Control Your Vagus Nerve to Improve Mood, Alertness & Neuroplasticity

0:00 Welcome to the Huberman Lab podcast, where we discuss science and science-based tools for everyday life. I'm Andrew Huberman and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. Today, we are discussing the vagus nerve. The vagus nerve, or what neuroanatomists call cranial nerve 10, is an extremely interesting nerve because when we hear the word nerve, we often think of a small, you know, connection between one thing and another, the wires of the nerve, which of course we call axons. If you didn't know that, now you know. They're called axons. But actually, the cranial nerve is an extensive pathway. It's a whole set of connections that link the brain and body. In fact, in many respects,

0:45 it looks kind of like its own nervous system, within the traditional nervous system of the brain and the spinal cord, the connections between spinal cord and muscle. The vagus nerve is so vast, it spreads out through so much of the body, and as you'll learn today, it's connected to so many interesting different brain areas, and has so many interesting different functions that it deserves, well, an entire episode of this podcast. The other great thing about the vagus nerve is it is highly actionable, meaning, what you will learn today, if you already know something about the vagus nerve, is going to change what you know and believe about the vagus nerve. What you hear today will also, if you don't know or you're not familiar with the vagus nerve, is going to educate you on the latest about the vagus nerve.

1:31 We've learned a lot about the vagus nerve and ways to control the vagus nerve in the last few years. And finally, and perhaps most importantly, the information that you're going to learn today includes actionable tools that will, for instance, allow you to make yourself more alert, when you want to, without the use of pharmacology. It will allow you to calm yourself down quickly, when you want to, on demand and quickly, without the use of pharmacology or devices. And, it will also allow you to alter your mood for the better, and indeed to improve your ability to learn. The vagus nerve is that important. It's involved in that many different things, and the pathways of the vagus nerve, as I mentioned, have been charted in more detail in recent years. And the ways that we can get into the vagus nerve and

2:16 stimulate its actions in specific ways to achieve those endpoints of improved mood, deeper relaxation, faster relaxation, elevated levels of alertness, and on and on, are now very well understood. So as you can probably tell, I'm extremely excited about today's episode because the vagus nerve is just one of the most fascinating aspects to our nervous system. You have one. I have one. So let's figure out how they work and how to put it to work for the better. Before we begin, I'd like to emphasize that this podcast is separate from my teaching and research roles at Stanford. It is, however, part of my desire and effort to bring zero-cost-to-consumer information about science and science-related tools to the general public. In keeping with that theme, today's episode does include sponsors. Our first sponsor is LMNT.

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5:22 If you'd like to try Joovv, you can go to Joovv, spelled J-O-O-V-V.com/huberman. Joovv is offering an exclusive discount to all Huberman Lab listeners, with up to $400 off Joovv products. Again, that's Joovv, spelled J-O-O-V-V.com/huberman to get up to $400 off. Okay, let's get familiar with the vagus nerve. The vagus nerve is cranial nerve 10. The vagus nerve is very different than the other cranial nerves because whereas it does have connections with areas on the face, head, and neck and deep to those areas too, so throat, et cetera, it also has connections, or I should say, it receives and provides connections to areas within the body. In fact, it has connections with the head area, the neck area, the chest area,

6:11 the abdomen, and even a bit lower into the lower intestines. So, the vagus nerve is super extensive in terms of its outputs and its inputs and I'll explain what I mean by outputs and inputs in just a moment. But what's very useful to understand and visualize in your mind a bit, anytime we're talking about the vagus nerve, is we're talking about a nerve of many, many different pathways that both receives and provides information from essentially all areas of the body down to the base of your pelvis. And that stands in stark contrast from the other cranial nerves, which tend to receive information, from restricted areas of the body most typically, the head and neck area, and that tend to provide connections to the head and neck area.

6:56 The word "vagus" actually translates more or less to 'vagabond', which means 'wandering'. So early neuroanatomists saw that this nerve, cranial nerve 10, had connections to large areas of the body, and head, and neck, and received inputs, from lots of areas of the body, and decided to call it essentially, 'the vagabond nerve' or the 'vagus nerve'. Now, even though the word 'vagabond' means essentially 'wandering', and the word 'wandering' kind of suggests random, there is nothing random about the wiring of the vagus nerve. The vagus nerve is incredibly precise in terms of where it receives information from, and where it provides information to. Now, I want to be very clear what I mean about information, okay? If you're a biologist, you'll probably understand some of this. If you're not, and I have to assume most of you are not,

7:43 it's still very important that you understand and it's very easy to understand that your nervous system, your brain, spinal cord, and of course, your nervous system includes all these cranial nerves, including the vagus nerve, are carrying different types of information along different pathways. Different neurons or different nerve cells within the vagus nerve, for instance, are receiving or giving different types of information for different purposes. For instance, there is sensory information carried by neurons, nerve cells in your nervous system. Sensory information is the kind of information that for instance, converts light into electrical signals at the level of your eyes, then your eyes are providing information to the brain, about what's out in the visual world. That's sensory information. Same could be said for sound waves.

8:31 That's sensory information that your auditory system converts to, basically your understanding of speech and sound and music, et cetera. Other neurons control motor functions, literally the movement of your limbs by controlling contraction of your muscles, or the movement of your lips or the closing or opening of your airways, for instance. So, motor information, of course, can be seen on the surface of the body. I'm moving my hands now. I'm moving my mouth. You don't even need to see me do that to know that I'm doing that. But within our body, we have organs that also need motor control, for instance, our gut. Our gut is not just a passive tube, through which food moves. The gut is contracting and relaxing. It's moving food through, from one end to the other, okay?

