Today’s episode provides an introduction to how the nervous system
works to create sensations, perceptions, emotions, thoughts and
behaviors, as well as how we can change our nervous system— a
phenomenon known as neuroplasticity.
-- Welcome to the Huberman Lab Podcast where we discuss science and
science-based tools for everyday life. (upbeat guitar music) 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 imagine, and what you accomplish from the day
you're born until the day you die. That parts list is really
incredible because it has a history associated with it that really
provides a window into all sorts of things like engineering, warfare,
religion, and philosophy. So I'm going to share with you the parts
list that makes up who you are through the lens of some of those other
aspects of life and other aspects of the history of the discovery of
the nervous system. By the end of this podcast I promise you're going
to understand a lot more about how you work and how to apply that
knowledge. There's going to be a little bit of story. There's going to
be a lot of discussion about the people who made these particular
discoveries. There'll be a little bit of technical language. There's
no way to avoid that. But at the end you're going to have in hand what
will be the equivalent of an entire semester of learning about the
nervous system and how you work So a few important points before we
get started. I am not a medical doctor. That means I don't prescribe
anything. I'm a professor, so sometimes I'll profess things. In fact,
I profess a lot of things. We are going to talk about some basic
functioning of the nervous system parts and et cetera, but we're also
going to talk about how to apply that knowledge. That said, your
healthcare, your wellbeing is your responsibility. So anytime we talk
about tools please filter it through that responsibility. Talk to a
healthcare professional if you're going to explore any new tools or
practices and be smart in your pursuit of these new tools. Also wanna
emphasize that this podcast and the other things I do on social media
are my personal goal of bringing zero cost to consumer information to
the general public. It is separate from my role at Stanford
University. In that spirit I really want to thank the sponsors of
today's podcast. The first one is Athletic Greens which is an all-in-
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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. You may have heard of
something called a Mobius strip. A Mobius strip is almost like one of
these impossible figures that no matter which angle you look at it
from you can't tell where it starts and where it ends. And that's
really how your nervous system is built. That's the structure that
allows you to, for instance, deploy immune cells, to release cells
that will go kill infection when you're in the presence of infection.
Most people just think about that as a function of the immune system
but actually it's your nervous system that tells organs like your
spleen to release killer cells that go and hunt down those bacterial
and viral invaders and gobble them up. If you have a stomach ache, for
instance, sure, you feel that in your stomach, but it's really your
nervous system that's causing the stomach ache. The ache aspect of it
is a nervous system feature. So when we want to talk about experience
or we want to talk about how to change the self in any way, we really
need to think about the nervous system first. It is fair to say that
the nervous system governs all other biological systems of the body,
and it's also influenced by those other biological systems. So if
we're talking about the nervous system we need to get a little
specific about what we mean. It's not just this big loop of wires. In
fact, there's a interesting story about that because at the turn of
the sort of 1800s to 1900s, it actually was believed that our nervous
system was just one giant cell. But two guys, that names aren't super
important, but in fairness to their important discovery, Ramon y
Cajal, a Spaniard, Camillo Golgi, an Italian guy, figured out how to
label or stain the nervous system in a way that revealed, oh my
goodness, we're actually made up of trillions of these little cells,
nerve cells that are called neurons. And that's what a neuron is. It's
just a nerve cell. They also saw that those nerve cells weren't
touching one another. They're actually separated by little gaps. And
those little gaps you may have heard of before, they're called
synapses. Those synapses are where the chemicals from one neuron are
kind of spit out or vomited into. And then the next nerve cell detects
those chemicals and then passes electricity down its length to the
next nerve cell and so forth. So really the way to think about your
body and your thoughts and your mind is that you are a flow of
electricity, right? There's nothing mystical about this. You're a flow
of electricity between these different nerve cells. And depending on
which nerve cells are active you might be lifting your arm or lowering
your arm. You might be seeing something and perceiving that it's red
or you might be seeing something and perceiving that it's green, all
depending on which nerve cells are electrically active at a given
moment. The example of perceiving red or perceiving green is a
particularly good example because so often our experience of the world
makes it seem as if these out these things that are happening outside
us are actually happening inside us.
