Essentials: Improving Health With Stronger Brain-Body Connection

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Andrew Huberman: Welcome to Huberman Lab Essentials, where we revisit past episodes for the most potent and actionable science-based tools for mental health, physical health, and performance.

I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. Today, we are going to talk about our sense of self, or what's called interoception. Interoception is our sensing of our internal landscape, things like our heartbeat, our breathing, and our gut. This discussion about sense of self and interoception has many important actionable items that relate to bodily health and brain health. Of all the topics I could cover, this thing that we call sense of self, which is also called interoception, has perhaps the most foundational level of importance for all that we feel, all that we do, and all that we are capable of doing. And I promise that if you can learn a little bit about the mechanisms of self-sensing, of understanding what's going on in your internal milieu, as we say, your internal environment, you will position yourself to do some very simple things that can lead to outsized positive effects on everything from sleep, to body composition, to mental focus, to mood, your ability to regulate stress, and indeed, even your ability to heal and recovery from injuries of different kinds, brain injury and bodily injury. We have a system in our body that connects our brain to all of our bodily organs, and connects all of those bodily organs to our brain. And that communication between brain and body in both directions

creates a situation where either we are positioned to do things well, or we are positioned to do things poorly. So, I really want to dive in and dissect, what is this system of brain body communication? What does it look like? What are the actual neurons and connections? The system that's most often associated with this is our 10th cranial nerve called the vagus nerve. The word vagus relates to the word vagabond, which is to wander. And indeed, the vagus nerve is a vast, enormous, wandering set of nerves. So, it's not one nerve. It's not like one fiber, one axon, as we say. So, where do they go? Well, they leave the brain and the brain stem. The brain stem is kind of the back of your brain. If you touch the back of your neck, it's about three inches deep to where you're touching.

The neurons that are there send information into the body to control your bodily organs. How fast your heart is beating, how fast you're breathing, how fast your digestion is occurring. Even things like whether or not you are going to secrete so-called killer cells, your immune cells from your spleen to go ward off bacteria. Now, the neurons there don't know what to do unless they receive information about what's going on within the body. So, everything from your intestines, to your stomach, et cetera, and your spleen are sending information also up to the brain. There are two fundamental features of what's going on in your body that need to be communicated to your brain, these neurons in your brain stem, in order for your brain and your body to work together correctly. And the two types of information are mechanical information and chemical information. So, when you think about your sense of self and your ability to understand what's going on in your body, if you feel good or if you feel bad, your sense of self is dependent on these mechanical phenomenon and these chemical phenomenon. If your gut is full or empty, whether or not your heart is beating fast or beating slowly, that's mechanical. And chemical information, whether or not your gut feels nice and whether, you know... When I say nice, I mean whether or not it has a balance of acidity and alkalinity that feels right to you, or whether or not your gut feels off, it doesn't feel quite right. That's chemical information. So, the first principle that everyone should understand about their sense of self is that they are sensing mechanical and chemical information about every organ in their body, except for one, and that's the brain. Your brain actually doesn't have pain receptors. It doesn't even have touch receptors. The brain is a command center. It helps drive and govern changes in the organs of the body. So, your organs are different. They need to tell your brain what's going on. And there are ways that you can control the mechanical and the chemical state of your organs in ways that are very powerful. So, let's talk about how you can adjust the mechanical and chemical environment of your organs in order to make your brain better, and how your brain can make the mechanical and chemical environment within your organs function better. Let's take one example of these and explain how mechanical and chemical information from this particular set of organs communicates to the brain, and how that changes how our brain works. And the organ I'd like to focus on first are the lungs and the diaphragm. So, we're all familiar with our lungs, these two big bags of air, but they're actually not two big bags of air. They actually have little tiny sacks within them, actually millions of little sacks called the alveoli of the lungs. The alveoli of the lungs are like little tiny balloons throughout our lungs. Those little bags of air can fill up or they can deflate, right? Just like your lungs overall can fill up or they can deflate. The diaphragm is a muscle and it sits below our lungs. And the way the diaphragm and the lungs work together is very interesting. The diaphragm is actually skeletal muscle, so it's just like a bicep or a quadriceps. And the fact that it is skeletal muscle is important because it has a unique property, which is that you can control it voluntarily. How the diaphragm moves up or down determines how you breathe. How you breathe is also dependent on little muscles that are between your ribs, uh, the intercostals and other muscles. When we inhale, these little sacks in our lungs fill up and our lungs expand. And when we do that, we take up space in our thoracic cavity and...... our diaphragm moves down, okay? When we exhale, the diaphragm moves up, the lungs get smaller. Okay? This actually controls our heart rate, and it works in the following way. Our heart actually has a little more space because the diaphragm's moved down, so that heart gets a little bit bigger, physically bigger, not in the emotional sense, but physically bigger. And as a consequence, whatever blood is in the heart flows at a slower rate, because it's a larger volume. So, bigger volume heart, same amount of, of blood inside the heart means slower flow. The brain registers that because there are a set of neurons on the heart called the sinoatrial node. That information is registered by the brain, and the brain sends a message back to the heart to speed the heart up. So, if you do long inhales or you inhale more vigorously, you actually are speeding your heart up. Now, of course, you have to exhale as well, but for instance, if I were to inhale very long, like [inhales deeply] the entire time my heart rate is increasing. And then if I did a quick exhale, [exhales sharply] something else will happen. But if I kept doing that, [inhales and exhales deeply] my heart rate would increase. It's not going to increase linearly and forever, but it will increase with each inhale. Or I can simply make my inhales more vigorous [inhales deeply] and my heart rate will speed up. This is an autonomic, an automatic relationship between the diaphragm, the lungs, the brain, and the heart. Now, if inhales speed the heart up, what happens on exhales? When we exhale, the diaphragm moves up, the heart has less space, meaning it gets a little bit smaller, which means that whatever volume of blood is inside the heart moves faster through that smaller volume. That information is sent to the brain via these collection of neurons called the sinoatrial node. The brain then sends information via the vagus nerve back to the heart to slow the heart down. So, while inhales speed up the heart, exhales slow the heart down, and you can leverage this in a very powerful way to set the conditions of your mind.

