back to indexHow Smell, Taste & Pheromone-Like Chemicals Control You | Huberman Lab Podcast #25
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Welcome to the Huberman Lab Podcast,
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where we discuss science and science-based tools
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for everyday life.
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I'm Andrew Huberman,
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and I'm a professor of neurobiology and ophthalmology
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at Stanford School of Medicine.
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This podcast is separate
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from my teaching and research roles at Stanford.
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It is, however, part of my desire and effort
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to bring zero cost to consumer information
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about science and science-related tools
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to the general public.
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In keeping with that theme,
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I'd like to thank the sponsors of today's podcast.
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Our first sponsor is Roka.
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Roka makes sunglasses and eyeglasses that, in my opinion,
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are the absolute best out there.
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The sunglasses and eyeglasses that are made by Roka
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have a number of properties that are really unique.
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First of all, they're extremely lightweight.
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You never even notice that they're on your face.
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Second, the optical clarity is fantastic.
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One of the things that's really hard to accomplish,
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but that Roka succeeded in accomplishing,
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is making sunglasses that you can wear
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in lots of different environments.
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As you move from bright to shadowed regions, for instance,
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or as the amount of sunlight changes,
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many eyeglasses will make it such
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that it's hard to see your environment
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and you need to take the eyeglasses off
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or you can't see or detect borders.
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With Roka sunglasses, all of that is seamless.
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They clearly understand the adaptation mechanisms
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and habituation mechanisms.
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All these fancy details about the human visual system
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have allowed them to design a sunglass
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that allows you to be in any environment
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and to see that environment extremely well.
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The eyeglasses are terrific.
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I wear readers at night.
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And again, they just make the whole experience of reading
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or working on a screen at night very, very easy,
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very easy on the eyes.
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The aesthetic of the eyeglasses and sunglasses
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You know, I chuckle sometimes when I see sports frames
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or sports glasses, a lot of them just look ridiculous,
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frankly, but the Roka eyeglasses and sunglasses
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have a terrific aesthetic.
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They have a huge variety to select from.
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If you'd like to try Roka glasses,
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you can go to Roka, that's R-O-K-A.com
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and enter the code Huberman
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and you'll get 20% off your first order.
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That's R-O-K-A.com and enter the code Huberman
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to get 20% off your first order.
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Today's podcast is also brought to us by Inside Tracker.
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Inside Tracker is a personalized nutrition platform
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that analyzes data from your blood and DNA
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to help you better understand your body
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and help you reach your health goals.
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I'm a big believer in getting regular blood work done
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for the simple reason that many of the factors
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that impact your immediate and long-term health
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can only be detected from a quality blood test.
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One of the major problems with blood tests, however,
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They have a dashboard that allows you to assess,
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for instance, whether or not you ought to make changes
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So really they're putting you
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in the driver's seat for your health.
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In fact, one of the listeners
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of this podcast contacted me recently
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I felt like I was in great health,
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but I noticed from the test
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C-reactive protein is a marker that if it's too high
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and even eye diseases.
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as a consequence of getting their blood work done
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and taking the Inside Tracker test.
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So I think that's just one of many examples
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that we hear about.
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I have examples from my own life, for instance,
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of different factors in my blood being off
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and making adjustments to nutrition
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and other aspects of my life that have allowed me
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to bring those into the proper range.
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So if you care about your health,
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Today's episode is also brought to us by Athletic Greens.
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Athletic Greens is an all-in-one
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I've been using Athletic Greens since 2012,
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so I'm delighted that they're sponsoring the podcast.
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Athletic Greens is terrific
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If I drink Athletic Greens once
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Almost everybody that tries it
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It's delicious to me.
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I drink it once or twice a day.
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This month, we've been talking about the senses,
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how we detect things in our environment.
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The last episode was all about vision,
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how we take light and convert that information
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into things that we can perceive,
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like colors and faces and motion, things of that sort,
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as well as how we use light to change our biology
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in ways that are subconscious, that we don't realize,
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things like mood and metabolism and levels of alertness.
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Today, we're going to talk about chemical sensing.
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We're going to talk about the sense of smell,
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our ability to detect odors in our environment.
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We're also going to talk about taste,
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our ability to detect chemicals and make sense of chemicals
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that are put in our mouth and into our digestive tract.
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And we are going to talk about chemicals
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that are made by other human beings
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that powerfully modulate the way that we feel,
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our hormones, and our health.
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Now, that last category are sometimes called pheromones.
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However, whether or not pheromones exist in humans
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is rather controversial.
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There actually hasn't been a clear example
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of a true human pheromonal effect,
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but what is absolutely clear, what is undeniable
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is that there are chemicals that human beings make
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and release in things like tears onto our skin and sweat
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and even breath that powerfully modulate
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or control the biology of other individuals.
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In fact, right now, even if you're completely alone,
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your chemical environment internally
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is being controlled by external chemicals.
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Your nervous system and your hormones and your metabolism
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are being modified by things in your environment.
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So we're going to talk about those.
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It's an absolutely fascinating aspect to our biology.
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It's one of our most primordial,
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meaning primitive aspects of our biology,
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but it's still very active in all of us today.
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This episode, believe it or not,
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will have a lot of tools, a lot of protocols.
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Even though I'm guessing most of you
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can probably smell your environment just fine,
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that you know what you like to eat and what tastes good
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and what doesn't taste good to you,
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today's episode is going to talk about tools
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that will allow you to actually leverage
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these chemical sensing mechanisms,
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including how you smell,
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not how you smell in the qualitative sense,
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but how you smell in the verb sense,
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the action of sniffing and smelling
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to enhance your sense of smell
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and to enhance your sense of taste,
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as well, believe it or not, to enhance your cognition,
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your ability to learn and remember things.
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Everything we're going to talk about, as always,
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is grounded in quality peer-reviewed studies
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from some excellent laboratories.
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I'll provide some resources along the way.
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So that means tools and protocols
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and also basic information.
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You're going to learn a ton of neuroscience
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and a lot of biology in general.
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And I think what you'll come to realize by the end
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is that while we are clearly different
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from the other animals,
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there are aspects to our biology that are very similar
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to that of other animals in very interesting ways.
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Before we dive into chemical sensing,
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I want to just briefly touch on a few things
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from the vision episode.
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One is a summary of a protocol.
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So I covered 13 protocols last episode.
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If you haven't seen that episode, check it out.
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Those protocols will allow you to be more alert
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and to see better over time if you follow them.
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All of them are zero cost.
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You can find any and all of them at hubermanlab.com.
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There's a link to those videos and tools and protocols.
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Everything is timestamped.
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The two protocols that I just want to remind everybody of
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are the protocol of near-far viewing,
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that all of us, regardless of age,
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should probably spend about five minutes,
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three times a week, doing some near-far viewing exercises.
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So that would be bringing a pen or pencil up close
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to the point where you're about to cross your eyes,
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but you don't cross your eyes,
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and then out at some distance,
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and then look beyond that pen or other object
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that you're using, off as far as you can into the distance.
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It would be great if you could do this on a balcony or deck
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and then look way off in the distance
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and then bring it back in.
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This is going to exercise that accommodation reflex,
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the change in the shape of the lens
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can help offset a number of things,
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including myopia, nearsightedness.
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The other one is this incredible study
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that showed that two hours a day outside,
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even if you're doing other things while you're outside,
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can help offset myopia and nearsightedness.
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So try and get outside.
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It's really the sunlight and the blue light, right?
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Everyone's been demonizing blue light out there,
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but blue light is great,
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provided it's not super, super bright
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and really close to your eyes.
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Blue light is terrific if it comes from sunlight.
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Two hours a day outside is going to help offset myopia,
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Now, that's a lot of time.
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I think most of us are not getting that time,
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but since you can do other things like gardening or reading
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or walking or running,
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if you can get that two hours outside,
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your visual system and your brain will benefit.
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I also would like to make one brief correction
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to something that I said incorrectly
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in the previous episode.
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At the end of the episode, I talked about lutein
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and how lutein may help offset some moderate
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to severe age-related macular degeneration.
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As well, I talked about how some people are supplementing
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with lutein even though they don't have
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age-related macular degeneration,
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with the idea in mind that it might help
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offset some vision loss as they get older.
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I said lutein, and lutein was the correct thing to say,
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but once or twice when I started speaking fast,
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I said leucine and not lutein.
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I want to emphasize that leucine and amino acid,
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very interesting, important for muscle building,
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covered in previous episodes,
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but lutein, L-U-T-E-I-N,
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is the molecule and compound that I was referring to
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in terms of supplementing for sake of vision.
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So I apologize, please forgive me, I misspoke.
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A couple of you caught that right away.
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In listening to the episode after it went up,
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I realized that I had misspoken.
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So lutein for vision, leucine for muscles
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and muscle growth and strength, et cetera.
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Before we dive into the content of today's episode,
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I want to just briefly touch on color vision.
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Many of you asked questions about color vision
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and color perception, and indeed color perception
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is a fascinating aspect of the human visual system.
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It's one of the things that makes us unique.
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There are certainly other animals out there
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that can detect all the colors of the rainbow.
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Some can even detect into the infrared
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and to the far red that we can't see,
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but nonetheless, human color vision,
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provided that somebody isn't colorblind,
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is really remarkable.
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And if you're interested in color vision
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or you want to answer questions about art
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or about, for instance, why that dress
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that showed up online a few years ago
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looks blue to you and yellow to somebody else,
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all the answers to that are in this terrific book,
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which is, What is Color?
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15 questions and answers on the science of color.
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I did not write this book, I wish I had.
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The book is by Ariel and Joan Ekstut,
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that's E-C-K-S-T-U-T.
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So it's, What is Color?
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50 questions and answers on the science of color.
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It's an absolutely fabulous book.
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I have no business relationship to them.
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I did help them get in contact
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with some color vision scientists
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when they reached out to me.
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And you can know that all the information in the book
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was vetted by excellent color vision scientists.
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It's a really wonderful and beautiful book.
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The illustrations are beautiful.
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If you're somebody who's interested in design or art,
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or you're just curious about the science of color,
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it's a terrific book, I highly recommend it.
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If you just look it up online,
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there are a variety of places
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that will allow you to access the book.
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So let's talk about sensing chemicals
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and how chemicals control us.
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In our environment,
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there are a lot of different physical stimuli.
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There is light photons, which are light energy,
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and those land on your retinas
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and your retinas tell your brain about them
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and your brain creates this thing we call vision.
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There are sound waves, literally particles
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moving through the air and reverberations
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that create what we call sound and hearing.
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And of course, there are mechanical stimuli,
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pressure, light touch, scratch, tickle, et cetera,
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that lands on our skin or the blowing of a breeze
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that deflects the hairs on our skin.
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And we can sense mechanical touch, mechanical sensation.
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And there are chemicals.
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There are things floating around in the environment,
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which we call volatile chemicals.
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So volatile sounds oftentimes like emotionally volatile,
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but it just means that they're floating around out there.
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So when you actually smell something,
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like let's say you smell a wonderfully smelling rose
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or cake, yes, you are inhaling the particles into your nose.
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There are literally little particles of those chemicals
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are going up into your nose
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and being detected by your brain.
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Also, if you smell something putrid, disgusting, or awful,
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use your imagination.
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Those particles are going up into your nose
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and being detected by neurons that are part of your brain.
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Other ways of getting chemicals into our system
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is by putting them in our mouth,
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by literally taking foods and chewing them
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or sucking on them and breaking them down
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into their component parts.
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And that's one way that we sense chemicals
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with this thing, our tongue.
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And there are chemicals that can enter
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through other mucosal linings and other kind of,
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just think damp, sticky linings of your body.
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And the main ones would be the eyes.
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So you've got your nose, your eyes, and your mouth,
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but mainly when we have chemicals coming into our system,
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it's through our nose or through our mouth.
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Although sometimes through our skin,
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certain things can go transdermal, not many,
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and through our eyes.
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So these chemicals, we sometimes bring into our body,
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into our biology through deliberate action.
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We select a food, we chew that food,
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and we do it intentionally.
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Sometimes they're coming into our body
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through non-deliberate action.
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We enter an environment and there's smoke
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and we smell the smoke, and as a consequence,
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Sometimes we are forced to eat something
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because somebody tells us we should eat it
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or we do it to be polite.
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So there are all these ways that chemicals
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can make it into our body.
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Sometimes, however, other people are actively
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making chemicals with their body.
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Typically this would be with their breath,
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with their tears, or possibly,
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I want to underscore possibly,
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by making what are called pheromones,
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molecules that they release into the environment,
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typically through the breath,
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that enter our system through our nose,
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or our eyes, or our mouth,
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that fundamentally change our biology.
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I will explain how smell and taste
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and these pheromone effects work,
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but I'll just give an example,
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which is a very salient and interesting one
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that was published about 10 years ago
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in the journal Science.
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Science Magazine is one of the three,
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what we call apex journals.
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There are a lot of journals out there,
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but for those of you that want to know,
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Science Magazine, Nature Magazine, and Cell
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are considered the three top kind of apex journals.
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They are the most stringent
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in terms of getting papers accepted there,
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even reviewed there.
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They have about a 95% rejection rate at the front gate,
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meaning they don't even review 95%
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of what gets sent to them.
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Of the things that they do decide to review,
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then get sent out,
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a very small percentage of those get published.
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It's very stringent.
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This paper came out in Science
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showing that humans,
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men in particular in this study,
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have a strong biological response and hormonal response
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to the tears of women.
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What they did is they had women,
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and in this case, it was only women for whatever reason,
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cry and they collected their tears.
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Then those tears were smelled by male subjects
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or male subjects got what was essentially the control,
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which was the saline.
