | Some people, including one member of my podcast staff,

01:00:01.760 | says it's absolutely disgusting to them.

01:00:05.060 | They feel like it's completely nauseating.

01:00:07.800 | I don't mind it at all.

01:00:08.640 | In fact, I kind of like it.

01:00:09.860 | I think the smell of microwave popcorn is kind of pleasant.

01:00:12.300 | I don't particularly like it,

01:00:13.520 | but it's certainly not unpleasant.

01:00:17.460 | Some people have a gene that makes them sensitive

01:00:21.740 | to the smell of things like microwave popcorn

01:00:24.360 | such that it smells like vomit.

01:00:26.720 | I probably don't have that gene

01:00:29.920 | because I find the smell of microwave popcorn

01:00:32.080 | pretty pleasant.

01:00:33.620 | Some people hate the smell of cilantro.

01:00:37.540 | Some people ingest asparagus,

01:00:40.500 | and when they urinate,

01:00:41.500 | they can smell the asparagus in a very pungent way.

01:00:44.660 | Other people can't smell it at all.

01:00:47.020 | These are variants in genes that encode

01:00:50.140 | for what are called olfactory receptors.

01:00:53.860 | Each olfactory sensory neuron expresses one odorant gene,

01:00:58.580 | one gene that codes for a receptor

01:01:01.220 | that responds to a particular odor.

01:01:03.400 | If you don't have that gene,

01:01:04.800 | you will not respond to that odor.

01:01:07.220 | So the reason why some people find

01:01:09.640 | the smell of microwave popcorn to be very noxious,

01:01:12.780 | putrid, in fact, is because they have a gene

01:01:14.880 | that allows them to smell the kind of putrid odor

01:01:18.420 | within that.

01:01:19.260 | Other people who lack that gene just simply can't smell it.

01:01:23.500 | So we are not all the same

01:01:25.400 | with respect to our sensory experience.

01:01:27.340 | What one person finds delicious,

01:01:29.400 | another person might find disgusting.

01:01:31.120 | I'll give a good example,

01:01:32.920 | which is that I absolutely despise

01:01:35.520 | Gorgonzola and blue cheese.

01:01:37.460 | I absolutely despise it.

01:01:38.560 | It smells and tastes like dirty, moldy socks to me.

01:01:44.800 | Some people love it.

01:01:45.720 | They crave it.

01:01:46.560 | Actually, some people get a visceral response to it.

01:01:49.080 | And we will talk about how certain tastes

01:01:51.720 | can actually evoke very deep biological responses,

01:01:55.580 | even hormonal responses,

01:01:57.160 | when we talk about taste in a few minutes.

01:01:59.580 | But there are these odors.

01:02:01.440 | For instance, in popcorn,

01:02:02.780 | it's the molecule 2-acetyl-1-pyroline,

01:02:07.780 | not proline, but pyroline,

01:02:09.740 | that gives off to some people, like me,

01:02:11.720 | that toasted smell as the sugars in the kernels heat.

01:02:14.840 | But the compound is also found

01:02:17.280 | in things like white bread and jasmine rice,

01:02:19.340 | which don't have as pungent an odor.

01:02:21.960 | But some people smell that and it smells like cat urine.

01:02:26.780 | Now there are scents like musky scents and musty scents

01:02:31.780 | that are secreted by animals like skunks

01:02:34.420 | and other animals of the so-called mustelid family.

01:02:37.780 | So these would be ferrets and other animals

01:02:40.520 | that can spray in response to fear,

01:02:43.660 | or if they just want to mark a territory

01:02:45.400 | because they want to say, "That's mine."

01:02:47.080 | Dogs instantly have scent glands that they rub on things.

01:02:49.640 | Cats have them too.

01:02:51.080 | This musty odor, some people find actually quite pleasant.

01:02:54.940 | Some people find it to be very noxious.

01:02:57.360 | And that will depend, of course, on the concentration.

01:03:00.720 | I'll never forget the first time Costello

01:03:03.400 | got sprayed by a skunk and it was awful.

01:03:06.100 | I actually don't mind the smell of skunk at a distance.

01:03:09.440 | It's actually a little bit pleasant.

01:03:10.680 | I admit it's a little bit pleasant to me.

01:03:12.780 | I don't think that makes me too weird

01:03:13.980 | because have you ever read the book

01:03:15.200 | "All's Quiet on the Western Front" about World War I?

01:03:18.200 | There's a description in there

01:03:19.760 | about the smell of skunk at a distance

01:03:21.540 | being mildly pleasant.

01:03:22.840 | So the author of that book probably shared

01:03:25.200 | a similar olfactory profile to me or I to them rather.

01:03:29.980 | But some people find even the tiniest bit

01:03:32.360 | of the smell of skunk or must to be noxious or awful.

01:03:36.360 | Now, of course, in high concentrations, it's really awful

01:03:38.500 | and unfortunately, poor Costello,

01:03:39.680 | he was like literally red-eyed and just snorting

01:03:43.380 | and it was awful.

01:03:44.440 | There's a joke about dogs.

01:03:45.580 | It says that dogs either get skunked one time

01:03:48.900 | and never again or 50 or 100 times.

01:03:51.460 | Costello has been skunked no fewer,

01:03:53.820 | I'm not making this up, has been skunked no fewer

01:03:56.340 | than 103 times.

01:03:58.160 | And that's because if he sees something

01:04:00.460 | or hears something in the bushes, he just goes straight in.

01:04:02.360 | He does not learn.

01:04:03.920 | But if you like the musty scent or musky scent,

01:04:08.660 | well, that says something about the genes

01:04:10.340 | that you express in your olfactory neurons.

01:04:12.460 | It is completely inherited.

01:04:14.900 | And if you don't like that scent, if it's really noxious

01:04:17.400 | or you have this response to microwave popcorn,

01:04:19.140 | well, that means you have a different complement,

01:04:21.180 | a different constellation, if you will,

01:04:23.740 | of genes that make up for these olfactory sensory neurons

01:04:27.700 | and the receptors that they express.

01:04:29.620 | Let's talk about taste.

01:04:31.260 | Not whether or not you have taste or you don't have taste.

01:04:33.860 | There's no way for me to assess that.

01:04:36.020 | But rather how we taste things,

01:04:39.480 | meaning how we sense chemicals in food and in drink.

01:04:44.400 | There are essentially five,

01:04:46.140 | but scientists now believe there may be six things

01:04:50.000 | that we taste alone or in combination.

01:04:53.840 | They are sweet tastes, salty tastes, bitter tastes,

01:04:58.840 | sour tastes, and umami taste.

01:05:04.760 | Most of you have probably heard of umami by now.

01:05:06.860 | It's U-M-A-M-I.

01:05:09.640 | Umami is actually the name for a particular receptor

01:05:14.020 | that you express on your tongue that detects savory tastes.

01:05:19.020 | So it's the kind of thing in braised meats.

01:05:22.780 | Sometimes people can even get the activation of umami

01:05:26.860 | by tomatoes or tomato sauces.

01:05:29.360 | What are each of these tastes

01:05:32.740 | and taste receptors responsible for?

01:05:34.980 | And then we'll talk about the sixth.

01:05:36.400 | Maybe you can guess what it is.

01:05:37.500 | I don't know if you can guess it now.

01:05:38.720 | I couldn't guess it, but of the five tastes,

01:05:42.080 | each one has a specific utility or function.

01:05:45.440 | Each one has a particular group of neurons in your mouth,

01:05:50.960 | in your tongue, believe it or not,

01:05:53.280 | that responds to particular chemicals

01:05:55.840 | and particular chemical structures.

01:05:58.340 | It is a total myth, complete fiction,

01:06:01.420 | that different parts of your tongue

01:06:03.100 | harbor different taste receptors.

01:06:06.060 | You know, that high school textbook diagram

01:06:07.840 | that, you know, sweet is in one part of the tongue

01:06:09.780 | and sour is in another and bitter is in another,

01:06:12.300 | complete fiction, just total fiction

01:06:14.740 | related to very old studies that were performed

01:06:16.860 | in a very poorly controlled way.

01:06:18.740 | No serious biologist,

01:06:20.940 | and certainly no one that works on taste,

01:06:22.340 | would contend that that's the way

01:06:25.220 | that the taste receptors are organized.

01:06:26.940 | They are completely intermixed along your tongue.

01:06:29.420 | If you have heightened or decreased sensitivity

01:06:32.580 | to one of those five things I mentioned,

01:06:34.620 | sweet, salty, bitter, umami, or sour,

01:06:36.620 | at one location in your tongue,

01:06:37.820 | it likely reflects the density of overall receptors

01:06:42.820 | or something going on in your brain,

01:06:45.860 | but not the differential distribution of those receptors.

01:06:49.600 | So the sweet receptors are neurons

01:06:53.220 | that express a receptor that respond to sugars.

01:06:57.540 | In the same way that you have cones, photoreceptors

01:06:59.900 | in your eye that respond to short, medium,

01:07:02.420 | or long wavelength light,

01:07:03.740 | meaning blue-ish, green-ish, or reddish light,

01:07:07.520 | you have a neuron in, or neurons, plural, in your tongue,

01:07:12.360 | that respond to sugars.

01:07:15.900 | And then those neurons, they don't say sweet,

01:07:18.700 | they don't actually send any sugar into the brain,

01:07:21.180 | they send what we call a volley,

01:07:23.180 | a barrage of action potentials,

01:07:24.860 | of electrical signals off into the brain.

01:07:26.860 | It's an amazing system.