9:17 We have our pancreas. We have our liver. We have our spleen. And you might think, "Oh, well, those are sort of vegetative organs. They just kind of sit there. Maybe the cells do stuff, but they don't move much." But actually, your spleen even has a contractile ability, so it can contract to release red blood cells, or immune cells into circulation and so on and so forth. Different organs, including your muscles, but other organs as well, need instructions as to when they should move, when they should contract, when they should relax. So we have sensory information, that's carried by essentially one set of neurons in our nervous system, so; carrying light information, or sound information, or as you'll see in a few minutes, chemical information about the acidity of the gut, for instance. And we have neurons that are considered motor neurons.

10:04 They control the contraction of muscles, or the contraction of these different organs, or the encouragement for different aspects of the digestive tract, to contract, or relax, to move food along, okay? So we've got sensory neurons and we have motor neurons. And then there are a lot of other neurons as well that we call modulatory neurons that kind of adjust the balance between the sensory information and motor information. We aren't going to talk so much today about modulatory neurons, but they are an important third category of neuron in the nervous system. Now, why am I telling you all this stuff about sensory and motor? Because the vagus nerve is also unique in that it is both a sensory pathway and a motor pathway, and this is something that most discussions about the vagus nerve, in fact, I would say 99% of discussions about the vagus nerve that you see online,

10:51 or when you hear about forgive me, in your yoga classes... By the way, I'm going to touch on how yoga and ancient yogic practices, actually managed to tease apart some very important functions of the vagus nerve, without knowing any of the underlying mechanisms. But it is the case that most of the time when you hear about the vagus nerve out there in the general world or in the media, it's about the vagus nerve being a calming pathway, that's involved in transmitting information, about the sensory milieu of the body, so, you know, heart rate, acidity of the gut, you know, how comfortable we are in our body, to our brain. And people will say, you want to activate the vagus nerve because you want to calm down. Well, that is true, but that is just one small fraction of the functions of the vagus nerve. Why? Because the vagus nerve includes both sensory and motor neurons within it.

11:40 And, while it is true that a ton of sensory information is coursing up from the organs of the body, into the brain, through what we call the vagus nerve, there's also motor information coming from the brain to the body. So, if we are going to have an accurate, meaningful, actionable conversation about the vagus nerve, it's very important that you know, that the vagus nerve contains sensory neurons, as well as motor neurons. And I want to be clear that I'm not just telling you about sensory versus motor neurons, in the vagus nerve, to just overload you with nomenclature. Turns out that if you want to access the calming aspects of vagus nerve activation, versus the energizing effects of vagus nerve activation, versus the immune enhancing effects of vagus nerve activation,

12:25 versus the ways that you can improve learning using vagus nerve activation, you need to know whether or not you're trying to activate a sensory pathway, or a motor pathway, within this vast set of connections that we call the vagus nerve. Okay, so I want to just briefly describe the sensory pathways, within the vagus nerve. And by the way, if you're a yoga teacher, if you are a therapist, if you are a teacher, if you are a human being on Earth, this information is going to be very useful to you, because this is the information that will allow you to understand why it is that when your body is in a certain comfortable or uncomfortable state, it has a particular effect on your mind and your brain to feel, well, in general, comfortable or uncomfortable.

13:11 Your vagus nerve includes very interesting and kind of unusually shaped neurons. Okay. The neurons of the vagus nerve are not like the ones that you see in the typical picture, if you were to look up neuron online. If you were to look up neuron online, what you would find is you'd see a picture of what's called a cell body, where the nucleus, the DNA is. You'd see what are called dendrites, which typically are the area where neurons receive input, and then you'd see the wire-like extension that we call the axon; out to the area that that neuron communicates with; and then you might see a little picture of some little blobs or what we call vesicles, being released at the end of that axon. That is not at all what vagal nerve neurons look like. Some of them do, but the vast majority, about 85% of the neurons in the vagus nerve,

13:57 have a cell body with that DNA, with the nucleus in it, sitting in an area kind of near your neck and back of your head, sort of, what we call the brain stem, and it's called the 'nodose ganglion'. Now, the nodose ganglion's a collection of cell bodies of neurons, so you can think of it kind of like a cluster of grapes, and they do indeed have an axon extending from them, a wire that goes out to the body, okay? That wire looks for all the world, like the axons on any other neurons, and that little axon can be very short if it terminates, as we say, in an area of the neck. It can be slightly longer, if it terminates in the chest area, and even longer if it goes to what we call our viscera, our lungs, our pancreas, our liver, down to any number of different organs,

14:45 within our major abdominal body compartment, okay? You also see an axon, a little wire, from a vagal sensory neuron, out to the spleen. Now, what I just described, a cell body, with an axon extending from it, out to the organs of the body, different organs of the body, tend to be innervated by different neurons, not always, but in general. But here's what's different about these vagal neurons. These vagal neurons have another axon, that goes from their cell body, so they're what we call a bipolar neuron. They have another axon that extends up into the brain stem, and terminates in generally one of three different, what we call brain stem nuclei, which are just areas of the brain stem. So this is very important to embed in your mind, right, because in reality,

15:32 embedded in your head and neck, or in your brain and neck, are these neurons, which are kind of like a cluster of grapes that have... Each one is going to have two branches, one that goes out to a particular organ of the body and another branch that goes up into your brain stem. Now, this visual understanding, which hopefully is starting to take place in your mind, is extremely important to understand how 85% of the vagus nerve works. 85% of the vagus nerve works, by having these neurons that have axons in, say, the spleen, or around the lungs, or that innervate the heart, or that innervate any number of different organs in your body, and they collect sensory information about what's going on in each and every one of those organs.

