October 9, 2023 • 39 mins
Did Joan of Arc turn the tide of the 100 Years War as the result of a brain disorder? Would you appreciate Taylor Swift if you only had an internal camera to watch her vocal chords? What do almost all drugs of abuse have in common? How can the tiny molecules of rabies virus control your behavior? Join Eagleman on a two-part deep dive into the fundamental question of how biological insights can shed light on the ancient question of who we are.
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Episode Transcript
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Speaker 1 (00:05):
In this episode.
Speaker 2 (00:06):
In the next one, I want to dive into a
fundamental philosophical question, probably the most important one that we
have as humans, which is what it means to know ourselves?
In other words, as people living in the twenty first century,
with all of this massive biological data and the insights,
(00:27):
what does that tell us about the ancient question of
who we are? Do we have something like souls? Are
we just a bunch of neurons? Are there other ways
to look at this? There's a sense in which I'm
constantly surprised that this question who am I? Isn't talked
about all the time. I mean, most people spend most
(00:50):
of their time talking about sports teams or the latest celebrity,
or traffic or whatever food they like or whatever.
Speaker 1 (00:58):
But we find ourselves.
Speaker 2 (00:59):
Here in this mysterious existence where you don't really remember
getting here, and you're told that one day you'll disappear
from here. And it surprises me that this isn't what
we're talking about all the time. Why isn't this what
we're using the internet to discuss. Why don't we have
(01:20):
world leaders coming together not for the United Nations Annual Meeting,
but to dig their teeth into this question and bring
evidence to bear on different hypotheses. Why isn't this the
topic of conversation on every single news program? So for
the next two episodes, we're going to dig in and
(01:41):
I always start with some questions to give you a
sense of the weirdness of the roadmap.
Speaker 1 (01:46):
So here we go.
Speaker 2 (01:47):
Would you appreciate Taylor Swift if you only had an
internal camera to watch her vocal cords jumping around? What
do almost all drugs of abuse have in common? How
can the tiny molecules of the rabies virus control your behavior?
Did Joan of arc turn the tide of the one
(02:07):
hundred Years War as the result of a brain disorder?
And what does any of this have to do with
who you are? And the question of your essence as
a person, the essence that your friends know and love
as you?
Speaker 1 (02:23):
Where does that come from? Welcome to Inner.
Speaker 2 (02:29):
Cosmos with me David Eagleman. I'm a neuroscientist and an
author at Stanford and in the next couple of episodes,
we're going to sail deeply into our three pound universe
to dig in to one of the most fundamental questions
of our experience in the world. Now I've talked about
(02:53):
this fact before, but I need to emphasize for this
episode that the brain is the most complex structure we
have ever discovered in our universe. It's got almost one
hundred billion neurons and hundreds of trillions of connections. Now,
this kind of complexity is simply not understandable by a
(03:16):
human mind. And yet we know that somehow your brain
is you. All of your hopes and dreams and aspirations,
the agony, the ecstasy, it's all contained in that three
pound organ in your skull. Now how do we know
that because every day in clinics all over the world,
we see people with damage to their brains, even very
(03:40):
tiny damage, and that changes who they are. Small bits
of damage caused by a stroke or a traumatic brain injury,
or a tumor or whatever. These can change your decision
making or your ability to see colors, or understand music
(04:00):
or name animals. It can make you more or less
prone to gambling, or more talkative or less talkative. It
can make you not know the names of objects or
not know how to interact with objects anymore, or make
you unable to speak or to understand speech, or one
hundred other things. And this is how we came to
(04:23):
have this strange hypothesis that you are your brain. So
to start this question of who are we, let's step
back a little bit. In history, people have always been
wondering who we are, mostly because our existence is so
deeply weird, and traditionally the answer has been about deities
(04:47):
and immortal souls, but not everyone has been willing to
stop there. So I was impressed some years ago when
I read about the French essayist Montaigne, who in fifteen
seventy one, on the morning of his thirty eighth birthday,
decided to make a radical change in his life's trajectory.
He quit his career in public life, and he set
(05:09):
up a library with one thousand books in a tower
at the back of his large estate, and he spent
the rest of his life writing essays about the subject
that interested him the most, the search for oneself. His
first conclusion was that the search to no one's self
is a fool's errand because the self who I am,
(05:33):
is always changing and staying a few steps ahead of
a firm description. But that didn't stop him from searching,
and his question has resonated through the centuries.
Speaker 1 (05:46):
Causasia, what do. I know.
Speaker 2 (05:49):
That was a good question, and it remains so because
when we dive in to explore the inner cosmos, as
we've been doing on this podcast, we can't help find
ourselves disabused of our initial notions that knowing ourselves will
be uncomplicated and intuitive, because we see that self knowledge
(06:11):
requires as much work from the outside in the form
of science as from the inside introspection.
Speaker 1 (06:18):
And this is not to.
Speaker 2 (06:19):
Say that we can't grow better at introspection. After all,
we can learn how to pay attention to what we're
really seeing out there, like painters do, and we can
attend more closely to our internal signals like Yogi's do.
But there are limits to introspection. Just consider the fact
(06:40):
that your peripheral nervous system employs one hundred million neurons
to control the activities in your gut. This is called
the enteric nervous system one hundred million neurons, and no
amount of your introspection can touch this, nor by the way,
would you want it to be. In The tek nervous
(07:00):
system is better off running as the automated optimized machinery
that it is, routing food along your gut and providing
chemical signals to control the digestion factory without asking your
opinion on the matter. Now, this has always fascinated me
to think that in some cases there may be not
(07:20):
only a lack of access, but even an active prevention
of access. For example, I was once chewing on this
with my thesis advisor, Read Montague, and he speculated that
we might have algorithms that protect us from ourselves. This
is analogous to your laptop computer, which has a boot
(07:42):
sector that's inaccessible by the operating system, because the boot
sector is too important for the operation of the computer
for any high level systems to find inroads and gain
admission under any circumstances.
Speaker 1 (07:57):
So Read noted.
Speaker 2 (07:58):
That whenever we try to think about ourselves too much,
we tend to blink out, and the analogy was that
we're getting too close to the boot sector. Now, he
was just speculating here, but the idea is fascinating that
maybe our system has evolved to make certain that we
can't access the details too deeply. Or, as Ralph Waldo
(08:20):
Emerson put the same idea from a more poetic point
of view, everything intercepts us from ourselves. So whether it's
just a lack of access or an active prevention of access.
The bottom line is that much of who we are
remains outside of our conscious control, or our opinion or
(08:41):
our choice. We talked in an earlier episode about the
impossibility of changing your sense of beauty or attraction. What
would happen if someone commanded you to be attracted to
someone that you're not, or to be attracted to a
gender that you're not attracted to, or to an animal
(09:01):
outside your species.