01:07:28.500 | So all these receptors in your tongue

01:07:30.360 | make up what are called the neurons

01:07:33.300 | that give rise to a nerve,

01:07:34.740 | a collection of wires, nerve bundles,

01:07:37.460 | of what's called the gustatory nerve.

01:07:39.820 | It goes from the tongue

01:07:41.620 | to the so-called nucleus of the solitary tracts,

01:07:44.620 | and some of you requested names,

01:07:46.260 | I usually don't like to include too many names

01:07:48.180 | for sake of clarity,

01:07:49.100 | but the gustatory nerve from the tongue

01:07:51.220 | goes to the nucleus of the solitary tract,

01:07:53.580 | and then to the thalamus and to insular cortex.

01:07:56.620 | You don't have to remember any of those names

01:07:58.500 | if you don't want to,

01:07:59.380 | but if you want mechanism, you want neural circuits,

01:08:01.260 | that's the circuit.

01:08:02.080 | Gustatory nerve from the tongue,

01:08:04.720 | nucleus of the solitary tract in the brainstem,

01:08:06.560 | then the thalamus, and then insular cortex.

01:08:09.100 | And it is an insular cortex,

01:08:10.580 | this region of our cortex that we sort out

01:08:12.700 | and make sense of and perceive the various tastes.

01:08:16.020 | Now, it's amazing because just taking a little bit of sugar

01:08:20.140 | or something sour, like a little bit of lemon juice,

01:08:22.520 | and touching it to the tongue within 100 milliseconds, right?

01:08:27.360 | Just 100 milliseconds, far less than one second,

01:08:30.760 | you can immediately distinguish,

01:08:32.680 | ah, that's sour, that's sweet, that's bitter, that's umami.

01:08:37.160 | And that's an assessment that's made by the cortex.

01:08:41.620 | Now, what do these different five receptors encode for?

01:08:46.140 | Well, sweet, salty, bitter, umami, sour,

01:08:47.900 | but what are they really looking for?

01:08:49.840 | What are they sensing?

01:08:51.480 | Well, sweet stuff signals the presence of energy, of sugars.

01:08:55.820 | And while we're all trying,

01:08:57.020 | or we're told that we should eat less sugar

01:08:59.180 | for a variety of reasons,

01:09:01.580 | the ability to sense whether or not a food

01:09:05.060 | has rapid energy source

01:09:07.860 | or could give rise to glucose is essential,

01:09:09.880 | so we have sweet receptors.

01:09:11.460 | The salty receptors, these neurons,

01:09:14.540 | are trying to sense whether or not there are electrolytes

01:09:18.080 | in a given food or drink.

01:09:20.780 | Electrolytes are vitally important

01:09:22.320 | for the function of our nervous system

01:09:23.600 | and for our entire body.

01:09:24.740 | Sodium is what allows neurons to fire,

01:09:28.140 | what allows them to be electrically active.

01:09:30.560 | We also need potassium and magnesium.

01:09:32.280 | Those are the ions that allow the neurons to be active.

01:09:35.440 | So the salty receptors, the reason that they are there

01:09:38.600 | is to make sure that we are getting enough,

01:09:40.520 | but not too much salt.

01:09:42.200 | We don't want to ingest things that are far too salty.

01:09:44.880 | Bitter receptors are there

01:09:49.180 | to make sure we don't ingest things that are poisonous.

01:09:52.300 | How do I know this?

01:09:53.180 | How can I say that?

01:09:54.040 | Even though I was definitely not consulted

01:09:55.980 | at the design phase, how can I say that?

01:09:57.580 | Well, the bitter receptors

01:09:59.860 | create a what we call labeled line, a unique trajectory

01:10:03.540 | to the neurons of the brainstem

01:10:05.580 | that control the gag reflex.

01:10:08.420 | If we taste something very bitter,

01:10:11.460 | it automatically triggers the gag reflex.

01:10:14.540 | Now, some people like bitter taste.

01:10:15.780 | I actually like the taste of bitter coffee.

01:10:17.780 | Children generally like sweet taste more than bitter taste,

01:10:20.740 | but even babies, if they taste something bitter,

01:10:22.640 | they'll just immediately spit it up as like the gag reflex.

01:10:26.020 | Putrid smells will also evoke these same neurons.

01:10:29.860 | So some people are very sensitive.

01:10:31.660 | They have a very sensitive or low threshold vomit reflex.

01:10:36.260 | There was somebody in my lab early on.

01:10:39.740 | We never did this intentionally.

01:10:40.700 | We were just laughing because it was so dramatic.

01:10:43.380 | We would have a discussion.

01:10:44.300 | Someone would say something about something kind of gross,

01:10:48.100 | appropriate for the workplace, but nonetheless gross.

01:10:50.080 | We are biologists.

01:10:51.380 | We'd say something and they would say,

01:10:52.860 | "Stop, stop, stop, I'm going to throw up."

01:10:54.580 | You know, and some people have a very low threshold,

01:10:57.620 | quick gag reflex.

01:10:59.740 | Other people don't.

01:11:00.820 | Other people have a very stable stomach.

01:11:02.900 | They don't, you know, they rarely, if ever, vomit.

01:11:05.540 | The umami receptor isn't sensing savory

01:11:10.020 | because the body loves savory.

01:11:12.460 | It's because savory is a signal

01:11:14.620 | for the presence of amino acids.

01:11:16.820 | And we'll talk more about this,

01:11:18.200 | but the presence of amino acids in our gut

01:11:21.820 | and in our digestive system

01:11:23.740 | and the presence of fatty acids is essential.

01:11:27.240 | There is in fact, no essential carbohydrate or sugar.

01:11:30.980 | Now I'm not a huge proponent of ketogenic diets,

01:11:33.580 | nor am I against them.

01:11:34.580 | I think it's highly individual.

01:11:36.740 | You have to decide what's right for you,

01:11:38.800 | but everybody needs amino acids to survive.

01:11:42.060 | The brain needs them and we need fatty acids,

01:11:44.640 | especially to build a healthy brain during development.

01:11:46.900 | You need amino acids and fatty acids.

01:11:49.880 | And the sour receptor, why would we have a sour receptor

01:11:53.300 | so that we could have those really like sour candies?

01:11:56.100 | I think they've gotten more and more sour over the years.

01:11:57.940 | I admit I don't eat candy much,

01:11:59.980 | but I do have a particular weakness

01:12:02.580 | for like a really good, really sour, like gummy peach.

01:12:07.580 | Or if the gummy cherries are dipped

01:12:09.800 | in whatever that sour powder.

01:12:11.180 | So I was a kid who, I admit it, I liked the Likomade thing.

01:12:14.340 | I like drink the powder.

01:12:15.620 | Please don't do this.

01:12:16.460 | Don't give this garbage to your kids.

01:12:18.460 | But I liked it, it was tasty.

01:12:21.680 | But sour receptors are not there

01:12:25.020 | so that you can ingest gummy, sour gummy peaches

01:12:27.960 | or something like that.

01:12:28.800 | That's not why the system evolved.

01:12:31.020 | It's there and we know it's there

01:12:33.980 | to detect the presence of spoiled or fermented food.

01:12:38.020 | Fermented fruit has a sour element to it.

01:12:40.780 | And fermented things,

01:12:42.080 | while certainly some fermented foods

01:12:44.140 | like sauerkraut and kimchi and things of that sort

01:12:46.180 | can be very healthy for us

01:12:47.320 | and are very healthy in reducing inflammation,

01:12:49.300 | there are great data on that,

01:12:50.800 | pro quality microbiome, et cetera.

01:12:56.220 | Fermented fruit can be poisonous, right?

01:12:59.700 | Alcohols are poisonous in many forms to our system.

01:13:03.900 | And the sour receptor bearing neurons

01:13:08.200 | communicate to an area of the brainstem

01:13:10.540 | that evokes the pucker response.

01:13:13.300 | Closing of the eyes and essentially shutting of the mouth

01:13:16.560 | and cringing away.

01:13:18.040 | I think cringe is like a thing now my niece,

01:13:20.040 | whenever I seem to say something or do something,

01:13:22.060 | it's either an eye roll, a cringe or both in combination.

01:13:26.460 | So the sour, the sweet, the salty, the bitter

01:13:30.780 | and the umami system were not there

01:13:33.220 | so that we could have this wonderful pallet of foods

01:13:35.820 | that we enjoy so much.

01:13:37.100 | They'll allow us to do that,

01:13:39.500 | but they're there to make sure

01:13:40.620 | that we bring in certain things to our system

01:13:42.400 | and that we don't ingest other things.

01:13:44.860 | Now what's the sixth sense within the taste system?

01:13:48.900 | Not sixth sense generally, but within the taste system.

01:13:50.760 | What's this putative possible sixth receptor?

01:13:54.440 | I already kind of hinted at it

01:13:56.200 | when I talked about fatty acids.

01:13:58.160 | There are now data to support the idea,

01:14:01.840 | although there's still more work that needs to be done,

01:14:03.900 | that we also have receptors on our tongue that sense fat.

01:14:08.060 | And that because fat is so vital

01:14:10.860 | for the function of our nervous system

01:14:13.020 | and the other organs of our body,

01:14:15.180 | that we are sensing the fat content in food.

01:14:17.920 | Maybe this is why I can only eat half,

01:14:21.220 | but no less than half of a jar of almond butter

01:14:23.580 | or peanut butter in one sitting.

01:14:25.220 | I just can't, unless it's not salt,

01:14:26.680 | in which case it makes no sense to me.