16:19 That information goes up the axon. Remember, there's the cell bodies in the nodose ganglion, and then it goes further up, past the cell body, into the brain stem. Okay? So when people talk about the vagus nerve, cranial nerve 10, as being a sensory pathway, it is mostly a sensory pathway. It's collecting information through these axons. Why is that weird? Well, it's not weird, but it's different than the way we normally talk about neurons where the axon is the output end, right, where it's dumping stuff onto the next neuron, to make things happen. The neurons in the nodose ganglion of the vagus nerve, I know that's a lot of language, but these neurons that send an axon branch out to the organs of the body, are collecting information about what's happening, what sensory information is occurring out at those organs,

17:05 and that information goes up those wires, past the cell body, and into the brain stem, and then that's communicated to the brain. So basically, we can think of 85% of the vagus nerve, this huge superhighway, from the body to the brain, as being sensory. And when we talk about sensory, it's important that you understand that two types of sensory information are coming in through these wires, through these axons, and that are delivered to the brain, and in response to that sensory information as you'll soon learn, Your brain will change its levels of alertness. Sometimes it gets more alert. Sometimes it gets calmer. Sometimes it primes you to learn better. Sometimes it will turn on a fever, right? It will literally heat up your entire body, based on what those axons are sensing out in the periphery.

17:54 The periphery of course being the organs and tissues of your body, outside your brain and spinal cord. So I realize that's a bit of neuroanatomy. For those of you that aren't familiar with neuroanatomy, it might seem like an overwhelming amount of neuroanatomy, but it's extremely important to have that idea, in your mind of sensory information, flowing up into the brain, from your organs because anatomically speaking and functionally speaking, it runs exactly opposite to how we typically see neurons, when they're drawn in diagrams for us, and how we talk about neurons, as just putting stuff out at the level of the axon, at the end of those wires. Information's coming up those wires, in the case of the vagus. Okay, so whereas for the visual system, or the auditory system, or for the smell system, or the taste system, typically, we have one type of sensory information coming in.

18:41 So for instance,in the visual system, light, photons of energy are converted into electrical signals that the rest of the visual system unpacks, to give you visual perceptions to control your circadian rhythms. Or in the case of the auditory system, you have sound waves, which are transduced by this beautiful mechanism of your inner ear, that then gets converted into your understanding of speech or music, et cetera. In the case of the vagus nerve, the sensory information coming from your organs, from your lungs, from your gut... And by the way, your gut- when I say that, I don't just mean your stomach. I also mean the large and small intestine, and all the stuff above your stomach as well. The sensory information that's coming from the body includes both chemical information and mechanical information.

19:28 Now, the mechanical information is pretty straightforward to understand. If your gut is full of food or air or water and it's very distended, you can feel that. The reason you can feel that is because you have mechanoreceptors that sense stretch in the lining of the gut, and send that information by way of those axons up to and past the nodose ganglion. There's some processing of that information in the nodose ganglion, but then it goes up and into your brain stem, okay? Now, also within the gut, you have chemical information. There's information about for instance, and we'll talk more about this later, how much serotonin is in the gut. You may have heard that 90% of the serotonin in your body is manufactured in the gut. And indeed, it's manufactured in your gut. It plays an important role in gut motility and gut health.

20:17 The serotonin in your gut is distinct from the serotonin released in your brain. Later, we'll talk about how the levels of serotonin in your gut are conveyed to the brain by way of, you guessed it, the vagus nerve, and your brain in turn, makes different levels of serotonin to impact your mood. Super interesting, super important pathway, has relevance for depression, and just for everyday mood and well-being. We'll talk about it. It's a highly actionable pathway. Super cool. So you have mechanical information and you have chemical information coming from, for instance, your gut, up through the sensory, in the technical nomenclature, it's called afferents. Afferents is a technical language- feel free to ignore this, but for those of you that want to know, you aficionados already know this, the afferents are the inputs to a structure; efferents are the inputs from a structure.

21:04 But, what we've got in the case of the gut, is mechanical and chemical information being sensed, by different neurons with different receptors, that pay attention to different things. Meaning, those receptors are activated by either mechanical stretch or by the presence or absence of particular chemicals in the gut, how acidic the gut is, and that information goes up, processed a bit in the nodose ganglion, and then relayed up to the brain stem, and we'll talk in a moment, about what happens to that information, after it lands in the brain stem. Now, chemical and mechanical information is also being conveyed from other structures in the body. You can probably imagine what some of these are, and we don't have to go through each and every one, but as one additional example to the gut, I'll just use, for instance, the lungs. When your lungs expand and contract as you breathe,

21:51 that information is relayed up through and past the nodose ganglion, and up into the brain stem. And as you can imagine, your lungs, because you're inhaling oxygen and you're also offloading carbon dioxide, your lungs are expanding and contracting. Your lungs are also communicating mechanical and chemical oxygen-carbon dioxide ratio information up to the brain. Now, if we wanted to, we could explore and discuss every single organ of your body that gets axon input from the vagus nerve, and therefore, can carry sensory information up the vagus. And again, there's going to be information about the chemical environment and the mechanical status of each of those organs, carried up to your brain stem. We're not going to do that now for sake of time, but it's very important that you now take a step back, and you realize - "Hmm, I understand what sensory information is.