If you want to be more calm, emphasize exhales. And the simplest way to do this is to emphasize exhales through what's called a physiological sigh. Two inhales [inhales deeply] followed by a long exhale. [exhales deeply] Those double inhales are kind of important because what they do is they maximally fill all those little sacks in your lungs, and then when you breathe out, you're exhaling as much of the carbon dioxide in your system as possible. When you make excels longer, you're slowing your heart rate, you're calming down.

The opposite is also true. If you inhale deeply or vigorously and then exhale less long or less vigorously, you will increase your level of alertness through these purely mechanical aspects of your interoception. It only takes two or three of those before you start to feel more alert. And that's because your heart rate is increasing, and actually, if you keep doing that for 25 or 30 breaths of inhale deep, short exhale, you will start to secrete a lot of adrenaline. You will actually feel as if you've had a couple espresso. You will immediately wake up. Through purely mechanical means, changing the way that you breathe, emphasizing inhales or exhales or keeping them the same will change the way that your brain works, how alert you are, and how well you function in anything. And again, this doesn't mean that breath work has no value, it's just simply to say that long extended protocols of breath work are simply, they are truly simply just an exploration of this fundamental relationship between the mechanics of your internal organs and your brain, and how your brain controls those internal organs. So now I want to shift away from breathing and diaphragm and lungs and move toward another organ within our viscera, which is our gut. So this includes our stomach and our intestines, our esophagus and so forth. It's been said before, both by me and by others, that we are but a series of tubes. And indeed that's true. Believe it or not every system in your body is a tube. Your brain is actually a tube that connects to your spinal cord, which is also a tube. Your digestive system starts with the tube at your mouth, and of course goes down through your throat, and then you've got all the elements of the stomach and the intestines, and then it comes out the other end. So you are about a series of different tubes. Your vascular system, a series of other tubes. The way your digestive system works is to communicate to your brain about the status of the mechanical pressures along this tube, so within your stomach and your intestines, et cetera, and the chemical status of that tube at various portions within that tube, to inform your brain about how your brain should control that tube.

So, let's start with the mechanical sensing of your gut.