01:14:28.760 | But it's remarkable how that texture

01:14:33.380 | and also the flavor, but that texture of fat,

01:14:36.480 | I love butter, I am guilty and Costello is definitely guilty

01:14:39.800 | of eating pats of butter from time to time.

01:14:41.920 | I have no guilt about this.

01:14:42.980 | People eat pats of cheese.

01:14:44.120 | Why shouldn't we eat a pat of butter?

01:14:46.220 | If you think that's gross,

01:14:47.300 | then maybe I have greater abundance

01:14:50.100 | of the fat receptors in my tongue.

01:14:52.300 | Maybe I have a fat tongue than you do.

01:14:55.340 | But nonetheless, the ability to sense fat here in our mouth

01:14:59.600 | seems to be critical.

01:15:01.320 | You can imagine why that is.

01:15:04.180 | I want to talk about the tongue and the mouth

01:15:06.900 | as an extension of your digestive tract.

01:15:09.880 | I know that might not be pleasant to think about,

01:15:12.040 | but when you look at it through the lens

01:15:13.920 | that I'm about to provide,

01:15:15.020 | it will completely change the way you think

01:15:16.620 | about the gut brain and about all the stuff

01:15:18.580 | that you've heard in these recent years about,

01:15:20.500 | oh, you know, we have this second brain,

01:15:22.480 | it's all these neurons in our gut.

01:15:23.640 | I've been chuckling through these last few years

01:15:26.960 | as people have gotten so excited about the gut brain,

01:15:29.360 | not because of their excitement.

01:15:30.800 | I think their excitement is wonderful,

01:15:32.240 | but we always knew that the nervous system

01:15:34.080 | extended out of the brain and into the body.

01:15:38.400 | And people seem kind of overwhelmed and surprised

01:15:41.200 | by the idea that we have neurons in our gut

01:15:43.660 | that can sense things like sugars and fatty acids.

01:15:46.520 | And I think those are beautiful discoveries,

01:15:48.240 | don't get me wrong.

01:15:49.080 | Diego Borges' lab out of Duke University

01:15:51.400 | has done beautiful studies showing

01:15:53.600 | that within the mucosal lining of our gut,

01:15:56.340 | we have neurons that sense fatty acids,

01:15:58.480 | sugars, and amino acids.

01:16:00.840 | And that when we ingest something

01:16:02.880 | that contains one or two or three of those things,

01:16:05.460 | there's a signal sent via the vagus nerve

01:16:07.920 | up into what's called the nodose ganglion, N-O-D-O-S-E,

01:16:12.920 | and then into the brain where it secretes dopamine,

01:16:15.520 | which makes us want more of that thing.

01:16:17.320 | It makes us more motivated to pursue

01:16:19.860 | and eat more of that thing

01:16:21.640 | that's either fatty or umami, it's savory,

01:16:25.240 | or has a sweet taste,

01:16:27.920 | any one or two or three of those qualities,

01:16:31.660 | independent of the taste.

01:16:33.520 | Now, I think those are beautiful data,

01:16:35.240 | but we know that this thing, the mouth,

01:16:38.360 | for those of you listening,

01:16:39.200 | I've got a couple fingers in my mouth,

01:16:40.600 | that's why I sound like I'm on something in my mouth.

01:16:43.260 | This thing in the front of our face,

01:16:46.640 | we use it for speaking,

01:16:47.560 | but it is the front of our digestive tract.

01:16:49.540 | We are essentially a series of tubes,

01:16:51.800 | and that tube starts with your mouth

01:16:53.600 | and heads down into your stomach.

01:16:56.400 | And so that you would sense

01:16:59.080 | so much of the chemical constituents of the stuff

01:17:01.460 | that you might bring into your body

01:17:03.700 | or that you might want to expel and not swallow

01:17:06.100 | or not interact with by being able to smell it.

01:17:09.160 | Is it putrid?

01:17:10.000 | Does it smell good?

01:17:11.360 | Does it taste good?

01:17:12.320 | Is this safe?

01:17:13.140 | Is it salty?

01:17:13.980 | Is it so sour that it's fermented and is going to poison me?

01:17:17.200 | Is it so bitter that it could poison me?

01:17:19.700 | Is it so savory that, yes, I want more and more of this?

01:17:23.880 | Well, then you'd want to trigger dopamine.

01:17:25.220 | That's all starting in the mouth.

01:17:27.300 | So you have to understand that you were equipped

01:17:31.080 | with this amazing chemical sensing apparatus

01:17:34.640 | we call your mouth and your tongue.

01:17:36.700 | And those little bumps on your tongue

01:17:38.400 | that they call the papillae,

01:17:39.920 | those are not your taste buds.

01:17:41.520 | Surrounding those little papillae,

01:17:44.340 | like little rivers, are these little dents and indentations.

01:17:48.280 | And what dents and indentations do in a tissue

01:17:50.900 | is they allow more surface area.

01:17:52.480 | They allow you to pack more receptors.

01:17:54.700 | So down in those grooves are where all these little neurons

01:17:57.600 | and their little processes are with these little receptors

01:18:01.680 | for sweet, salty, bitter, umami, sour,

01:18:03.640 | and maybe fat as well.

01:18:05.300 | So it's this incredible device

01:18:06.720 | that you've been equipped with

01:18:08.000 | that you can use to interact with various components

01:18:10.920 | of the outside world

01:18:11.960 | and decide whether or not you want to bring them in or not.

01:18:15.320 | Just as you can lose those olfactory neurons

01:18:17.640 | if you happen to get hit on the head

01:18:19.640 | or you have some other thing,

01:18:22.040 | maybe it was an infection that caused loss

01:18:24.000 | of those olfactory sensory neurons,

01:18:25.980 | you can also lose taste receptors in your mouth.

01:18:29.640 | If you've ever eaten something that's too hot,

01:18:33.820 | not spicy hot, but too hot,

01:18:36.300 | you burn your tongue, you burn receptors.

01:18:40.020 | It takes about a week to recover those receptors.

01:18:43.500 | For some people, it's a little bit more quickly,

01:18:45.840 | but if you burn your tongue badly

01:18:47.800 | by ingesting a soup that's too hot

01:18:49.340 | or a beverage that's too hot,

01:18:50.420 | you will greatly reduce your sense of taste

01:18:53.080 | for essentially all tastes.

01:18:56.680 | And that's because those neurons sit very shallow

01:19:01.280 | beneath the tongue's surface.

01:19:02.920 | And so that if you put something too hot on it,

01:19:04.240 | you literally just burn those neurons away.

01:19:06.000 | Luckily, those neurons also can replenish themselves.

01:19:09.380 | Those neurons are of the peripheral nervous system.

01:19:12.740 | And like all peripheral system neurons,

01:19:14.740 | they can replenish or regenerate.

01:19:17.500 | So if you burn your mouth in about a week or so,

01:19:20.080 | hopefully sooner, you'll be able to taste again.

01:19:23.040 | In fact, everybody's ability to taste

01:19:26.960 | is highly subject to training.

01:19:29.080 | You can really enhance your ability to taste

01:19:31.400 | and taste the different component parts of different foods

01:19:35.160 | simply by paying attention to what you're trying to taste.

01:19:38.880 | This is an amazing aspect of the taste system.

01:19:42.360 | I think more than any other system,

01:19:44.120 | the taste system and perhaps the smell system as well

01:19:47.160 | can be trained so that you can learn

01:19:49.840 | to pick out the tones, if you will,

01:19:53.300 | of different ice cream or different beverages.

01:19:58.300 | Somebody who, I don't drink much alcohol,

01:20:00.780 | I occasionally have a drink or something,

01:20:02.400 | but a while ago I got to taste

01:20:05.180 | a bunch of different white tequilas.

01:20:08.360 | These are different kinds of tequilas that are,

01:20:10.320 | they're not brown, they're white.

01:20:11.680 | And I sort of assumed that all tequila was disgusting.

01:20:15.920 | That was my assumption before doing this.

01:20:17.280 | And then I tasted a couple of white tequilas

01:20:18.720 | and I realized, oh, those aren't too bad.

01:20:20.500 | I tasted a few more.

01:20:22.080 | And then pretty soon I could really start to detect

01:20:24.480 | the nuance and the difference.

01:20:25.800 | Now, I haven't had a tequila in a long time now.

01:20:28.200 | I sort of tend to not drink it all these days.

01:20:30.480 | But in a very short period of time, like a couple of days,

01:20:33.260 | I got very good at detecting which things I liked

01:20:35.800 | and I could start to pick out tones.

01:20:37.660 | So I'm not a wine drinker, but for those of you that are,

01:20:40.680 | you hear about, oh, it has floral tones

01:20:42.780 | or berry tones or chocolate tones.

01:20:44.960 | Some of that is just kind of menu based

01:20:48.680 | and kind of marketing based silliness

01:20:50.820 | designed to get you excited

01:20:52.940 | about what you're about to ingest.

01:20:54.200 | But some of it is real.

01:20:55.700 | And for people that are skilled in assessing wines

01:20:59.280 | or assessing foods, much more of an eater than a drinker,

01:21:03.120 | you can really start to develop a sensitive palette,

01:21:06.000 | a nuanced palette through what we call top-down mechanisms.

01:21:09.580 | This olfactory cortex that takes these five,

01:21:12.980 | maybe the sixth fat receptor two information

01:21:16.160 | and tries to make sense of what's out there in the world

01:21:18.960 | and what its utility is.

01:21:21.380 | Is it good? Is it bad?

01:21:22.360 | Do I want more of it or less than it?