22:40 I understand, that it's different than motor information. It's carried by different neurons in the nervous system. The vagus nerve has both sensory and motor neurons. The sensory neurons are collecting information from all these bodily organs. And by the way, those bodily organs don't just stop at the level of the lungs. It includes the heart, it includes some stuff that's happening in the neck, some of the muscles that are controlling the constriction of the airways. We'll get into this a little bit more in a few minutes. But, you now also know that when we talk about collecting sensory information from the body and sending it to the brain by these vagal pathways that the types of sensory information include both chemical and mechanical information. And the reason that's important is not just academic and intellectual, it's not just to fill the airspace with nomenclature, it's because,

23:25 if you're going to think about ways to change the activity of the vagus system, the ways to, for instance, calm down or the ways to improve your immune system function or to improve your mood in the short and long term, you need to ask yourself, "Am I going to do that through a mechanical change, or am I going to do that, by making a change to the chemical milieu of a given organ or set of organs?" So to drive the point I just made home, let's take an example that we see a lot out there, which is that if you want to increase the activity of your vagus nerve, you want to calm down. Why am I saying calm down? I neglected to say earlier that by the way, every medical student and pre-med student should know... which is that cranial nerve 10, the vagus nerve, is classified as a 'parasympathetic nerve'. Parasympathetic refers to one branch of the so-called autonomic nervous system.

24:14 The autonomic nervous system controls your levels of alertness and your levels of calm. It has two major branches. One branch is called the 'sympathetic nervous system', has nothing to do with emotional sympathy. The sympathetic nervous system is generally responsible for increasing our levels of alertness, everything from being alert, like I am now, all the way up to full-blown panic attack, which fortunately I'm not right now. The parasympathetic nervous system is often referred to as the 'rest and digest system'. And indeed, it has roles in rest and digestion, but it controls a lot more than just that. The parasympathetic branch of the autonomic nervous system controls, for instance, digestion. It controls our ability to fall asleep at night. If the parasympathetic nervous system is overly activated, it can make us sleepy when we don't want to be sleepy.

25:01 It can make us pass out when we don't want to pass out. It can be responsible for putting people into a state of coma. So it's not good to think about the sympathetic nervous system, simply as fight or flight, how it's often referred to, because it's also responsible for generating healthy, wakeful, non-anxious, non-stressed levels of alertness, as well as stressed-out, panicked states. And the parasympathetic nervous system is responsible for putting us into a calm and relaxed state or a deep sleep state, or a coma state, if it were to be hyperactivated. The autonomic nervous system is a seesaw, where the levels of alertness and calm that we experience at any one moment, reflect the relative balance of sympathetic nervous system and parasympathetic nervous system activity. They're sort of in a push-pull with one another. Increase the parasympathetic nervous system activity a little bit,

25:48 you get a bit calmer. Increase the sympathetic nervous system activity a little bit, you get a bit more alert. But they're always both active. The vagus nerve is classified as a parasympathetic nerve. However, it's a bit of a misnomer because, as you'll soon realize, there are pathways within the vagus nerve that, were you to activate these pathways within the vagus nerve, you would become more alert, not less alert. This is one of the things that I'm hoping to dispel through the course of this episode, which is this very common myth out there. It's almost pervasive that when you activate the vagus nerve, you're going to calm down. It is simply not true, okay? There are instances where that is true. There are instances where the opposite is true, depending on which branch of the vagus nerve you happen to activate or suppress.

26:37 One example however, where activating a particular branch of the vagus nerve, does indeed lead to more relaxation, is the branch of the vagus nerve that, again, is sensory, okay? So it's taking information about mechanical phenomenon, in this case pressure, or touch, and it's sending that information down into the brain stem areas that are going to interpret that information. This branch of the vagus nerve that is carrying sensory information, doesn't come from the viscera or the neck. It comes from the head, and it's the branch of the vagus nerve that essentially goes behind the ear and in some of the deeper components of the ear. Remember they tell you, don't put anything into your ear that's smaller than your elbow? Well, I'm breaking that rule right now,

27:23 and I'm putting my index finger into my ear, and kind of rubbing in a circular way, the kind of, the area right outside the hole of the ear. There's a branch of the vagus nerve there. There's also as I mentioned, a branch of the vagus nerve behind the ear. And were you to rub behind the ear just gently or you know with a little bit of pressure indeed you're going to activate that branch of the vagus nerve. That branch of the vagus nerve is carrying sensory information, so that mechanical pressure is being conveyed into the brain stem. And indeed, that pathway satisfies all the criteria of being a parasympathetic or calming-inducing pathway. Now, you can find all over the internet that you know rubbing behind the ears is really going to calm us down, and really bring our level of overall autonomic arousal way, way down. In reality, it doesn't bring our overall level of autonomic arousal way, way down.

28:10 It brings our level of autonomic arousal down a bit, depending on how active our sympathetic nervous system happens to be. Why do I tell you this? Well, I'm not trying to rain on any parties out there, but the truth is, if you're super stressed, if you're in a panic attack, rubbing behind your ears might help a little bit, but it's not going to suddenly bring you into a state of calm. Soon we're going to talk about things that can bring you into a state of calm very fast, and I will explain exactly how they work and why they work so quickly and why they are so robust. I don't want to be disparaging of the area behind the ear or the area within their ear. Some people really like their ears rubbed. I certainly like the area behind my ears rubbed, like I'm doing now, or the areas within my ears gently rubbed. Who doesn't like that? And indeed, it's calming. But it's one minor branch of the vagus nerve carrying sensory information.