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Men that smelled these tears that were evoked by sadness
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had a reduction in their testosterone levels
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that was significant.
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They also had a reduction in brain areas
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that were associated with sexual arousal.
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Now, before you run off with your interpretations
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about what this means and criticize the study
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for any variety of reasons,
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let's just take a step back.
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I will criticize the study for a variety of reasons.
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Two, one is that they only used female tears
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and male subjects.
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So it would have been nice for them to also use
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female tears and female subjects smelling those,
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male tears and male subjects smelling those,
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male tears and female subjects smelling those, and so on.
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They didn't do that.
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They did have a large number of subjects, so that's good.
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That adds power to the study.
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And they did have to collect these tears
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by having the women watch what was essentially
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a sad scene from a movie.
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They actually recruited subjects that had a high propensity
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for crying at sad movies, which was not all women.
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It turns out that the people that they recruited
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for the study were people who said, yes,
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I tend to cry when I see sad things in movies.
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What they were really trying to do is just get tears
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that were authentically cried in response to sadness
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as opposed to putting some irritant in the eye
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and collecting tears that were evoked by something else
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like just having the eyes irritated.
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Nonetheless, what this study illustrates
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is that there are chemicals in tears that are evoking
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or changing the biology of other individuals.
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Now, most of us don't think about sniffing
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or smelling other people's tears,
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but you can imagine how in close couples
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or in family members or even close friendships, et cetera,
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that we are often in close proximity
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to other people's tears.
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Now, I didn't select this study as an example
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because I want to focus on the effects of tears
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on hormones per se,
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although I do find the results really interesting.
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I chose it because I wanted to just emphasize
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or underscore the fact that chemicals that are made
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by other individuals are powerfully modulating
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our internal state.
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And that's something that most of us don't appreciate.
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I think most of us can appreciate the fact
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that if we smell something putrid, we tend to retract,
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or if we smell something delicious, we tend to lean into it.
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But there are all these ways in which chemicals
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are affecting our biology,
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and interpersonal communication using chemicals
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is not something that we hear that often about,
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but it's super interesting.
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So let's talk about smell and what smell is
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I'm going to make this very basic,
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but I am going to touch on some of the core elements
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of the neurobiology.
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So here's how smell works.
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Smell starts with sniffing.
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Now, that may come as no surprise,
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but no volatile chemicals can enter our nose
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unless we inhale them.
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If our nose is occluded or if we're actively exhaling,
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it's much more difficult for smells to enter our nose,
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which is why people cover their nose
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when something smells bad.
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Now, the way that these volatile odors
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come into the nose is interesting.
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The nose has a mucosal lining, mucus,
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that is designed to trap things,
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to actually bring things in and get stuck there.
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At the base of your brain,
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so you could actually imagine this,
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or if you wanted, you could touch the roof of your mouth,
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but right above your mouth,
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about two centimeters is your olfactory bulb.
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The olfactory bulb is a collection of neurons,
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and those neurons actually extend out of the skull,
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out of your skull, into your nose, into the mucosal lining.
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So what this means in kind of a literal sense
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is that you have neurons
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that extend their little dendrites
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and axonoid-like things,
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their little processes, as we call them,
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out into the mucus,
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and they respond to different odorant compounds.
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Now, the olfactory neurons
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also send a branch deeper into the brain,
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and they split off into three different paths.
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So one path is for what we call innate odor responses.
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So you have some hardwired aspects
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to the way that you smell the world
link |
that were there from the day you were born
link |
and that will be there until the day you die.
link |
These are the pathways and the neurons
link |
that respond to things like smoke,
link |
which, as you can imagine,
link |
there's a highly adaptive function
link |
to being able to detect burning things,
link |
because burning things generally means lack of safety
link |
or impending threat of some kind.
link |
It calls for action,
link |
and indeed, these neurons
link |
project to a central area of the brain called the amygdala,
link |
which is often discussed in terms of fear,
link |
but it's really a fear and threat detection.
link |
So some compounds, some chemicals in your environment,
link |
when you smell them,
link |
unless you're trained to overcome them
link |
because you're a firefighter,
link |
you will naturally have a heightened level of alertness,
link |
you will sense threat,
link |
and if you're in sleep even, it will wake you up.
link |
So that's a good thing.
link |
It's kind of an emergency system.
link |
You also have neurons in your nose
link |
that respond to odorants or combinations of odorants
link |
that evoke a sense of desire
link |
and what we call appetitive behaviors, approach behaviors,
link |
that make you want to move toward something.
link |
So when you smell a delicious cookie
link |
or some dish that's really savory that you really like,
link |
or a wonderful orange,
link |
and you say, mm, or it feels delicious,
link |
or it smells delicious,
link |
that's because of these innate pathway,
link |
these pathways that require no learning whatsoever.
link |
Now, some of the pathways from the nose,
link |
these olfactory neurons into the brain,
link |
are involved in learned associations with odors.
link |
Many people have this experience
link |
that they can remember the smell
link |
of their grandmother's home
link |
or their grandmother's hands even,
link |
or the smell of particular items baking
link |
or on the stove in a particular environment.
link |
Typically, these memories tend to be
link |
of a kind of nurturing sort of feeling safe and protected,
link |
but one of the reasons why olfaction, smell,
link |
is so closely tied to memory
link |
is because olfaction is the most ancient sense that we have,
link |
or I should say chemical sensing
link |
is among the most primitive and ancient senses that we have,
link |
probably almost certainly evolved
link |
before vision and before hearing.
link |
But when we come into the world,
link |
because we're still learning about the statistics of life,
link |
about who's friendly and who's not friendly
link |
and where's a fun place to be
link |
and where's a boring place to be,
link |
that all takes a long time to learn,
link |
but the olfactory system seems to imprint,
link |
seems to lay down memories very early
link |
and to create these very powerful associations.
link |
And if you think about it long enough and hard enough,
link |
many of you can probably realize
link |
that there are certain smells
link |
that evoke a memory of a particular place
link |
or person or context.
link |
And that's because you also have pathways out of the nose
link |
that are not for innate behaviors
link |
like cringing or repulsion or gagging
link |
or for that appetitive sensation,
link |
but that just remind you of a place or a thing or a context.
link |
Could be flowers in spring,
link |
could be grandmother's home and cookies.
link |
This is a very common occurrence
link |
and it's a very common occurrence
link |
because this generally exists in all of us.
link |
So we have pathway for innate responses
link |
and a pathway for learned responses.
link |
And then we have this other pathway
link |
and in humans, it's a little bit controversial
link |
as to whether or not it sits truly separate
link |
from the standard olfactory system
link |
or whether or not it's its own system embedded in there,
link |
but that they call the accessory olfactory pathway.
link |
Accessory olfactory pathway is what in other animals
link |
is responsible for true pheromone effects.
link |
We will talk about true pheromone effects,
link |
but for example, in rodents and in some primates,
link |
including mandrills, if you've ever seen mandrills,
link |
they have these like big beak noses things,
link |
you may have seen them at the zoo,
link |
look them up if you haven't seen them already,
link |
M-A-N-D-R-I-L-S, mandrills,
link |
there are strong pheromone effects.
link |
Some of those include things like
link |
if you take a pregnant female rodent or mandril,
link |
you take away the father that created those fetuses or fetus
link |
and you introduce the scent of the urine
link |
or the fur of a novel male,
link |
she will spontaneously abort or miscarry those fetuses.
link |
It's a very powerful effect.
link |
In humans, it's still controversial
link |
whether or not anything like that can happen,
link |
but it's a very powerful pheromonal effect in other animals.
link |
Another example of a pheromone effect
link |
is called the Vandenberg effect,
link |
named after the person who discovered this effect,
link |
where you take a female of a given species
link |
that has not entered puberty,
link |
you expose her to the scent or the urine
link |
from a sexually competent, meaning post-pubertal male,
link |
and she spontaneously goes into puberty earlier.
link |
So something about the scent triggers something
link |
through this accessory olfactory system,
link |
this is a true pheromonal effect,
link |
and creates ovulation and menstruation,
link |
or in rodents, it's an estrous cycle, not a menstrual cycle.
link |
So this is not to say
link |
that the exact same things happen in humans.
link |
In humans, as I mentioned earlier,
link |
there are chemical sensing between individuals
link |
that may be independent of the nose,
link |
and we will talk about those,
link |
but those are basically the three paths
link |
by which smells, odors, impact us.
link |
So I want to talk about the act of smelling,
link |
and if you are not somebody who's very interested in smell,
link |
but you are somebody who's interested
link |
in making your brain work better,
link |
learning faster, remembering more things,
link |
this next little segment is for you,
link |
because it turns out that how you smell,
link |
meaning the act of smelling, not how good or bad you smell,
link |
but the act of smelling, sniffing and inhalation,
link |
powerfully impacts how your brain functions
link |
and what you can learn and what you can't learn.
link |
Breathing generally consists of two actions,
link |
inhaling and exhaling, and we have the option, of course,
link |
to do that through our nose or our mouth.
link |
I've talked on previous episodes
link |
about the fact that there are great advantages
link |
to being a nasal breather,
link |
and there are great disadvantages to being a mouth breather.
link |
There are excellent books and data on this.
link |
There's the recent book, Breath by James Nestor,
link |
which is an excellent book that describes
link |
some of the positive effects of nasal breathing
link |
as well as other breathing practices.
link |
There's also the book Jaws by my colleagues,
link |
Paul Ehrlich and Sandra Kahn,
link |
with a forward by Jared Diamond
link |
and an introduction by Robert Sapolsky from Stanford.
link |
So that's a book, Chock-a-block with heavy hitter authors,
link |
that describes how being a nasal breather
link |
is beneficial for jaw structure,
link |
for immune system function, et cetera.
link |
Breathing in through your nose, sniffing,
link |
actually has positive effects on the way
link |
that you can acquire and remember information.
link |
Noam Sobel's group, originally at UC Berkeley
link |
and then at the Weizmann Institute,
link |
has published a number of papers
link |
that I'd like to discuss today.
link |
One of them, Human Non-Olfactory Cognition,
link |
Phase-Locked with Inhalation.
link |
This was published in Nature Human Behavior,
link |
an excellent journal, showed that the act of inhaling
link |
has a couple of interesting and powerful consequences.
link |
First of all, as we inhale, the brain increases in arousal.
link |
Our level of alertness and attention increases
link |
when we inhale as compared to when we exhale.
link |
Now, of course, with every inhale, there's an exhale.
link |
You could probably double up on your inhales
link |
if you're doing size or some of the physiological size.
link |
I've talked about these before.
link |
It's a double inhales, followed by an exhale,
link |
something like that.
link |
Or if you're speaking, you're going to change your cadence
link |
and ratio of inhales and exhales.
link |
But typically, we inhale, then we exhale.
link |
As we inhale, what this paper shows is that
link |
the level of alertness goes up in the brain.
link |
And this makes sense because as the most primitive
link |
and primordial sense by which we interact
link |
with our environment and bring chemicals into our system
link |
and detect our environment, inhaling is a cue
link |
for the rest of the brain to essentially to pay attention
link |
to what's happening, not just to the odors.
link |
As the name of this paper suggests,
link |
human non-olfactory cognition, phase locked with inhalation.
link |
What that means is that the act of inhaling itself
link |
wakes up the brain.
link |
It's not about what you're perceiving or what you're smelling
link |
and indeed sniffing as an action, inhaling as an action
link |
has a powerful effect on your ability to be alert,
link |
your ability to attend, to focus,
link |
and your ability to remember information.
link |
When we exhale, the brain goes through a subtle
link |
but nonetheless significant dip in level of arousal
link |
and ability to learn.
link |
So what does this mean?
link |
How should you use this knowledge?
link |
Well, you could imagine, and I think this would be
link |
beneficial for most people to focus on nasal breathing
link |
while doing any kind of focused work that doesn't require
link |
that you speak or eat or ingest something.
link |
There is a separate paper published
link |
in the Journal of Neuroscience that showed that indeed,
link |
if subjects, human subjects are restricted
link |
to breathing through their nose, they learn better
link |
than if they have the option of breathing
link |
through their mouth or a combination
link |
of their nose and mouth.
link |
These are significant effects in humans
link |
using modern techniques from excellent groups.
link |
So sniffing itself is a powerful modulator
link |
of our cognition and our ability to learn.
link |
You can imagine all sorts of ways
link |
that you might apply that as a tool.
link |
And I suggest that you play with it a bit,
link |
that if you're having a hard time staying awake and alert,
link |
you're having a hard time remembering information,
link |
you feel like you have a kind of attention deficit,
link |
nonclinical, of course, nasal breathing ought to help,
link |
extending or making your inhales more intense ought to help.
link |
Now, this isn't really about chemical sensing per se,
link |
but here's where it gets interesting and exciting.
link |
If you are somebody who doesn't have
link |
a very good sense of smell,
link |
or you're somebody who simply wants to get better
link |
at smelling and tasting things,
link |
you can actually practice sniffing.
link |
I know that sounds ridiculous,
link |
but it turns out that simply sniffing nothing,
link |
so doing something like this,
link |
I guess the microphone sort of has a smell,
link |
I guess my pen doesn't have a smell,
link |
turns out that doing a series of inhales,
link |
and of course each one is followed by an exhale,
link |
10 or 15 times, and then smelling an object like an orange
link |
or another item of food,
link |
or even the skin of somebody else,
link |
will lead to an increase in your ability
link |
to perceive those odors.
link |
Now, there are probably two reasons for that.
link |
One reason is that the brain systems of detecting things
link |
are waking up as a mere consequence of inhaling.
link |
So this is sort of the olfactory equivalent
link |
of opening your eyes wider in order to see, more or less.