If you drink a lot of fluid or if you eat a lot of food, your gut will fill up. If there's a lot of that food, pressure receptors communicate to the areas of your brain that are involved in feeding and will say, "Don't eat anymore. You don't need to consume anymore." The converse is also true. When these receptors signal to the brain that the gut is empty, so when you find yourself at the refrigerator or you find yourself almost, you know, manically trying to get food of different kinds, you're not even thinking about what you're eating because you're so hungry, in part that's because the lack of food in your gut has sent that information to your brain and is driving particular fixed action patterns that are associated with eating. So if you've eaten anything, even if it's a small volume of food in the last hour to three hours, it's actually a worthwhile practice to take a few moments, maybe 10, 20 seconds, and actually just try and concentrate on sensing the neurons in your gut and how full you are. The consequence of that is actually rather interesting. It's been shown that the consequence of that is actually that you can better override the signals of gut fullness or emptiness. So there are other ways that our guts communicate with our brain. It's not just our stomach talking to our brain, it's also our intestines talk to our brain.The Lieberlies lab, the guy's name is Steven Lieberlies. He runs a lab at Harvard Medical School. They discovered a category of neurons called the GLP1R neurons. And those neurons send little wires down into the intestines and deep into the stomach, but mostly into the intestines, and they sense stretch of your intestines, and then those neurons send another branch. So, they have a branch in one direction, senses what's going on in your intestines, and they have another branch that goes up from your neck into your brain to either trigger the desire to eat more or to stop eating. So, these are really, really cool neurons, and they're basically stretch receptors. And in addition to that, the Lieberlies lab discovered neurons that detect nutrients themselves. These neurons are activated by the presence of fatty acids, amino acids, and as a third food item, sugars are coming from the foods that we eat. These neurons will fire a lot to the brain that says, "Hey, whatever you're doing up there, do more of it." Okay? Now, the sugars are a little bit cryptic, because when I say sugars or I say amino acids or I say fatty acids, this has nothing to do with taste. In fact, beautiful experiments have been done by the Borges lab and by other labs showing that even if you numb the mouth, even if you gavage, which is a really just a... It's a fancy word for basically tube feeding. You put a tube down into the gut, you just deliver the food to the gut so you get no opportunity to taste it. Sounds pretty awful. If you force feed by gavage or you numb the mouth, these neurons don't care about the mouth. They only care about the nutrients coming from these foods, and then they signal to the brain, "Hey, do that thing. Do that thing where you lift that object we call a fork or a spoon. Do that thing where you drink the milkshake. Do that thing where you move your mouth like this, not talking, but do that thing where you swallow." So, that's how the nutrients in our gut control us, and this is why for people that experience extreme sugar cravings or even mild sugar cravings, replacing those foods with foods that have high levels of omega-three or amino acids can reduce sugar cravings, and I've talked about this on a previous episode, but the point is these neurons don't really know taste. They only know nutrients, and so you can work with that system. If your... If you crave sugar, and I do believe that most, if not all of us should be trying to limit, if not eliminate simple sugars as much as possible most of the time, then things like high omega-three foods, et cetera, maybe you even want to supplement with fish oil or something similar to get omega-threes, there are other reasons for wanting to do that too, can be very beneficial, and here's what we're talking about is interoception. It's your ability to sense your inner real estate, but in this case by way of chemical signaling, not by way of mechanical signaling. So, now I'd like to talk about another aspect of gut chemistry that has profound effects on the brain, as well as on the immune system. Your gut needs to maintain a certain level of acidity or alkalinity. For those of you without any chemistry background, basically the low numbers on the pH scale, that means more acidic. The higher the numbers, more alkaline. So, more alkaline means more basic and acidic means acidic. Your gut needs to be more acidic than essentially all other tissues of your body in order to function properly. Gastric juices are actually powerful modulators of brain state. Put differently, one of the best things that you can do to have a healthy brain, a well-functioning brain, and a healthy and well-functioning body is to maintain proper gut chemistry, and that's basically accomplished by getting the right level of acidity and alkalinity in your gut. Now, this is not quack pseudoscience. What we're going to talk about now are peer-reviewed data that point to the gut microbiome and its relationship to acidity of the gut, and how the gut microbiome can help enhance autoimmune function and various other aspects of brain and body health. So, within all the mucosal line tissues of our body, we have what are called microbiota, little microorganisms that we didn't make that actually come from our environment or our food and live inside us, and there are good microbiota and there are bad microbiota.