28:57 It's not going to suddenly shift your autonomic nervous system. It's not going to suddenly tilt that seesaw into parasympathetic dominance, as it were. To do that, you need to leverage some of the other, more robust branches of the vagus nerve, and I'll teach you how to do that in just a moment here. The point is that the vagus nerve does carry sort of classic parasympathetic information. If you're asked on an exam, students, med students, I don't want to be responsible for you getting this wrong. I'd love to be responsible for you getting it right. I teach neuroanatomy to medical students. If you are asked, "Is cranial nerve 10, the vagus nerve, parasympathetic or sympathetic?" You should answer, "Parasympathetic." If you're asked if it's sensory or motor, you should say, "It's mixed. It's both." So it's mixed, parasympathetic. However, for everybody out there, med student or not,

29:43 just understand that when you activate certain branches of the vagus nerve, you're either going to get an elevation in alertness, that is, an increase in sympathetic nervous system activity, or a decrease in alertness, that is, an elevation in parasympathetic activity, depending on which branch you activate and the context matters. So, if you want to relax, you can rub behind your ears. You can rub inside your ears. If you have permission, you can do that to the person next to you if they like it. But it's not the case that activating any branch of the vagus nerve is going to calm us down. That's simply not the case, and in a moment, I'll tell you why. I'd like to take a quick break and acknowledge our sponsor, AG1. AG1 is a vitamin mineral probiotic drink that also includes prebiotics and adaptogens.

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32:02 of red lens glasses. These red lens glasses are meant to be worn in the evening after the sun goes down. They filter out short-wavelength light that comes from screens, and from LED lights, which are the most common indoor lighting nowadays. I want to emphasize that ROKA red lens glasses are not traditional blue blockers. They do filter out blue light, but they filter out a lot more than just blue light. In fact, they filter out the full range of short-wavelength light that suppresses the hormone melatonin. By the way, you want melatonin high in the evening and at night. It makes it easy to fall and stay asleep. And those short-wavelengths trigger increases in cortisol. Increases in cortisol are great in the early part of the day, but you do not want increases in cortisol in the evening and at night. These ROKA red lens glasses ensure normal, healthy increases in melatonin, and that your cortisol levels stay low, which is, again,

32:50 what you want in the evening and at night. In doing so, these ROKA red lens glasses really help you calm down and improve your transition to sleep. ROKA red lens glasses also look great. They have a ton of different frames to select from, and you can wear them out to dinner or concerts, and you can still see things. I don't recommend you wear them while driving, just for safety purposes, but if you're out to dinner, you're at a concert, you're at a friend's house, or you're just at home, pop those ROKA red lens glasses on, and you'll really notice the difference in terms of your levels of calm, and all the sleep stuff that I mentioned earlier. So, it really is possible to support your biology, be scientific about it, and remain social at the same time, if you like. If you'd like to try ROKA, go to roka.com, that's R-O-K-A.com, and enter the code "HUBERMAN" to save 20% off your first order. Again, that's roka.com

33:35 and enter the code "HUBERMAN" at checkout. Okay, so we've talked about all the sensory information coming in from behind the ear, from deep in the ear, from the body, coursing up past nodose ganglion into the brainstem. I told you earlier, and it's still true now, that 85% of the vagus nerve pathways are sensory in nature, carrying chemical and mechanical information. So, what about this other 15% of the vagus nerve that is not carrying sensory information from the body, from the head into these brainstem nuclei? By the way, when I say brainstem nuclei, I don't mean nuclei in the context of one neuron. This can be a little bit confusing, but when we hear about the nucleus of a neuron, we mean the area that generally contains the DNA, and we're distinguishing it

34:24 from the axon and the other parts. These neuroanatomists should have been more creative, but when we're hearing about a nucleus in the brain, it means a collection of different neurons, so a big group of neurons. So, when I say brainstem nuclei, I mean a lot of neurons, thousands of neurons in little clumps there that we call nuclei. So, the vagus nerve includes different nuclei, different collections of neurons, and these neurons have what we call efferents, outputs to, as you might have guessed, the body, back to the various organs of the body. They also have connections to things within the head and face area, but for the time being, I'm mostly going to talk about the motor outputs of the vagus nerve that come from these brainstem nuclei.

35:11 So, these motor outputs are not themselves paying attention to mechanical or chemical information. They are going to control the organs of the body. This is extremely important if you want to be able to understand and leverage your vagus nerve for health and well-being, mental health, physical health, performance, and even for accelerated learning. I guess that would fall under performance, or for recovery from different diseases. There are really nice papers starting to emerge, that if you can selectively activate these motor pathways, you can accelerate and increase the recovery from stroke. So, this is of serious significance. But for those of us that fortunately don't have strokes, it's still of serious significance. And in fact, right now, I'm going to tell you about an actionable tool whereby you can leverage one of these motor pathways to a very specific endpoint

35:58 anytime you want. So, let's talk about how you can leverage these motor pathways of the vagus in order to what's called 'autoregulate.' Autoregulation is not just a fancy word for calming down. We are going to talk about calming down, but autoregulation is the way in which your vagus nerve makes sure that that seesaw of sympathetic nervous system to parasympathetic nervous system balance doesn't get tilted too far to the side of sympathetic nervous system activation, that your levels of alertness, your heart rate, your breathing rate, et cetera, don't get too high. And the reason that it's called 'autoregulation' and not just 'calming down,' is that autoregulation is something that's always happening in the background as you're going about your daily activities. In fact, it's also happening while you sleep. In fact, now we're going to talk about

36:44 things that you can do deliberately to indeed calm down, but to also increase the amount of autoregulation that occurs during your entire day when you're not focusing on doing these particular protocols, as well as during sleep. And that will result in elevated what's called 'HRV,' or Heart Rate Variability. Now, I realize that's a tall order, but what we're going to do is we're going to step through this first by focusing on the protocol. And then now that you're familiar with all the business about sensory and motor and para, et cetera, now that you have all of that science and nomenclature in mind, it will all make perfect sense as I describe this protocol for autoregulation, and improving HRV, and all the protocols that follow. Okay, so embedded in your brain, and in your vagal nerve pathways, and in your body, you have an incredible neural circuit.

