Essentials: How Your Nervous System Works & Changes

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. For today's podcast, we're going to talk about the parts list of the nervous system. Now that might sound boring but these are the bits and pieces that together make up everything about your experience of life, from what you think about to what you feel, what you imagined, and what you accomplished from the day you're born, until the day, you die, by the end of this podcast. I promise you're going to understand a lot more about how you

you work and how to apply that knowledge. So, let's talk about the nervous system. The reason I say your nervous system and not your brain is because your brain is actually just one piece of this larger, more important thing, frankly that we call the nervous system. The nervous system includes your brain

and your spinal cord but also all the connections between your brain and your spinal

cord and the organs of your body. It also includes very importantly all the connections between your

Organs

back to your spinal cord and brain.

So, the way to think about how you function at every level from the moment, you're born

until the day you die, everything you think. And remember and feel, and imagine

is that your nervous

system is, this continuous loop of communication between the brain, spinal cord and body and body spinal cord and brain. In fact, we really can't even separate them. It's one continuous loop the way to think about how the nervous system works.

Is that our

Experiences are memories. Everything is sort of like the keys on a piano being played in a

particular order, right?

If I play the keys on a piano, in a particular order and with a particular

intensity, that's a given song.

We can make that analogous to a given experience. Our brain is really a

map of our experience.

Are we come into the world and our brain has a kind of biased towards learning particular kinds of things. It's ready to receive information and learn that information. But the brain is

really a map.

Of experience. So let's

talk about what experience really is. What does it

mean for your brain to work?

Well, I think it's fair to say that the nervous system really

does five things. Maybe six, the first

one is sensation, sensation is a

non-negotiable element of your nervous system. You have neurons in your eye, that perceive certain colors of light and certain directions of movement you have neurons in your skin. That perceive particular kinds of touch

like light touch or firm touch or painful.

Touch. You have neurons in your ears that perceive certain sounds. Your entire experience of

life is filtered by these what we call sensory receptors. If you want to know what the name is, perception is our ability to take what we're sensing and focus on it

and make sense of it to explore it, to remember it. So really perceptions are just whichever

Sensations. We happen to be paying attention to at any moment. Perception is under the control of your

Attention. And the way to think about attention is,

it's like a spotlight except it's not one Spotlight, you actually have to attentional spotlights.

Anyone that tells you you can't

multitask tell them they're wrong

and if they disagree with you, tell them to contact me because

in Old World

primates of which humans are, we are able to do what's called covert attention. We can place a spotlight of attention on something. For instance, something we're reading or looking at where someone that we're listening

to, and we can place a second

Spotlight of attention on something, we're eating, and how it tastes

or our child running around in the room or my dog.

You can split your attention into two locations, but

of course you can also bring your attention that is your perception to one particular location. You can dilate your attention kind of like making a spotlight more diffuse or you can make it more concentrated.

This is very

important to understand. If you're going to think about tools

to improve your nervous. System attention is something that is

absolutely under your control.

The nervous system can be reflexive in its action or it can be deliberate.

Thoughts are

top-down, they require some effort and

some Focus, but that's the

point. You can decide to focus your behavior in any way you want. But it will always feel like it requires some effort and some strain, whereas, when you're in reflexive mode, just walking and talking and eating and doing your thing, it's going to feel very easy

and that's because your nervous system basically wired up,

to be able to do most things, easily, without much, metabolic demand, without consuming much

energy. But the moment you try and do something very specific.

Eric. It's going to, you're going to feel a sort of

mental friction. It's going to be challenging.

So we've got Sensations perceptions, and then we've got things that we call feelings / emotions. And these get a little complicated because almost all of us, I would hope all of us are familiar with things like, happiness, and sadness, or boredom or frustration. Certainly, emotions and feelings are the product of the nervous system. They involve the activity of neurons, but, as I mentioned,

Earlier neurons are electrically active, but they also release

chemicals. And there's a certain category of chemicals

that has a very profound

influence on our emotional states. They're called neuromodulators.

And those neuromodulators have names that probably you've heard of,

before things like dopamine and serotonin and acetylcholine epinephrine.