But the language of the nervous system is just electricity. It's just
like a Morse code of some sort or the syllables and words and
consonants and vowels of language. It just depends on how they're
assembled, what order. And so that brings us to the issue of how the
nervous system works. The way to think about how the nervous system
works is that our experiences, our 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. It's not really that the key, you know, A sharp or E flat
is the song. It's just one component of the song. So when you hear
that, you know, for instance, there's a brain area called the
hippocampus, which there is, that's involved in memory. Well, it's
involved in memory, but it's not that memories are stored there as,
you know, sentences. They're stored there as patterns of electricity
in neurons that when repeated, give you the sense that you are
experiencing the thing again. In fact, deja vu, the sense that what
you're experiencing is so familiar and like something that you've
experienced previously is merely that the neurons that were active in
one circumstance are now becoming active in the same circumstance
again. And so it's really just like hearing the same song maybe not
played on a piano but next time on a classical guitar, there's
something similar about that song even though it's being played on two
different instruments. So I think it's important that people
understand the parts of their nervous system, and that it includes so
much more than just the brain and that there are these things, neurons
and synapses. But really that it's the electrical activity of these
neurons that dictates our experience. So if the early 1900s were when
these neurons were discovered, certainly a lot has happened since
then.
And in that time between the early 1900s and now there's some
important events that actually happened in history that gave us
insight into how the nervous system works. One of the more surprising
ones was actually warfare. So as most everybody knows in warfare
people get shot and people often die but many people get shot and they
don't die. And in World War One, there were some changes in artillery,
in bullets that made for a situation where bullets would enter the
body and brain at very discrete locations and would go out the other
side of the body or brain and also make a very small hole at that exit
location. And in doing so produced a lot of naturally occurring
lesions of the nervous system. Now you say, okay, well, how does that
relate to neuroscience? Well, unlike previous years where a lot of the
artillery would create these big sort of holes as the bullets would
blow out of the brain or body, I know this is rather gruesome, when
the holes were very discrete they entered at one point and left at
another point, they would take out or destroy very discrete bits of
neural tissue, of the nervous system. So people were coming back from
war with holes in their brain and in other parts of their nervous
system that were limited to very specific locations. In addition to
that, there was some advancement in the cleaning of wounds that
happened so many more people were surviving. What this meant was that
neurologists now had a collection of patients that would come back and
they'd have holes in very specific locations of their brain. And
they'd say things like, well, I can recognize faces but I can't
recognize who those faces belong to. I know it's a face, but I don't
know who it belongs to. And after that person eventually died the
neurologist would figure out, ah, I've had 10 patients that all told
me that they couldn't recognize faces. And they all had these bullet
holes that went through a particular region of the brain. And that's
how we know a lot about how particular brain regions like the
hippocampus work. In fact, some of the more amazing examples of this,
where people would come back and they, for instance, would speak in
complete gibberish whereas previously they could speak normally. And
even though they were speaking in complete gibberish they could
understand language perfectly. That's how we know that speech and
language are actually controlled by separate portions of the nervous
system. And there are many examples like that. People that couldn't
recognize the faces of famous people or, and that actually brings us
to an interesting example in modern times.
Many, many years later in the early 2000s there was actually a paper
that was published in the journal "Nature", excellent journal, showing
that in a human being, a perfectly healthy human being, there was a
neuron that would become electrically active only when the person
viewed the picture of Jennifer Aniston, the actress. So literally a
neuron that represented Jennifer Aniston, so-called Jennifer Aniston
cells, neuroscientists know about the Jennifer Aniston cells. If you
can recognize Jennifer Aniston's face you have Jennifer Aniston
neurons, and presumably also have neurons that can recognize the faces
of other famous and non-famous people. So that indicates that our
brain is really a map of our experience. We come into the world and
our brain has a kind of bias 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.
So this is important to understand for any and all of you that want to
change your nervous system or to apply tools to make your nervous
system work better. 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. So this always raises an interesting question. People ask,
well, is there much more out there? Is there a lot more happening in
the world that I'm not experiencing or that humans aren't
experiencing? And the answer of course is yes, there are many species
on this planet that are perceiving things that we will never perceive
unless we apply technology. The best example I could think of off the
top of my head would be something like infrared vision. There are
snakes out there, pit vipers and so forth, that can sense heat
emissions from other animals. They don't actually see their shape.
They sense their heat shape and their heat emissions. Humans can't do
that unless of course they put on infrared goggles or something that
would allow them to detect those heat emissions. There are turtles and
certain species of birds that migrate long distances that can detect
magnetic fields because they have neurons, again, it's the nervous
system that allows them to do this.