Speaker 1 (09:03):
Could you muster attraction there? Doubtful.
Speaker 2 (09:06):
Your most fundamental drives are stitched into the fabric of
your neural circuitry, and they are inaccessible to you. You
can't reach in there and change them around. You find
certain things more attractive than others, and you don't know why. So,
like your nervous system in your gut and your sense
of attraction, almost the entirety of your inner universe is
(09:31):
foreign to you. Consider when an idea strikes you, you
don't know where the heck that came from. One minute
you didn't have it, and the next moment it's there.
It just appears even though it came from your brain,
it may as well have been handed to you from
somewhere else. You don't know the neuronal history of the idea,
and you don't care. You just think, oh, that's a
(09:52):
good idea. And this is the same with your train
of thought during a day dream, or the bizarre content
of your nighttime dreams. All these are just served up
to you from unseen intracranial caverns. So what does all
of this mean for the Greek admonition to know thyself?
(10:16):
These were the words inscribed in the Temple of Apollo
at Delphi, know thyself? Can we ever know ourselves more
deeply by studying our neurobiology? And I'm going to argue yes,
but with some interesting nuances, And I'll give you an
analogy here to physics. In the face of the deep
(10:38):
mysteries presented by quantum physics, the physicist Neils Brer suggested
that an understanding of the structure of the atom could
be accomplished only by changing the definition of to understand,
because with quantum mechanics you couldn't any longer draw pictures
(10:59):
of an atom, so that was lost. But instead one
could now predict experiments about an atom's behavior out to
fourteen decimal places, So lost assumptions were replaced by something richer.
And by the same token, to know one's self may
require a change of definition of to know. Knowing yourself
(11:23):
now requires the understanding that the conscious you occupies only
a small room in the mansion of the brain, and
that it has very little control over the reality that
gets constructed for you. So the invocation to know thyself
needs to be considered in new ways because when we
look at the trillions of neurons and there are sex
(11:46):
tillions of proteins and biochemicals, what does it mean to
know ourselves from that totally unfamiliar perspective, As we're going
(12:14):
to see, we need the neurobiological data and we also
need quite a bit more to know ourselves. Why because
the biological data is fundamental, but it has its limitations.
Imagine that you got Taylor Swift to come to your
house and sing for you, but instead of listening to her,
(12:36):
you put on ear muffs and you lower a medical
scope down her throat and you get.
Speaker 1 (12:41):
A good close up view of her vocal chords.
Speaker 2 (12:44):
They're slimy and shiny, and they're contracting in and out
and spasms. Now, you could watch this and study the
details all day, but it wouldn't get you any closer
to understanding why her songs are big hits, or what
the words mean to you, or how they make you feel.
By itself, in its raw form, the biology is only
(13:07):
going to give you partial insight there. It's the best
that we can do for now, but it's far from complete.
So this is what we're going to talk about today.
What does and doesn't it mean to be constructed out
of physical parts. So let's start with a clear and
famous example of brain damage. I've mentioned this story in
(13:27):
a previous episode, but i'll retell it here with more detail.
In eighteen forty eight, there was a work gang foreman
twenty five years old. His name was Phineas Gage. On
September twenty first of that year, the Boston Post wrote
a short article under the headline horrible accident. Here's how
it went. Quote as Phineas P. Gage, a foreman on
(13:50):
the railroad in Cavendish, was yesterday engaged in tamping.
Speaker 1 (13:55):
For a blast.
Speaker 2 (13:56):
The powder exploded, carrying an instrument and threw his head
an inch and a fourth in diameter and three feet
and seven inches in length, which he was using at
the time. The iron entered on the side of his face,
shattering the upper jaw and passing back of the left
eye and out at the top of the head.
Speaker 1 (14:19):
So this was an iron tamping rod, and.
Speaker 2 (14:21):
Because of an explosion of gunpowder, this blew through his
head and it clattered to the ground twenty five yards away. Now,
while Phineas Gage wasn't the first person to have his
skull punctured and a portion of his brain spirited away
by a projectile, he was the first, so far as
we know, to not die from it. And in fact,
(14:44):
Gauge didn't even lose consciousness. So the first physician to
arrive at the scene, a doctor Williams, didn't believe Gauge's
statements of what had just happened, but instead he quote
thought that he Gauge was this. But doctor Williams soon
understood the gravity of what had happened when quote mister
(15:07):
Gage got up and vomited, and the effort of vomiting
pressed out about half a tea cupful of brain, which
fell upon the floor end quote. The Harvard surgeon who
studied his case noted that quote, the leading feature of
this case is its improbability. It is unparalleled in the
(15:28):
annals of surgery.
Speaker 1 (15:30):
End quote.
Speaker 2 (15:31):
The Boston Post article summarized this improbability with just one
more sentence. Quote, The most singular circumstance connected with this
melancholy affair is that he was alive at two o'clock
this afternoon and in full possession of his reason and
free from pain unquote. Now Gage's survival alone would have
(15:55):
made this an interesting medical case, it became a famous
case because of some thing else that came to light.
Two months after the accident, his physician reported that Gage
was quote feeling better in every respect walking about the
house again, says he feels no pain in the head unquote,
(16:15):
but foreshadowing a larger problem. The doctor also noted that
Gauge quote appears to be in a way of recovering
if he can be controlled end quote. So what did
he mean here, if he can be controlled? It turned
out that the pre accident, Phineas Gage had been described
(16:36):
as a great favorite among his team, and his employers
had hailed him as the most efficient and capable foreman
in their employ But after the brain damage, his employers
considered him to be such a different person that they
decided they couldn't give him his place again. Now, what
was this change in his personality. Here's what Gauge's Physics
(17:00):
wrote twenty years later in eighteen sixty eight. This is
a long quotation, but I'm going to read the whole
thing because it's fascinating and gives us insight into how
a person can change when his brain changes.
Speaker 1 (17:13):
Quote.
Speaker 2 (17:14):
The equilibrium or balance, so to speak, between his intellectual
faculties and animal propensities seems to have been destroyed. He
is fitful, irreverent, indulging at times in the grossest profanity,
which was not previously his custom manifesting, but little deference
(17:34):
for his fellows, impatient of restraint or advice when it
conflicts with his desires, at times pertinaciously obstinate, yet capricious
and vacillating, devising many plans of future operations which are
no sooner arranged than they are abandoned in turn for others,
(17:55):
Appearing more feasible a child in his intellectual capacity and
manner infestations. He has the animal passions of a strong
man previous to his injury. Although untrained in the schools,
he possessed a well balanced mind and was looked upon
by those who knew him as a shrewd, smart businessman.
(18:17):
Very energetic and persistent in executing all his plans of operation.