Neuromodulators are really interesting because they bias which

neurons are likely to be active and which ones are

Likely to be inactive

a simple way to think about neuromodulators, is they are sort of like playlist that you

would have on any kind of device where you're going to play particular categories of

music. So, for instance, dopamine, which is often discussed as the molecule of reward or

joy

is involved in reward, and it does tend to create a sort

of upbeat mood in when released in appropriate amounts in the brain. But the reason it does that is because it makes certain neurons.

And neural. Neural circuits as we call them more active and others less

active. Okay, so serotonin for instance is a molecule that when released tends to make us feel really good with what we have are sort of internal

landscape and the resources that we

have, whereas dopamine more than being a molecule of reward, is really more, a molecule of motivation toward things that are

outside us and that we want to pursue

and we can look at healthy conditions.

Or situations like being in pursuit of a goal where every time we accomplish something

in route to that goal, a little bit of dopamine is released and we feel more motivation that happens.

We can also look at the extreme example of something like Mania where somebody is. So

you know,

relentlessly in pursuit of external things

like money and relationships that they're sort of

in this delusional state of thinking that they have the resources that they need in order to pursue all

these things. When in fact, they don't, I

want to emphasize also

Emotions are something that we

generally feel are not under our control. We feel like they kind of geyser up within us and they just kind of happen

to us. And that's because they are somewhat reflexive. We don't really set out

with a deliberate thought to be happy or deliberate thought to be sad.

We tend to experience

them in kind of a passive reflexive way.

And that brings us to the next thing which our

thoughts thoughts are really interesting. Because in many ways, there are like perceptions except that they draw on.

Just what's happening in the

present. But also things we remember from the

past and things that we anticipate about the future. The other thing about thoughts, that's really interesting. Is that thoughts can be both reflexive, they can just be occurring all the time, sort of like, pop-up windows on a poorly filtered web browser or they can be deliberate, we can decide to have a thought and a lot of people don't understand or at least appreciate that the thought patterns and the neural circuits that underlie thoughts can actually be controlled in this

Deliberate way,

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actions actions or behaviors are perhaps the most important aspect our nervous system

because first of all, our behaviors are actually. The only thing

that are going to create any fossil record of our existence, you know, after we die the nervous system deteriorates, our

skeleton will remain but it's you know, in the moment

of of experiencing something very joyful or something,

Sad. It can feel so all-encompassing

that we actually think that it has

some meaning, beyond that moment. But actually for humans. And I think for all species, the sensations, the perceptions and the thoughts, and the feelings that we have in our life span. None

of that is actually carried forward. Except the ones that we take

and we convert into actions, such as writing actions such as word.

Is action such as engineering, new things. And so, the

fossil record of our species and each one of us is really through

action. And that in part is why

so much of our nervous system is devoted to

converting sensation, perception feelings, and thoughts into actions.

The other way to think about it is that one of the reasons that our central nervous system, our brain and spinal cord include the stuff in our skull but

also connects so heavily to the body is because

Most everything that we

experience including our thoughts and feelings was really

designed to either impact our Behavior or

not. And the fact that thoughts allow us to reach into the past and anticipate the future and not just experience. What's happening in the

moment, gave rise to an incredible capacity for us to engage in behaviors that are not just for the moment. They're

based on things that we know from the past and that we would like to see in the future.

And this aspect our nervous system of creating movement

Occurs through some very simple Pathways. The reflexive pathway basically includes areas of the brain stem. We call Central pattern, generators. When you walk provided you already know how to

walk. You are basically walking because you have the central pattern,

generators groups of neurons, that generate right

foot Left Foot, Right? Foot left foot kind

of movement. However, when you decide to move in a particular deliberate way, that requires a little more attention, you start to engage areas of your brain for

Top-down processing, where your for brain works from the top down to control those Central pattern

generator. So that maybe it's right foot, right foot, Left Foot, Right Foot, Right Foot left foot. If maybe you're hiking along some rocks or something, and you have to engage in that kind of movement.

So, movement is just like thoughts can

be either reflexive or

deliberate. And when we talk about deliberate, I want to be very specific about how your brain works

in the deliberate way, because it give or gives rise to

a very

Important feature

of the nervous system that we're going to talk about next, which is your ability to change your nervous system

and what I'd like to Center on for a second. Is this notion of what does it mean for the nervous system to do something deliberately? Well, when you do something deliberately, you pay attention, you are bringing your perception to an analysis of three things. Duration, how long something is going to take or should be done path? What you should be doing and outcome. If you

Do something for a given length of time. What's going to happen? Now when you're walking down the street or you're eating or you're just talking reflexively, you're not doing this. What I called, EPO duration, path, outcome type of deliberate function in your brain and nervous system. Let's give an example where perhaps somebody says something that's triggering to you, you don't like it and, you know, you shouldn't respond. You feel like I shouldn't respond. I shouldn't respond action. Responding. You're actively suppressing your behavior through top-down.