So they have neurons in their nose and in their head that allow them
to migrate along magnetic fields in order to, as amazing as this
sounds, go from one particular location in the ocean, thousands of
miles away to all aggregate on one particular beach at a particular
time of year so that they can mate, lay eggs, and then wander back off
into the sea to die. And then their young will eventually hatch, those
cute little turtles will shuffle to the ocean, swim off and go do the
exact same thing. They don't migrate that distance by vision. They
don't do it by smell. They do it by sensing magnetic fields. And many
other species do these incredible things. We don't, humans are not
magnetic sensing organisms. We can't do that because we don't have
receptors that sense magnetic fields. There's some data that maybe
some humans can sense magnetic fields but you should be very skeptical
of anyone that's convinced that they can do that with any degree of
robustness or accuracy, because even the people that can do this
aren't necessarily aware that they can. Maybe a topic for a future
podcast. So we have sensation, then we have perception.
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. And you can do this right now. You can
experience perception and the difference between perception and
sensation very easily. If, for instance, I tell you to pay attention
to the contact of your feet, the bottoms of your feet, with whatever
surface they happen to be in contact with, maybe it's shoes, maybe
it's the floor, if your feet are up maybe it's air. The moment you
place your, what we call the spotlight of attention or the spotlight
of perception on your feet. You are now perceiving what was happening
there, what was being sensed there. The sensation was happening all
along however. So while sensation is not negotiable you can't change
your receptors unless you adopt some new technology, 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 two 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 or 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, whether or
not that tool is in the form of a chemical that you decide to take,
maybe a supplement to increase some chemical in your brain if that's
your choice, or a brain machine device or you're going to try and
learn something better by engaging in some focus or motivated pursuit
for some period of time each day. Attention is something that is
absolutely under your control, in particular when you're rested. And
we'll get back to this. But when you are rested, and we'll define rest
very clearly, you are able to direct your attention in very deliberate
ways. And that's because we have something in our nervous system which
is sort of like a two way street.
And that two way street is a communication between the aspects of our
nervous system that are reflexive and the aspects of our nervous
system that are deliberate. So we all know what it's like to be
reflexive. You go through life, you're walking. If you already know
how to walk you don't think about your walking. You just walk. And
that's because the nervous system wants to pass off as much as it can
to reflexive action. That's called bottom up processing. It really
just means that information is flowing in through your senses,
regardless of what you're perceiving, that information is flowing up
and it's directing your activity. But at any moment, for instance,
let's say a car screeches in front of you around the corner, and you
suddenly pause. You are now moving into deliberate action. You would
start looking around in a very deliberate way. The nervous system can
be reflexive in its action or it can be deliberate. If reflexive
action tends to be what we call bottom up, deliberate action and
deliberate perceptions and deliberate thoughts are top down.
They require some effort and some focus. But that's the point, you can
decide to focus your attention and energy on anything you want. 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, 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 slash 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. Scientists argue like crazy, neuroscientists
and psychologists and philosophers for that matter, argue like crazy
about what these are and how they work. 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
playlists 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, it is
involved in reward. And it does tend to create a sort of upbeat mood
when released in appropriate amounts in the brain. But the reason it
does that is because it makes certain neurons and 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, our 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 en 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 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. So these
neuromodulators can exist in normal levels, low levels, high levels.
And that actually gives us a window into a very important aspect of
neuroscience history that all of us are impacted by today, which is
the discovery of antidepressants and so-called anti-psychotics.