link |
Last episode, I talked about how opening your eyes wider
link |
actually increases your level of alertness.
link |
It's not just that your level of alertness
link |
causes your eyes to be open wider.
link |
Opening your eyes wider
link |
can actually increase your level of alertness.
link |
Well, it turns out that breathing more deeply
link |
through the nose wakes up your brain,
link |
and it creates a heightened sensitivity
link |
of the neurons that relate to smell.
link |
And there's a close crossover,
link |
I'm sure you know this, between smell and taste.
link |
If any of you have ever had a cold,
link |
or for whatever reason you've lost your sense of smell,
link |
you become what they call anosmic,
link |
your sense of taste suffers also.
link |
We'll talk a little bit more
link |
about why that is in a few minutes.
link |
But as a first protocol,
link |
I'd really like all of you to consider
link |
becoming nasal breathers while you're trying to learn,
link |
while you're trying to listen,
link |
while you're trying to wake up your brain in any way
link |
and learn and retain information.
link |
This is a powerful tool.
link |
Now, there are other ways
link |
to wake up your brain more as well.
link |
For instance, the use of smelling salts.
link |
I'm not recommending that you do this necessarily,
link |
but there are excellent peer-reviewed data
link |
showing that indeed, if you use smelling salts,
link |
which are mostly of the sort
link |
that include ammonia,
link |
ammonia is a very toxic scent,
link |
but it's toxic in a way that triggers this innate pathway,
link |
the pathway from the nose to the amygdala
link |
and wakes up the brain and body in a major way.
link |
This is why they use smelling salts when people pass out.
link |
This is why fighters used to use,
link |
or maybe sometimes still use smelling salts
link |
in order to heighten their level of alertness.
link |
This is why power lifters will inhale smelling salts.
link |
They work because they trigger the fear
link |
and kind of overall arousal systems of the brain.
link |
This is why I think most people
link |
probably shouldn't use ammonia or smelling salts
link |
to try and wake up, but they really do work.
link |
If you've ever smelled smelling salts,
link |
and I have, I tried this, they give you a serious jolt.
link |
It's like six espresso
link |
infused into your bloodstream all at once.
link |
You are wide awake immediately,
link |
and you feel a heightened sense of kind of desire to move
link |
because you release adrenaline into your body.
link |
Now, inhaling through your nose
link |
and doing nasal breathing is not going to do that.
link |
It's going to be a more subtle version
link |
of waking up your system, of alerting your brain overall.
link |
And for those of you that are interested in having a richer,
link |
a more deep connection to the things
link |
that you smell and taste,
link |
including other individuals perhaps, not just food,
link |
practicing or enhancing your sense of sniffing,
link |
your ability to sniff
link |
might sound like a kind of ridiculous protocol,
link |
but it's actually a kind of fun
link |
and cool experiment that you can do.
link |
You just do the simple experiment of taking,
link |
for instance, an orange, you smell it,
link |
try and gauge your level of perception
link |
of how orangish it smells or lemony, lemony-ish, lemony?
link |
I don't know, is it lemony-ish or lemony?
link |
Lemony, it smells, then set it away,
link |
do 10 or 15 inhales, followed by exhales, of course,
link |
or just through the nose, not going to do all 10 or 15,
link |
and then smell it again,
link |
and you'll notice that your perception of that smell,
link |
the kind of richness of that smell
link |
will be significantly increased.
link |
And that's, again, for two reasons.
link |
One, the brain is in a position to respond to it better.
link |
Your brain has been aroused by the mere act of sniffing,
link |
but also the neurons that respond to that lemon odor,
link |
that lemony or odor, are going to respond better.
link |
So you can actually have a heightened experience
link |
of something, and that, of course,
link |
will also be true for the taste system.
link |
You also can really train your sense of smell
link |
to get much, much better.
link |
When Noam Sobel's group was at Berkeley,
link |
I happened to be a graduate student around that time,
link |
and every once in a while, I'd look outside,
link |
and there would be people crawling around on the grass
link |
with goggles on, gloves on, and these hoods on,
link |
with earmuffs, and they looked ridiculous.
link |
But what they were doing is they were actually learning
link |
to follow scent trails.
link |
So in the world of dogs, you have sight hounds
link |
that use their eyes in order to navigate and find things,
link |
and you have scent hounds that use their nose.
link |
And the scent hounds are remarkable.
link |
They can be trained to detect a scent.
link |
These are the sniffing, the bomb sniffing
link |
and the drug sniffing dogs in airports.
link |
There are now dogs, actually,
link |
that can sniff out COVID infections
link |
with a very high degree of accuracy.
link |
They can be trained to that.
link |
There's something about the COVID and similar infections
link |
that the body produces probably in the immune response,
link |
some odors, and the dogs are, I think,
link |
as high as 90%, in some cases,
link |
maybe even 95% accuracy, just remarkable.
link |
There are theories that dogs can sniff out cancer.
link |
This stuff all exceeds statistical significance.
link |
It's still a little bit mysterious in some ways,
link |
but you may not ever achieve
link |
the olfactory capabilities of a scent hound,
link |
but what Noam Sobel's lab did is they had people
link |
completely eliminate their visual experience
link |
by having them wear dark glasses or goggles.
link |
So they couldn't see and they couldn't hear.
link |
They couldn't sense anything with their sense of touch.
link |
They had thick gloves on, but they had these masks on
link |
where just their nasal passages were open.
link |
And people could, in a fairly short amount of time,
link |
learn to follow a chocolate scent trail on the ground,
link |
which is not something that most people want to do.
link |
But what they showed using brain imaging, et cetera,
link |
in subsequent studies is that the human brain,
link |
you can learn to really enhance your sense of smell
link |
and become very astute in distinguishing
link |
whether or not one particular odor or combinations of odors
link |
is such that it's less than or more than
link |
a different odor, for instance.
link |
Now, why would you want to do this?
link |
Well, if you like to eat as much as I do,
link |
one of the things that can really enhance
link |
your sense of pleasure from the experience
link |
of ingesting food is to enhance your sense of smell.
link |
And if you don't have a great sense of smell,
link |
or if you have a sense of smell that's really so good
link |
that it's always picking up bad odors,
link |
we'll talk about that in a minute,
link |
well, then you might want to tune up your sense of smell
link |
by doing this practice of 10 or 15 breaths,
link |
excuse me, sniffs, not breaths,
link |
sniffs and then interacting with some food item
link |
or thing that you're interested in smelling more of.
link |
So these could be the ingredients that you're cooking with.
link |
I really encourage you to try and really smell them.
link |
You sometimes hear this as kind of a mindfulness practice,
link |
like, ooh, really smell the food, really taste the food.
link |
And we always hear about that as kind of a mindfulness
link |
and presence thing,
link |
but you actually can increase the sensitivity
link |
of your olfactory and your taste system by doing this.
link |
And it has long-term effects.
link |
That's what's so interesting.
link |
This isn't the kind of thing
link |
that you have to do every time you eat.
link |
You don't have to be the weirdo in the restaurant
link |
that's like picking up the radish
link |
and like jamming it up your nostrils.
link |
Please don't do that.
link |
You don't have to necessarily smell everything,
link |
although it's nice sometimes to smell the food
link |
that you're about to eat and as you eat it,
link |
but it has long-term effects in terms of your ability
link |
to distinguish and discriminate different types of odors.
link |
And these don't even have to be very pungent foods,
link |
The studies show that it doesn't have to be
link |
some really stinky cheese.
link |
There are cheese shops that I've walked into
link |
where like, I just basically gag, I can't handle it.
link |
I just can't be in there.
link |
It just overwhelms me.
link |
Other people, they love that smell.
link |
So you have to tune it to your interest and experience,
link |
but I think even for you Fasters out there,
link |
everybody eats at some point.
link |
Everybody ingests chemicals through their mouth.
link |
And one of the ways that you can powerfully increase
link |
your relationship to that experience
link |
and make it much more positive
link |
is through just the occasional practice
link |
of 10 or 15 sniffs of nothing,
link |
which almost sounds ridiculous.
link |
Like how could that be?
link |
But now you understand why.
link |
It's because of the way that the sniffing action
link |
increases the alertness of the brain,
link |
as well as increasing the sensitivity of the system.
link |
No other system that I'm aware of in our body
link |
is as amenable to these kinds of behavioral training shifts
link |
and allow them to happen so quickly.
link |
I would love to be able to tell you
link |
that just doing 10 or 15 near far exercises with a pen
link |
or going outside for 10 or 15 seconds each morning
link |
is going to completely change the way that you see the world
link |
but it actually isn't the case.
link |
You actually, it requires more training,
link |
a little bit more effort in the visual system.
link |
In the olfactory system, in your smell system,
link |
and in your taste system,
link |
just the tiniest bit of training and attention
link |
and sniffing, inhaling can radically change
link |
your relationship to food
link |
such that you actually start to feel very different
link |
as a consequence of ingesting those foods,
link |
as well as becoming more discerning about which foods
link |
you like and which ones you don't like.
link |
And we're going to talk about that
link |
because there's a really wonderful thing that happens
link |
when you start developing a sensitive palate
link |
and a sensitive sense of smell
link |
in a way that allows you to guide your eating
link |
and smelling decisions
link |
and maybe even interpersonal decisions
link |
about who you spend time with or mate with or whatever
link |
in a way that is really in line with your biology.
link |
In fact, how well we can smell and taste things
link |
is actually a very strong indication of our brain health.
link |
Now that's not to say that if you have a poor sense of smell
link |
or a poor sense of taste that you're somehow brain damaged
link |
or you're going, you're going to have dementia.
link |
Although sometimes early signs of dementia
link |
or loss of neurons in other regions of the brain
link |
related to say Parkinson's can show up first
link |
as a loss of sense of smell.
link |
Again, it's not causal and it's certainly not the case
link |
that every time you have a sudden loss of smell
link |
that there's necessarily brain damage.
link |
I want to be very clear about that,
link |
but they are often correlated.
link |
There's also a lot of interest right now
link |
in loss of sense of smell
link |
because one of the early detection signs of COVID-19
link |
was a loss of sense of smell.
link |
So I just briefly want to talk about loss of sense of smell
link |
and regaining sense of smell and taste
link |
because these have powerful implications for overall health
link |
and in fact can indicate something about brain damage
link |
and can even inform how quickly we might be recovering
link |
from something like a concussion.
link |
So our olfactory neurons, these neurons in our nose
link |
that detect odors are really unique among other brain neurons
link |
because they get replenished throughout life.
link |
They don't just regenerate, but they get replenished.
link |
So regeneration is when something is damaged and it regrows.
link |
These neurons are constantly turning over
link |
throughout our lifespan.
link |
They're constantly being replenished.
link |
They're dying off and they're being replaced by new ones.
link |
This is an amazing aspect of our brain
link |
that's basically unique to these neurons.
link |
There's one other region of the brain
link |
where there's a little bit of this maybe,
link |
but these olfactory neurons,
link |
about every three or four weeks, they die.
link |
And when they die, they're replaced by new ones
link |
that come from a different region of the brain,
link |
a region called the subventricular zone.
link |
The name isn't as important as the phenomenon,
link |
but these neurons are born in the ventricle,
link |
the area of your brain that's a hole that contains,
link |
it's not an empty hole,
link |
it's a hole basically that contains cerebral spinal fluid.
link |
Well, there's a little subventricular zone.
link |
There's a little zone below sub, the ventricles,
link |
and that zone, if you are exercising regularly,
link |
if your dopamine levels are high enough,
link |
those little cells there are like stem cells.
link |
They are stem cells and they spit out
link |
what are called little neuroblasts.
link |
Those little neuroblasts migrate
link |
into the front of your brain and then shimmy
link |
they kind of move through
link |
what's called the rostral migratory stream.
link |
They kind of shimmy along
link |
and land back in your olfactory bulb,
link |
settle down and extend little wires
link |
into your olfactory mucosa.
link |
This is an ongoing process of what we call neurogenesis
link |
or the birth of new neurons.
link |
Now, this is really interesting
link |
because other neurons in your cortex,
link |
in your retina, in your cerebellum, they do not do this.
link |
They are not continually replenished throughout life,
link |
but these neurons, these olfactory neurons are,
link |
And there are a number of things
link |
that seem to increase the amount
link |
of olfactory neuron neurogenesis.
link |
There is evidence that exercise, blood flow,
link |
can increase olfactory neuron neurogenesis,
link |
although those data are fewer in comparison
link |
to things like social interactions
link |
or actually interacting with odorants of different kinds.
link |
So if you're somebody who doesn't smell things well,
link |
you have a poor sense of smell,
link |
your olfactory system doesn't seem very sensitive,
link |
more sniffing, more smelling is going to be good.
link |
And then the molecule dopamine, this neuromodulator
link |
that is associated with motivation and drive,
link |
and in some cases, if it's very, very high with mania,
link |
or if it's very, very low with depression or Parkinson's,
link |
but for most people where dopamine
link |
is in essentially normal ranges,
link |
dopamine is also a powerful trigger
link |
of the establishment of these new neurons
link |
and their migration into the olfactory bulb
link |
and your ability to smell.
link |
Now, you don't want to confuse correlation with causation.
link |
So if you're not good at smelling,
link |
does that mean you have low dopamine?
link |
No, not necessarily.
link |
If you have low dopamine,
link |
does that mean that you have a poor sense of smell?
link |
No, not necessarily.
link |
Some people who take antidepressants of the sort
link |
that impact the dopamine system strongly,
link |
like, well, butrin, will report a sudden,
link |
meaning within a couple of days,
link |
increase in their ability to smell particular odors.
link |
And it's a very striking effect.