Processing your for brain is actually preventing you from

saying the thing that, you know, you shouldn't say or that, maybe you should wait to say, or say in a different form.

This feels like, agitation and stress because you're actually suppressing a circuit. We actually can see

examples of what happens when you're not doing this. Well,

some of the examples come from children, if you look at young children, they don't have the for brain circuitry to engage in this top-down

processing until they reach age. 22, even

25. But in young

children you see this in a really robust

way a kid sees a piece of candy that it wants him will just reach out and grab it. Whereas an adult probably would

ask if they could have a piece or wait until they were offered a piece in most cases

people that have damage to the certain areas of the frontal

lobes. Don't have this kind of restriction, they'll just blurt things out. They'll just say, things impulsivity is a lack of top-down control. A lack of top-down processing. So a lot of the

motor system,

Mm is designed to just work in a reflexive way and then when we decide, we want to learn something or do something or not, do something

we have to engage in this top-down restriction. And it feels like agitation because it's accompanied by the release of a neuromodulator called norepinephrine which in the

body, we call

Adrenaline and it actually makes us feel agitated.

So for those of you that are trying to learn something new or to learn to suppress your responses or be more,

deliberate and careful in your responses,

That is going to feel challenging for a particular reason. It's kind of feel challenging because the chemicals in your body that are released in association with

that effort are

designed to make you feel kind of agitated. And so this is really important to understand because if you want understand neural

plasticity, you want to understand how to shape your behavior, how to shape your thinking, how to change how you're

able to perform in any context. The most important thing to understand is that it requires

Wires top-down

processing. It

requires this feeling of agitation. In fact I would say the agitation and strain is the entry point to neural plasticity.

So let's take a look at what neural plasticity is. Neuroplasticity is the

ability for these Connections in the brain and body to change in response to experience and

what's so incredible about the

human nervous system in particular, is that we can direct our own neural changes. We can decide that we want to change our brain. In other words, our

Can change itself and our nervous system can change itself for a long time. It was thought that neuroplasticity was the unique gift of young animals and humans that it could only

occur when we're young. And in fact, the young brain is

incredibly plastic. Children can learn three languages without an accent

reflexively. Whereas

adults it's very challenging, it takes a lot more effort and strain a lot more of that duration. Path outcome kind of thinking in order to achieve those plastic changes

we now

Know, however, that the adult brain

can change in response to

experience. In order to understand that process, we really have to understand something that

might at first seem totally divorced from

neuroplasticity, but actually lies at the

center of neuroplasticity and for any of you that are interested in changing your nervous system. So that

something that you want can go from being very hard or seemed almost impossible in Out Of Reach to being very reflexive. This is an especially important to pay attention to

Plasticity in the adult human nervous system is gated meaning it is controlled by neuromodulators these things that we talked about earlier dopamine serotonin and one in particular called acetylcholine are what open up plasticity. They literally unveil plasticity and allow brief periods of time in which whatever information whatever thing we're sensing or perceiving or thinking, whatever emotions we feel.

And literally be mapped in the brain. Such that later, it will become much easier for us to

experience and feel that thing.

Now, this has a dark side in a positive side.

The dark side is it's

actually very easy to get neural

plasticity as an adult through traumatic or terrible or challenging experiences. But the important question is to say, why is that? And the reason that's the case is

because when something very bad happens, there's the

release of two sets.

It's of neuromodulators in the brain epinephrine which tends to make us feel alert and agitated which is associated with moats, bad circumstances and acetylcholine

which tends to create a even more

intense. And focused perceptual Spotlight. Remember earlier we were talking about perception and how it's kind of like a spotlight. Acetylcholine makes that light particularly bright and particularly restricted to one

region of our experience and it does that by making

certain neurons in our

And and body active much more than all the rest.