In the 1950s, '60s, and '70s, it was discovered that there are
compounds, chemicals that can increase or decrease serotonin, that can
increase or decrease dopamine. And that led to the development of most
of what we call antidepressants. Now, the trick here or the problem is
that most of these drugs, especially in the 1950s and '60s, they would
reduce serotonin but they would also reduce dopamine or they would
increase serotonin, but they would also increase some other
neuromodulator chemical. And that's because all these chemical systems
in the body, but the neuromodulators in particular, have a lot of
receptors. Now, these are different than the receptors we were talking
about earlier. The receptors I'm talking about now are sort of like
parking spots where dopamine is released. And if it attaches to a
receptor, say on the heart, it might make the heart beat faster
because there's a certain kind of receptor on the heart. Whereas if
dopamine is released and goes and attaches to muscle it might have a
completely different effect on the muscle. And in fact, it does. So
different receptors on different organs of the body are the ways that
these neuromodulators can have all these different effects on
different aspects of our biology. This is most salient in the example
of some of the antidepressants that have sexual side effects or that
blunt appetite or that blunt motivation. You know, many of these which
increase serotonin can be very beneficial for people. It can elevate
their mood. It can make them feel better. But they also if their, the
doses are too high or if that particular drug isn't right for somebody
that person experiences challenges with motivation or appetite or
libido because serotonin is binding to receptors in the areas of the
brain that control those other things as well. So we talked about
sensation. We talked about perception. When we talk about feelings, we
have to consider these neuromodulators. And we have to consider also
that feelings and emotions are contextual. In some cultures showing a
lot of joy or a lot of sadness is entirely appropriate, in other
cultures it's considered inappropriate. So I don't think it's fair to
say that there is a sadness circuit or area of the brain or a
happiness circuit or area of the brain. However, it is fair to say
that certain chemicals and certain brain circuits tend to be active
when we are in motivated states, tend to be active when we are in non-
motivated lazy states, tend to be active when we are focused and tend
to be active when we are not focused. I want to emphasize also that
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 a
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 are
thoughts.
Thoughts are really interesting because in many ways they're like
perceptions except that they draw on not 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. In fact, right now you could decide to have a thought just
like you would decide to write something out on a piece of paper. You
could decide that you're listening to a podcast, that you are in a
particular location. You're not just paying attention to what's
happening, you're directing your thought process. 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. And then finally there are actions.
Actions or behaviors are perhaps the most important aspect of 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
experiencing something very joyful or something very 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 lifespan, none of that is actually
carried forward except the ones that we take and we convert into
actions such as writing, actions such as words, actions 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,
perceptions, feelings, and thoughts into actions. In fact, the great
neuroscientist or physiologist Sherrington won a Nobel prize for his
work in mapping some of the circuitry, the connections between nerve
cells that give rise to movement. And he said, "Movement is the final
common pathway". The other way to think about it is that one of the
reasons that our central nervous system, our brain and spinal cord
include this 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 of 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 these 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 forebrain works from the top down to control
those central pattern generators 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, 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 a deliberate way
because it 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 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 call DPO, duration, path,
outcome, type of deliberate function in your brain and nervous system.
But the moment you decide to learn something or to resist speaking or
to speak up when you would rather be quiet, anytime you're
deliberately kind of forcing yourself over a threshold, you're
engaging these brain circuits and these nervous system circuits that
suddenly make it feel as if something is challenging. Something has
changed. Well, what's changed? What's changed is that when you engage
in this duration, path, and outcome type of thinking or behavior or
way of being you start to recruit these neuromodulators that are
released from particular areas of your brain, and also it turns out
from your body. and they start cuing to your nervous system.
Something's different. Something's different now about what I'm doing.
Something's different about what I'm feeling. 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,
oh, I shouldn't respond, I shouldn't respond, I shouldn't respond.
You're actively suppressing your behavior through top down processing.
Your forebrain 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
forebrain 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. You'll see they'll be rocking back and forth. It's hard
for them to sit still because those central pattern generators are
constantly going in the background. Whereas adults can sit still. A
kid sees a piece of candy that it wants and 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. We all know people like this. Impulsivity is a lack of top
down control, a lack of top-down processing. The other thing that will
turn off the forebrain and make it harder to top-down processing is a
couple of drinks containing alcohol. The removal of inhibition is
actually removal of neural inhibition, of nerve cells suppressing the
activity of other nerve cells. And so when you look at people that
have damage to their frontal lobes or you look at puppies or you look
at young children, everything's a stimulus. Everything is a potential
interaction for them. And they have a very hard time restricting their
behavior and their speech. So a lot of the motor system 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 going to 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. That low-level
tremor that sometimes people feel when they're really, really angry is
actually a chemically induced low-level tremor. And it's the, what I
call limbic friction. There's an area of your brain that's involved in
our more primitive reflexive responses called the limbic system. And
the frontal cortex is in a friction, it's in a tug of war with that
system all the time. Unless of course you have damage to the frontal
lobe or you've had too much to drink or something. In which case you
tend to just say and do whatever. And so this is really important to
understand because if you want to understand neuroplasticity, 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 top-down processing.