01:21:24.160 | That neural circuitry is unlike other neural circuitry

01:21:27.760 | in that it seems very amenable to behavioral plasticity

01:21:32.140 | for whatever reason.

01:21:33.240 | And we could talk about what those reasons might be.

01:21:35.840 | It's interesting sometimes to think about

01:21:37.480 | how your taste literally, chemical taste,

01:21:41.200 | is probably very different than that of other people.

01:21:43.840 | How a food tastes to you is probably very different

01:21:46.680 | than how it tastes to somebody else.

01:21:47.880 | The same probably cannot be said

01:21:49.840 | of something like vision or hearing,

01:21:51.960 | unless you're somebody who has perfect pitch

01:21:53.920 | or your color vision is disrupted or you're a mantis shrimp,

01:21:57.940 | chances are when you look at the same object,

01:22:00.120 | two people are seeing more or less the same object

01:22:03.000 | or perceiving it in a very similar way.

01:22:05.360 | There are experiments that essentially establish that.

01:22:08.040 | Now, we have taste receptors

01:22:10.120 | and a lot of those taste receptors,

01:22:11.400 | their chemical structures are known.

01:22:13.120 | They come with fancy names like the T1R1 or the T1R2

01:22:17.920 | which were identified as the sweet and umami receptor.

01:22:21.920 | So what's interesting is that this umami flavor

01:22:25.080 | is the savory flavor rather that's sensed by umami receptors

01:22:29.000 | is very close to the receptor that detects sweet things.

01:22:34.000 | Similarly, bitter is sensed

01:22:37.360 | by a whole other set of receptors.

01:22:39.580 | Now, there's a fun naturally occurring experiment

01:22:42.760 | that will forever change the way that you look at animals

01:22:47.000 | and the way certainly that I think about dogs

01:22:49.160 | and Costello in particular.

01:22:50.600 | Carnivorous large animals like tigers

01:22:55.360 | and some grizzly bears, for instance,

01:22:58.040 | we know that they have no ability to detect sweet.

01:23:02.040 | They don't actually have the receptors

01:23:04.320 | for detecting sweet on their tongue,

01:23:06.740 | but their concentration of umami receptors,

01:23:09.400 | of their ability to detect savory

01:23:12.080 | is at least 5,000 times that which it is in humans.

01:23:16.840 | In other words, if I eat a little piece of steak

01:23:19.440 | or Costello eats a little piece of steak,

01:23:23.720 | that steak probably tastes much, much more savory

01:23:28.720 | than it does to me.

01:23:31.000 | So dogs and tigers and bears, et cetera,

01:23:35.040 | they're going to taste savory things and smell savory things

01:23:38.480 | with a much higher degree of sensitivity,

01:23:41.000 | but they can't taste sweet things.

01:23:42.600 | Other large animals, which are mostly herbivores,

01:23:45.300 | like the panda bear, for instance,

01:23:48.220 | it's hard to believe that thing is even a bear.

01:23:50.240 | I got nothing against pandas.

01:23:51.480 | I just think that they get a little bit too much

01:23:53.640 | of the limelight, frankly.

01:23:55.960 | So no vendetta against panda, save the pandas.

01:23:58.200 | I hope they replenish all the pandas,

01:23:59.440 | but pandas in all their whatever have no umami receptors.

01:24:04.440 | They can't taste savory,

01:24:07.580 | but they have greatly heightened density of sweet receptors.

01:24:11.700 | So there they are eating these whatever bamboos all day

01:24:14.720 | or not bamboozle, but bamboos all day.

01:24:18.500 | And they can taste things that are very sweet

01:24:21.940 | with a much higher degree of intensity.

01:24:24.620 | And in general, animals that are more gentle,

01:24:27.880 | more that are herbivores, excuse me,

01:24:32.260 | or animals that have the propensity for aggression,

01:24:34.980 | that's where you really see the divergence

01:24:36.700 | of the umami receptor,

01:24:38.020 | because it's associated with meat and amino acids,

01:24:40.640 | and where you see the enhancement of the sweet receptors

01:24:44.360 | for animals that eat a lot of plants and fruits.

01:24:47.080 | And they probably taste very different to them

01:24:49.300 | than they do to you and me.

01:24:51.000 | And so it's interesting to note that animals that eat meat,

01:24:54.600 | that eat other organisms,

01:24:57.160 | can actually extract more savory experience from that.

01:25:00.200 | What does this mean for you?

01:25:01.480 | All right, do you associate yourself

01:25:03.600 | as a tiger or a grizzly bear or a panda

01:25:05.800 | or a combination of both?

01:25:06.840 | Most people are omnivores.

01:25:08.400 | However, you may find it interesting that people that,

01:25:12.560 | for instance, eat a pure carnivore type diet

01:25:15.960 | or a keto diet where they are ingesting a lot of meats,

01:25:19.280 | so therefore are sensing a lot of umami flavors,

01:25:22.640 | and I realize not everyone who's keto eats meat,

01:25:25.380 | but those who do that will develop a more sensitive palette

01:25:29.240 | and likely, there are some data, although early data,

01:25:32.460 | craving for umami-like foods.

01:25:35.280 | Whereas people that eat a more plant-based diet

01:25:38.920 | are likely developing a heightened sensitivity

01:25:43.480 | and desire for, and maybe even dopamine response

01:25:46.460 | to sugars and plant-based foods.

01:25:49.080 | Now, this is my partial attempt to reconcile

01:25:52.160 | the kind of online battle that seems to exist

01:25:55.440 | between plant-based versus animal-based,

01:25:58.160 | purely plant-based or purely animal-based diets.

01:26:02.080 | I think most people are omnivores,

01:26:03.840 | but it's kind of interesting to think that the systems

01:26:06.920 | are plastic such that people might want more meat

01:26:10.420 | if they eat more meat.

01:26:11.360 | People might want more plants if they eat enough plants

01:26:14.120 | for a long period of time, and this might explain

01:26:16.680 | some of the chasm that exists between these two groups.

01:26:19.780 | Now, this is not to say anything about the ethical

01:26:23.000 | or the environmental impacts of different things.

01:26:24.720 | I don't even want to get into that

01:26:25.840 | because the meat people say that the plant-based diets

01:26:28.060 | have as much a negative impact

01:26:29.680 | as the plant people say that the meat-based diets.

01:26:31.600 | That's a totally different discussion.

01:26:33.080 | What I'm talking about here is food craving

01:26:35.080 | and food seeking, and one's ability to detect

01:26:38.640 | these umami savory flavors is going to be enhanced

01:26:41.400 | by ingesting more meat and less activation

01:26:44.460 | of the sweet receptor.

01:26:45.440 | So in other words, the more meat you eat,

01:26:47.360 | the more you're going to become like a tiger, so to speak.

01:26:50.840 | And the more that you avoid these umami flavors and meats,

01:26:54.960 | and the more that you would eat plant-based foods

01:26:57.320 | and in particular, sweet foods,

01:26:58.820 | the more you will likely suppress that umami system

01:27:02.520 | and that you will have a heightened desire for,

01:27:06.480 | appetite for, and sensing of sweet foods

01:27:09.900 | or foods that contain sugars.

01:27:11.960 | What I'm about to tell you is going to seem crazy,

01:27:15.120 | but is extremely interesting

01:27:17.540 | with respect to taste and taste receptors.

01:27:21.080 | Remember, even though we can enjoy food

01:27:24.040 | and we can evolve our sense of what's tasty or not tasty,

01:27:27.460 | depending on life decisions, environmental changes, et cetera,

01:27:31.000 | the taste system, just like the olfactory system

01:27:32.960 | and the visual system was laid down for the purpose

01:27:36.600 | of moving towards things that are good for us

01:27:39.380 | and moving away from things that are bad for us.

01:27:41.380 | That's the kind of core function of the nervous system.

01:27:44.220 | Well, taste receptors are not just expressed on the tongue.

01:27:49.760 | They are expressed in other cells and other tissues as well.

01:27:54.160 | Some of you may be able to imagine foods

01:27:57.060 | that are so delicious to you

01:27:58.440 | that they make your entire body feel good.

01:28:01.560 | Or foods that are so horrifically awful to think about,

01:28:06.400 | let alone taste, that they create a whole body shuttering

01:28:10.300 | or kind of repellent type response

01:28:12.680 | where you just either cringe or turn your face away,

01:28:15.760 | even in the absence of that food.

01:28:17.640 | That's sort of how I feel about pungent Gorgonzola cheese.

01:28:21.720 | If you like Gorgonzola cheese, I don't judge you.

01:28:24.600 | I just, that's an individual difference.

01:28:27.560 | I happen to love certain foods.

01:28:29.600 | I do like savory foods very much.

01:28:31.600 | When I think about them, they just, they make me feel good.

01:28:36.980 | And I'm oftentimes not even associating

01:28:39.920 | with the taste of those foods.

01:28:41.260 | It feels almost like a visceral thing.

01:28:43.520 | Well, it turns out that some of the taste receptors

01:28:45.720 | extend beyond the tongue, that they actually can extend

01:28:49.120 | into portions of the gut and digestive system.

01:28:52.040 | And if that's not strange enough,

01:28:53.960 | turns out that some of the taste receptors

01:28:57.280 | are actually expressed on the ovaries and the testes.

01:29:01.820 | So what that means is that the gonads,

01:29:04.720 | the very cells and tissues and organs in our body

01:29:08.120 | that make up the reproductive axis

01:29:10.960 | are expressing taste receptors.

01:29:13.040 | Okay, so how do we interpret this?