Whether or not we have good microbiota or bad microbiota depends on one thing, and that one thing is how acid or alkaline the given mucosal tissue is. What you essentially want to do is create an environment where the proper microbiota can thrive, because when you do that, you greatly decrease what are called inflammatory cytokines. So, these are things that are secreted both by cells within the body and cells within the brain to impact brain health and brain function and bodily health. The simple way to adjust these things in the proper ratios is to adjust your gut microbiome. The best way to adjust your microbiome is to ingest certain types of foods. There was a study done by my colleague, Justin Sonnenburg, at Stanford School of Medicine. They explored how different foods or different diets I should say, impact the gut microbiome and inflammatory markers, and what they did is they explored two types of diets. One is a high fiber diet, and they compared that to diets that were unchanged except for the inclusion of a few to a few more servings of fermented foods each day, and the takeaway message from this study is that the fermented foods far outperformed the high fiber diet. The bigger message is that all of us should be ingesting on a regular basis, daily basis, fermented foods of different kinds, and why I say that is because the inflammatory markers went down. The markers of autoimmune disruption went down, and the chemistry of the gut therefore was adjusted in the appropriate ways, and it's been shown in other studies that when...... the correct gut microbiota are present and these inflammatory markers are reduced, cognition improves, so ability to focus, ability to sleep, ability to ward off infection, and wound healing all enhanced. So, while today is about interoception, we're talking about sensing, we're also talking about subconscious sensing. And we're talking about subconscious sensing of the milieu of the body. When the milieu of the gut and the body is right, then the brain and the immune system function very well. It's very clear, that's fermented foods, and that's keeping the stomach slightly more acid than one might think you would want to. So, now I want to talk about two other forms of mechanical and chemical sensing that we very much can detect at a conscious level, and those are fever and barfing. So, let's talk about barfing first. Barfing, AKA vomiting, is when the contents of your guts run in reverse, meaning when they go up from your stomach, out the esophagus and mouth, and onto whatever surface happens to be in front of you. It's a terrible thing, nobody likes to do it, but it's a very interesting aspect to our biology because it reveals a beautiful and absolutely fundamental relationship between our chemistry and our brain. So, your brain is actually locked behind a gate, and that gate is not your skull. That gate is the so-called blood-brain barrier. It's absolutely fundamental that only certain molecules get across the blood-brain barrier and that others don't. And the reason for that is that most all, 99.9999% of your neurons do not regenerate. I don't care what you've read, especially in the news recently about how psychedelics cause neurogenesis, because they don't. It's absolutely wrong. Psychedelics have effects on brain plasticity, but they have nothing to do with neurogenesis, at least no data support it. But because you can't make new neurons, you also can't damage the ones you've got, or you shouldn't, as much as possible. And that's why you have a blood-brain barrier, or a BBB. So, the BBB, as it's called, prevents substances from getting to the brain.

However, like any fence, it is not always uniform along its length. And there are little spots within that fence where chemicals can sneak across to the brain, but through a beautiful design of some sort, there are little holes in that fence and there are little neurons that sit right behind those holes, and those neurons sense what the chemistry of the blood is. So, I'm guessing you probably didn't imagine that today's discussion about sensing the self would be sensing your own blood, but you do. There's a little area of your brain that's little indeed, but is very, very important, called area postrema, P-O-S-T-R-E-M-A. And area postrema is an area of the brain stem that sits right next to another brain area called the chemoreceptor trigger zone. And when the contents in your bloodstream are of a particular kind, meaning when there are pathogens or it's too acidic, the neurons in area postrema and the neurons in the chemo receptor tr- trigger zone trigger a bunch of motor reflexes in the abdominal wall that make you barf, okay? The contr- the feeling that you need to throw up is triggered by these neurons in the brain stem, and those neurons in the brain stem are triggered by the presence of certain chemicals. And the reason why you don't have any blood-brain barrier at that location is because postrema has to be there like a crossing guard, making sure that everything that's coming through the blood is okay. And if it even senses just the tiniest bit that things are off, it's going to trigger that reflex.

Some people, the memory of or the thought of something like blood or vomit, or use your imagination, can actually trigger the vomit reflex. And that's because these neurons in area postrema are very sensitive to prior experience of interactions with negative things. The neurons of area postrema are there basically to keep your whole system safe. So, let's talk for a second about how to reduce nausea, because nausea, it... that salivation, that feeling that you're going to vomit, can be very beneficial in an ad- in an adaptive circumstance like you've ingested something bad, but some people experience nausea for other reasons. There are good ways to regulate nausea, and the ways they regulate nausea are very interesting. They actually adjust the activity of these neurons in area postrema, or they change the chemistry of the blood directly. And many of you have heard this before perhaps, but it turns out that there are good data, 11 research studies were the ones that I could find, peer-reviewed research studies with no bias, so independent studies, showing that ginger can cause a notable reduction in nausea. How much ginger? One to three grams. And some of you will not be surprised to learn that cannabis can reduce nausea, but cannabis, THC and/or it turns out CBD, can reduce nausea, and it probably does that by changing the f- threshold for firing of these neurons in area postrema. Now let's talk about fever. A fever is simply an increase in body temperature. That increase in body temperature is triggered by neurons in the brain, and those neurons in the brain are triggered by the presence of particular things in the bloodstream.