It requires this feeling of agitation. In fact, I would say the
agitation and strain is the entry point to neuroplasticity. So let's
take a look at what neuroplasticity is. Let's explore it, not as the
way it's normally talked about in modern culture, neuroplasticity,
plasticity is great. Well, what exactly do people mean? Plasticity
itself is just a process by which neurons can change their connections
and the way they work so that you can go from things being very
challenging and deliberate, requiring a lot of effort and strain, to
them being reflexive. And typically when we hear about plasticity,
we're thinking about positive or what I call adaptive plasticity. A
lot of plasticity can be induced, for instance by brain damage, but
that's generally not the kind of plasticity that we want. So when I
say plasticity, unless I say otherwise I mean adaptive plasticity. And
in particular most of the neuroplasticity that people want is self-
directed plasticity. Because if there's one truism to neuroplasticity,
it's that from birth until about age 25 the brain is incredibly
plastic. Kids are learning all sorts of things but they can learn it
passively. They don't have to work too hard or focus too hard,
although focus helps, to learn new things, acquire new languages,
acquire new skills. But if you're an adult and you want to change your
neural circuitry at the level of emotions or behavior or thoughts or
anything really, you absolutely need to ask two important questions.
One, what particular aspect of my nervous system am I trying to
change? Meaning, am I trying to change my emotions or my perceptions,
my sensations? And which ones are available for me to change? And then
the second question is how are you going to go about that? What is the
structure of a regimen to engage neuroplasticity? And it turns out
that the answer to that second question is governed by how awake or
how sleepy we are. So let's talk about that next. 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 brain can change itself and our nervous system can change
itself. And the same can't be said for other organs of the body. Even
though our other organs of the body have some ability to change, they
can't direct it. They can't think and decide, you know your gut
doesn't say, oh, you know, I want to be able to digest spicy foods
better so I'm going to rearrange the connections to be able to do
that. Whereas your brain can decide that you want to learn a language
or you want to be less emotionally reactive or more emotionally
engaged, and you can undergo a series of steps that will allow your
brain to make those changes so that eventually it becomes reflexive
for you to do that, which is absolutely incredible. 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, a
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. Nobel prizes were given for the understanding
that the young brain can change very dramatically. I think one of the
most extreme examples would be for people that are born blind from
birth they use the area of their brain that normally would be used for
visualizing objects and colors and things outside of them for braille
reading. In brain imaging studies it's been shown that, you know,
people who are blind from birth, when they braille read, the area of
the brain that would normally light up, if you will, for vision lights
up for braille reading. So that real estate is reallocated for an
entirely different function. If someone is made blind in adulthood,
it's unlikely that their entire visual brain will be taken over by the
areas of the brain that are responsible for touch. However, there's
some evidence that areas of the brain that are involved in hearing and
touch can kind of migrate into that area. And there's a lot of
interest now in trying to figure out how more plasticity can be
induced in adulthood, more positive plasticity. And 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 seem
almost impossible and out of reach to being very reflexive, this is
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 can
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 and a positive side. The dark side is it's actually very easy to
get neuroplasticity 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 of neuromodulators in the
brain, epinephrine which tends to make us feel alert and agitated,
which is associated with most 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 brain
and body active much more than all the rest. So acetylcholine is sorta
like a highlighter 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 happened. So the way it works is this, you can think of
epinephrine as creating this alertness and 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 happens during that period of heightened
alertness. So just to be clear, it's epinephrine creates 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 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 neuroplasticity 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. Now, 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. But there's
another side to it. The dirty secret of neuroplasticity is that no
neuroplasticity 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 neuroplasticity,
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 deep rest. And so neuroplasticity, 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's 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 agitation and a feeling of
strain are actually required for this process of neuro-plasticity to
get triggered. But the actual rewiring occurs during periods of sleep
and non-sleep deep rest. There's a study published last year that's
particularly relevant here that I want to share, it was not done by my
laboratory, that showed that 20 minutes of deep rest, this is not deep
sleep, but essentially doing something very hard and very intense and
then taking 20 minutes immediately afterwards to deliberately turn off
the deliberate focused thinking and engagement actually accelerated
neuroplasticity.