link |
Some people, when they are in a new relationship,
link |
because dopamine and the hormones testosterone and estrogen
link |
are associated with novelty and the sorts of behaviors
link |
that often are associated with new relationships,
link |
those three molecules, dopamine, testosterone, and estrogen,
link |
kind of work together and oftentimes people will say
link |
or report when they're newly in love
link |
or in a new relationship that they're just obsessed with
link |
or they just so enjoy the scent of another person,
link |
so much so that they like to borrow
link |
the other person's clothing
link |
or they'll sniff the other person's clothing,
link |
or they can even just, in the absence of the person,
link |
they can imagine their smell and feel a biological response,
link |
something that we'll talk more about.
link |
So these neurons turn over throughout the lifespan
link |
and as we age, we actually can lose our sense of smell.
link |
And it's likely, I want to underscore likely,
link |
that that loss of sense of smell as we age
link |
is correlated with a loss of other neurons
link |
in the retina, in the ear.
link |
So loss of vision, loss of hearing, loss of smell,
link |
loss of the sense apparati, which are neurons,
link |
is correlated with aging.
link |
So what we've been talking about today
link |
is the ability to sense these odors,
link |
but what I'd like to do is empower you with tools
link |
that will allow you to keep these systems tuned up.
link |
Last time, we talked about tuning up
link |
and keeping your visual system tuned up and healthy,
link |
regardless of age.
link |
Here, we're talking about really enhancing
link |
your olfactory abilities, your taste abilities,
link |
as well by interacting a lot with odors,
link |
preferably positive odors, and sniffing more,
link |
inhaling more, which almost sounds crazy,
link |
but now you understand why,
link |
even though it might sound crazy,
link |
it's grounded in real mechanistic biology
link |
of how the brain wakes up and responds to these chemicals.
link |
Now, speaking of brain injury, olfactory dysfunction
link |
is a common theme in traumatic brain injury
link |
for the following reason.
link |
These olfactory neurons, as I mentioned,
link |
extend wires into the mucosa of the nose,
link |
but they also extend a wire up into the skull,
link |
and they extend up into the skull
link |
through what's called the cribriform plate.
link |
It's like a Swiss cheese-type plate
link |
where they're going through,
link |
and if you get a head hit, that bone,
link |
the cribriform plate shears those little wires off,
link |
and those neurons die.
link |
Now, eventually, they'll be replaced,
link |
but there's a phenomenon by which concussion
link |
and the severity of concussion
link |
and the recovery from a head injury
link |
can actually be gauged in part, in part, not in whole,
link |
but in part by how well or fully
link |
one recovers their sense of smell.
link |
So if you're somebody
link |
that unfortunately has suffered a concussion,
link |
your sense of smell is one readout
link |
by which you might evaluate
link |
whether or not you're regaining
link |
some of your sensory performance.
link |
Of course, there will be others
link |
like balance and cognition and sleep, et cetera,
link |
but I'd like to refer you to a really nice paper
link |
Olfactory Dysfunction in Traumatic Brain Injury,
link |
the Role of Neurogenesis.
link |
The first author is Marin, M-A-R-I-N.
link |
The paper was published
link |
in Current Allergy and Asthma Report.
link |
I spent some time with this paper.
link |
It's a review article.
link |
I like reviews if they're peer-reviewed reviews
link |
and in quality journals.
link |
And what they discuss is,
link |
and I'll just read here briefly
link |
because they said it better than I could,
link |
olfactory functioning disturbances are common
link |
following traumatic brain injury, TBI,
link |
and can have a significant impact on the quality of life,
link |
although there's no standard treatment for patients
link |
with the loss of smell.
link |
Now I'm paraphrasing post-injury.
link |
Olfactory training has shown promise
link |
for beneficial effects.
link |
Some of this involves,
link |
they go on to tell us the role of dopamine,
link |
dopaminergic signaling, as I mentioned before.
link |
But what does this mean?
link |
This means that if you've had a head injury
link |
or repeated head injuries,
link |
that enhancing your sense of smell is one way
link |
by which you can create new neurons.
link |
And now you know how to enhance your sense of smell
link |
by interacting with things that have an odor very closely
link |
and by essentially inhaling more,
link |
focusing on the inhale to wake up the brain
link |
and to really focus on some of the nuance of those smells.
link |
So you might do, for instance, a smell test
link |
by which you smell something like a lemon,
link |
put it down, do 10 inhales or so, smell again, et cetera.
link |
You might also just take a more active role
link |
in trying to taste and smell your food
link |
and taste and smell various things.
link |
I mean, please don't ingest anything that's poisonous
link |
so that you're not supposed to be ingesting,
link |
but you know what I mean.
link |
Really tuning up this system,
link |
I think is an excellent review.
link |
We're going to do an entire episode
link |
all about the use of the visual system in particular,
link |
but also the olfactory system for treatment
link |
of traumatic brain injury, as well as other methods.
link |
But I wanted to just mention it here
link |
because a number of people asked me about TBI.
link |
And here again, we're in this place where the senses
link |
and our ability to sense these chemicals,
link |
so these two holes in the front of our face, our nostrils,
link |
is a powerful readout and way to control brain function
link |
and nervous system function generally.
link |
Just a quick note about the use of smelling salts.
link |
I have a feeling that some of you may be interested in that
link |
and its application.
link |
If you are interested in that,
link |
I recommend you go to the scientific literature first,
link |
rather than, you know, straight to some vendor
link |
or to the, what do they call it these days?
link |
Costello, bro science, he says, bro science,
link |
You can go to this paper, which is excellent
link |
and is real science,
link |
which is acute effects of ammonia inhalants
link |
on strength and power performance in trained men.
link |
It's a randomized control trial.
link |
It was published in the Journal
link |
of Strength and Conditioning Research in 2018,
link |
and it should be very easy to find.
link |
I will provide a link to the so-called PubMed ID,
link |
which is a string of numbers,
link |
and we'll put that in the caption
link |
if you want to go straight to that article.
link |
It does show a significant, what they call,
link |
this is what the words they use,
link |
literally in quotes, psyching up effect
link |
through the use of these ammonia inhalants
link |
and a significant increase in maximal force,
link |
in force development, in a variety of different movements.
link |
So for those of you that are interested
link |
in ammonia inhalants, so-called smelling salts,
link |
that might be a good reference.
link |
The other thing I wanted to talk about
link |
with reference to odors is this myth,
link |
which is that we don't actually smell things in our dreams,
link |
that we don't have a sense of smell.
link |
That's pure fiction.
link |
I don't know who came up with that.
link |
It's very clear that we are capable
link |
of smelling things in our sleep.
link |
However, when we are in REM sleep,
link |
rapid eye movement sleep,
link |
which is the sleep that predominates
link |
toward the second half of the night,
link |
our ability to wake up in response to odors is diminished.
link |
It's not absent, but it's diminished.
link |
If smoke comes into the room,
link |
we will likely wake up if the concentration of smoke
link |
is high enough, regardless of the stage of sleep we're in.
link |
But in REM sleep, we tend to be less likely
link |
to smell, to sniff.
link |
And that actually was measured in a number of studies
link |
that sniffing in sleep is possible.
link |
So if you put an odor like a lemon
link |
underneath someone's nostrils
link |
in the early portion of the night, they will smell.
link |
And they will later, they will sniff, excuse me,
link |
whether or not they smell or not,
link |
I guess depends on them and when they showered last,
link |
but they will definitely sniff.
link |
And they will report later,
link |
especially if you wake them up soon after,
link |
that they had a dream or a percept
link |
of the scent of a lemon, for instance.
link |
Later in the night,
link |
it's harder for that relationship to be established.
link |
It's likely that because of some of the paralysis
link |
associated with rapid eye movement, sleep,
link |
which is a healthy paralysis, so-called sleepatonia,
link |
you don't want to act out your dreams in REM sleep,
link |
that there is a less active tendency to sniff.
link |
And actually this has real clinical implications.
link |
The ability to sniff in response
link |
to the introduction of an odor is actually one way
link |
in which clinicians assess whether or not somebody's brain
link |
is so-called brain dead, that's not a nice term,
link |
but brain dead, or whether or not they have the capacity
link |
to recover from things like coma
link |
and other states of deep unconsciousness,
link |
or I guess you could call it subconsciousness.
link |
So what will happen is if someone has an injury
link |
and they're essentially out cold,
link |
the production of a sniffing reflex or a sniffing response
link |
to say a lemon or some other odor
link |
presented below the nostrils is considered a sign
link |
that the brain is capable of waking up.
link |
Now that's not always the case, but it's one indication.
link |
So just like you could use mechanosensation,
link |
so a toe pinch, for instance,
link |
or scraping the bottom of somebody's bare foot
link |
to see if they're conscious,
link |
or shining light in their eyes,
link |
these are all things that you've seen
link |
in movies and television,
link |
or maybe you've seen in real life as well.
link |
Well, odors and chemical sensing is another way
link |
by which you can assess whether or not
link |
the brain is capable of arousal.
link |
And actually olfactory stimulation
link |
is one of the more prominent ones
link |
that's being used in various clinics.
link |
As a last point about specific odors and compounds
link |
that can increase arousal and alertness,
link |
and this was simply through sniffing them,
link |
not through ingesting them.
link |
There are data, believe it or not,
link |
there are good data on peppermint
link |
and the smell of peppermint.
link |
Minty type scents, whether you like them or not,
link |
will increase attention,
link |
and they can create the same sort of arousal response,
link |
although not as intensely
link |
or as dramatically as ammonia salts can, for instance.
link |
By the way, please don't go sniff real ammonia.
link |
You could actually damage your olfactory epithelium
link |
if you do that too close to the ammonia.
link |
If you're going to use smelling salts,
link |
be sure you work with someone
link |
or you know what you're getting and how you're using this.
link |
You can damage your olfactory pathway
link |
in ways that are pretty severe.
link |
You can also damage your vision.
link |
If you've ever teared up
link |
because you inhaled something that was really noxious,
link |
that is not a good thing,
link |
doesn't mean you necessarily cause damage,
link |
but it means that you have irritated the mucosal lining
link |
and possibly even the surfaces of your eyes.
link |
So please be very, very careful.
link |
Scents like peppermint, like these ammonia smelling salts,
link |
the reason they wake you up
link |
is because they trigger specific olfactory neurons
link |
that communicate with the specific centers of the brain,
link |
namely the amygdala and associated neural circuitry
link |
and pathways that trigger alertness of the same sort
link |
that a cold shower or an ice bath or a sudden surprise
link |
or a stressful text message would evoke.
link |
Remember, the systems of your body
link |
that produce arousal and alertness and attention
link |
and that cue you for optimal learning, AKA focus,
link |
those are very general mechanisms.
link |
They involve very basic molecules
link |
like adrenaline and epinephrine,
link |
same thing actually, adrenaline and epinephrine.
link |
The number of stimuli,
link |
whether it's peppermint or ammonia or a loud blast,
link |
the number of stimuli that can evoke
link |
that adrenaline response and that wake up response
link |
are near infinite.
link |
And that's the beauty of your nervous system.
link |
It was designed to take any variety of different stimuli,
link |
place them into categories
link |
and then evoke different categories
link |
of very general responses.
link |
Now you know a lot about olfaction
link |
and how the sense of smell works.
link |
Here's another experiment that you can do.
link |
I'll ask you right now.
link |
Do you like, hate, or are you indifferent
link |
to the smell of microwave popcorn?
link |
Some people, including one member of my podcast staff,
link |
says it's absolutely disgusting to them.
link |
They feel like it's completely nauseating.
link |
I don't mind it at all.
link |
In fact, I kind of like it.
link |
I think the smell of microwave popcorn is kind of pleasant.
link |
I don't particularly like it,
link |
but it's certainly not unpleasant.
link |
Some people have a gene that makes them sensitive
link |
to the smell of things like microwave popcorn
link |
such that it smells like vomit.
link |
I probably don't have that gene
link |
because I find the smell of microwave popcorn
link |
Some people hate the smell of cilantro.
link |
Some people ingest asparagus,
link |
and when they urinate,
link |
they can smell the asparagus in a very pungent way.
link |
Other people can't smell it at all.
link |
These are variants in genes that encode
link |
for what are called olfactory receptors.
link |
Each olfactory sensory neuron expresses one odorant gene,
link |
one gene that codes for a receptor
link |
that responds to a particular odor.
link |
If you don't have that gene,
link |
you will not respond to that odor.
link |
So the reason why some people find
link |
the smell of microwave popcorn to be very noxious,
link |
putrid in fact, is because they have a gene
link |
that allows them to smell the kind of putrid odor
link |
Other people who lack that gene just simply can't smell it.
link |
So we are not all the same
link |
with respect to our sensory experience.
link |
What one person finds delicious,
link |
another person might find disgusting.
link |
I'll give a good example,
link |
which is that I absolutely despise gorgonzola and blue cheese
link |
I absolutely despise it.
link |
It smells and tastes like dirty moldy socks to me.
link |
Some people love it, they crave it.
link |
Actually, some people get a visceral response to it.
link |
And we will talk about how certain tastes
link |
can actually evoke very deep biological responses,
link |
even hormonal responses
link |
when we talk about taste in a few minutes.
link |
But there are these odors, for instance, in popcorn,
link |
it's the molecule 2-acetyl-1-pyroline,
link |
not proline, but pyroline,
link |
that gives off to some people like me a toasted smell
link |
as the sugars in the kernels heat.
link |
But the compound is also found
link |
in things like white bread and jasmine rice,
link |
which don't have as pungent an odor.
link |
But some people smell that and it smells like cat urine.
link |
Now there are scents like musky scents and musty scents
link |
that are secreted by animals like skunks
link |
and other animals of the so-called mustelid family.