37:32 This neural circuit is one that you are born with, and it's one that you will have your entire life. This is also a pathway that you want to keep tuned up, that is, that you'll want to make sure is activated on a pretty frequent basis, and it's super easy to do as you'll soon see, so that the pathway does not deteriorate. This is a pathway that originates in an area of your brain called the dorsolateral prefrontal cortex. Now, the dorsolateral prefrontal cortex, by the way, it's the left dorsolateral prefrontal cortex in particular, sort of on the left upper part of the front of your skull. If you were to go deep to that area, you would be on the left; dorsal, top; lateral, side; prefrontal cortex, kind of toward the front, right behind your forehead, okay? Dorsolateral prefrontal cortex sits deep to that area.

38:19 The dorsolateral prefrontal cortex has outputs to a couple of other brain areas called the cingulate, called the insula. You don't have to worry about those names unless you're really interested in them. Those areas have communication with one of the brainstem nuclei, one of those brainstem areas that gets input from the sensory pathways from the body, from the head, of the vagus, and that also contains neurons that have motor output to particular areas of your body. And that brain area, and you're going to love this, is called 'nucleus ambiguus.' I kid you not. It's called 'nucleus ambiguus.' Nucleus ambiguus contains some neurons that project down to what's called the sinoatrial node of the heart, and those neurons are responsible for deceleration of heart rate.

39:09 And it turns out that you can selectively activate those neurons, in no small part, because they receive input, albeit several synapses away, from the left dorsolateral prefrontal cortex, because the prefrontal cortex is involved in deliberate action, in planning and execution of action. It doesn't do it alone. It does it through communication with some other brain structures. But if you, for instance, decide that you're going to activate this deceleration pathway, you can do it. The beautiful thing is that these neurons that also control deceleration of heart rate are active in the background. They're under autonomic control, but you can take control of them. When does that happen? Well, for instance, in sleep, if your heart rate starts to increase, these decelerating neurons, which are neurons of the vagus nerve, they're motor output neurons. They release acetylcholine, and they act on the sinoatrial node,

39:56 which is a node within the heart that controls heart rate to slow your heart rate down, okay? This is the way in which your heart rate never gets too high. The seesaw that is the autonomic nervous system is kind of weighted to the sympathetic nervous system side. A simple example of this, is if you have to stay awake, you can probably do it. At some point, you'll fall asleep. But if you really want to fall asleep, it's harder to make yourself fall asleep. The sympathetic nervous system is one that we can more easily leverage in order to push through things, deadlines, stay up to take care of a sick relative, push ourselves to migrate out from a dangerous place or away from a famine, another example of a dangerous place, I guess. The idea here is that the sympathetic nervous system has kind of a bias towards activity. And in fact, your heart rate is driven by

40:44 the sympathetic nervous system, and that heart rate would continue to accelerate unless there was this deceleration pathway that every once in a while would pump the brake on heart rate. And that's what this vagal pathway from nucleus ambiguus, down to the sinoatrial node is doing. And by the way, this deceleration of heart rate that goes from the vagus motor pathway to the sinoatrial node, is the basis of what's called 'HRV,' or Heart Rate Variability. We hear a lot nowadays about Heart Rate Variability. For those of you that have heard of it and for those of you that haven't, having a higher HRV or Heart Rate Variability is a good thing, right? Normally, if you hear something like Heart Rate Variability, it sounds like a bad thing. Turns out it's a great thing. Heart Rate Variability is essentially the distance or the time, rather,

41:30 between beats of the heart. So, you might think that it's great to have a really consistent heart rate, "boom, doom." Or actually, in reality, it's more like, "doo-doom, doo-doom," and I'm missing some of the beats within the waveform, but you get the idea. But actually, it's well-known to be correlated with a number of positive health outcomes, including things related to brain, and body, and longevity, and performance to have high Heart Rate Variability. Heart Rate Variability is going to lead to a pattern of heartbeats that is more like, "doom-doom-doom-doom, doom doom doom, doom-doom-doom doom-doom." Now, you might say, "That's arrhythmia." Ah, but there are cases of arrhythmia that are good, and there are cases of arrhythmia that are bad. Higher HRV in general, is a good thing. You want it during sleep,

42:18 and you want it during wakeful states. In sleep, Heart Rate Variability comes about because this vagal pathway from nucleus ambiguus, so the cell bodies, the nuclei, literally the DNA within those nuclei of those neurons that reside in nucleus ambiguus, project to the sinoatrial node. And every once in a while, they'll just pump the brake on heart rate and slow heart rate down, and then they'll come off that brake. Slow it down, come off heart rate. And here's the really beautiful part, and the way that you get actionable leverage over the system. The control by the vagus nerve of the sinoatrial node and heart rate is coordinated with your breathing. Now, as I tell you this, it'll make perfect sense, but I just want you to step back for a minute, a second, and realize that these systems of the body are so elegantly coordinated,

43:04 and here's how it works with respect to heart rate and breathing. When you inhale air, of course, your lungs expand. You have a muscle that sits below your lungs called the diaphragm. As you inhale air, of course, that diaphragm moves down. Now, as your diaphragm moves down and your lungs expand, your heart literally has a bit more space in the thoracic cavity to expand. Okay, it's not going to swell massively, but it's going to expand. Now, as a consequence of that expansion, the blood that's moving through your heart is going to move a little bit more slowly per unit volume. That is sensed by a particular group of neurons in your heart, and that sends a signal to your sympathetic nervous system to speed your heart rate up. Put differently, inhaling speeds

43:51 your heart rate up. Now, the converse is also true. When you exhale, your lungs deflate. Your diaphragm moves up, and as a consequence, there's slightly less space for the heart. So, the heart shrinks a little bit, not a ton, but it's enough such that whatever blood is in the heart moves through more quickly per unit volume. That faster movement is sensed by neurons within the heart, sends a signal to the brain, and the brain activates those neurons within nucleus ambiguus, and very quickly sends a signal to the sinoatrial node to slow your heart rate down. Put differently, exhales slow your heart rate down, and they do so by way of vagal control over the sinoatrial node. This is the deceleration pathway over heart rate.