In this regard, his mind was radically changed, so decidedly
that his friends and acquaintances said he was quote no
longer gauge end quote. Now in the intervening century in half,
(18:38):
we've seen lots of cases like Phineas Gages, because tragically,
there are lots of ways for the delicate pink material
of the brain to get hurt, and they all surface
the same lesson. When the brain changes, the person changes.
And of course the more common thing seen in hospitals
(19:00):
every day are all of nature's tragic experiments strokes, tumors, neurodegeneration,
And it's the same lesson. The condition of your brain
is central to who you are. You that all your
friends know and love cannot exist unless all the fine
(19:22):
microscopic details of your brain, all the nuts and bolts,
are in place. If you don't believe me, step into
any neurology ward in any hospital. Damaged to even small
parts of the brain can lead to the loss of
shockingly specific abilities, the ability to understand music, or to
(19:43):
manage risky behavior, or to distinguish colors, or to arbitrate
simple decisions. We see examples of this when we meet
patients who lose the ability to see movement even though
they're not blind. We see it when a person gets
front do temporal dementia and starts shoplifting, even though that's
(20:04):
something they would have never done before. We see it
when a person no longer understand how a mirror reflection works.
We see it when medications for Parkinson's disease turn someone
into a compulsive gambler, or a million other examples that
tell us that your essence can be changed by changes
(20:26):
in your brain. So all of this leads to a
key question. Do we possess a soul that is separate
from our physical biology? Or are we simply an enormously
complex biological network that mechanically produces our hopes and aspirations
and dreams and desires and humor and passion. So over
(20:48):
this and the next episode, this is the question I'm
going to unpack. Now, the majority of people on the
planet vote for the extra biological soul, but all the
evidence from neuroscience suggests it's the biology. It's a vast
physical system from which the essence of a person emerges,
(21:10):
and nothing more than that. Now, do we know which
answer is correct, not with certainty, but cases like Phineas
Gauges and every case of brain damage we see in
the hospitals certainly seem to weigh in on the problem.
They make it more and more difficult to ignore or
deny that we are biological creatures. So the materialist viewpoint
(21:35):
holds that we are fundamentally made only of physical materials.
In this view, the brain is a system whose operation
is governed by the laws of chemistry and physics, with
the end result that all of your thoughts and emotions
and decisions are produced by natural reactions following local laws
(21:57):
to lowest potential energy. We are our brain and its chemicals,
and any dialing of the knobs of your neural system
changes who you are now. A common approach to materialism
is called reductionism, and this theory puts forth the hope
that we can successively reduce the problems down to their
(22:21):
small scale biological pieces and parts, and eventually come to
explain complex phenomena like happiness or greed, or narcissism or
compassion or malice or caution or amazement by understanding the
pieces and parts at first blush the materialist and reductionist
(22:43):
viewpoints sound absurd to a lot of people. Not to
everyone I work with, and possibly not to a lot
of the listeners of this podcast, but probably to many
of the people on this planet. And I know this
in part because when I sit next to strangers on
a plane or a subway, I ask their opinions about
this kind of stuff, and people will often say something like, look,
(23:06):
why I chose my job, how I fell in love
with my wife, what TV shows I like to watch?
That has nothing to do with the cells of my brain.
That's just who I am. And they're right to think
that the connection between your essence as a person and
a squishy confederacy of cells that seems distant at best,
(23:28):
that person's decisions came from them, not from a bunch
of chemicals cascading through invisibly small cycles.
Speaker 1 (23:36):
Right.
Speaker 2 (23:37):
But what happens when we run into enough cases like
Phineas Gauges or people who have strokes or tumors or neurodegeneration,
And what happens when we turn the spotlight on even
more subtle influences, far more subtle than a tamping rod,
where changes in the brain change people's personalities. Just consider
(24:00):
this as an example, Think about the powerful effects of
the small molecules that we call narcotics. These are invisibly small,
but they alter consciousness, they affect cognition, they navigate behavior.
We are slave to these molecules tobacco, alcohol, and cocaine.
(24:21):
These are self administered universally for the purpose of mood changing.
And if we knew nothing else about neurobiology, the mere
existence of narcotics would give us all the evidence we
need to tell us that our behavior and psychology can
be commandeered at the molecular level. Take cocaine as an example.
(24:44):
Cocaine interacts with a very specific network in the brain,
one that registers rewarding events. This is known as the
mesolimbic dopamine system. It registers rewarding events like you satisfying
your thirst with a a cool iced tea, or winning
a smile from the right person, or cracking a tough
(25:06):
problem at work and your boss says good job. By
tying positive outcomes to the behaviors that led to them,
this neural circuit learns how to optimize behavior in the world.
It's what helps us get food and drink and mates
and navigate life's daily decisions now out of context. Cocaine
(25:47):
is a totally uninteresting molecule. It has seventeen carbon atoms
and twenty one hydrogens and one nitrogen and four oxygens.
What makes cocaine cocaine is the fact that its shape
happens to fit lock and key into the microscopic machinery
of this reward circuit. So suddenly the cocaine gets to
(26:12):
act like the most rewarding thing you've done, which causes you,
in the language of the reward system, to want to
do that again. And by the way, the same thing
goes for all four major classes of drugs of abuse, alcohol, nicotine,
psychostimulants like amphetamines, and opiates like morphine. By one inroad
(26:35):
or another, they all plug into this same reward circuitry.
All these types of molecules rev the engine of the
mesolimbic dopamine system, and so they all become self reinforcing.
Your brain experiences them and then chases.
Speaker 1 (26:52):
More of that.
Speaker 2 (26:54):
And these effects are so powerful that users will end
up robbing stores and mugging elderly people to continue obtaining
these specific molecular shapes. And what's really amazing to note
is that These chemicals work their magic at scales one
thousand times smaller than the width of a human hair,
(27:15):
but by attaching in the right spots, they can make
the consumers feel invincible and euphoric. By plugging into this
dopamine system, cocaine and its cousins command beer the reward system,
and they tell the brain that this is the best
possible thing that could be happening. So these ancient circuits
(27:38):
that are there for steering our behavior, these become hijacked. Now,
these cocaine molecules are hundreds of millions of times smaller
than the tamping rod that shot through Phineas Gage's brain,
But the lesson is the same. Who you are depends
on the precise details of your neurobiology, and the dopamine
(28:03):
system is only one of hundreds of examples. The exact
levels of other neurotransmitters, for example, serotonin, are critical for
who you believe yourself to be. If you suffer from
clinical depression, you'll probably get prescribed a medication known as
a selective serotonin uptake inhibitor abbreviated as an SSRII, for
(28:26):
example fluoxetine. Now, everything you need to know about how
these drugs work is contained in the words uptake inhibitor. Normally,
channels called transporters take up the serotonin from the space
between the neurons, and when you inhibit that uptake, you
get a larger concentration of serotonin in the brain, and
(28:48):
the increased concentration has direct consequences on cognition and emotion.