link |
So these would be ferrets and other animals
link |
that can spray in response to fear,
link |
or if they just want to mark a territory
link |
because they want to say, that's mine.
link |
Dogs incidentally have scent glands
link |
that they rub on things, cats have them too.
link |
This musty odor, some people find actually quite pleasant.
link |
Some people find it to be very noxious.
link |
And that will depend, of course, on the concentration.
link |
I'll never forget the first time Costello
link |
got sprayed by a skunk and it was awful.
link |
I actually don't mind the smell of skunk at a distance.
link |
It's actually a little bit pleasant.
link |
I admit it's a little bit pleasant to me.
link |
I don't think that makes me too weird
link |
because have you ever read the book,
link |
"'All's Quiet on the Western Front' about World War I?"
link |
There's a description in there
link |
about the smell of skunk at a distance
link |
being mildly pleasant.
link |
So the author of that book probably shared
link |
a similar olfactory profile to me or I to them rather.
link |
But some people find even the tiniest bit
link |
of the smell of skunk or must to be noxious or awful.
link |
Now, of course, in high concentrations, it's really awful.
link |
And unfortunately, poor Costello,
link |
he was like literally red-eyed and just snorting
link |
There's a joke about dogs that says that dogs
link |
either get skunked one time and never again
link |
or 50 or 100 times.
link |
Costello has been skunked no fewer, I'm not making this up,
link |
has been skunked no fewer than 103 times.
link |
And that's because if he sees something
link |
or hears something in the bushes,
link |
he just goes straight in, he does not learn.
link |
But if you like the musty scent or musky scent,
link |
well, that says something about the genes
link |
that you express in your olfactory neurons.
link |
It is completely inherited.
link |
And if you don't like that scent, if it's really noxious
link |
or you have this response to microwave popcorn,
link |
well, that means you have a different complement,
link |
a different constellation, if you will,
link |
of genes that make up for these olfactory sensory neurons
link |
and the receptors that they express.
link |
Let's talk about taste.
link |
Not whether or not you have taste or you don't have taste,
link |
there's no way for me to assess that,
link |
but rather how we taste things,
link |
meaning how we sense chemicals in food and in drink.
link |
There are essentially five,
link |
but scientists now believe there may be six things
link |
that we taste alone or in combination.
link |
They are sweet tastes, salty tastes, bitter tastes,
link |
sour tastes, and umami taste.
link |
Most of you have probably heard of umami by now.
link |
Umami is actually the name for a particular receptor
link |
that you express on your tongue
link |
that detects savory tastes.
link |
So it's the kind of thing in braised meats.
link |
Sometimes people can even get the activation of umami
link |
by tomatoes or tomato sauces.
link |
What are each of these tastes
link |
and taste receptors responsible for?
link |
And then we'll talk about the sixth.
link |
Maybe you can guess what it is.
link |
I don't know if you can guess it now.
link |
I couldn't guess it, but of the five tastes,
link |
each one has a specific utility or function.
link |
Each one has a particular group of neurons in your mouth,
link |
in your tongue, believe it or not,
link |
that responds to particular chemicals
link |
and particular chemical structures.
link |
It is a total myth, complete fiction,
link |
that different parts of your tongue
link |
harbor different taste receptors.
link |
You know, that high school textbook diagram
link |
that sweet is in one part of the tongue
link |
and sour is in another and bitter is in another,
link |
complete fiction, just total fiction
link |
related to very old studies that were performed
link |
in a very poorly controlled way.
link |
No serious biologist,
link |
and certainly no one that works on taste,
link |
would contend that that's the way
link |
that the taste receptors are organized.
link |
They are completely intermixed along your tongue.
link |
If you have heightened or decreased sensitivity
link |
to one of those five things I mentioned,
link |
sweet, salty, bitter, umami, or sour,
link |
at one location in your tongue,
link |
it likely reflects the density of overall receptors
link |
or something going on in your brain,
link |
but not the differential distribution of those receptors.
link |
So the sweet receptors are neurons that express a receptor.
link |
That respond to sugars.
link |
In the same way that you have cones,
link |
photoreceptors in your eye that respond to short,
link |
medium, or long wavelength light,
link |
meaning bluish, greenish, or reddish light,
link |
you have a neuron in, or neurons, plural, in your tongue
link |
that respond to sugars.
link |
And then those neurons, they don't say sweet.
link |
They don't actually send any sugar into the brain.
link |
They send what we call a volley,
link |
a barrage of action potentials of electrical signals
link |
off into the brain.
link |
It's an amazing system.
link |
So all these receptors in your tongue
link |
make up what are called the neurons
link |
that give rise to a nerve,
link |
a collection of wires, nerve bundles
link |
of what's called the gustatory nerve.
link |
It goes from the tongue
link |
to the so-called nucleus of the solitary tracts.
link |
And some of you requested names.
link |
I usually don't like to include too many names
link |
for sake of clarity,
link |
but the gustatory nerve from the tongue
link |
goes to the nucleus of the solitary tract,
link |
and then to the thalamus, and to insular cortex.
link |
You don't have to remember any of those names
link |
if you don't want to,
link |
but if you want mechanism, you want neural circuits,
link |
that's the circuit.
link |
Gustatory nerve from the tongue,
link |
nucleus of the solitary tract in the brainstem,
link |
then the thalamus, and then insular cortex.
link |
And it is an insular cortex,
link |
this region of our cortex that we sort out
link |
and make sense of and perceive the various tastes.
link |
Now, it's amazing because just taking a little bit of sugar
link |
or something sour, like a little bit of lemon juice,
link |
and touching it to the tongue within 100 milliseconds,
link |
right, just 100 milliseconds, far less than one second,
link |
you can immediately distinguish,
link |
ah, that's sour, that's sweet, that's bitter, that's umami.
link |
And that's an assessment that's made by the cortex.
link |
Now, what do these different five receptors encode for?
link |
Well, sweet, salty, bitter, umami, sour,
link |
but what are they really looking for?
link |
What are they sensing?
link |
Well, sweet stuff signals the presence of energy, of sugars.
link |
And while we're all trying,
link |
or we're told that we should eat less sugar
link |
for a variety of reasons,
link |
the ability to sense whether or not a food
link |
has rapid energy source
link |
or could give rise to glucose is essential,
link |
so we have sweet receptors.
link |
The salty receptors, these neurons,
link |
are trying to sense whether or not there are electrolytes
link |
in a given food or drink.
link |
Electrolytes are vitally important
link |
for the function of our nervous system
link |
and for our entire body.
link |
Sodium is what allows neurons to fire,
link |
what allows them to be electrically active.
link |
We also need potassium and magnesium.
link |
Those are the ions that allow the neurons to be active.
link |
So the salty receptors, the reason that they are there
link |
is to make sure that we are getting enough,
link |
but not too much salt.
link |
We don't want to ingest things that are far too salty.
link |
Bitter receptors are there to make sure
link |
we don't ingest things that are poisonous.
link |
How do I know this?
link |
How can I say that?
link |
Even though I was definitely not consulted
link |
at the design phase, how can I say that?
link |
Well, the bitter receptors create a,
link |
what we call labeled line,
link |
a unique trajectory to the neurons of the brainstem
link |
that control the gag reflex.
link |
If we taste something very bitter,
link |
it automatically triggers the gag reflex.
link |
Now, some people like bitter taste.
link |
I actually like the taste of bitter coffee.
link |
Children generally like sweet tastes
link |
more than bitter tastes,
link |
but even babies, if they taste something bitter,
link |
they'll just immediately spit it up
link |
as like the gag reflex.
link |
Putrid smells will also evoke these same neurons.
link |
So some people are very sensitive.
link |
They have a very sensitive or low threshold vomit reflex.
link |
There was somebody in my lab early on.
link |
We never did this intentionally.
link |
We were just laughing because it was so dramatic.
link |
We would have a discussion.
link |
Someone would say something about something kind of gross,
link |
appropriate for the workplace, but nonetheless gross.
link |
We are biologists.
link |
We'd say something and they would say,
link |
stop, stop, stop, I'm going to throw up, you know?
link |
And some people have a very low threshold,
link |
Other people don't.
link |
Other people have a very stable stomach.
link |
They don't, you know, they rarely, if ever, vomit.
link |
The umami receptor isn't sensing savory
link |
because the body loves savory.
link |
It's because savory is a signal
link |
for the presence of amino acids.
link |
And we'll talk more about this,
link |
but the presence of amino acids in our gut
link |
and in our digestive system
link |
and the presence of fatty acids is essential.
link |
There is in fact, no essential carbohydrate or sugar.
link |
Now I'm not a huge proponent of ketogenic diets,
link |
nor am I against them.
link |
I think it's highly individual.
link |
You have to decide what's right for you,
link |
but everybody needs amino acids to survive.
link |
The brain needs them and we need fatty acids,
link |
especially to build a healthy brain during development.
link |
You need amino acids and fatty acids.
link |
And the sour receptor, why would we have a sour receptor
link |
so that we could have those really like sour candies?
link |
I think they've gotten more and more sour over the years.
link |
I admit I don't eat candy much,
link |
but I do have a particular weakness
link |
for like a really good, really sour, like gummy peach.
link |
Or if the gummy cherries are dipped
link |
in whatever that sour powder.
link |
So I was a kid who, I admit it,
link |
I liked the liquor made thing.
link |
I like drink the powder.
link |
Please don't do this.
link |
Don't give this garbage to your kids.
link |
But sour receptors are not there
link |
so that you can ingest gummy, sour gummy peaches
link |
or something like that.
link |
That's not why the system evolved.
link |
It's there and we know it's there
link |
to detect the presence of spoiled or fermented food.
link |
Fermented fruit has a sour element to it.
link |
And fermented things,
link |
while certainly some fermented foods
link |
like sauerkraut and kimchi and things of that sort
link |
can be very healthy for us
link |
and are very healthy in reducing inflammation.
link |
There are great data on that.
link |
Pro quality microbiome, et cetera.
link |
Fermented fruit can be poisonous, right?
link |
Alcohols are poisonous in many forms to our system.
link |
And the sour receptor bearing neurons
link |
communicate to an area of the brainstem
link |
that evokes the pucker response.
link |
Closing of the eyes and essentially shutting of the mouth
link |
and cringing away.
link |
I think cringe is like a thing now my niece,
link |
whenever I seem to say something or do something,
link |
it's either an eye roll, a cringe or both in combination.
link |
So the sour, the sweet, the salty, the bitter
link |
and the umami system were not there
link |
so that we could have this wonderful pallet of foods
link |
that we enjoy so much.
link |
They'll allow us to do that,
link |
but they're there to make sure
link |
that we bring in certain things to our system
link |
and that we don't ingest other things.
link |
Now what's the sixth sense within the taste system?
link |
Not sixth sense generally, but within the taste system.
link |
What's this putative possible sixth receptor?
link |
I already kind of hinted at it
link |
when I talked about fatty acids.
link |
There are now data to support the idea,
link |
although there's still more work that needs to be done,
link |
that we also have receptors on our tongue that sense fat.
link |
And that because fat is so vital
link |
for the function of our nervous system
link |
and the other organs of our body,
link |
that we are sensing the fat content in food.
link |
Maybe this is why I can only eat half,
link |
but no less than half of a jar of almond butter
link |
or peanut butter in one sitting.
link |
I just can't, unless it's not salt,
link |
in which case it makes no sense to me,
link |
but it's remarkable how that texture
link |
and also the flavor, but that texture of fat,
link |
I am guilty and Costello is definitely guilty
link |
of eating pats of butter from time to time.
link |
I have no guilt about this.
link |
People eat pats of cheese.
link |
Why shouldn't we eat a pat of butter?
link |
If you think that's gross,
link |
then maybe I have greater abundance
link |
of the fat receptors in my tongue.
link |
Maybe I have a fat tongue than you do.
link |
But nonetheless, the ability to sense fat here in our mouth
link |
seems to be critical.
link |
You can imagine why that is.
link |
I want to talk about the tongue and the mouth
link |
as an extension of your digestive tract.
link |
I know that might not be pleasant to think about,
link |
but when you look at it through the lens
link |
that I'm about to provide,
link |
it will completely change the way you think
link |
about the gut brain and about all the stuff
link |
that you've heard in these recent years about,
link |
oh, you know, we have the second brain.
link |
It's all these neurons in our gut.
link |
I've been chuckling through these last few years
link |
as people have gotten so excited about the gut brain,
link |
not because of their excitement.
link |
I think their excitement is wonderful,
link |
but we always knew that the nervous system
link |
extended out of the brain and into the body.
link |
And people seem kind of overwhelmed and surprised
link |
by the idea that we have neurons in our gut
link |
that can sense things like sugars and fatty acids.
link |
And I think those are beautiful discoveries.
link |
Don't get me wrong.
link |
Diego Borges' lab out of Duke University
link |
has done beautiful studies showing
link |
that within the mucosal lining of our gut,
link |
we have neurons that sense fatty acids,
link |
sugars, and amino acids.
link |
And that when we ingest something
link |
that contains one or two or three of those things,
link |
there's a signal sent via the vagus nerve
link |
up into what's called the nodose ganglion, N-O-D-O-S-E,
link |
and then into the brain where it secretes dopamine,
link |
which makes us want more of that thing.
link |
It makes us more motivated to pursue
link |
and eat more of that thing
link |
that's either fatty or umami, it's savory,
link |
or has a sweet taste,
link |
any one or two or three of those qualities,
link |
independent of the taste.
link |
Now, I think those are beautiful data,
link |
but we know that this thing, the mouth,
link |
for those of you listening,
link |
I've got a couple fingers in my mouth.