So acetylcholine is sort of like a highlighter and marker upon which neuroplasticity, then comes in later and says, wait, which neurons were active in this particularly

alerting phase of whatever, you know, day or night whenever this thing happen to happen. So the way it works is this, you can think of epinephrine as creating this alertness in this kind of unbelievable level of increased attention.

Compared to what you were experiencing before. And you can think of acetylcholine as being the molecule that highlights, whatever it happens during that period of heightened alertness. So, just to be clear, it's epinephrine crates, the alertness that's coming from a subset of neurons in the brain stem. If you're interested and acetylcholine coming from an area of the forebrain is tagging or marking the neurons that are particularly active. During this heightened level of alertness.

Now, that marks the cells, the neurons and the synapses for strengthening for becoming more

likely to be active in the future, even without us, thinking about it,

okay? So, in bad

circumstances, this all happens without us having to do much

when we want

something to happen. However,

we want to learn a new language. We want to learn a new skill. We want to become more motivated. What do we know for certain? We know that, that

process of

Getting neural plasticity. So that we have more focus more motivation. Absolutely requires the release of epinephrine, we have to have alertness in order to have

focus and we have to have focus in order to

direct those plastic changes to particular parts of our nervous system. This has immense

implications in thinking about the various

tools whether or not those are chemical tools or machine tools

or just self-induced regimens of

How long, or how intensely you're going to focus in order to get neuroplasticity,

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The dirty secret of neural

plasticity. Is

that no neural plasticity, occurs

during the thing, you're trying to learn during the terrible event during

the great event. During the thing that you're really trying to shape and learn nothing is actually changing between the neurons that is going to

last, all the neural plasticity, the

strengthening of the

synapses. The addition in some cases of new nerve cells or at least connections between nerve cells,

all of that occurs at a very different phase of life,

which is when we are in sleep and non sleep depressed, and so neural plasticity, which is the kind of Holy Grail of Human Experience of, you know, this is

the new year and everyone's thinking New Year's resolutions and right now perhaps everything is organized and people

are highly motivated but what happens in March or April or May, well that all depends

on how much attention and focus one can continually bring to whatever it is. They're trying to learn so much so that

at agitation and a feeling of strain are actually required for

this process of neuroplasticity to get triggered. But the

actual rewiring occurs during

periods of sleep and non sleep depressed. There's a study published last year. That's particularly relevant here that I want to share was not done by my laboratory that showed that 20 minutes of depressed. This is not deep sleep, but essentially doing something very hard and very intense and then

King 20 minutes, afterward immediately

afterwards to deliberately turn off

the deliberate focused thinking and engagement. Actually accelerated neural plasticity.

There's another study. That's just incredible. And we're going to go

into this in a future episode of the podcast. Not too long from now that showed that if people are learning a particular skill, it could be a language skill or a motor skill

and they hear a tone

just playing in the background and the tone is

Playing periodically, their background like just a bell in deep

Sleep. If that Bell is played learning is much faster for the thing that

they were learning while they were awake,

it's somehow cues. The nervous system in sleep doesn't even have to be in dreaming. That something that happened in our, the waking phase was, especially important, so much. So that that Bell is sort of a pavlovian q. It's sort of a reminder to the sleeping brain. Oh you need to

What it is that you were learning at that particular time of day and the learning rates and the rates of retention meaning, how much people can remember from the thing they learned are significantly higher, under those conditions.

So I'm going to talk about

how to apply all this knowledge in a little bit more in this podcast episode, but also in future episodes.

But it really speaks to the really key importance of sleep and focus, these

two opposite ends of our attentional state. When we're in

sleep, these days,

Dpos duration, path and outcome. Analysis are impossible. We just can't do that. We are only in relation to what's happening inside of us. So sleep is key. Also key our periods of non sleep, deep rest where we're turning off our analysis of duration, path and outcome in particular, for the thing that we were just trying to learn and we're in this kind of liminal state where our attention is kind of drifting all over. It turns out that's very important for the consolidation, for the changes between the nerve

Those that will allow what we were trying to learn to go from being deliberate and hard and stressful, and a strain too

easy and reflexive. This also points to how

different people including many modern clinicians are thinking about how to prevent bad

circumstances traumas

from routing their way into our nervous system permanently. It says

that you might want to interfere with certain aspects of brain states that are away from the bad thing that happened that

It happened the brain states that happen the next day or the next month or the next year.