People can go on these medications and they can transition
from crying on the edge of the bed to standing
up and showering and getting their job back and rescuing
healthy relationships with the people in their lives, all because
(29:09):
of a subtle fine tuning of a neurotransmitter system. If
this story weren't so common, we would more easily appreciate
its bizarreness. And it's not just neurotransmitters that influence your cognition.
The same goes for hormones, the invisibly small molecules that
(29:29):
surf the bloodstream and cause commotion at every port that
they visit. If you inject a female rat with estrogen,
she'll begin seeking a sexual partner. If you inject a
male rat with testosterone, he'll become aggressive. Actually, in episode fifteen,
I told you about the wrestler Chris Benoit, who took
(29:51):
massive doses of testosterone and then murdered his wife and
his own child in a roid rage. Or just think
about the hormone fluctuation that accompany normal menstrual cycles. Recently,
a female friend of mine was at the bottom of
her menstrual mood changes, and she said to me, you know,
I'm just not myself for a few days each month.
(30:14):
But because she's a neuroscientist, she then reflected for just
a moment. Then she said, or maybe this is the
real me, and I'm actually someone else the other twenty
seven days of the month. She wasn't afraid to view
herself as the sum total of her chemicals at any moment.
She understood that what we think of as her is
(30:35):
something like a time averaged version. All these examples add
up to something of a strange notion of the self.
Because of inaccessible fluctuations in our biological soup, some days
we find ourselves more irritable or more humorous, or more
(30:56):
well spoken, or more calm or energized or clear thinking.
Our internal life and our external actions are steered by
these biological cocktails to which we don't have any direct
access or any direct acquaintance. And don't forget that the
long list of influences on your mental life. This stretches
(31:19):
way beyond chemicals. It includes the details of the circuitry
as well. So consider something like epilepsy. If an epileptic
seizure is focused in a particular spot in the temporal lobe,
a person won't have motoric seizures with their body, but
instead something more subtle. The effect is something like a
(31:42):
cognitive seizure, and this translates to changes of personality and
hyper religiosity, which is an obsession with religion, and hypergraphia,
which is where you write pages and pages on a subject,
usually about religion, and often the hearing of voe voices
that get attributed to a god. Some fraction of histories,
(32:05):
prophets and martyrs and leaders appear to have had temporal
lobe epilepsy. Consider Joan of Arc, the sixteen year old
girl who managed to turn the tide of the Hundred Years'
War because she believed and convinced the French soldiers that
she was hearing voices from Saint Michael and Saint Catharine,
(32:29):
and Saint Margaret and Saint Gabriel as she described her experience, quote,
when I was thirteen, I had a voice from God
to help me to govern myself. The first time I
was terrified. The voice came to me about noon. It
was summer and I was in my father's garden. Later,
she reported, quote, since God had commanded me to go,
(32:53):
I must do it. Although it's impossible to retrospectively diagnose
with certainty what is known about her, including the increasing
religiosity and ongoing voices. This is consistent with temporal lobe epilepsy.
When brain activity is kindled in just the right spot,
people hear voices. If a physician prescribes in anti epileptic medication,
(33:19):
the electrical spikes go away and the voices disappear. So again,
our reality depends on what our biology is up to
and influences on your cognitive life also include tiny non
human creatures. Microorganisms, like viruses in bacteria, hold sway over
(33:40):
behavior in extremely specific ways. Here's my favorite example of
a microscopically small organism taking over the behavior of a
giant machine, the rabies virus. After a bite from one
mammal to another, this tiny bullet shaped virus climbs its
way up the nerves and into the temporal lobe of
(34:03):
the brain, and there it ingratiates itself into the local
neurons and it changes the local patterns of activity, and
by this route it steers the infected host to aggression
and rage and a propensity to bite. The virus also
moves into the salivary glands and in this way it's
(34:27):
passed on through the bite to the next host. So
by maneuvering the behavior of the animal, this is how
the virus ensures it spread to other hosts. So just
think about that the virus, a measly seventy five billions
of a meter in diameter, survives by command during the
(34:49):
massive body of an animal, an animal twenty five million
times larger than it. It would be like you finding
a creature that's twenty eight one thousand miles tall and
doing something very clever to bend its will to yours,
and then you drive it around.
Speaker 1 (35:07):
The critical take home.
Speaker 2 (35:09):
Lesson here is that invisibly small changes inside the brain
can cause massive changes to behavior. Our choices are inseparably
married to the tiniest details of our machinery. And as
another example of our dependence on our biology, note that
tiny mutations in single genes also determine and change or behavior.
(35:34):
Consider Huntington's disease, in which creeping damage in the frontal
cortex leads to changes in personality such as aggressiveness and hypersexuality,
and impulsive behavior and disregard for social norms, all happening
years before the more recognizable symptom of spastic limb movement
(35:56):
ever appears. The point to appreciate is that Huntington's is
caused by a mutation.
Speaker 1 (36:01):
In a single gene.
Speaker 2 (36:04):
My colleague Robert Supolski summarized the situation in Huntington's like
this quote. Alter one gene among tens of thousands, and
approximately halfway through one's life there occurs a dramatic transformation
of personality. So, in the face of all these observations
we've talked about, can we conclude anything other than a
(36:27):
dependence of our essence on the details of our biology.
Could you tell a person with Huntingtons to just use
his free will to quit acting so strangely? So we
can see that the invisibly small molecules that we call
narcotics or neurotransmitters, or hormones or viruses or genes, these
(36:49):
can all place their little hands on the steering wheel
of our behavior. As soon as your drink is spiked,
or your sandwich gets sneezed on, or your genome picks
up a mutation, your ship can move in a different direction,
try as we might to make it otherwise, the changes
in our machinery equate to changes in us. Given these
(37:15):
facts on the ground, it's far from clear that we
hold the option of choosing who we would like to be.
As my friend Martha Farah puts it, quote, if an
antidepressant pill can help us take everyday problems in stride,
and if a stimulant can help us meet our deadlines
and keep our commitments at work, then must not unflappable
(37:38):
temperaments and conscientious characters also be features of people's bodies.
And if so, is there anything about people that is
not a feature of their bodies?
Speaker 1 (37:50):
End quote?
Speaker 2 (37:52):
So, where we are now, as we've established the connection
between your biology and who you are, But this depends
on such a vast network of factors that it's presumably
going to remain impossible to make a one to one
mapping between molecules and behavior. And this is what we're
going to dig into in the next episode. But despite
(38:14):
this complexity, we can conclude that your world is directly
tied to your biology. If there could even exist something
like a soul, we'd have to conclude at minimum that
it is tangled irreversibly with the molecular and cellular details.