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 in the
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 somehow cues the nervous system in sleep, doesn't
even have to be in dreaming, that something that happened in the
waking phase was especially important. So much so that that bell is
sort of a Pavlovian cue, it's sort of a reminder to the sleeping
brain, oh, you need to remember 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 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 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 are 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 cells that will allow what we were
trying to learn to go from being deliberate and hard and stressful and
a strain to 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, the brain states that happened the next day or the next
month or the next year. And also, I want to make sure that I pay
attention to the fact that for many of you you're thinking about
neuro-plasticity 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
some thing 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
themselves get erased, but the emotional load of memories can be
reduced. And there are a number of different ways that that can happen
but they all require this thing that we're 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 process. What governs the transition
between alert and focused and these deep rest 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 it the alertness system
and the calmness system, because even though sympathetic and
parasympathetic are sometimes used, 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
neuroplasticity and engaging in these focus states and in these de-
focused 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 we're more alert.
And then as evening comes around we tend to become a little more
relaxed and sleepy. 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, and 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 neuroplasticity and
doing all sorts of things. We have energy as well. And at another
phase of our day we're tired and we have 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 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,
and outcome 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 run. 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 non DPO 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 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 and 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,
these duration, path, outcome types of engagements for learning and
for changing and when are their brain is probably better suited for
more reflexive thinking and behaviors. And it turns out that there's a
vast amount of scientific data which points to the existence of what
are called ultradian rhythms.
You may have heard of circadian rhythms. Circadian means, circa, about
a day. So it's 24 hour rhythms because the earth spins once every 24
hours. Ultradian rhythms occur throughout the day and they require
less time, they're shorter. The most important ultradian rhythm for
sake of this discussion is the 90 minute rhythm that we're going
through all the time in our ability to attend and focus. And in sleep,
we are, our sleep is broken up into 90 minute segments. Early in the
night we have more phase one and phase two lighter sleep. And then we
go into our deeper phase three and phase four sleep. And then we
return to phase one, two, three, four. So all night, you're going
through these ultradian rhythms of stage one, two, three, four, one,
two, three, four, it's repeating. Most people perhaps know that. Maybe
they don't. But you wake up in the morning, these ultradian rhythms
continue. And it turns out that we are optimized for focus and
attention within these 90 minute cycles so that at the beginning of
one of these 90 minute cycles maybe you sit down to learn something
new or to engage in some new challenging behavior, for the first five
or 10 minutes of one of those cycles it's well-known that the brain
and the neural circuits and the neuromodulators are not going to be
optimally tuned to whatever it is you're trying to do. But as you drop
deeper into that 90 minute cycle your ability to focus and to engage
in this DPO process and to direct neuroplasticity and to learn is
actually much greater. And then you eventually pop out of that at the
end of the 90 minute cycle. So these cycles are occurring in sleep and
these cycles are occurring in wakefulness. And all of those are
governed by this seesaw of alertness to calmness that we call the
autonomic nervous system. So if you want to master and control your
nervous system, regardless of what tool you reach to, whether or not
it's a pharmacologic tool or whether or not it's a behavioral tool or
whether or not it's a brain machine interface tool, it's vitally
important to understand that your entire existence is occurring in
these 90 minute cycles, whether or not you're asleep or awake. And so
you really need to learn how to wedge into those 90 minute cycles. And
for instance, it would be completely crazy and counterproductive to
try and just learn information while in deep sleep by listening to
that information because you're not able to access it. It would be
perfectly good, however, to engage in a focused bout of learning each
day. And now we know how long that focused bout of learning should be,
it should be at least one 90 minute cycle. And the expectation should
be that the early phase of that cycle is going to be challenging. It's
going to hurt. It's not going to feel natural. It's not going to feel
like flow. But that you can learn and the circuits of your brain that
are involved in focus and motivation can learn to drop into a mode of
more focus, get more neuroplasticity in other words, by engaging these
ultradian cycles at the appropriate times of day. For instance, some
people are very good learners early in the day and not so good in the
afternoon. So you can start to explore this process even without any
information about the underlying neurochemicals by simply paying
attention, not just to when you go to sleep and when you wake up each
morning, how deep or how shallow your sleep felt to you subjectively.