01:29:14.200 | Does this mean that when you eat something

01:29:15.880 | that's very savory or very sweet, for instance,

01:29:19.160 | that it's triggering activation of the ovaries

01:29:22.660 | or of the testes?

01:29:24.420 | Well, it's possible.

01:29:26.980 | Now, how those molecules, those chemical molecules

01:29:30.160 | would actually get there isn't clear.

01:29:31.800 | The digestive tract does not run directly

01:29:34.740 | to the testes or to the ovaries.

01:29:36.820 | But nonetheless, what this means is that chemical sensing

01:29:40.040 | of the very things that we detect on our tongue

01:29:42.160 | and that we call taste in quotes, in food,

01:29:46.680 | is also evoking cellular responses

01:29:50.840 | within the reproductive gonads.

01:29:54.440 | Now, whether or not this underlies the positive association

01:29:57.540 | that we have with certain foods isn't clear,

01:30:00.280 | but I'd be remiss if I didn't point out the obvious,

01:30:04.600 | which is that the relationship

01:30:07.400 | between the sensual nature of particular foods

01:30:11.920 | and sensuality generally and the reproductive axis

01:30:16.160 | is something that's been covered in many movies.

01:30:19.100 | There are entire movies that are focused

01:30:21.240 | on the relationship between, for instance, chocolate

01:30:24.640 | and love and reproductive behaviors,

01:30:26.940 | or certain feasts of meat and their wonderful tastes

01:30:31.940 | and the kind of sensuality around feasts

01:30:36.640 | of different types of foods.

01:30:38.480 | But in general, it's the sweet and the savory.

01:30:41.760 | Rarely is it the sour or the bitter, the salty or the fat.

01:30:46.200 | And not surprisingly, perhaps,

01:30:49.240 | it is the T2Rs and the T1Rs,

01:30:51.920 | the receptors that are associated with the sweet

01:30:54.720 | and with the umami, the savory flavors

01:30:57.560 | that are expressed not just on the tongue

01:30:59.680 | and in portions of the digestive tract,

01:31:02.060 | but on the gonads themselves.

01:31:04.280 | So what does this mean?

01:31:05.340 | Does this mean that eating certain foods

01:31:06.960 | can stimulate the gonads?

01:31:08.720 | Maybe.

01:31:09.560 | There's no data that immediately support that right now,

01:31:12.660 | but this is an emerging area.

01:31:14.640 | If you'd like to read more about this,

01:31:17.080 | there's a great review entitled Taste Perception

01:31:20.280 | from the Tongue to the Testes,

01:31:21.940 | although they do also talk about the ovaries.

01:31:24.720 | Why they didn't include that in the title

01:31:26.200 | is I think a reflection of the sort of bias of the author.

01:31:29.700 | The author, not incidentally, is Fang Li, last name Li.

01:31:34.700 | It's a very interesting paper published

01:31:38.520 | in Molecular Human Reproduction.

01:31:42.160 | You can find it easily online.

01:31:43.560 | It's downloadable.

01:31:44.380 | I'll also provide a link to it.

01:31:45.960 | I just think it's fascinating

01:31:47.600 | that these taste receptors are expressed in other tissues.

01:31:50.040 | And I should mention that they're expressed

01:31:51.320 | in tissues of other areas of the body as well,

01:31:54.480 | including the respiratory system,

01:31:56.780 | but the richest aggregation or concentration

01:32:01.160 | of these receptors for umami and sweet, of course,

01:32:03.000 | is on the tongue, but also on the gonads.

01:32:05.720 | And I think it does speak to the possible bridge

01:32:09.180 | between what we think of as a sensory

01:32:12.120 | or a sensual experience of food

01:32:14.480 | and the deeper kind of visceral sense within the gut

01:32:18.040 | and maybe even within the gonads as well

01:32:20.060 | of something that we find extremely pleasurable

01:32:22.600 | or even a repetitive that we want to move toward it.

01:32:26.280 | We are actually going to return to that general theme

01:32:28.840 | in the discussion about touch sensation.

01:32:32.200 | Some people, for instance, when they touch certain surfaces

01:32:36.420 | like furs or sheepskins or velvet or soft, smooth surfaces,

01:32:43.580 | it feels good elsewhere in their body,

01:32:46.240 | not just at the point of contact with that surface.

01:32:49.860 | And similarly, if there's the, how about this one,

01:32:54.800 | the screech of chalk on a chalkboard?

01:32:57.120 | It's a sound, but it has a very strong visceral component

01:33:00.720 | or sandpaper like fingers, fingernails on a chalkboard,

01:33:04.440 | not the sound, but the feeling, right?

01:33:06.620 | Exactly.

01:33:07.540 | So our whole nervous system is tuned

01:33:09.460 | to either be drawn toward, repetitive,

01:33:12.340 | or repelled by aversive behaviors, right?

01:33:15.800 | So there's this push-pull that exists.

01:33:17.760 | And what I'm referring to in terms of these receptors

01:33:19.920 | on the tongue that are also expressed on the gonads

01:33:22.120 | is yet another example of what, at least in this case,

01:33:24.360 | seems to be an appetitive thing,

01:33:26.740 | a desire to move toward certain foods

01:33:29.500 | and maybe even the experiences

01:33:30.820 | that are associated with those foods.

01:33:32.400 | I want to talk about a particular aspect of food

01:33:35.040 | and a chemical reaction in cooking

01:33:37.680 | called the Maillard reaction.

01:33:39.300 | Some of you have probably heard of the Maillard reaction.

01:33:41.560 | It's spelled M-A-I-L-L-A-R-D.

01:33:45.520 | The D is silent, so don't call it the Maillard reaction.

01:33:48.720 | And it's not the Maillard reaction.

01:33:51.020 | It is the Maillard reaction.

01:33:52.680 | And the Maillard reaction is a reaction

01:33:54.980 | that for the aficionados is a non-enzymatic browning.

01:33:58.520 | The other form of non-enzymatic browning is caramelization.

01:34:01.720 | Although when you hear caramel, caramel,

01:34:03.840 | I think it's caramel, you think sweet.

01:34:06.800 | And indeed caramelization is a sugar-sugar chemical

01:34:11.660 | interaction that leads to a kind of nicely toasted,

01:34:15.620 | not burnt, but nicely toasted sweet taste.

01:34:18.640 | Whereas the Maillard reaction is that really savory reaction

01:34:22.480 | that occurs when you have a sugar amino acid reaction.

01:34:25.380 | Remember we have neurons in our gut,

01:34:26.980 | but also neurons in our tongue and neurons deep in the brain

01:34:31.040 | that are comparing the amount of sugar to savory, okay?

01:34:36.280 | And the Maillard reaction is very interesting.

01:34:38.520 | For you chemists out there,

01:34:39.960 | this is going to be way too elementary.

01:34:41.420 | And for you non-chemists,

01:34:42.360 | it's probably going to be a little bit of a reach,

01:34:43.960 | but just bear with me.

01:34:45.520 | All these chemicals that we sense

01:34:47.280 | have a different structure.

01:34:48.400 | It's like hydrogens and oxygens and aldehyde groups

01:34:50.780 | and all these things.

01:34:51.620 | And basically the Maillard reaction

01:34:53.200 | involves what's called a free aldehyde.

01:34:55.040 | If you didn't like chemistry, don't worry about it.

01:34:57.560 | It's basically got a group there that kind of sits open

01:35:01.060 | that allows it to interact with other things.

01:35:03.240 | And actually through the use of heat

01:35:05.720 | and the process that we call brazing,

01:35:08.640 | which I'll talk about in a moment,

01:35:10.200 | you create what's called a ketone group.

01:35:13.080 | Now, most people now have heard of ketones

01:35:14.700 | 'cause they think about the ketogenic diet,

01:35:16.640 | but a ketone group is actually a chemical compound

01:35:20.600 | that can be used for energy.

01:35:21.920 | That's why people say you can use ketones for energy.

01:35:24.420 | But if you've ever actually encountered ketones,

01:35:28.120 | if you, for instance, get liquid ketones, a ketone ester,

01:35:31.840 | and you smell it, what does it smell like?

01:35:34.080 | It smells a little bit like an alcohol,

01:35:36.520 | but it has a kind of savory taste

01:35:39.920 | even when you smell it, okay?

01:35:42.080 | There are other smells that have these tastes too,

01:35:44.160 | but for the Maillard reaction,

01:35:46.200 | which could be created, for instance,

01:35:47.880 | like if you took a piece of meat

01:35:49.240 | or if you're not a meat eater,

01:35:50.400 | if you took tomatoes and you cooked them in a pan

01:35:53.040 | and you cooked it nice and slow till it simmered

01:35:54.920 | and almost started to brown and burn a little bit.

01:35:57.200 | Usually if I do it, it burns.

01:35:58.400 | I'm not a good cook, as Costello points out a lot.

01:36:02.000 | But it gets that like almost tangy, very umami-like flavor.

01:36:07.000 | And sometimes it will even stick to the pan

01:36:10.000 | if you scrape it off.

01:36:11.380 | It actually, you can taste it in your mouth

01:36:13.400 | as you're cooking it.

01:36:14.600 | That's the Maillard reaction.

01:36:15.880 | That's that free aldehyde group.

01:36:17.200 | And that's the production of a ketone group.

01:36:20.100 | When you smell ketones, it smells very much like that, okay?

01:36:25.560 | Some people talk about the ketones

01:36:27.200 | will produce like fruity breath.

01:36:28.720 | And that's true if people are really far into ketosis.