What sorts of things? Well, toxins, bacteria, viruses. When something bad gets in our system, the body doesn't know it's bad.It just knows it's foreign. Your body has this intelligence, and that intelligence is to know, hmm, these proteins are normally not seen in this region. And then your body, or the cells there I should say, will release something that then will travel to the brain and will trigger an increase in body temperature so that your body cooks the bad thing, or the cause of the bad thing. It's really a beautiful adaptive mechanism. So, what's beautiful about the fever mechanism is that it looks a lot like the barfing mechanism. Basically, you have a set of neurons that sit near the ventricles. You are a tube, a series of tubes, and your brain has a hole down the middle and it extends down to the bottom of your spinal cord. At the front it's called the ventricles, and you have one ventricle. The third ventricle, along that third ventricle there's, there are little neurons that can sense what's in the cerebral spinal fluid that fills the ventricles. So, in other words, you have neurons that are sensing the chemistry of your cerebral spinal fluid, and that have access, therefore, to the chemistry of your body. Because that cerebral spinal fluid is going up and down the brain and spinal cord, but into that cerebral spinal fluid are signals about the various chemicals within the body. So, this is not a mechanical system, this is a chemical system. Remember, we're talking about mechanical information and chemical information accessing the brain. The neurons that line these ventricles with cerebral spinal fluid go by a particular name, they're called circumventricular organs, meaning near, circumventricular, near the ventricles. And you have these organs and they're a set of neurons, has a really cool name called the OVLT. I don't know why I like that, but I just like it. It's the organum vasculosum of the lateral terminalis. Organum vasculosum lateral terminalis, OVLT, are the neurons that respond to toxins and bad stuff in your bloodstream, however minor or major. What's going to happen is when those OVLT neurons are activated because you have something bad in your body or something bad is happening in your body, they communicate with an area of the brain called the preoptic area of your hypothalamus. And the preoptic area cranks up your temperature and tries to cook that bad thing.

Now, it's worth talking about fever for a moment and talking about thermal regulation, because I think this actually could save some lives. So, if you are overheated to a point where, you know, you're getting up past 102 or 103, it's going to vary depending on person to person, and certainly age. You know, kids some people think can tolerate higher levels of fever than adults. But look, you always want to be cautious about heating up the brain too much, because once those neurons are gone, they do not come back and neurons do not do well in very high temperatures. Once your body temperature starts getting up to 102, 103, certainly 104, you are starting to enter serious danger zone. This can happen through exercise in hot environments, or an inability to escape heat because you don't have covering or adequate, um, ventilation or cooling. It can also be because of excessive fever for whatever reason. A lot of people think the way to deal with this is to put a cool compress on the back of the neck, or to cool the torso. It's very clear that that's the wrong response to try and cool off the body.

If you put a cold towel or you put an, an ice pack on the back of the neck, what you effectively do is cool the blood that's going to the brain. And if you do that, then your brain will react by turning up the crank in, so to speak, on the neurons in the preoptic area and will heat you up further, and can cook your brain and organs further. So, what you want to do is, as I've talked about before, you want to cool the bottoms of the feet, the palms of the hands, and the upper part of the face. Now, you can also cool the rest of the body, but it's not okay to just stay under the covers and just cool, uh, you know, the neck or something like that. You really want to try and create a systemic or whole body cooling if the goal is to bring fever down. Now I want to turn our attention to interoception as it relates to feelings, the way that interception is most commonly described. And I want to highlight a term that many of you have probably heard, which is the vagus nerve. We talked about vagus a little bit earlier, but the vagus nerve, this vagabonding, wandering nerve is involved in everything I've talked about up until now. And the reason I saved it till now rather than mentioning all along is to highlight a specific point, which is that whenever we hear about the vagus in popular culture, it's like, "The vagus calms you down, it'll mellow you out." Actually, most of the time the vagus is stimulatory. When you ingest foods with amino acid, sugars, or fatty acids, the vagus nerve s- gets activated and triggers the release of dopamine. It makes you more alert and go seek more of those [laughs] foods, or what led to those conditions.