44:39 So, as I mentioned, this is happening all the time during sleep. You don't have to be consciously aware for this to happen. It's a fortunate consequence of nature that the neurons within your brainstem that control breathing, and the neurons within your brainstem that control heart rate, and the other neurons within the heart itself that control heart rate, the pacemaker cells, all can function without you having to think about it. That's a wonderful thing for obvious reasons. It's also the case that because we have this input from the left dorsolateral prefrontal cortex down through a couple other structures like the cingulate, and the insula, and that converge on nucleus ambiguus, if you decide to slow your heart rate down, you can do it. And you do so by doing a deliberate exhale, and/or by increasing the intensity or the duration of your exhale. So, you can do that right now.

45:26 If you want to slow your heart rate down, that is, if you want to increase parasympathetic nervous system activity, and you want to calm down fast, you can literally just... [exhales] Exhales slow your heart rate down, and exhales tilt that seesaw that is the autonomic nervous system more toward the parasympathetic side. Now, I've talked before on this podcast, and all over social media about the so-called physiological sigh, a naturally occurring form of breathing that occurs in sleep, and that we can deliberately do anytime we want to calm down fast. And the physiological sigh consists of, as many of you know, two inhales through the nose, followed by a long, until lungs empty, exhale through the mouth. Typically, the first inhale is longer. Again, it's done through the nose. The second inhale is shorter, kind of a sharp inhale

46:12 to make sure you maximally inflate all of the little sacs within your lungs. And then the exhale is a long, slow exhale that dumps all of your air. I'll just demonstrate the physiological sigh for you, for those of you that haven't seen it. You, again, big inhale through the nose, second sharp inhale through the nose to make sure you maximally inflate the lungs, and then long exhale until lungs empty. It goes like this. [inhales and exhales slowly] Okay, lungs are empty. That is indeed the fastest way to activate the parasympathetic nervous system,

46:57 and to tilt that seesaw from levels of high sympathetic nervous system activation, to lower levels of sympathetic nervous system activation. In fact, I immediately feel calmer. Maybe you can even hear it in my voice. So, when you do a physiological effect, you're getting both a chemical signal into the brain, that is, the adjustment of that carbon dioxide-oxygen ratio. It's mainly due to the offloading of carbon dioxide. That lower level of carbon dioxide is registered by the brain very quickly, and leads to an increase in calm. The deceleration of heart rate driven by the exhale is also registered by the brain very quickly, and leads to an increase in calm. When you just emphasize an exhale, meaning you extend it, or you make it more intense, and you don't do the two inhales first, that is, you don't do the physiological sigh, well, you get the mechanical signal, but you don't get the chemical signal,

47:45 at least not to the same degree you do with the physiological sigh. Put simply, if you want to calm down fast, ideally you do the physiological sigh. However, it turns out that one of the best ways to improve your HRV, both in sleep and in wakeful states, which takes a very minimum of effort and is rarely, if ever, discussed, is simply throughout the day, I would say 10, 15, or maybe even 20 times per day, any time it occurs to you, to just deliberately extend your exhale, that is, to pump the brake on your heart rate through the vagus nerve pathway that I've been describing, just [exhales] exhale. Slow your heart rate down, and then get about your normal routine. You can do that essentially anytime you remember to. This is literally going to increase your HRV. You now know the mechanism by which it does that.

48:31 And get this. It will also increase your HRV in sleep at night. And the reason is that this pathway that originates with the left dorsolateral prefrontal cortex, and goes down to nucleus ambiguus, and then to the sinoatrial node of the heart, because it's under conscious control, and because it's subject to what we call plasticity, to strengthening and to weakening, that is, if you use it deliberately, it gets strengthened. If you don't use it deliberately, it gets weakened. Well, that's a great thing because it means that if you just simply remember to do some extended exhales throughout the day, you're going to strengthen this pathway such that it operates in the background through autoregulation without you ever having to think about it. Now, of course, that effect wears off over time if you don't occasionally remember to just do some [exhales] longer exhales.

49:19 But this is a wonderful protocol, in my opinion, because it capitalizes on an inborn circuit, right? A circuit that you were born with that is already installed, that you can use at any point; it doesn't take any learning. But that if you just ping every once in a while with some extended exhales throughout the day, it takes essentially no time. You get the benefit of feeling a little bit calmer, slowing your heart rate down. And your HRV, which is correlated with a host of positive health outcomes in the short and long term, will increase. Two interesting things everyone should be aware of, is that as we age, of course, a number of things happen. Memory gets slightly to much poorer, all right? There are ways to offset that. Heart Rate Variability gets much worse. Now, an interesting finding from Nolan Williams' lab at Stanford, is that if you activate dorsolateral prefrontal cortex

50:06 using what's called transcranial magnetic stimulation... This is a procedure where you take a stimulator, and you non-invasively place it on the skull outside and just above dorsolateral prefrontal cortex, and you stimulate through the skull dorsolateral prefrontal cortex. You observe, as you would expect, a deceleration of heart rate. And it's known to be carried through this vagal pathway, to the sinoatrial node. Even after the stimulation is removed, you find that Heart Rate Variability increases because this pathway has been stimulated into neural plasticity. It's strengthened. The other way to strengthen this pathway is to do exactly what I just described, to deliberately engage this long exhale mechanism at various times throughout the day. Now, if you miss a day, is the pathway going to atrophy? No.