But also, throughout the day, when your brain tends to be most
anxious. Because it turns out that has a correlate related to
perception that we will talk about. You can ask yourself when are you
most focused? When are you least anxious? When do you feel most
motivated? When do you feel least motivated? By understanding how the
different aspects of your perception, sensation, feeling, thought, and
actions, tend to want to be engaged or not want to be engaged. You
develop a very good window into what's going to be required to shift
your ability to focus or shift your ability to engage in creative type
thinking at different times of day, should you choose. And so that's
where we're heading, going forward. It all starts with mastering this
seesaw that is the autonomic nervous system, that at a course level is
a transition between wakefulness and sleep, but at a finer level, and
just as important, are the various cycles, these ultradian 90 minute
cycles that govern our life all the time, 24 hours a day every day of
our life. And so we're going to talk about how you can take control of
the autonomic nervous system so that you can better access
neuroplasticity, better access sleep, even take advantage of the phase
that is the transition between sleep and waking to access things like
creativity and so forth. All based on studies that have been published
over the last 100 years, mainly within the last 10 years and some that
are very, very new. And that point to the use of specific tools that
will allow you to get the most out of your nervous system. So today we
covered a lot of information. It was sort of a whirlwind tour of
everything from neurons and synapses to neuroplasticity and the
autonomic nervous system. We will revisit a lot of these themes going
forward. So if all of that didn't sink in in one pass, please don't
worry. We will come back to these themes over and over again. I wanted
to equip you with a language so that we're all developing a kind of
common base set of information going forward. And I hope the
information is valuable to you in your thinking about what is working
well for you and what's working less well and what's been exceedingly
challenging, what's been easy for you in terms of your pursuit of
particular behaviors or emotional states where your challenges or the
challenges of people that you know might reside. As promised in our
welcome video, the format of the "Huberman Lab" podcast is to dive
deep into individual topics for an entire month at a time. So for the
entire month of January we're going to explore this incredible state
that is sleep and a related state, which is non-sleep deep rest and
what they do for things like learning, resetting our emotional
capacity. Everyone's probably familiar with the fact that when we're
sleep deprived we're so much less good at dealing with life
circumstances. We're more emotionally labile. Why is that? How is
that? But most importantly, we're going to talk about how to get
better at sleeping and how to access better sleep even when your sleep
timing or duration is compromised. We're also going to talk about the
data that support this very interesting state called non-sleep deep
rest where one is neither asleep nor awake, but it turns out one can
recover some of the neuromodulators and more importantly the processes
involved in sensation, perception, feeling, thought, and action. It's
sure to be a very rich discussion back and forth where I'm answering
your questions and providing tools. And I'm certain you're also going
to learn a lot of information about neuroscience and what makes up
this incredible phase of your life where you think you're not
conscious, but you're actually resetting and renewing yourself in
order to perform better, feel better, et cetera, in the waking state.
If you want to support the podcast, please click the like button and
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week. (upbeat guitar music)
The information sets the stage for all Huberman Lab Podcast episodes that follow by covering neurons, synapses, brain chemicals and the rhythms that control our ability to focus, learn and sleep… and more.
Timestamps for the episode can be found below. Thank you for your interest in science. We'll see you next week.
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Introduction 0:00
What is the Nervous System 5:00
Deja Vu 8:55
How War, Guns & Soap Shaped Our Understanding of the Brain 10:50
Jennifer Aniston Neurons 13:30
Sensations 14:30
Magnetic Sensing & Mating 16:10
Perceptions & The Spotlight of Attention 17:30
Multi-Tasking Is Real 18:30
Bottom-Up vs. Top-Down Control of Behavior 20:10
Focusing the Mind 21:15
Emotions + The Chemicals of Emotions 21:55
Antidepressants 24:30
Thoughts & Thought Control 27:40
Actions 28:35
How We Control Our Impulses 33:20
Neuroplasticity: The Holy Grail of Neuroscience 36:25
The Portal to Neuroplasticity 41:20
Accelerating Learning in Sleep 46:40
The Pillar of Plasticity 50:20
Leveraging Ultradian Cycles & Self Experimentation 55:00
Please note that The Huberman Lab Podcast is distinct from Dr.
Huberman's teaching and research roles at Stanford University School
of Medicine. The information provided in this show is not medical
advice, nor should it be taken or applied as a replacement for medical
advice. The Huberman Lab Podcast, its employees, guests and affiliates
assume no liability for the application of the information discussed.
[Title Card Photo Credit: Mike Blabac https://www.blabacphoto.com/]