Whatever else might be going on with our mysterious existence.
(38:36):
The fact is that your essence is irreversibly yoked to
your biology.
Speaker 1 (38:42):
That is beyond doubt.
Speaker 2 (38:45):
So join me next week for part two, when we're
going to go to the next level and reveal some surprises.
Speaker 1 (38:56):
To find out more and to share your thoughts, head over.
Speaker 2 (38:59):
To egoman dot com slash podcasts. Send me an email
at podcasts at eagleman dot com with questions or discussions,
and I'll be making episodes in which I address those
until next time. I'm David Eagleman, and this is Inner Cosmos.
In this episode.
Speaker 2 (00:06):
In the next one, I want to dive into a
fundamental philosophical question, probably the most important one that we
have as humans, which is what it means to know ourselves?
In other words, as people living in the twenty first century,
with all of this massive biological data and the insights,
(00:27):
what does that tell us about the ancient question of
who we are? Do we have something like souls? Are
we just a bunch of neurons? Are there other ways
to look at this? There's a sense in which I'm
constantly surprised that this question who am I? Isn't talked
about all the time. I mean, most people spend most
(00:50):
of their time talking about sports teams or the latest celebrity,
or traffic or whatever food they like or whatever.
Speaker 1 (00:58):
But we find ourselves.
Speaker 2 (00:59):
Here in this mysterious existence where you don't really remember
getting here, and you're told that one day you'll disappear
from here. And it surprises me that this isn't what
we're talking about all the time. Why isn't this what
we're using the internet to discuss. Why don't we have
(01:20):
world leaders coming together not for the United Nations Annual Meeting,
but to dig their teeth into this question and bring
evidence to bear on different hypotheses. Why isn't this the
topic of conversation on every single news program? So for
the next two episodes, we're going to dig in and
(01:41):
I always start with some questions to give you a
sense of the weirdness of the roadmap.
Speaker 1 (01:46):
So here we go.
Speaker 2 (01:47):
Would you appreciate Taylor Swift if you only had an
internal camera to watch her vocal cords jumping around? What
do almost all drugs of abuse have in common? How
can the tiny molecules of the rabies virus control your behavior?
Did Joan of arc turn the tide of the one
(02:07):
hundred Years War as the result of a brain disorder?
And what does any of this have to do with
who you are? And the question of your essence as
a person, the essence that your friends know and love
as you?
Speaker 1 (02:23):
Where does that come from? Welcome to Inner.
Speaker 2 (02:29):
Cosmos with me David Eagleman. I'm a neuroscientist and an
author at Stanford and in the next couple of episodes,
we're going to sail deeply into our three pound universe
to dig in to one of the most fundamental questions
of our experience in the world. Now I've talked about
(02:53):
this fact before, but I need to emphasize for this
episode that the brain is the most complex structure we
have ever discovered in our universe. It's got almost one
hundred billion neurons and hundreds of trillions of connections. Now,
this kind of complexity is simply not understandable by a
(03:16):
human mind. And yet we know that somehow your brain
is you. All of your hopes and dreams and aspirations,
the agony, the ecstasy, it's all contained in that three
pound organ in your skull. Now how do we know
that because every day in clinics all over the world,
we see people with damage to their brains, even very
(03:40):
tiny damage, and that changes who they are. Small bits
of damage caused by a stroke or a traumatic brain injury,
or a tumor or whatever. These can change your decision
making or your ability to see colors, or understand music
(04:00):
or name animals. It can make you more or less
prone to gambling, or more talkative or less talkative. It
can make you not know the names of objects or
not know how to interact with objects anymore, or make
you unable to speak or to understand speech, or one
hundred other things. And this is how we came to
(04:23):
have this strange hypothesis that you are your brain. So
to start this question of who are we, let's step
back a little bit. In history, people have always been
wondering who we are, mostly because our existence is so
deeply weird, and traditionally the answer has been about deities
(04:47):
and immortal souls, but not everyone has been willing to
stop there. So I was impressed some years ago when
I read about the French essayist Montaigne, who in fifteen
seventy one, on the morning of his thirty eighth birthday,
decided to make a radical change in his life's trajectory.
He quit his career in public life, and he set
(05:09):
up a library with one thousand books in a tower
at the back of his large estate, and he spent
the rest of his life writing essays about the subject
that interested him the most, the search for oneself. His
first conclusion was that the search to no one's self
is a fool's errand because the self who I am,
(05:33):
is always changing and staying a few steps ahead of
a firm description. But that didn't stop him from searching,
and his question has resonated through the centuries.
Speaker 1 (05:46):
Causasia, what do. I know.
Speaker 2 (05:49):
That was a good question, and it remains so because
when we dive in to explore the inner cosmos, as
we've been doing on this podcast, we can't help find
ourselves disabused of our initial notions that knowing ourselves will
be uncomplicated and intuitive, because we see that self knowledge
(06:11):
requires as much work from the outside in the form
of science as from the inside introspection.
Speaker 1 (06:18):
And this is not to.
Speaker 2 (06:19):
Say that we can't grow better at introspection. After all,
we can learn how to pay attention to what we're
really seeing out there, like painters do, and we can
attend more closely to our internal signals like Yogi's do.
But there are limits to introspection. Just consider the fact
(06:40):
that your peripheral nervous system employs one hundred million neurons
to control the activities in your gut. This is called
the enteric nervous system one hundred million neurons, and no
amount of your introspection can touch this, nor by the way,
would you want it to be. In The tek nervous
(07:00):
system is better off running as the automated optimized machinery
that it is, routing food along your gut and providing
chemical signals to control the digestion factory without asking your
opinion on the matter. Now, this has always fascinated me
to think that in some cases there may be not
(07:20):
only a lack of access, but even an active prevention
of access. For example, I was once chewing on this
with my thesis advisor, Read Montague, and he speculated that
we might have algorithms that protect us from ourselves. This
is analogous to your laptop computer, which has a boot
(07:42):
sector that's inaccessible by the operating system, because the boot
sector is too important for the operation of the computer
for any high level systems to find inroads and gain
admission under any circumstances.
Speaker 1 (07:57):
So Read noted.
Speaker 2 (07:58):
That whenever we try to think about ourselves too much,
we tend to blink out, and the analogy was that
we're getting too close to the boot sector. Now, he
was just speculating here, but the idea is fascinating that
maybe our system has evolved to make certain that we
can't access the details too deeply. Or, as Ralph Waldo
(08:20):
Emerson put the same idea from a more poetic point
of view, everything intercepts us from ourselves. So whether it's
just a lack of access or an active prevention of access.