50:52 If you do it 50 times a day, is it going to strengthen more than if you do it one time per day? Yes. Do we know the exact thresholds of how many times per day you should be doing these deliberate exhales in order to keep this pathway robust? No, unfortunately, we do not. However, we do know that in human patients that suffer atrophy of the dorsolateral prefrontal cortex that's associated with normal aging, or with accelerated atrophy of dorsolateral prefrontal cortex, or lesions of dorsolateral prefrontal cortex that tend to occur in older people who get strokes, or just associated with the normal aging process, heart rate variability declines with age. And it is now thought that Heart Rate Variability declines with age, of course, in part through lower levels of physical activity because there are, of course, certain forms of physical activity, like high intensity interval training,

51:38 to keep that Heart Rate Variability elevated over time using exercise. But it's also true that if this pathway degenerates, you see a decrease in Heart Rate Variability. If you keep this pathway engaged by behaviorally and deliberately doing these long exhales, or if you take the more robust approach of transcranial magnetic stimulation, something that most people unfortunately won't have the opportunity to do, although maybe in the future, there will be commercial devices that will allow us to do this, you can keep Heart Rate Variability higher as you age, which, as I mentioned before, is correlated with a number of different positive health outcomes. So, these pathways by which we can tap into deliberate activation of this vagal control over the sinoatrial node are not just incidental. They turn out to be central to the aging process. They turn out to be central

52:25 to countering the aging process, and you now know that you have some agency and control over them. So, earlier, I was talking about how, despite the fact that the vagus nerve is classified as a parasympathetic nerve, that it also can be alerting. It can increase levels of sympathetic nervous system activity, and that runs counter to the concept of parasympathetic, which is always labeled as rest and digest. I'm now going to tell you a tool that you can use when you're feeling less than energized, less than motivated, and when you need to exercise and you don't feel like doing it, and when you want to leverage exercise as a way to improve brain function and plasticity. It all involves the vagus nerve, and it involves an aspect

53:12 of the vagus nerve that very few people are aware of, but in my opinion, is one of the coolest aspects of the vagus nerve. It's at least as cool as vagal control over Heart Rate Variability and autoregulation. And it goes like this: there's a beautiful set of findings from a guy named Peter Strick at the University of Pittsburgh, who used these really cool methods for tracing connections between the brain and body to ask the question, "What areas of the brain are communicating with our adrenal glands?" Our adrenal glands are two glands that sit atop your two different kidneys, so one on top of each kidney, and release, as the name suggests, adrenaline. Adrenaline is also called epinephrine. Your adrenal glands also release cortisol. But for sake of this discussion, let's just think about adrenaline released

53:57 from your adrenals. What he found, through a bunch of experiments done in non-human primates, and that seemed to correspond very well to what we observe in humans as well, is that there are three general groups of brain areas. Motor activation areas, so what we call upper motor neurons. So, these are the neurons in the brain that control the lower motor neurons in the spinal cord that control the muscles of the body, as well as neurons within our brain that are involved in cognition and planning, and areas of the brain that are involved in emotion, that can communicate with the adrenals, and cause them to release adrenaline. Now, that's great, but it sort of points to a pathway whereby, okay, you know that you should exercise, you tell yourself that you should exercise, you're emotional about it, and your adrenals release adrenaline, and you exercise.

54:44 Now, that's interesting. But what is perhaps far more interesting, is that the data from Strick Lab, and other labs as well, shows that when we move the large muscles of our body, the adrenals release adrenaline, epinephrine. Now, epinephrine has an activating sympathetic nervous system stimulatory effect, right? It tends to make the tissues of the body that are associated with movement, and with so-called fight or flight... Although again, fight or flight is kind of an extreme example, it tends to activate the organs of the body, and make them more likely to be active. It increases the probability that movement will occur, overall body movement. So, when we move the large muscles of our body, our legs, and in particular our trunk muscles, we release adrenaline.

55:30 That adrenaline activates the organs of our body, and further makes it likely that we're going to move our musculature more. But get this, adrenaline, epinephrine, doesn't cross the blood-brain barrier. So, how does it increase our level of alertness in our brain, right? You don't want your body to be super active, and your brain to be kind of sleepy. That's not good. That's not adaptive. It turns out that when the adrenals release adrenaline, it binds to receptors on the vagus nerve itself, those sensory axons that extend into the body. There are receptors on those wires, right? Not all of the receptors are at one end or the other. They're also on those axons. The adrenaline binds to the receptors on those axons, and the vagus nerve in turn releases glutamate, an excitatory neurotransmitter, in a structure in the brain

56:18 called the nucleus tractus solitarius. The neurons, in what I'm just going to call the NTS for simplicity, in turn activate neurons in a brain structure called the locus coeruleus. The locus coeruleus contains neurons that release what's called norepinephrine. And the neurons of locus coeruleus send their axons out very extensively across the brain, in kind of a sprinkler-system-like organization, such that, when you move the large musculature of your body, you release adrenaline. That adrenaline activates the tissues of your body, makes them more likely to move, and also binds to receptors on the vagus. The vagus nerve in turn releases glutamate, an excitatory neurotransmitter, in the NTS. The NTS then passes off that excitatory signal like a bucket brigade off to the locus coeruleus.

57:04 The locus coeruleus dumps a bunch of norepinephrine into the brain, and increases your levels of alertness. What this means, is that the vagus nerve

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