And also I want to be aware. I want to make sure that I pay attention to the fact that for many of you, you're thinking about neuroplasticity, not just in changing, your nervous system

to add something new, but to also, get rid of things that you don't like, right. That you want to forget bad experiences or at least remove the

emotional contingency

of a bad relationship or a bad relationship to something or some person or some event.

Learning to fear certain things less to eliminate a phobia to erase a

trauma. The memories themselves don't get

erased. I'm sorry to say that the memories don't selves get a race, but the emotional load of memories can be reduced and there are number of different ways that that can happen but

they all require this thing

that we're calling all Calling neuroplasticity. We're going to have a large number of discussions about neuroplasticity in depth, but

the most important thing to understand is that it is indeed a two-phase

Is

what governs the transition between alert and

focused and these depressed and deep sleep States is a system in our brain and body. A certain aspect of the nervous system called the autonomic nervous system

and it is immensely important to understand how this autonomic nervous system works. It has names like the sympathetic nervous system and parasympathetic nervous system which frankly are

complicated names because they're a little bit misleading. Sympathetic is the one that's associated with

more alertness.

Parasympathetic

is the one that's associated with more

calmness and it gets really misleading because the sympathetic nervous system sounds like sympathy and then people think it's related to calm. I'm going to call the alertness system and the calmness system because even though sympathetic and parasympathetic or

sometimes use people really get confused.

So the way to think about the autonomic nervous system and the reason it's important for every aspect of your life but in particular for neural plasticity and engaging in these Focus States in these

Oka States. Is that it works sort of like a seesaw every 24 hours. We're all familiar with the fact that when we wake up in the morning we might be a little bit groggy, but then generally were more alert. And then, as evening comes around, we tend to become a little more relaxed and sleeping eventually at some point at night, we go to sleep. So we go from alert

to deeply calm. And as we do

that, we go from an ability to engage in these very focused,

duration path, outcome types of

analyses to States in sleep that are completely

divorced from duration path, an outcome in which everything is completely random and untethered in terms of our

Sensations, perceptions and feelings and so forth.

So every 24 hours, we have a phase of our

day. That is optimal

for thinking and focusing and learning and neural

plasticity and doing all sorts of things. We have

energy as well and add another phase of our day. We're tired and we have it. No ability to focus. We have no ability to engage in duration

path, outcome types of analyses and it's

Interesting that both phases are important for shaping our

nervous system in the ways that we want.

So if we want to engage neuroplasticity and we want to get the most out of our nervous

system, we each have to

master that both the transition between wakefulness and sleep and the transition

between sleep and

wakefulness now, so much has been made of the importance of sleep and it is critically important for wound. Healing for learning, as I just mentioned

for consolidating learning for all

aspects of our immune system.

It is the one period of time in which we're not

doing these duration path in outcomes types of analyses. And it is critically important to all aspects of our health, including our longevity. Much less has been made, however, of how to get better at sleeping, how to get better at the process? That involves falling asleep, staying asleep, and accessing the states of mind and body that involve total paralysis. Most people don't know this but you're actually paralyzed during much of your sleep so that you can't act out your dreams. Presumably

But also where your brain is in a total idle

state where it's not controlling anything, it's just left to kind of free

And there are certain things that we can all do in order to

master that transition in order to get better at sleeping

and it involves much more than just how much we sleep. We're all being told, of course that we need to sleep more but there's also the

issue of Sleep Quality accessing those deep states of nandi. Po thinking accessing the right timing of sleep.

Not a lot has been discussed publicly as far as I'm aware of

when to time your sleep. I think we all can appreciate that sleeping

for half an hour

throughout the day.

Day. So that you get a total of eight hours of sleep. Every

24 hour cycle is probably very different and not optimal compared to a

solid block of eight hours of sleep. Although, there are people that have tried this. I think it's been written about in various books. Not many people can stick to that schedule. Incidentally, I think it's called the uberman schedule, not to be confused with the huberman schedule because first of all, my schedule doesn't look anything like that. And second of all I would never attempt such a sleeping regime.

The other thing that is really important to understand is that we have not explored as a culture, The rhythms that

occur in our waking States.

So much has been focused on the value of sleep, in the importance

of sleep, which is great,

but I don't think that most people are paying attention to what's happening in their waking States. And when their brain is optimized for focus, when their brain is optimized for these dpos,