The bottom line is that much of who we are
remains outside of our conscious control, or our opinion or
(08:41):
our choice. We talked in an earlier episode about the
impossibility of changing your sense of beauty or attraction. What
would happen if someone commanded you to be attracted to
someone that you're not, or to be attracted to a
gender that you're not attracted to, or to an animal
(09:01):
outside your species.
Speaker 1 (09:03):
Could you muster attraction there? Doubtful.
Speaker 2 (09:06):
Your most fundamental drives are stitched into the fabric of
your neural circuitry, and they are inaccessible to you. You
can't reach in there and change them around. You find
certain things more attractive than others, and you don't know why. So,
like your nervous system in your gut and your sense
of attraction, almost the entirety of your inner universe is
(09:31):
foreign to you. Consider when an idea strikes you, you
don't know where the heck that came from. One minute
you didn't have it, and the next moment it's there.
It just appears even though it came from your brain,
it may as well have been handed to you from
somewhere else. You don't know the neuronal history of the idea,
and you don't care. You just think, oh, that's a
(09:52):
good idea. And this is the same with your train
of thought during a day dream, or the bizarre content
of your nighttime dreams. All these are just served up
to you from unseen intracranial caverns. So what does all
of this mean for the Greek admonition to know thyself?
(10:16):
These were the words inscribed in the Temple of Apollo
at Delphi, know thyself? Can we ever know ourselves more
deeply by studying our neurobiology? And I'm going to argue yes,
but with some interesting nuances, And I'll give you an
analogy here to physics. In the face of the deep
(10:38):
mysteries presented by quantum physics, the physicist Neils Brer suggested
that an understanding of the structure of the atom could
be accomplished only by changing the definition of to understand,
because with quantum mechanics you couldn't any longer draw pictures
(10:59):
of an atom, so that was lost. But instead one
could now predict experiments about an atom's behavior out to
fourteen decimal places, So lost assumptions were replaced by something richer.
And by the same token, to know one's self may
require a change of definition of to know. Knowing yourself
(11:23):
now requires the understanding that the conscious you occupies only
a small room in the mansion of the brain, and
that it has very little control over the reality that
gets constructed for you. So the invocation to know thyself
needs to be considered in new ways because when we
look at the trillions of neurons and there are sex
(11:46):
tillions of proteins and biochemicals, what does it mean to
know ourselves from that totally unfamiliar perspective, As we're going
(12:14):
to see, we need the neurobiological data and we also
need quite a bit more to know ourselves. Why because
the biological data is fundamental, but it has its limitations.
Imagine that you got Taylor Swift to come to your
house and sing for you, but instead of listening to her,
(12:36):
you put on ear muffs and you lower a medical
scope down her throat and you get.
Speaker 1 (12:41):
A good close up view of her vocal chords.
Speaker 2 (12:44):
They're slimy and shiny, and they're contracting in and out
and spasms. Now, you could watch this and study the
details all day, but it wouldn't get you any closer
to understanding why her songs are big hits, or what
the words mean to you, or how they make you feel.
By itself, in its raw form, the biology is only
(13:07):
going to give you partial insight there. It's the best
that we can do for now, but it's far from complete.
So this is what we're going to talk about today.
What does and doesn't it mean to be constructed out
of physical parts. So let's start with a clear and
famous example of brain damage. I've mentioned this story in
(13:27):
a previous episode, but i'll retell it here with more detail.
In eighteen forty eight, there was a work gang foreman
twenty five years old. His name was Phineas Gage. On
September twenty first of that year, the Boston Post wrote
a short article under the headline horrible accident. Here's how
it went. Quote as Phineas P. Gage, a foreman on
(13:50):
the railroad in Cavendish, was yesterday engaged in tamping.
Speaker 1 (13:55):
For a blast.
Speaker 2 (13:56):
The powder exploded, carrying an instrument and threw his head
an inch and a fourth in diameter and three feet
and seven inches in length, which he was using at
the time. The iron entered on the side of his face,
shattering the upper jaw and passing back of the left
eye and out at the top of the head.
Speaker 1 (14:19):
So this was an iron tamping rod, and.
Speaker 2 (14:21):
Because of an explosion of gunpowder, this blew through his
head and it clattered to the ground twenty five yards away. Now,
while Phineas Gage wasn't the first person to have his
skull punctured and a portion of his brain spirited away
by a projectile, he was the first, so far as
we know, to not die from it. And in fact,
(14:44):
Gauge didn't even lose consciousness. So the first physician to
arrive at the scene, a doctor Williams, didn't believe Gauge's
statements of what had just happened, but instead he quote
thought that he Gauge was this. But doctor Williams soon
understood the gravity of what had happened when quote mister
(15:07):
Gage got up and vomited, and the effort of vomiting
pressed out about half a tea cupful of brain, which
fell upon the floor end quote. The Harvard surgeon who
studied his case noted that quote, the leading feature of
this case is its improbability. It is unparalleled in the
(15:28):
annals of surgery.
Speaker 1 (15:30):
End quote.
Speaker 2 (15:31):
The Boston Post article summarized this improbability with just one
more sentence. Quote, The most singular circumstance connected with this
melancholy affair is that he was alive at two o'clock
this afternoon and in full possession of his reason and
free from pain unquote. Now Gage's survival alone would have
(15:55):
made this an interesting medical case, it became a famous
case because of some thing else that came to light.
Two months after the accident, his physician reported that Gage
was quote feeling better in every respect walking about the
house again, says he feels no pain in the head unquote,
(16:15):
but foreshadowing a larger problem. The doctor also noted that
Gauge quote appears to be in a way of recovering
if he can be controlled end quote. So what did
he mean here, if he can be controlled? It turned
out that the pre accident, Phineas Gage had been described
(16:36):
as a great favorite among his team, and his employers
had hailed him as the most efficient and capable foreman
in their employ But after the brain damage, his employers
considered him to be such a different person that they
decided they couldn't give him his place again. Now, what
was this change in his personality. Here's what Gauge's Physics
(17:00):
wrote twenty years later in eighteen sixty eight. This is
a long quotation, but I'm going to read the whole
thing because it's fascinating and gives us insight into how
a person can change when his brain changes.
Speaker 1 (17:13):
Quote.
Speaker 2 (17:14):
The equilibrium or balance, so to speak, between his intellectual
faculties and animal propensities seems to have been destroyed. He
is fitful, irreverent, indulging at times in the grossest profanity,
which was not previously his custom manifesting, but little deference
(17:34):
for his fellows, impatient of restraint or advice when it
conflicts with his desires, at times pertinaciously obstinate, yet capricious
and vacillating, devising many plans of future operations which are
no sooner arranged than they are abandoned in turn for others,
(17:55):
Appearing more feasible a child in his intellectual capacity and
manner infestations. He has the animal passions of a strong
man previous to his injury. Although untrained in the schools,
he possessed a well balanced mind and was looked upon
by those who knew him as a shrewd, smart businessman.