When you feel nauseous, it's rarely calming. When you feel like you have a fever, it's rarely calming. So, you're starting to get the picture that even though the vagus nerve is in the parasympathetic branch of the autonomic nervous system, it's not a calming system, it's a communication system, and it's a motor system. It communicates brain to body and body to brain, and it changes the function of different organs. Now, one thing that's important to highlight is that stress itself will alter the chemistry of your gut because of the ways that it shuts down the vagus nerve and quiets the neurons that communicate from gut to brain. I want to say that again. Stress will disrupt your gut and make you feel not good, poor digestion and just lousy, because of the way this, that it shuts down the vagus nerve and the neurons of your gut. It doesn't mess up your gut, it just doesn't let your gut get the signals up to your brain, and it also th- then throws off the chemistry and then there's a whole cascade of effects. The vagus nerve, however, is responsible for emotion. And the way it does that is to pull...... to aggregate the conditions of your gut, the conditions of your heart, and the conditions of your breathing, which includes your diaphragm and lungs, and takes that, kind of as a, a collection of information, and sends it to the brain, and controls what we call your emotions.

Now, that might seem obvious to some people, but to other people, that might seem totally crazy. You thought your emotions were because the market was down and you had invested, or because something that you thought was going to happen is not going to happen. Whatever it is that bothers you, you think of generally as a purely cognitive event. But the brain doesn't really know what to do with that information. It doesn't act directly on that information to create moods. Moods are created through the heart's response to reading that headline, to the change in your breathing that's caused by someone that you love telling you that actually they're not interested in spending time with you anymore. Emotions can be good, or bad, or neutral. So, this thing that we call interoception, the sense of self, I've been building up from very fundamental layers, gut chemistry, spleens, immune systems, autoimmune. All of those things are plugging in like a series of ingredients in a recipe that gives rise to your mood and how you feel. And that mood and how you feel is shown in one location in your body that other people can see, and that's in your facial expressions. And indeed, there are now beautiful data showing that your face, including the size of your pupils, the tonality of your face, how flushed you are, or how pale you are, even the degree to which you are frowning or smiling relative to other periods of time, that is all an aggregate of, or a reflection rather, of your gut, your heart, and your breathing, and the chemistry of your body. And what's remarkable, and this is where interoception really, really takes a leap into the incredible, is that there are beautiful studies that show that, for instance, when we know somebody pretty well, and they are going through some sort of experience of any kind, our heart rate actually starts to mimic their heart rate. Our breathing starts to mimic their breathing, even if we aren't conscious of their breathing. Somehow, human beings are able to register the internal state of other beings, and I think probably for animals too, but certainly for other humans, even at a distance. And so your sense of your internal landscape is linked to others. Now, you can enhance this interoceptive capacity for how you feel and how others feel. In other words, you can start getting a better readout of your internal state by doing a simple t... exercise, what is really a tool, and that is to learn to sense your heartbeat. And I think this is one of the reasons why meditation is powerful. When you stop taking in exteroceptive information, information from the outside world, by closing your eyes and focusing inward, as they say, you start paying attention to your breathing cadence. You start directing your mind's attention to your heart rate. And if you can start to perceive your heart beating, you actually are very quickly strengthen the vagal connections between the body and the brain. And so there's no real practice here. There's no breathe this way, or do this thing, except to direct your awareness toward your heartbeat. And some people can get very good at this very fast. Most people find that just by doing this for a minute or so every once in a while, they start to tap into this sixth sense. They start to notice when they don't feel quite right about something, or somebody, or some situation. So, this interoceptive awareness can be tuned up. It used to be called vagal tone, but I think that term doesn't take into account all the other things that are going on with the vagus, so I don't really like that term. It's more of an interoceptive awareness. So, what I've effectively tried to do today is to give you a window into this incredible relationship between your viscera and your brain, and your brain and your viscera, all these organs of your body. And I, what I hope is that you'll appreciate that it's a system, that you aren't just a system of tubes. I said that in sort of in jest. I mean, you have a lot of tubes and you are a system of tubes, but that system of tubes is linked through the nervous system. And those links work in very specific ways. So, whether or not you remember about piezos and all the GLP1Rs and all that stuff, it doesn't really matter. What I encourage you to do is start sort of pushing and pulling on the various levers within this beautiful system that we call the interoceptive system, the sense of self. Thank you for your time and attention, and thank you for your interest in science.