link |
That's why I sound like I'm on something in my mouth.
link |
This thing in the front of our face,
link |
we use it for speaking,
link |
but it is the front of our digestive tract.
link |
We are essentially a series of tubes,
link |
and that tube starts with your mouth
link |
and heads down into your stomach.
link |
And so that you would sense
link |
so much of the chemical constituents of the stuff
link |
that you might bring into your body
link |
or that you might want to expel
link |
and not swallow or not interact with
link |
by being able to smell it.
link |
Does it smell good?
link |
Does it taste good?
link |
Is it so sour that it's fermented and is going to poison me?
link |
Is it so bitter that it could poison me?
link |
Is it so savory that, mm,
link |
yes, I want more and more of this?
link |
Well, then you'd want to trigger dopamine.
link |
That's all starting in the mouth.
link |
So you have to understand that you were equipped
link |
with this amazing chemical sensing apparatus
link |
we call your mouth and your tongue.
link |
And those little bumps on your tongue
link |
that they call the papillae,
link |
those are not your taste buds.
link |
Surrounding those little papillae,
link |
like little rivers,
link |
are these little dents and indentations.
link |
And what dents and indentations do in a tissue
link |
is they allow more surface area.
link |
They allow you to pack more receptors.
link |
So down in those grooves are where all these little neurons
link |
and their little processes are with these little receptors
link |
for sweet, salty, bitter, umami, sour,
link |
and maybe fat as well.
link |
So it's this incredible device
link |
that you've been equipped with
link |
that you can use to interact with various components
link |
of the outside world
link |
and decide whether or not you want to bring them in or not.
link |
Just as you can lose those olfactory neurons
link |
if you happen to get hit on the head
link |
or you have some other thing,
link |
maybe it was an infection
link |
that caused loss of those olfactory sensory neurons,
link |
you can also lose taste receptors in your mouth.
link |
If you've ever eaten something that's too hot,
link |
not spicy hot, but too hot,
link |
you burn your tongue, you burn receptors.
link |
It takes about a week to recover those receptors.
link |
For some people, it's a little bit more quickly,
link |
but if you burn your tongue badly
link |
by ingesting a soup that's too hot
link |
or a beverage that's too hot,
link |
you will greatly reduce your sense of taste
link |
for essentially all tastes.
link |
And that's because those neurons sit very shallow
link |
beneath the tongue's surface
link |
and so that if you put something too hot on it,
link |
you literally just burn those neurons away.
link |
Luckily, those neurons also can replenish themselves.
link |
Those neurons are of the peripheral nervous system
link |
and like all peripheral system neurons,
link |
they can replenish or regenerate.
link |
So if you burn your mouth in about a week or so,
link |
hopefully sooner, you'll be able to taste again.
link |
In fact, everybody's ability to taste
link |
is highly subject to training.
link |
You can really enhance your ability to taste
link |
and taste the different component parts of different foods
link |
simply by paying attention to what you're trying to taste.
link |
This is an amazing aspect of the taste system.
link |
I think more than any other system,
link |
the taste system and perhaps the smell system as well
link |
can be trained so that you can learn
link |
to pick out the tones, if you will,
link |
of different ice cream or different beverages.
link |
Somebody who, I don't drink much alcohol,
link |
I occasionally have a drink or something,
link |
but a while ago I got to taste
link |
a bunch of different white tequilas.
link |
These are different kinds of tequilas that are,
link |
they're not brown, they're white.
link |
And I sort of assumed that all tequila was disgusting.
link |
That was my assumption before doing this.
link |
And then I tasted a couple of white tequilas
link |
and I realized, oh, those aren't too bad.
link |
I tasted a few more.
link |
And then pretty soon I could really start
link |
to detect the nuance and the difference.
link |
Now, I haven't had a tequila in a long time now.
link |
I sort of tend to not drink it all these days.
link |
But in a very short period of time, like a couple of days,
link |
I got very good at detecting which things I liked
link |
and I could start to pick out tones.
link |
So I'm not a wine drinker, but for those of you that are,
link |
you hear about, oh, it has floral tones
link |
or berry tones or chocolate tones.
link |
Some of that is just kind of menu based
link |
and kind of marketing based silliness
link |
designed to get you excited
link |
about what you're about to ingest.
link |
But some of it is real.
link |
And for people that are skilled in assessing wines
link |
or assessing foods, much more of an eater than a drinker,
link |
you can really start to develop a sensitive palette,
link |
a nuanced palette through what we call top-down mechanisms.
link |
This olfactory cortex that takes these five,
link |
maybe the sixth fat receptor two information
link |
and tries to make sense of what's out there in the world
link |
and what its utility is.
link |
Is it good? Is it bad?
link |
Do I want more of it or less than it?
link |
That neural circuitry is unlike other neural circuitry
link |
in that it seems very amenable to behavioral plasticity
link |
for whatever reason.
link |
And we could talk about what those reasons might be.
link |
It's interesting sometimes to think about
link |
how your taste literally, chemical taste,
link |
is probably very different than that of other people.
link |
How a food tastes to you is probably very different
link |
than how it tastes to somebody else.
link |
The same probably cannot be said
link |
of something like vision or hearing,
link |
unless you're somebody who has perfect pitch
link |
or your color vision is disrupted or you're a mantis shrimp.
link |
Chances are, when you look at the same object,
link |
two people are seeing more or less the same object
link |
or perceiving it in a very similar way.
link |
There are experiments that essentially establish that.
link |
Now, we have taste receptors
link |
and a lot of those taste receptors,
link |
their chemical structures are known.
link |
They come with fancy names like the T1R1 or the T1R2,
link |
which were identified as the sweet and umami receptor.
link |
So what's interesting is that this umami flavor
link |
is the savory flavor, rather,
link |
that's sensed by umami receptors is very close
link |
to the receptor that detects sweet things.
link |
Similarly, bitter is sensed
link |
by a whole other set of receptors.
link |
Now, there's a fun naturally occurring experiment
link |
that will forever change the way that you look at animals
link |
and the way certainly that I think about dogs
link |
and Costello in particular.
link |
Carnivorous large animals like tigers
link |
and some grizzly bears, for instance,
link |
we know that they have no ability to detect sweet.
link |
They don't actually have the receptors
link |
for detecting sweet on their tongue,
link |
but their concentration of umami receptors,
link |
of their ability to detect savory
link |
is at least 5,000 times that which it is in humans.
link |
In other words, if I eat a little piece of steak
link |
or Costello eats a little piece of steak,
link |
that steak probably tastes much, much more savory
link |
than it does to me.
link |
So dogs and tigers and bears, et cetera,
link |
they're going to taste savory things and smell savory things
link |
with a much higher degree of sensitivity,
link |
but they can't taste sweet things.
link |
Other large animals, which are mostly herbivores,
link |
like the panda bear, for instance,
link |
it's hard to believe that thing is even a bear.
link |
I got nothing against pandas.
link |
I just think that they get a little bit too much
link |
of the limelight, frankly.
link |
So no vendetta against panda, save the pandas.
link |
I hope they replenish all the pandas,
link |
but pandas in all their whatever have no umami receptors.
link |
They can't taste savory,
link |
but they have greatly heightened density of sweet receptors.
link |
So there they are eating these whatever bamboos all day
link |
or not bamboozle, but bamboos all day.
link |
And they can taste things that are very sweet
link |
with a much higher degree of intensity.
link |
And in general, animals that are more gentle,
link |
more that are herbivores, excuse me,
link |
or animals that have the propensity for aggression,
link |
that's where you really see the divergence
link |
of the umami receptor,
link |
because it's associated with meat and amino acids,
link |
and where you see the enhancement of the sweet receptors
link |
for animals that eat a lot of plants and fruits.
link |
And they probably taste very different to them
link |
than they do to you and me.
link |
And so it's interesting to note that animals that eat meat,
link |
that eat other organisms,
link |
can actually extract more savory experience from that.
link |
What does this mean for you?
link |
All right, do you associate yourself
link |
as a tiger or a grizzly bear or a panda
link |
or a combination of both?
link |
Most people are omnivores.
link |
However, you may find it interesting
link |
that people that, for instance,
link |
eat a pure carnivore type diet or a keto diet
link |
where they are ingesting a lot of meats,
link |
so therefore are sensing a lot of umami flavors.
link |
And I realize not everyone who's keto eats meat,
link |
but those who do that will develop a more sensitive palette
link |
and likely, there are some data, although early data,
link |
craving for umami-like foods.
link |
Whereas people that eat a more plant-based diet
link |
are likely developing a heightened sensitivity
link |
and desire for, and maybe even dopamine response
link |
to sugars and plant-based foods.
link |
Now, this is my partial attempt to reconcile
link |
the kind of online battle that seems to exist
link |
between plant-based versus animal-based,
link |
purely plant-based or purely animal-based diets.
link |
I think most people are omnivores,
link |
but it's kind of interesting to think that the systems
link |
are plastic such that people might want more meat
link |
if they eat more meat.
link |
People might want more plants if they eat enough plants
link |
for a long period of time.
link |
And this might explain some of the chasm
link |
that exists between these two groups.
link |
Now, this is not to say anything about the ethical
link |
or the environmental impacts of different things.
link |
I don't even want to get into that
link |
because the meat people say that the plant-based diets
link |
have as much a negative impact
link |
as the plant people say that the meat-based diets.
link |
That's a totally different discussion.
link |
What I'm talking about here is food craving
link |
and food seeking, and one's ability to detect
link |
these umami savory flavors is going to be enhanced
link |
by ingesting more meat and less activation
link |
of the sweet receptor.
link |
So in other words, the more meat you eat,
link |
the more you're going to become like a tiger, so to speak.
link |
And the more that you avoid these umami flavors and meats,
link |
and the more that you would eat plant-based foods
link |
and in particular sweet foods,
link |
the more you will likely suppress that umami system
link |
and that you will have a heightened desire for,
link |
appetite for, and sensing of sweet foods
link |
or foods that contain sugars.
link |
What I'm about to tell you is going to seem crazy,
link |
but is extremely interesting
link |
with respect to taste and taste receptors.
link |
Remember, even though we can enjoy food
link |
and we can evolve our sense of what's tasty or not tasty,
link |
depending on life decisions, environmental changes, et cetera,
link |
the taste system, just like the olfactory system
link |
and the visual system was laid down for the purpose
link |
of moving towards things that are good for us
link |
and moving away from things that are bad for us.
link |
That's the kind of core function of the nervous system.
link |
Well, taste receptors are not just expressed on the tongue.
link |
They are expressed in other cells and other tissues as well.
link |
Some of you may be able to imagine foods
link |
that are so delicious to you
link |
that they make your entire body feel good.
link |
Or foods that are so horrifically awful to think about,
link |
let alone taste, that they create a whole body shuttering
link |
or kind of repellent type response
link |
where you just either cringe or turn your face away,
link |
even in the absence of that food.
link |
That's sort of how I feel about pungent Gorgonzola cheese.
link |
If you like Gorgonzola cheese, I don't judge you.
link |
I just, that's an individual difference.
link |
I happen to love certain foods.
link |
I do like savory foods very much.
link |
When I think about them, they just, they make me feel good.
link |
And I'm oftentimes not even associating
link |
with the taste of those foods.
link |
It feels almost like a visceral thing.
link |
Well, it turns out that some of the taste receptors
link |
extend beyond the tongue, that they actually can extend
link |
into portions of the gut and digestive system.
link |
And if that's not strange enough,
link |
turns out that some of the taste receptors
link |
are actually expressed on the ovaries and the testes.
link |
So what that means is that the gonads,
link |
the very cells and tissues and organs in our body
link |
that make up the reproductive axis
link |
are expressing taste receptors.
link |
Okay, so how do we interpret this?
link |
Does this mean that when you eat something
link |
that's very savory or very sweet, for instance,
link |
that it's triggering activation of the ovaries
link |
Well, it's possible.
link |
Now, how those molecules, those chemical molecules
link |
would actually get there isn't clear.
link |
The digestive tract does not run directly
link |
to the testes or to the ovaries.
link |
But nonetheless, what this means is that chemical sensing
link |
of the very things that we detect on our tongue
link |
and that we call taste in quotes, in food,
link |
is also evoking cellular responses
link |
within the reproductive gonads.
link |
Now, whether or not this underlies the positive association
link |
that we have with certain foods isn't clear,
link |
but I'd be remiss if I didn't point out the obvious,
link |
which is that the relationship
link |
between the sensual nature of particular foods
link |
and sensuality generally and the reproductive axis
link |
is something that's been covered in many movies.
link |
There are entire movies that are focused
link |
on the relationship between, for instance,
link |
chocolate and love and reproductive behaviors,
link |
or certain feasts of meat and their wonderful tastes
link |
and the kind of sensuality around feasts
link |
of different types of foods.
link |
But in general, it's the sweet and the savory.
link |
Rarely is it the sour or the bitter, the salty or the fat.
link |
And not surprisingly, perhaps,
link |
it is the T2Rs and the T1Rs,
link |
the receptors that are associated with the sweet
link |
and with the umami, the savory flavors
link |
that are expressed not just on the tongue
link |
and in portions of the digestive tract,
link |
but on the gonads themselves.
link |
So what does this mean?
link |
Does this mean that eating certain foods
link |
can stimulate the gonads?
link |
There's no data that immediately support that right now,
link |
but this is an emerging area.
link |
If you'd like to read more about this,
link |
there's a great review entitled Taste Perception
link |
from the Tongue to the Testes,
link |
although they do also talk about the ovaries.
link |
Why they didn't include that in the title
link |
is I think a reflection of the sort of bias of the author.