(18:17):
Very energetic and persistent in executing all his plans of operation.
In this regard, his mind was radically changed, so decidedly
that his friends and acquaintances said he was quote no
longer gauge end quote. Now in the intervening century in half,
(18:38):
we've seen lots of cases like Phineas Gages, because tragically,
there are lots of ways for the delicate pink material
of the brain to get hurt, and they all surface
the same lesson. When the brain changes, the person changes.
And of course the more common thing seen in hospitals
(19:00):
every day are all of nature's tragic experiments strokes, tumors, neurodegeneration,
And it's the same lesson. The condition of your brain
is central to who you are. You that all your
friends know and love cannot exist unless all the fine
(19:22):
microscopic details of your brain, all the nuts and bolts,
are in place. If you don't believe me, step into
any neurology ward in any hospital. Damaged to even small
parts of the brain can lead to the loss of
shockingly specific abilities, the ability to understand music, or to
(19:43):
manage risky behavior, or to distinguish colors, or to arbitrate
simple decisions. We see examples of this when we meet
patients who lose the ability to see movement even though
they're not blind. We see it when a person gets
front do temporal dementia and starts shoplifting, even though that's
(20:04):
something they would have never done before. We see it
when a person no longer understand how a mirror reflection works.
We see it when medications for Parkinson's disease turn someone
into a compulsive gambler, or a million other examples that
tell us that your essence can be changed by changes
(20:26):
in your brain. So all of this leads to a
key question. Do we possess a soul that is separate
from our physical biology? Or are we simply an enormously
complex biological network that mechanically produces our hopes and aspirations
and dreams and desires and humor and passion. So over
(20:48):
this and the next episode, this is the question I'm
going to unpack. Now, the majority of people on the
planet vote for the extra biological soul, but all the
evidence from neuroscience suggests it's the biology. It's a vast
physical system from which the essence of a person emerges,
(21:10):
and nothing more than that. Now, do we know which
answer is correct, not with certainty, but cases like Phineas
Gauges and every case of brain damage we see in
the hospitals certainly seem to weigh in on the problem.
They make it more and more difficult to ignore or
deny that we are biological creatures. So the materialist viewpoint
(21:35):
holds that we are fundamentally made only of physical materials.
In this view, the brain is a system whose operation
is governed by the laws of chemistry and physics, with
the end result that all of your thoughts and emotions
and decisions are produced by natural reactions following local laws
(21:57):
to lowest potential energy. We are our brain and its chemicals,
and any dialing of the knobs of your neural system
changes who you are now. A common approach to materialism
is called reductionism, and this theory puts forth the hope
that we can successively reduce the problems down to their
(22:21):
small scale biological pieces and parts, and eventually come to
explain complex phenomena like happiness or greed, or narcissism or
compassion or malice or caution or amazement by understanding the
pieces and parts at first blush the materialist and reductionist
(22:43):
viewpoints sound absurd to a lot of people. Not to
everyone I work with, and possibly not to a lot
of the listeners of this podcast, but probably to many
of the people on this planet. And I know this
in part because when I sit next to strangers on
a plane or a subway, I ask their opinions about
this kind of stuff, and people will often say something like, look,
(23:06):
why I chose my job, how I fell in love
with my wife, what TV shows I like to watch?
That has nothing to do with the cells of my brain.
That's just who I am. And they're right to think
that the connection between your essence as a person and
a squishy confederacy of cells that seems distant at best,
(23:28):
that person's decisions came from them, not from a bunch
of chemicals cascading through invisibly small cycles.
Speaker 1 (23:36):
Right.
Speaker 2 (23:37):
But what happens when we run into enough cases like
Phineas Gauges or people who have strokes or tumors or neurodegeneration,
And what happens when we turn the spotlight on even
more subtle influences, far more subtle than a tamping rod,
where changes in the brain change people's personalities. Just consider
(24:00):
this as an example, Think about the powerful effects of
the small molecules that we call narcotics. These are invisibly small,
but they alter consciousness, they affect cognition, they navigate behavior.
We are slave to these molecules tobacco, alcohol, and cocaine.
(24:21):
These are self administered universally for the purpose of mood changing.
And if we knew nothing else about neurobiology, the mere
existence of narcotics would give us all the evidence we
need to tell us that our behavior and psychology can
be commandeered at the molecular level. Take cocaine as an example.
(24:44):
Cocaine interacts with a very specific network in the brain,
one that registers rewarding events. This is known as the
mesolimbic dopamine system. It registers rewarding events like you satisfying
your thirst with a a cool iced tea, or winning
a smile from the right person, or cracking a tough
(25:06):
problem at work and your boss says good job. By
tying positive outcomes to the behaviors that led to them,
this neural circuit learns how to optimize behavior in the world.
It's what helps us get food and drink and mates
and navigate life's daily decisions now out of context. Cocaine
(25:47):
is a totally uninteresting molecule. It has seventeen carbon atoms
and twenty one hydrogens and one nitrogen and four oxygens.
What makes cocaine cocaine is the fact that its shape
happens to fit lock and key into the microscopic machinery
of this reward circuit. So suddenly the cocaine gets to
(26:12):
act like the most rewarding thing you've done, which causes you,
in the language of the reward system, to want to
do that again. And by the way, the same thing
goes for all four major classes of drugs of abuse, alcohol, nicotine,
psychostimulants like amphetamines, and opiates like morphine. By one inroad
(26:35):
or another, they all plug into this same reward circuitry.
All these types of molecules rev the engine of the
mesolimbic dopamine system, and so they all become self reinforcing.
Your brain experiences them and then chases.
Speaker 1 (26:52):
More of that.
Speaker 2 (26:54):
And these effects are so powerful that users will end
up robbing stores and mugging elderly people to continue obtaining
these specific molecular shapes. And what's really amazing to note
is that These chemicals work their magic at scales one
thousand times smaller than the width of a human hair,
(27:15):
but by attaching in the right spots, they can make
the consumers feel invincible and euphoric. By plugging into this
dopamine system, cocaine and its cousins command beer the reward system,
and they tell the brain that this is the best
possible thing that could be happening. So these ancient circuits
(27:38):
that are there for steering our behavior, these become hijacked. Now,
these cocaine molecules are hundreds of millions of times smaller
than the tamping rod that shot through Phineas Gage's brain,
But the lesson is the same. Who you are depends
on the precise details of your neurobiology, and the dopamine
(28:03):
system is only one of hundreds of examples. The exact
levels of other neurotransmitters, for example, serotonin, are critical for
who you believe yourself to be. If you suffer from
clinical depression, you'll probably get prescribed a medication known as
a selective serotonin uptake inhibitor abbreviated as an SSRII, for
(28:26):
example fluoxetine. Now, everything you need to know about how
these drugs work is contained in the words uptake inhibitor. Normally,
channels called transporters take up the serotonin from the space
between the neurons, and when you inhibit that uptake, you
get a larger concentration of serotonin in the brain, and
(28:48):
the increased concentration has direct consequences on cognition and emotion.