01:36:31.080 | Their breath has a kind of fruity odor.

01:36:32.560 | That's a little bit of a different thing.

01:36:34.300 | So the relationship between smell and taste

01:36:36.900 | is a very, very close one.

01:36:39.400 | And this is why when people drink wine,

01:36:40.920 | they often will inhale and then sip.

01:36:43.440 | Some of that is just kind of like

01:36:44.800 | pomp and circumstance, frankly.

01:36:46.640 | They make a big deal of it.

01:36:48.320 | But they can sense things with their mouth.

01:36:51.060 | The combination of odor receptors being activated

01:36:56.260 | in a particular way and taste receptors in the mouth

01:36:58.640 | being activated in a particular way

01:37:00.480 | triggers the activation of multiple brain areas

01:37:03.100 | that are associated with taste

01:37:04.560 | and circuitry within the body

01:37:06.780 | that's associated with the behaviors

01:37:09.120 | that relate to that taste, like leaning toward it

01:37:11.960 | or leaning away from it,

01:37:13.080 | depending on whether or not it's a pettative or aversive.

01:37:15.920 | So the Maillard reaction is a very interesting reaction

01:37:18.840 | involving this sugar amino acid thing.

01:37:21.860 | But really what it's doing is heating up food

01:37:25.120 | such that the amino acids are more available,

01:37:29.860 | literally in their chemical form,

01:37:31.320 | for detection by the neurons.

01:37:33.360 | This is a phenomenon that occurs in other domains

01:37:35.600 | of the taste system.

01:37:37.840 | For instance, a lot of what's happened

01:37:40.400 | with highly processed foods

01:37:42.880 | is that manufacturers have figured out

01:37:45.680 | how to trigger more dopamine response

01:37:48.340 | by ingestion of these sugary foods

01:37:50.340 | and created textures

01:37:52.360 | and created essentially design of foods for two purposes.

01:37:55.720 | I'm not out to completely demonize processed foods.

01:37:58.900 | I did that in a previous episode.

01:38:00.720 | But processed foods are really designed

01:38:03.480 | to take foods that ordinarily would spoil,

01:38:05.740 | that would have a shelf life and extend their shelf life,

01:38:07.680 | to turn foods, which are not a commodity, into a commodity.

01:38:10.680 | Something that could be stored and used essentially

01:38:12.600 | as a tradable, purchasable, sellable resource.

01:38:17.600 | In doing that, they've also decided to change the texture

01:38:22.560 | so that you want to chew more of them.

01:38:24.720 | Like I have this thing,

01:38:25.680 | I don't know what it is for those Triscuit crackers.

01:38:29.140 | Why are those things so good?

01:38:30.120 | It's probably the texture.

01:38:31.420 | Yeah, those layers, they're just kind of perfectly salty.

01:38:33.780 | Haven't had one in a long time,

01:38:34.800 | so I bet if I had one now,

01:38:35.940 | it wouldn't taste as good as I'm imagining it.

01:38:38.000 | But those combinations of texture, smell, and taste

01:38:42.560 | are what combine to activate these different brain areas

01:38:44.800 | that make you really want to desire something.

01:38:47.440 | And the people who make foods,

01:38:49.100 | processed foods in particular,

01:38:50.860 | are phenomenally good at figuring out

01:38:53.580 | what drives the dopamine system and makes you want more

01:38:56.040 | of these things, either because of the way they taste

01:38:58.740 | and/or because of the way they trigger neurons in your gut

01:39:01.060 | that have nothing to do with taste

01:39:02.460 | that simply make you desire more of the food.

01:39:04.620 | In other words, many of the foods that are processed foods

01:39:08.400 | make you desire more of them,

01:39:10.340 | it's impossible to eat one chip kind of thing,

01:39:13.260 | not because they taste good, but because in your gut,

01:39:16.380 | they're activating the neurons that activate dopamine,

01:39:18.660 | which make you seek more of those foods,

01:39:20.900 | independent of blood sugar or anything else.

01:39:23.820 | So you may actually be eating more particular foods,

01:39:26.700 | not because they taste good,

01:39:28.580 | but because they feel good on your tongue and mouth,

01:39:32.820 | and because the neurons in your gut,

01:39:34.780 | which are totally independent of conscious taste,

01:39:37.140 | are triggering the release of dopamine,

01:39:38.700 | which is a molecule that makes you seek more of

01:39:41.340 | and do more of anything that led

01:39:43.120 | to the ingestion of that food.

01:39:44.960 | There's a fun experiment that you can do,

01:39:47.300 | which is to completely invert your sense of sweet and sour.

01:39:52.300 | There's actually a way to do this readily.

01:39:54.940 | When I was a postdoc,

01:39:56.820 | I used to have a journal club at my house,

01:39:58.980 | people would come over in the evening once a month,

01:40:01.860 | and we would read a paper,

01:40:03.160 | typically the weirdest paper we could find,

01:40:05.120 | and we would eat food and hang out.

01:40:08.420 | That was what nerds did and do for fun.

01:40:11.660 | So that's what we did.

01:40:12.880 | And one time someone brought what's called miracle berry.

01:40:17.760 | So this isn't some psychedelic plant medicine thing.

01:40:20.000 | Miracle berry you can purchase online,

01:40:22.400 | it's relatively inexpensive.

01:40:24.440 | It actually causes a change in the configuration

01:40:28.120 | of taste receptors such that when you eat something sour,

01:40:32.320 | it tastes sweet.

01:40:33.600 | And so what's really wild is you ingest miracle berry,

01:40:37.240 | and then you bite into a lemon, maybe even the lemon peel,

01:40:40.760 | and it tastes as sweet as a peach.

01:40:43.160 | And this effect lasts several hours.

01:40:45.500 | Definitely check any warnings.

01:40:48.460 | I don't know what sort of warnings miracle berry carries,

01:40:51.120 | but I'm sure there's always something you can imagine.

01:40:54.640 | There are a number of papers on miracle berry,

01:40:56.620 | or miracle fruit it's called,

01:40:59.320 | but it changes your perception of sour

01:41:02.320 | at a perceptual level,

01:41:04.480 | but it does that by changing the activity of the receptors

01:41:07.800 | in the mouth and tongue.

01:41:09.560 | Now, this is important as a principle,

01:41:11.440 | and it's underscored by experiments that have been done

01:41:13.840 | by, for instance, Charles Zucker's lab

01:41:15.480 | at Columbia University,

01:41:16.880 | where they've essentially genetically engineered animals

01:41:20.160 | such that the bitter receptor is swapped

01:41:23.300 | with the sweet receptor,

01:41:24.400 | or the sweet receptor is swapped with the bitter receptor.

01:41:26.680 | And what they show is that the actual food,

01:41:30.000 | the experience on the tongue

01:41:32.360 | drives different pathways in the brain.

01:41:34.960 | Here's what they did.

01:41:35.800 | They essentially took mice and swapped out the sweet receptor

01:41:39.320 | and put in a bitter receptor.

01:41:40.620 | And then what they found is that,

01:41:42.040 | whereas normally mice would actively seek out

01:41:45.560 | and even work for sugar water, sucrose,

01:41:48.220 | they really liked that,

01:41:49.500 | if they replace the sweet receptor with the bitter receptor,

01:41:52.280 | the mice would avoid sugar water.

01:41:53.940 | And the reverse was also true,

01:41:55.120 | that mice would drink a bitter solution avidly.

01:41:58.200 | They liked a bitter solution

01:41:59.560 | if they swapped out the bitter receptor for sweet receptor.

01:42:03.020 | What this means is that our entire experience

01:42:04.960 | of what we taste is dependent on how we experienced

01:42:08.200 | that taste at the level of the tongue.

01:42:09.440 | And so you're hopefully not going to do genetic engineering

01:42:12.580 | of your taste receptors,

01:42:13.800 | but if you'd like to do this sort of experiment,

01:42:16.140 | you actually can do it very easily using miracle fruit.

01:42:18.760 | The instructions of how much to ingest, et cetera,

01:42:21.680 | any safety concerns are usually on the package

01:42:23.980 | and should be easy to find.

01:42:26.120 | And there's a lot of science to support how this works.

01:42:28.240 | It's kind of a fun experiment that anyone can do

01:42:31.240 | and will completely change your perception

01:42:33.240 | of any food that you're accustomed to eating.

01:42:35.460 | In fact, you can figure out how much sweet

01:42:38.760 | or the sense of sweetness is contributing

01:42:41.720 | to your experience of a food,

01:42:42.980 | even if you don't think of that as a sweet food,

01:42:44.960 | through this miracle fruit experiment.

01:42:47.260 | You could take miracle fruit,

01:42:48.280 | you could eat a slice of pepperoni pizza or cheese pizza,

01:42:51.200 | which perhaps normally to you would taste just like pizza.

01:42:54.780 | And you'll notice it tastes very different.

01:42:56.940 | What you are detecting is how much the sense of sweet

01:43:01.240 | was contributing to that particular flavor.

01:43:04.560 | Now I'd like to return to pheromones.

01:43:07.840 | So I mentioned earlier,

01:43:09.080 | true pheromonal effects are well-established in animals.

01:43:12.580 | And one of the most remarkable pheromonal effects

01:43:15.080 | that's ever been described is one that actually

01:43:16.820 | I've mentioned before on this podcast,

01:43:18.300 | but I'll mention again just briefly,

01:43:20.040 | which is the Coolidge effect.

01:43:21.600 | The Coolidge effect is the effect of a male

01:43:25.860 | of a given species.

01:43:26.880 | In most cases, it tended to be a rodent or a rooster mating.