link |
The author, not incidentally, is Fang Li, last name Li.
link |
It's a very interesting paper
link |
published in Molecular Human Reproduction.
link |
You can find it easily online.
link |
It's downloadable.
link |
I'll also provide a link to it.
link |
I just think it's fascinating
link |
that these taste receptors are expressed in other tissues.
link |
And I should mention that they're expressed
link |
in tissues of other areas of the body as well,
link |
including the respiratory system,
link |
but the richest aggregation or concentration
link |
of these receptors for umami and sweet, of course,
link |
is on the tongue, but also on the gonads.
link |
And I think it does speak to the possible bridge
link |
between what we think of as a sensory
link |
or a sensual experience of food
link |
and the deeper kind of visceral sense within the gut
link |
and maybe even within the gonads as well
link |
of something that we find extremely pleasurable
link |
or even a repetitive that we want to move toward it.
link |
We are actually going to return to that general theme
link |
in the discussion about touch sensation.
link |
Some people, for instance, when they touch certain surfaces
link |
like furs or sheepskins or velvet or soft, smooth surfaces,
link |
it feels good elsewhere in their body,
link |
not just at the point of contact with that surface.
link |
And similarly, if there's the, how about this one,
link |
the screech of chalk on a chalkboard?
link |
It's a sound, but it has a very strong visceral component
link |
or sandpaper like fingers, fingernails on a chalkboard,
link |
not the sound, but the feeling, right?
link |
So our whole nervous system is tuned
link |
to either be drawn toward, appetitive,
link |
or repelled by aversive behaviors, right?
link |
So there's this push-pull that exists.
link |
And what I'm referring to in terms of these receptors
link |
on the tongue that are also expressed on the gonads
link |
is yet another example of what, at least in this case,
link |
seems to be an appetitive thing,
link |
a desire to move toward certain foods
link |
and maybe even the experiences
link |
that are associated with those foods.
link |
I want to talk about a particular aspect of food
link |
and a chemical reaction in cooking
link |
called the Maillard reaction.
link |
Some of you have probably heard of the Maillard reaction.
link |
It's spelled M-A-I-L-L-A-R-D.
link |
The D is silent, so don't call it the Maillard reaction.
link |
And it's not the Maillard reaction.
link |
It is the Maillard reaction.
link |
And the Maillard reaction is a reaction
link |
that for the aficionados is a non-enzymatic browning.
link |
The other form of non-enzymatic browning is caramelization.
link |
Although when you hear caramel, caramel,
link |
I think it's caramel, you think sweet.
link |
And indeed caramelization
link |
is a sugar, sugar chemical interaction
link |
that leads to a kind of nicely toasted,
link |
not burnt, but nicely toasted sweet taste.
link |
Whereas the Maillard reaction
link |
is that really savory reaction
link |
that occurs when you have a sugar amino acid reaction.
link |
Remember we have neurons in our gut,
link |
but also neurons in our tongue
link |
and neurons deep in the brain
link |
that are comparing the amount of sugar to savory, okay?
link |
And the Maillard reaction is very interesting.
link |
For you chemists out there,
link |
this is going to be way too elementary.
link |
And for you non-chemists,
link |
it's probably going to be a little bit of a reach,
link |
but just bear with me.
link |
All these chemicals that we sense
link |
have a different structure.
link |
It's like hydrogens and oxygens and aldehyde groups
link |
and all these things.
link |
And basically the Maillard reaction
link |
involves what's called a free aldehyde.
link |
If you didn't like chemistry, don't worry about it.
link |
It's basically got a group there that kind of sits open
link |
that allows it to interact with other things.
link |
And actually through the use of heat
link |
and the process that we call brazing,
link |
which I'll talk about in a moment,
link |
you create what's called a ketone group.
link |
Now, most people now have heard of ketones
link |
because they think about the ketogenic diet,
link |
but a ketone group is actually a chemical compound
link |
that can be used for energy.
link |
And that's why people say you can use ketones for energy.
link |
But if you've ever actually encountered ketones,
link |
if you, for instance, get liquid ketones, a ketone ester,
link |
and you smell it, what does it smell like?
link |
It smells a little bit like an alcohol,
link |
but it has a kind of savory taste,
link |
even when you smell it, okay?
link |
There are other smells that have these tastes too.
link |
But for the Maillard reaction,
link |
which could be created, for instance,
link |
like if you took a piece of meat
link |
or if you're not a meat eater,
link |
if you took tomatoes and you cooked them in a pan
link |
and you cooked it nice and slow till it simmered
link |
and almost started to brown and burn a little bit.
link |
Usually if I do it, it burns.
link |
I'm not a good cook, as Costello points out a lot.
link |
But it gets that like almost tangy,
link |
very umami-like flavor.
link |
And sometimes it will even stick to the pan
link |
if you scrape it off.
link |
It actually, you can taste it in your mouth
link |
as you're cooking it.
link |
That's the Maillard reaction.
link |
That's that free aldehyde group.
link |
And that's the production of a ketone group.
link |
When you smell ketones, it smells very much like that, okay?
link |
Some people talk about the ketones
link |
will produce like fruity breath.
link |
And that's true if people are really far into ketosis.
link |
Their breath has a kind of fruity odor.
link |
That's a little bit of a different thing.
link |
So the relationship between smell and taste
link |
is a very, very close one.
link |
And this is why when people drink wine,
link |
they often will inhale and then sip.
link |
Some of that is just kind of like
link |
pomp and circumstance, frankly.
link |
They make a big deal of it.
link |
But they can sense things with their mouth.
link |
The combination of odor receptors being activated
link |
in a particular way and taste receptors in the mouth
link |
being activated in a particular way
link |
triggers the activation of multiple brain areas
link |
that are associated with taste
link |
and circuitry within the body
link |
that's associated with the behaviors
link |
that relate to that taste, like leaning toward it
link |
or leaning away from it,
link |
depending on whether or not it's a pettative or aversive.
link |
So the Maillard reaction is a very interesting reaction
link |
involving this sugar amino acid thing.
link |
But really what it's doing is heating up food
link |
such that the amino acids are more available,
link |
literally in their chemical form
link |
for detection by the neurons.
link |
This is a phenomenon that occurs in other domains
link |
of the taste system.
link |
For instance, a lot of what's happened
link |
with highly processed foods
link |
is that manufacturers have figured out
link |
how to trigger more dopamine response
link |
by ingestion of these sugary foods
link |
and created textures
link |
and created essentially design of foods for two purposes.
link |
I'm not out to completely demonize processed foods.
link |
I did that in a previous episode,
link |
but processed foods are really designed
link |
to take foods that ordinarily would spoil,
link |
that would have a shelf life and extend their shelf life
link |
to turn foods, which are not a commodity into a commodity.
link |
Something could be stored and used essentially
link |
as a tradable, purchasable, sellable resource.
link |
In doing that, they've also decided to change the texture
link |
so that you want to chew more of them.
link |
Like I have this thing,
link |
I don't know what it is for those Triscuit crackers.
link |
I don't know, why are those things so good?
link |
It's probably the texture, those layers,
link |
they're just kind of perfectly salty.
link |
Haven't had one in a long time,
link |
so I bet if I had one now,
link |
it wouldn't taste as good as I'm imagining it.
link |
But those combinations of texture, smell, and taste
link |
are what combine to activate these different brain areas
link |
that make you really want to desire something.
link |
And the people who make foods, processed foods in particular,
link |
are phenomenally good at figuring out
link |
what drives the dopamine system
link |
and makes you want more of these things,
link |
either because of the way they taste
link |
and or because of the way they trigger neurons in your gut
link |
that have nothing to do with taste
link |
that simply make you desire more of the food.
link |
In other words, many of the foods that are processed foods
link |
make you desire more of them,
link |
it's impossible to eat one chip kind of thing,
link |
not because they taste good, but because in your gut,
link |
they're activating the neurons that activate dopamine,
link |
which make you seek more of those foods,
link |
independent of blood sugar or anything else.
link |
So you may actually be eating more particular foods,
link |
not because they taste good,
link |
but because they feel good on your tongue and mouth,
link |
and because the neurons in your gut,
link |
which are totally independent of conscious taste,
link |
are triggering the release of dopamine,
link |
which is a molecule that makes you seek more of
link |
and do more of anything that led
link |
to the ingestion of that food.
link |
There's a fun experiment that you can do,
link |
which is to completely invert your sense of sweet and sour.
link |
There's actually a way to do this readily.
link |
When I was a postdoc,
link |
I used to have a journal club at my house,
link |
people would come over in the evening once a month,
link |
and we would read a paper,
link |
typically the weirdest paper we could find,
link |
and we would eat food and hang out,
link |
as the nerds did and do for fun.
link |
So that's what we did.
link |
And one time someone brought what's called miracle berry.
link |
Okay, so this isn't some psychedelic plant medicine thing.
link |
Miracle berry you can purchase online,
link |
it's relatively inexpensive.
link |
It actually causes a change in the configuration
link |
of taste receptors, such that when you eat something sour,
link |
And so what's really wild is you ingest miracle berry,
link |
and then you bite into a lemon, maybe even the lemon peel,
link |
and it tastes as sweet as a peach.
link |
And this effect lasts several hours.
link |
Definitely check any warnings,
link |
I don't know what sort of warnings the miracle berry carries,
link |
but I'm sure there's always something you can imagine.
link |
There are a number of papers on miracle berry,
link |
or miracle fruit it's called,
link |
but it changes your perception of sour
link |
at a perceptual level,
link |
but it does that by changing the activity of the receptors
link |
in the mouth and tongue.
link |
Now, this is important as a principle,
link |
and it's underscored by experiments that have been done
link |
by, for instance, Charles Zucker's lab
link |
at Columbia University,
link |
where they've essentially genetically engineered animals
link |
such that the bitter receptor is swapped
link |
with the sweet receptor,
link |
or the sweet receptor is swapped with the bitter receptor.
link |
And what they show is that the actual food,
link |
the experience on the tongue,
link |
drives different pathways in the brain.
link |
Here's what they did.
link |
They essentially took mice and swapped out the sweet receptor
link |
and put in a bitter receptor.
link |
And then what they found is that,
link |
whereas normally mice would actively seek out
link |
and even work for sugar water, sucrose,
link |
they really liked that,
link |
if they replace the sweet receptor with the bitter receptor,
link |
the mice would avoid sugar water.
link |
And the reverse was also true,
link |
that mice would drink a bitter solution avidly,
link |
they liked a bitter solution,
link |
if they swapped out the bitter receptor for sweet receptor.
link |
What this means is that our entire experience
link |
of what we taste is dependent on how we experience
link |
that taste at the level of the tongue.
link |
And so you're hopefully not going to do genetic engineering
link |
of your taste receptors,
link |
but if you'd like to do this sort of experiment,
link |
you actually can do it very easily using miracle fruit,
link |
the instructions of how much to ingest, et cetera.
link |
Any safety concerns are usually on the package
link |
and should be easy to find.
link |
And there's a lot of science to support how this works.
link |
It's kind of a fun experiment that anyone can do
link |
and will completely change your perception
link |
of any food that you're accustomed to eating.
link |
In fact, you can figure out how much sweet
link |
or the sense of sweetness is contributing
link |
to your experience of a food,
link |
even if you don't think of that as a sweet food
link |
through this miracle fruit experiment.
link |
You could take miracle fruit,
link |
you could eat a slice of pepperoni pizza or cheese pizza,
link |
which perhaps normally to you would taste just like pizza.
link |
And you'll notice it tastes very different.
link |
What you are detecting is how much the sense of sweet
link |
was contributing to that particular flavor.
link |
Now I'd like to return to pheromones.
link |
So I mentioned earlier,
link |
true pheromonal effects are well-established in animals.
link |
And one of the most remarkable pheromone effects
link |
that's ever been described is one
link |
that actually I've mentioned before on this podcast,
link |
but I'll mention again just briefly,
link |
which is the Coolidge effect.
link |
The Coolidge effect is the effect
link |
of a male of a given species.
link |
In most cases, it tended to be a rodent or a rooster mating,
link |
and at some point reaching exhaustion
link |
or the inability to mate again
link |
because they just simply couldn't for whatever reason.
link |
The Coolidge effect establishes that if you swap out
link |
the hen with a new hen or the female rat or mouse
link |
with a new one, then the rat or the rooster
link |
spontaneously regains their ability to mate.
link |
Somehow their vigor is returned,
link |
the refractory period after mating that normally occurs
link |
is abolished and they can mate again.
link |
Turns out that the Coolidge effect
link |
runs in the opposite direction too.
link |
I did not know this, but I recently learned of a study.
link |
It was actually done in hamsters, not in mice,
link |
but it turns out that females also will,
link |
female rodents will mate to exhaustion.
link |
And at some point, excuse me,
link |
they will refuse to mate any longer
link |
unless you swap in a new male.
link |
And then because mating in rodents
link |
involves the female being receptive,
link |
there are a certain number of behaviors
link |
that mean that she, that tell you that she's willing
link |
and wanting to mate, so-called lordosis reflex.
link |
Then if there's a new male,
link |
she will spontaneously regain the lordosis reflex
link |
and the desire to mate.
link |
And how do you know this?
link |
How do we know it's a pheromonal effect?
link |
Well, this recovery of the desire and ability to mate,
link |
both in males and in females,
link |
can be evoked completely by the odor
link |
of a new male or female.
link |
It doesn't even have to be the presentation
link |
of the actual animal.
link |
And that's how you know that it's not some visual interaction
link |
or some other interaction, it's a pheromonal interaction.
link |
Now, as I mentioned earlier, pheromonal effects,
link |
humans have been debated for a long period of time.