01:43:32.960 | And at some point reaching exhaustion

01:43:35.920 | or the inability to mate again

01:43:37.960 | because they just simply couldn't for whatever reason.

01:43:41.320 | The Coolidge effect establishes that if you swap out

01:43:45.960 | the hen with a new hen or the female rat or mouse

01:43:49.280 | with a new one, then the rat or the rooster

01:43:53.800 | spontaneously regains their ability to mate.

01:43:56.360 | Somehow their vigor is returned,

01:43:58.480 | the refractory period after mating that normally occurs

01:44:02.100 | is abolished and they can mate again.

01:44:05.560 | Turns out that the Coolidge effect

01:44:06.920 | runs in the opposite direction too.

01:44:09.020 | I did not know this, but I recently learned of a study.

01:44:11.560 | It was actually done in hamsters, not in mice,

01:44:14.280 | but it turns out that females also will,

01:44:17.540 | female rodents will mate to exhaustion.

01:44:19.960 | And at some point, excuse me,

01:44:22.200 | they will refuse to mate any longer

01:44:24.080 | unless you swap in a new male.

01:44:26.200 | And then because mating in rodents

01:44:28.560 | involves the female being receptive,

01:44:30.280 | there are a certain number of behaviors

01:44:31.860 | that tell you that she's willing and wanting to mate,

01:44:36.860 | so-called lordosis reflex.

01:44:38.600 | Then if there's a new male,

01:44:42.120 | she will spontaneously regain the lordosis reflex

01:44:46.280 | and the desire to mate.

01:44:47.320 | And how do you know this?

01:44:49.520 | How do we know it's a pheromonal effect?

01:44:51.360 | Well, this recovery of the desire and ability to mate,

01:44:54.960 | both in males and in females,

01:44:58.240 | can be evoked completely by the odor of a new male or female.

01:45:03.240 | It doesn't even have to be the presentation

01:45:05.000 | of the actual animal.

01:45:06.180 | And that's how you know that

01:45:07.020 | it's not some visual interaction or some other interaction.

01:45:09.780 | It's a pheromonal interaction.

01:45:12.000 | Now, as I mentioned earlier, pheromonal effects,

01:45:14.720 | humans have been debated for a long period of time.

01:45:17.620 | We are thought to have a vestigial,

01:45:19.700 | meaning a kind of shrunken down

01:45:22.940 | miniature accessory olfactory bulb

01:45:25.800 | called Jacobson's organ or the vomeronasal organ.

01:45:29.560 | Some people don't believe that Jacobson's organ is this.

01:45:31.740 | Some people do.

01:45:33.220 | There is anatomical evidence for it in some cadavers.

01:45:37.000 | It sits not very high up in the brain

01:45:41.040 | or where your olfactory bulb is,

01:45:42.800 | but it's actually in the nasal passages.

01:45:45.400 | So there's like little dents

01:45:46.680 | as you go up through your nasal passages.

01:45:48.440 | And there is evidence of something that's vomeronasal-like.

01:45:52.740 | Vomeronasal is the pheromonal organ.

01:45:54.560 | They call it Jacobson's organ.

01:45:55.700 | If it's present in humans,

01:45:57.220 | kind of tucked into some of the divots in the nasal passage.

01:46:01.740 | Even if that Jacobson's organ isn't there

01:46:06.680 | or is not responsible for the chemical signaling

01:46:09.420 | between individuals,

01:46:10.820 | there is chemical signaling between human beings.

01:46:13.380 | As I mentioned earlier, the effect of tears

01:46:16.740 | in suppressing the areas of the brain

01:46:19.100 | that are involved in sexual desire and testosterone of males.

01:46:23.740 | That's a concrete result.

01:46:25.620 | It's a very good result published by an excellent group

01:46:28.520 | with no preexisting bias going in.

01:46:30.260 | That's just what they found.

01:46:32.160 | There is also evidence both for and against

01:46:37.160 | chemical signaling between females

01:46:40.420 | in terms of synchronization of menstrual cycles.

01:46:42.940 | Now, the original paper on this

01:46:44.560 | was published in the 1970s by McClintock.

01:46:48.580 | And it essentially said that when women live together

01:46:53.020 | in group housing dormitories and similar,

01:46:55.220 | that their menstrual cycles were synchronized

01:46:57.020 | and that was due to what was hypothesized

01:46:58.900 | to be for hormonal effects.

01:47:00.580 | Over the years,

01:47:01.420 | that study has been challenged many, many times.

01:47:04.820 | The more recent data point to the idea

01:47:07.780 | that there is chemical signaling between women

01:47:10.980 | in ways that impact the timing of the menstrual cycle,

01:47:14.420 | but that depending on whether or not some of the women

01:47:17.980 | are in the ovulation phase,

01:47:19.980 | the ovulatory phase of that cycle,

01:47:21.580 | or whether or not they are in the follicular phase,

01:47:23.420 | the phase when the follicle is maturing

01:47:26.060 | before the egg actually ovulates.

01:47:30.420 | So two separate phases of the 28-day menstrual cycle

01:47:35.560 | will either lengthen or shorten the menstrual cycle

01:47:39.900 | of the person that smells those women.

01:47:42.000 | Translated into English,

01:47:43.020 | what that means is that it is very likely, it seems,

01:47:46.220 | that something, maybe pheromones,

01:47:47.940 | but maybe some other chemical

01:47:49.300 | that is independent of pheromones,

01:47:51.220 | is being conveyed between women that are housed together

01:47:55.840 | or spend a lot of time together

01:47:57.480 | to shift their menstrual cycle,

01:47:58.960 | but it doesn't necessarily mean that they synchronize.

01:48:02.120 | So for instance,

01:48:02.960 | if one woman is in the follicular phase

01:48:04.960 | of the menstrual cycle,

01:48:07.860 | it might shorten or delay ovulation, excuse me,

01:48:12.040 | it might accelerate ovulation in another woman,

01:48:14.820 | whereas if somebody is in the ovulatory phase

01:48:17.020 | of their cycle,

01:48:17.840 | it might lengthen the menstrual cycle out

01:48:21.320 | so that the woman who smells that person's scent

01:48:25.680 | or who smells her sweat,

01:48:27.360 | we still don't know the origin of the chemical,

01:48:29.060 | would ovulate later.

01:48:30.560 | So all of this is to say

01:48:31.920 | is that chemical-chemical signaling is happening

01:48:33.980 | from females to males through tears, we know that.

01:48:36.560 | Is that a pheromonal effect?

01:48:38.000 | Well, by the strict definition of a pheromone,

01:48:40.100 | a molecule that's released from one individual

01:48:42.140 | that impacts the biology of another individual, yes,

01:48:44.920 | but in terms of identifying what the pheromone is in tears,

01:48:48.380 | that's still unknown.

01:48:49.680 | It's not clear what the chemical compound is.

01:48:52.120 | So we're reluctant as scientists

01:48:53.940 | to call it a true pheromonal effect.

01:48:55.560 | The menstrual cycle

01:48:57.000 | and the synchronization of the menstrual cycle effect

01:48:59.300 | seems to hold up under some conditions,

01:49:01.040 | but in some cases,

01:49:02.120 | there's a kind of clash of menstrual cycles

01:49:04.520 | that's created by chemicals

01:49:07.920 | that are emitted from one female to another.

01:49:11.640 | So there are many examples of this in humans.

01:49:14.420 | For instance, people can recognize the T-shirt of their mate

01:49:19.420 | if you give, this experiment has been done many times.

01:49:24.380 | I know it's been challenged a number of times,

01:49:25.740 | but the data are pretty good by now

01:49:27.140 | that if you offer,

01:49:29.560 | you take a collection of women

01:49:31.300 | who are in stable relationships with somebody,

01:49:35.100 | you offer them the smell of a hundred different shirts

01:49:37.700 | and they can very readily pick out

01:49:39.360 | their significant other's scent.

01:49:41.300 | Okay, that's pure old faction.

01:49:42.480 | That's not pheromonal.

01:49:43.980 | But nonetheless is a remarkable degree of discrimination,

01:49:47.300 | olfactory discrimination.

01:49:49.360 | You can dilute their partner's scent

01:49:53.120 | down to the point where they themselves

01:49:55.240 | can't consciously detect the difference

01:49:57.160 | between the sweat or the T-shirt

01:49:59.220 | of a hundred different T-shirts or so.

01:50:01.200 | And they might say, I don't really smell the difference,

01:50:02.960 | but I think it's this one.

01:50:04.640 | Yeah, this one belongs to the person that I've been with.

01:50:07.480 | And they are much greater than chance

01:50:09.120 | at detecting the T-shirt or identifying the T-shirt correctly.

01:50:12.920 | So there's no question really

01:50:14.460 | that there is chemical chemical signaling between humans.

01:50:17.820 | The question is whether or not

01:50:19.000 | it's truly pheromonal in basis.

01:50:21.200 | Now you'll notice that a lot of the examples I gave,

01:50:23.480 | aside from the one of tears,

01:50:25.280 | is women detecting the sense of men or of other women.

01:50:30.280 | And it turns out that there are a number of papers.

01:50:33.680 | The best one I think that I could find

01:50:37.100 | is published in Physiology and Behavior in 2009

01:50:39.800 | to review entitled Sex Differences in Reproductive Hormone

01:50:43.240 | Influences on Human Odor Perception

01:50:45.720 | by Doddy, D-O-T-Y, and Cameron.

01:50:48.600 | I encourage you to check out this review.

01:50:50.040 | It's available free as a download.

01:50:51.600 | We'll provide a link to it.

01:50:53.120 | You can get the full PDF if you want.

01:50:55.080 | But it does seem that women are better at detecting odors

01:51:00.080 | in these odor discrimination tasks than are men.

01:51:03.820 | And yes, that it does vary according

01:51:05.720 | to where they are in their menstrual cycle.

01:51:08.720 | And yes, they also looked at people

01:51:10.840 | who had received gonadectomy,

01:51:12.280 | that had their ovaries removed,

01:51:13.720 | a number of different important controls.

01:51:16.180 | None of this surprises me.

01:51:17.900 | None of this should surprise you.

01:51:19.440 | It's very clear that hormones have a profound effect

01:51:22.220 | on a large number of systems in our biology,

01:51:24.720 | and that smell and taste and the ability

01:51:27.280 | to sense the chemical states of others,

01:51:29.600 | either consciously or subconsciously,

01:51:31.200 | have a profound influence on whether or not

01:51:33.280 | we might want to spend time with them,

01:51:34.500 | whether or not this is somebody that we're pair bonded with,

01:51:36.860 | whether or not this is somebody that we just met

01:51:39.480 | and don't trust yet, things of this sort.

01:51:42.420 | And given what's at stake in terms of reproductive biology,

01:51:46.200 | not just offspring,

01:51:47.480 | but given the possibility of transmission of diseases,

01:51:50.980 | et cetera, the risks of childbirth, et cetera,

01:51:55.720 | it makes so much sense that much of our biology

01:52:00.480 | is wired toward detecting and sensing

01:52:02.860 | whether or not things and people

01:52:04.940 | are things that we should approach or avoid,

01:52:07.160 | whether or not reproduction with that person

01:52:10.320 | is the appropriate response

01:52:11.480 | or suppression of the reproductive response

01:52:13.720 | is the appropriate response, right?

01:52:15.400 | As in the case with the tears.

01:52:17.420 | So I think these are fascinating studies.

01:52:19.980 | It's an area that still needs a lot of work,

01:52:22.920 | but there are some really wonderful papers on this.

01:52:25.600 | And the one that I mentioned a few minutes ago,

01:52:27.200 | sex differences and reproductive hormone influences

01:52:29.260 | on human odor perception is one of the better reviews

01:52:33.140 | that are out there.

01:52:34.680 | There are also a number of other reviews, for instance,

01:52:37.540 | that talk about pheromone effects

01:52:39.500 | and their impact on mood and sexual responses

01:52:43.060 | and things of that sort.

01:52:43.900 | And we will also provide some links to those.

01:52:45.460 | A lot of this is still speculative, but I want to say,

01:52:47.720 | I know I said it three times,

01:52:48.720 | but I really want to underscore

01:52:50.180 | because it is vitally important

01:52:51.560 | and people seem to get a little triggered

01:52:52.940 | by the notion of pheromones.

01:52:54.440 | Just because we haven't identified

01:52:58.800 | the actual chemical compound that's acting as a pheromone

01:53:03.180 | or putative pheromone does not mean

01:53:06.020 | that chemical-chemical signaling

01:53:07.500 | between individuals doesn't exist.

01:53:09.260 | Clearly it does.

01:53:10.860 | Actually, you and every other human

01:53:13.740 | from the time you're born until the time you die

01:53:15.820 | are actively seeking out and sensing and evaluating

01:53:20.820 | the chemicals that come from other individuals.

01:53:24.980 | There's a really nice study that was done

01:53:27.540 | by the Weizmann Institute, a group there.

01:53:29.740 | I think it was also Noam Sobel's group,

01:53:31.260 | but another group as well, as I recall,

01:53:33.220 | looking at human-human interactions

01:53:35.460 | when they meet for the first time.

01:53:37.460 | It's a remarkable study because what they found

01:53:40.940 | was people would reach out and shake hands.

01:53:44.340 | This is a typical response.

01:53:45.860 | Pre-pandemic, people would meet,

01:53:48.100 | they'd reach out and they would shake hands.

01:53:50.180 | And what they observed was almost every time

01:53:54.300 | within just a few seconds of having shaken hands

01:53:58.020 | with this new individual, people will touch their eyes.

01:54:01.740 | Almost without fail.

01:54:03.060 | Occasionally they would touch their eyebrow,

01:54:04.620 | occasionally someone would touch their hair.

01:54:06.380 | We always associate that with people having some sort of,

01:54:09.760 | or us having some sort of self-conscious response,

01:54:12.260 | like, oh, we want to make sure we're, you know,

01:54:14.020 | shirt tucked in and all prim and proper, whatever it is,

01:54:16.540 | or looking right, is there something in my teeth,

01:54:18.380 | this kind of thing.

01:54:19.400 | But actually people are doing that

01:54:21.220 | even if the person they just met left the room.

01:54:24.600 | So someone's sitting there, someone comes in,

01:54:26.200 | they shake hands, and the person inevitably subconsciously

01:54:29.920 | touches their eyes.

01:54:31.060 | They are taking chemicals from the skin contact

01:54:34.180 | and they are placing it on a mucosal membrane of some sort,

01:54:37.260 | typically not up their nose or in their mouth,

01:54:39.360 | typically on their eyes.

01:54:40.840 | Now, animals do this all the time.

01:54:42.240 | There's a phenomenon in animals called bunting.

01:54:44.600 | If you have a overeager dog that when you meet them

01:54:48.300 | or you see them again after you've been away for the day,

01:54:50.420 | they'll rub their head against you, right?

01:54:52.560 | Cats will do this too, it's called bunting.

01:54:54.560 | They're rubbing their scent glands on you,

01:54:56.300 | they're marking you.

01:54:57.740 | And believe it or not,

01:54:58.760 | you're marking other people when you shake their hand.

01:55:01.360 | And they are then taking your mark

01:55:03.840 | and rubbing it on themselves subconsciously.

01:55:07.140 | So we all do these kinds of behaviors.

01:55:08.940 | And now that you're aware of it,

01:55:10.100 | you can watch for it in your environment,

01:55:11.800 | you can pay attention to people.

01:55:13.880 | Some of this has probably changed

01:55:15.140 | in light of the events of 2020, et cetera.

01:55:17.460 | But nonetheless, we are evaluating the molecules

01:55:21.240 | on people's breath.

01:55:22.600 | We are evaluating the molecules on people's skin

01:55:25.120 | by actively rubbing it on ourselves.

01:55:28.520 | And we are actively involved in sensing

01:55:31.360 | not just their facial expressions,

01:55:32.740 | the size of their pupils and things like that,

01:55:34.800 | but the chemicals that they are emitting,

01:55:36.740 | their hormone status, how they smell.

01:55:39.040 | We're detecting the pheromones possibly,

01:55:43.480 | but certainly the odors in their breath.

01:55:45.700 | You might say, well,

01:55:46.540 | I don't actually go around sniffing people's breath.

01:55:49.340 | Unless if it's bad, in which case it's aversive,

01:55:51.240 | but breath is communicating a lot of signals.

01:55:53.560 | And this handshake eye rub experiment

01:55:56.320 | shows that we are actively going through behaviors

01:55:59.580 | reflexively to wipe ourselves or smear ourselves

01:56:03.300 | with other people's chemicals.

01:56:04.720 | Now that might seem odd or even gross to you,

01:56:07.540 | but I think it's beautiful.

01:56:09.440 | I think that it illustrates the extent

01:56:11.520 | to which we as human beings are in some ways

01:56:14.320 | among the other animals in our subconscious,

01:56:17.320 | sometimes conscious, but certainly subconscious,

01:56:20.080 | tendency to try and evaluate our chemical environment

01:56:22.980 | through what we inhale through our nose,

01:56:25.160 | what we ingest through our mouth,

01:56:27.400 | and what we actively take off other people's skin

01:56:31.460 | and rub on ourselves to evaluate it

01:56:34.500 | and what we should do about it

01:56:35.920 | and perhaps that person as well.

01:56:38.140 | So today we talked a lot about olfaction, taste,

01:56:40.960 | and chemical sensing between individuals.

01:56:43.320 | I like to think that you now know a lot

01:56:45.400 | about how your smell system works

01:56:47.320 | and why inhaling is a really good thing to do in general

01:56:51.440 | for waking up your brain and for cognitive function

01:56:54.020 | and for enhancing your sense of smell.

01:56:56.120 | We talked about how to enhance your sense of taste.

01:56:58.420 | And we talked about chemical signaling between individuals

01:57:01.380 | as a way of communicating some important aspects

01:57:03.680 | about biology.

01:57:04.780 | People are shaping each other's biology all the time

01:57:07.360 | by way of these chemicals that are being traded

01:57:09.420 | from one body to the next through air

01:57:11.960 | and skin-to-skin contact and tears.

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01:58:38.980 | Today, we didn't really talk about supplements,

01:58:40.700 | but in previous episodes and in future episodes,

01:58:43.100 | we'll talk about supplements and things that you can take

01:58:45.040 | to modify your biology and nervous system if you like.

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01:59:21.120 | Last but not least,

01:59:22.120 | I want to thank you for your time and attention

01:59:24.140 | and your willingness to embrace new concepts and terms

01:59:26.960 | and to learn about science and biology and protocols

01:59:29.920 | that hopefully can benefit you and the people that you know.

01:59:32.660 | And of course, thank you for your interest in science.

01:59:35.600 | [upbeat music]

01:59:38.180 | (upbeat music)

How Smell, Taste & Pheromone-Like Chemicals Control You

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