link |
We are thought to have a vestigial,
link |
meaning a kind of shrunken down
link |
miniature accessory olfactory bulb
link |
called Jacobson's organ or the vomeronasal organ.
link |
Some people don't believe that Jacobson's organ exists.
link |
There is anatomical evidence for it in some cadavers.
link |
It sits not very high up in the brain
link |
or where your olfactory bulb is,
link |
but it's actually in the nasal passages.
link |
So there's like little dents
link |
as you go up through your nasal passages.
link |
And there is evidence of something that's vomeronasal-like.
link |
Vomeronasal is the pheromonal organ.
link |
They call it Jacobson's organ if it's present in humans,
link |
kind of tucked into some of the divots in the nasal passage.
link |
Even if that organ, Jacobson's organ, isn't there
link |
or is not responsible for the chemical signaling
link |
between individuals, there is chemical signaling
link |
between human beings.
link |
As I mentioned earlier, the effect of tears
link |
in suppressing the areas of the brain
link |
that are involved in sexual desire and testosterone of males.
link |
That's a concrete result.
link |
It's a very good result published by an excellent group
link |
with no preexisting bias going in.
link |
That's just what they found.
link |
There is also evidence both for and against
link |
chemical signaling between females
link |
in terms of synchronization of menstrual cycles.
link |
Now, the original paper on this was published in the 1970s
link |
And it essentially said that when women live together
link |
in group housing dormitories and similar,
link |
that their menstrual cycles were synchronized
link |
and that was due to what was hypothesized
link |
to be pheromonal effects.
link |
Over the years, that study has been challenged
link |
The more recent data points to the idea
link |
that there is chemical signaling between women
link |
in ways that impact the timing of the menstrual cycle,
link |
but that depending on whether or not some of the women
link |
are in the ovulation phase,
link |
the ovulatory phase of that cycle,
link |
or whether or not they are in the follicular phase,
link |
the phase when the follicle is maturing
link |
before the egg actually ovulates.
link |
So two separate phases of the 28 day menstrual cycle
link |
will either lengthen or shorten the menstrual cycle
link |
of the person that smells those women.
link |
Translated into English, what that means is that
link |
it is very likely it seems that something,
link |
maybe pheromones, but maybe some other chemical
link |
that is independent of pheromones
link |
is being conveyed between women that are housed together
link |
or spend a lot of time together
link |
to shift their menstrual cycle,
link |
but it doesn't necessarily mean that they synchronize.
link |
So for instance, if one woman is in the follicular phase
link |
of the menstrual cycle,
link |
it might shorten or delay ovulation, excuse me,
link |
it might accelerate ovulation in another woman.
link |
Whereas if somebody is in the ovulatory phase
link |
of their cycle, it might lengthen the menstrual cycle out
link |
so that the woman who smells that person's scent
link |
or who smells her sweat,
link |
we still don't know the origin of the chemical,
link |
would ovulate later.
link |
So all of this is to say is that chemical chemical signaling
link |
is happening from females to males through tears.
link |
Is that a pheromonal effect?
link |
Well, by the strict definition of a pheromone,
link |
a molecule that's released from one individual
link |
that impacts the biology of another individual, yes.
link |
But in terms of identifying what the pheromone is in tears,
link |
that's still unknown.
link |
It's not clear what the chemical compound is.
link |
So we're reluctant as scientists
link |
to call it a true pheromonal effect.
link |
The menstrual cycle and the synchronization
link |
of the menstrual cycle effect seems to hold up
link |
under some conditions, but in some cases,
link |
there's a kind of clash of menstrual cycles
link |
that's created by chemicals that are emitted
link |
from one female to another.
link |
So there are many examples of this in humans.
link |
For instance, people can recognize
link |
the T-shirt of their mate.
link |
If you give, this experiment has been done many times,
link |
I know it's been challenged a number of times,
link |
but the data are pretty good by now that if you offer,
link |
you take a collection of women
link |
who are in stable relationships with somebody,
link |
you offer them the smell of 100 different shirts
link |
and they can very readily pick out
link |
their significant other's scent.
link |
Okay, that's pure olfaction.
link |
That's not pheromonal,
link |
but nonetheless is a remarkable degree of discrimination,
link |
olfactory discrimination.
link |
You can dilute their partner's scent
link |
down to the point where they themselves
link |
can't consciously detect the difference
link |
between the sweat or the T-shirt
link |
of 100 different T-shirts or so.
link |
And they might say, I don't really smell the difference,
link |
but I think it's this one.
link |
Yeah, this one belongs to the person that I've been with.
link |
And they are much greater than chance
link |
at detecting the T-shirt or identifying the T-shirt correctly.
link |
So there's no question really
link |
that there is chemical chemical signaling between humans.
link |
The question is whether or not
link |
it's truly pheromonal in basis.
link |
Now you'll notice that a lot of the examples I gave,
link |
aside from the one of tears,
link |
is women detecting the sense of men or of other women.
link |
And it turns out that there are a number of papers.
link |
The best one I think that I could find
link |
is published in Physiology and Behavior in 2009.
link |
It's a review entitled,
link |
Sex Differences and Reproductive Hormone Influences
link |
on Human Odor Perception by Dottie, D-O-T-Y and Cameron.
link |
I encourage you to check out this review.
link |
It's available free as a download.
link |
We'll provide a link to it.
link |
You can get the full PDF if you want.
link |
But it does seem that women are better at detecting odors
link |
in these odor discrimination tasks than are men.
link |
And yes, that it does vary
link |
according to where they are in their menstrual cycle.
link |
And yes, they also looked at people
link |
who had received gonadectomy,
link |
they had their ovaries removed,
link |
a number of different important controls.
link |
None of this surprises me.
link |
None of this should surprise you.
link |
It's very clear that hormones have a profound effect
link |
on a large number of systems in our biology
link |
and that smell and taste
link |
and the ability to sense the chemical states of others,
link |
either consciously or subconsciously,
link |
have a profound influence on whether or not
link |
we might want to spend time with them,
link |
whether or not this is somebody that we're pair bonded with,
link |
whether or not this is somebody that we just met
link |
and don't trust yet, things of this sort.
link |
And given what's at stake in terms of reproductive biology,
link |
not just offspring,
link |
but given the possibility of transmission of diseases,
link |
et cetera, the risks of childbirth, et cetera,
link |
it makes so much sense that much of our biology
link |
is wired toward detecting and sensing
link |
whether or not things and people
link |
are things that we should approach or avoid.
link |
Whether or not reproduction with that person
link |
is the appropriate response
link |
or suppression of the reproductive response
link |
is the appropriate response, right?
link |
As in this case with the tears.
link |
So I think these are fascinating studies.
link |
It's an area that still needs a lot of work,
link |
but there are some really wonderful papers on this.
link |
And the one that I mentioned a few minutes ago,
link |
sex differences and reproductive hormone influences
link |
on human odor perception
link |
is one of the better reviews that are out there.
link |
There are also a number of other reviews, for instance,
link |
that talk about pheromone effects
link |
and their impact on mood and sexual responses
link |
and things of that sort.
link |
And we will also provide some links to those.
link |
A lot of this is still speculative,
link |
but I want to say, I know I said it three times,
link |
but I really want to underscore
link |
because it is vitally important
link |
and people seem to get a little triggered
link |
by the notion of pheromones.
link |
Just because we haven't identified
link |
the actual chemical compound
link |
that's acting as a pheromone or putative pheromone
link |
does not mean that chemical chemical signaling
link |
between individuals doesn't exist.
link |
Actually, you and every other human
link |
from the time you're born until the time you die
link |
are actively seeking out
link |
and sensing and evaluating
link |
the chemicals that come from other individuals.
link |
There's a really nice study
link |
that was done by the Weizmann Institute, a group there.
link |
I think it was also Noam Sobel's group,
link |
but another group as well, as I recall,
link |
looking at human-human interactions
link |
when they meet for the first time.
link |
It's a remarkable study
link |
because what they found was
link |
people would reach out and shake hands.
link |
This is a typical response.
link |
Pre-pandemic, people would meet,
link |
they'd reach out and they would shake hands.
link |
And what they observed was almost every time
link |
within just a few seconds of having shaken hands
link |
with this new individual, people will touch their eyes.
link |
Almost without fail.
link |
Occasionally they would touch their eyebrow.
link |
Occasionally someone would touch their hair.
link |
We always associate that with people having some sort of
link |
or us having some sort of self-conscious response,
link |
like, oh, we want to make sure we're
link |
tucked in and all prim and proper, whatever it is,
link |
or looking right, is there something in my teeth,
link |
this kind of thing.
link |
But actually people are doing that
link |
even if the person they just met left the room.
link |
So someone's sitting there, someone comes in,
link |
they shake hands, and the person inevitably,
link |
subconsciously touches their eyes.
link |
They are taking chemicals from the skin contact
link |
and they are placing it on a mucosal membrane of some sort,
link |
typically not up their nose or in their mouth,
link |
typically on their eyes.
link |
Now, animals do this all the time.
link |
There's a phenomenon in animals called bunting.
link |
If you have a overeager dog that when you meet them
link |
or you see them again, after you've been away for the day,
link |
they'll rub their head against you, right?
link |
Cats will do this too.
link |
It's called bunting.
link |
They're rubbing their scent glands on you.
link |
They're marking you.
link |
And believe it or not, you're marking other people
link |
when you shake their hand.
link |
And they are then taking your mark
link |
and rubbing it on themselves subconsciously.
link |
So we all do these kinds of behaviors.
link |
And now that you're aware of it,
link |
you can watch for it in your environment.
link |
You can pay attention to people.
link |
Some of this has probably changed
link |
in light of the events of 2020, et cetera.
link |
But nonetheless, we are evaluating the molecules
link |
on people's breath.
link |
We are evaluating the molecules on people's skin
link |
by actively rubbing it on ourselves.
link |
And we are actively involved in sensing
link |
not just their facial expressions,
link |
the size of their pupils and things like that,
link |
but the chemicals that they are emitting,
link |
their hormone status, how they smell.
link |
We're detecting the pheromones possibly,
link |
but certainly the odors in their breath.
link |
You might say, well,
link |
I don't actually go around sniffing people's breath.
link |
I don't, you know, unless if it's bad,
link |
in which case it's aversive,
link |
but breath is communicating a lot of signals.
link |
And this handshake eye rub experiment
link |
shows that we are actively going through behaviors
link |
reflexively to wipe ourselves or smear ourselves
link |
with other people's chemicals.
link |
Now that might seem odd or even gross to you,
link |
but I think it's beautiful.
link |
I think that it illustrates the extent
link |
to which we as human beings are in some ways
link |
among the other animals in our subconscious,
link |
sometimes conscious,
link |
but certainly subconscious tendency
link |
to try and evaluate our chemical environment
link |
through what we inhale through our nose,
link |
what we ingest through our mouth,
link |
and what we actively take off other people's skin
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and rub on ourselves to evaluate it
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and what we should do about it
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and perhaps that person as well.
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So today we talked a lot about olfaction, taste,
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and chemical sensing between individuals.
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I like to think that you now know a lot
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about how your smell system works
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and why inhaling is a really good thing to do in general
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for waking up your brain and for cognitive function
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and for enhancing your sense of smell.
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We talked about how to enhance your sense of taste.
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And we talked about chemical signaling between individuals
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as a way of communicating some important aspects
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People are shaping each other's biology all the time
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by way of these chemicals that are being traded
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from one body to the next through air
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and skin-to-skin contact and tears.
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If you're enjoying this podcast
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and you're finding the information useful,
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please subscribe on YouTube.
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That's one of the best ways to support us.
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You can also put any questions you have and feedback
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in the comment section on YouTube.
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If you don't already subscribe on Apple and Spotify,
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you can support us by subscribing on Apple and Spotify.
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And on Apple, you get the opportunity to leave us a review
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If you think we deserve five stars,
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please give us a five-star review.
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In any case, you can leave us comments there.
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And we are also very active on Instagram.
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Huberman Lab on Instagram is where I post,
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yes, clips from the podcast,
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but also additional new and original content.
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And you have the opportunity to put your questions
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in the comment section below those posts as well.
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I do read all the comments on YouTube, on Apple,
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and also on Instagram.
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We have a website, hubermanlab.com,
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where all the podcasts are housed
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with links to YouTube, Apple, and Spotify,
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as well as downloadable links.
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Everything's zero cost, of course.
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And there, you can also find any links
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to additional resources that we might post.
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As well, please check out our sponsors
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that we mentioned at the beginning of each podcast episode.
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Those sponsors are the way that we are able
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to bring zero cost to consumer information
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about all these topics to you each week.
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And we also have a Patreon.
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It's patreon.com slash Andrew Huberman.
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And there, you can support us at any level that you like.
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Today, we didn't really talk about supplements,
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but in previous episodes and in future episodes,
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we'll talk about supplements and things that you can take
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to modify your biology and nervous system if you like.
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We've partnered with Thorne, T-H-O-R-N-E,
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because Thorne has the highest levels of stringency
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with respect to the amounts of given compounds
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that are in their supplements
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and the quality and purity of those compounds.
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If you go to Thorne, thorne.com slash the letter U
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slash Huberman, you can see all the supplements that I take
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and get 20% off any of those supplements,
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as well as any of the other supplements that Thorne makes.
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You just go to thorne.com slash U slash Huberman.
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And if you enter their website through that portal,
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you get 20% off any of their things at checkout.
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Last but not least,
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I want to thank you for your time and attention
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and your willingness to embrace new concepts and terms
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and to learn about science and biology and protocols
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that hopefully can benefit you
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and the people that you know.
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And of course, thank you for your interest in science.
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And I'll see you in the next one.