People can go on these medications and they can transition
from crying on the edge of the bed to standing
up and showering and getting their job back and rescuing
healthy relationships with the people in their lives, all because
(29:09):
of a subtle fine tuning of a neurotransmitter system. If
this story weren't so common, we would more easily appreciate
its bizarreness. And it's not just neurotransmitters that influence your cognition.
The same goes for hormones, the invisibly small molecules that
(29:29):
surf the bloodstream and cause commotion at every port that
they visit. If you inject a female rat with estrogen,
she'll begin seeking a sexual partner. If you inject a
male rat with testosterone, he'll become aggressive. Actually, in episode fifteen,
I told you about the wrestler Chris Benoit, who took
(29:51):
massive doses of testosterone and then murdered his wife and
his own child in a roid rage. Or just think
about the hormone fluctuation that accompany normal menstrual cycles. Recently,
a female friend of mine was at the bottom of
her menstrual mood changes, and she said to me, you know,
I'm just not myself for a few days each month.
(30:14):
But because she's a neuroscientist, she then reflected for just
a moment. Then she said, or maybe this is the
real me, and I'm actually someone else the other twenty
seven days of the month. She wasn't afraid to view
herself as the sum total of her chemicals at any moment.
She understood that what we think of as her is
(30:35):
something like a time averaged version. All these examples add
up to something of a strange notion of the self.
Because of inaccessible fluctuations in our biological soup, some days
we find ourselves more irritable or more humorous, or more
(30:56):
well spoken, or more calm or energized or clear thinking.
Our internal life and our external actions are steered by
these biological cocktails to which we don't have any direct
access or any direct acquaintance. And don't forget that the
long list of influences on your mental life. This stretches
(31:19):
way beyond chemicals. It includes the details of the circuitry
as well. So consider something like epilepsy. If an epileptic
seizure is focused in a particular spot in the temporal lobe,
a person won't have motoric seizures with their body, but
instead something more subtle. The effect is something like a
(31:42):
cognitive seizure, and this translates to changes of personality and
hyper religiosity, which is an obsession with religion, and hypergraphia,
which is where you write pages and pages on a subject,
usually about religion, and often the hearing of voe voices
that get attributed to a god. Some fraction of histories,
(32:05):
prophets and martyrs and leaders appear to have had temporal
lobe epilepsy. Consider Joan of Arc, the sixteen year old
girl who managed to turn the tide of the Hundred Years'
War because she believed and convinced the French soldiers that
she was hearing voices from Saint Michael and Saint Catharine,
(32:29):
and Saint Margaret and Saint Gabriel as she described her experience, quote,
when I was thirteen, I had a voice from God
to help me to govern myself. The first time I
was terrified. The voice came to me about noon. It
was summer and I was in my father's garden. Later,
she reported, quote, since God had commanded me to go,
(32:53):
I must do it. Although it's impossible to retrospectively diagnose
with certainty what is known about her, including the increasing
religiosity and ongoing voices. This is consistent with temporal lobe epilepsy.
When brain activity is kindled in just the right spot,
people hear voices. If a physician prescribes in anti epileptic medication,
(33:19):
the electrical spikes go away and the voices disappear. So again,
our reality depends on what our biology is up to
and influences on your cognitive life also include tiny non
human creatures. Microorganisms, like viruses in bacteria, hold sway over
(33:40):
behavior in extremely specific ways. Here's my favorite example of
a microscopically small organism taking over the behavior of a
giant machine, the rabies virus. After a bite from one
mammal to another, this tiny bullet shaped virus climbs its
way up the nerves and into the temporal lobe of
(34:03):
the brain, and there it ingratiates itself into the local
neurons and it changes the local patterns of activity, and
by this route it steers the infected host to aggression
and rage and a propensity to bite. The virus also
moves into the salivary glands and in this way it's
(34:27):
passed on through the bite to the next host. So
by maneuvering the behavior of the animal, this is how
the virus ensures it spread to other hosts. So just
think about that the virus, a measly seventy five billions
of a meter in diameter, survives by command during the
(34:49):
massive body of an animal, an animal twenty five million
times larger than it. It would be like you finding
a creature that's twenty eight one thousand miles tall and
doing something very clever to bend its will to yours,
and then you drive it around.
Speaker 1 (35:07):
The critical take home.
Speaker 2 (35:09):
Lesson here is that invisibly small changes inside the brain
can cause massive changes to behavior. Our choices are inseparably
married to the tiniest details of our machinery. And as
another example of our dependence on our biology, note that
tiny mutations in single genes also determine and change or behavior.
(35:34):
Consider Huntington's disease, in which creeping damage in the frontal
cortex leads to changes in personality such as aggressiveness and hypersexuality,
and impulsive behavior and disregard for social norms, all happening
years before the more recognizable symptom of spastic limb movement
(35:56):
ever appears. The point to appreciate is that Huntington's is
caused by a mutation.
Speaker 1 (36:01):
In a single gene.
Speaker 2 (36:04):
My colleague Robert Supolski summarized the situation in Huntington's like
this quote. Alter one gene among tens of thousands, and
approximately halfway through one's life there occurs a dramatic transformation
of personality. So, in the face of all these observations
we've talked about, can we conclude anything other than a
(36:27):
dependence of our essence on the details of our biology.
Could you tell a person with Huntingtons to just use
his free will to quit acting so strangely? So we
can see that the invisibly small molecules that we call
narcotics or neurotransmitters, or hormones or viruses or genes, these
(36:49):
can all place their little hands on the steering wheel
of our behavior. As soon as your drink is spiked,
or your sandwich gets sneezed on, or your genome picks
up a mutation, your ship can move in a different direction,
try as we might to make it otherwise, the changes
in our machinery equate to changes in us. Given these
(37:15):
facts on the ground, it's far from clear that we
hold the option of choosing who we would like to be.
As my friend Martha Farah puts it, quote, if an
antidepressant pill can help us take everyday problems in stride,
and if a stimulant can help us meet our deadlines
and keep our commitments at work, then must not unflappable
(37:38):
temperaments and conscientious characters also be features of people's bodies.
And if so, is there anything about people that is
not a feature of their bodies?
Speaker 1 (37:50):
End quote?
Speaker 2 (37:52):
So, where we are now, as we've established the connection
between your biology and who you are, But this depends
on such a vast network of factors that it's presumably
going to remain impossible to make a one to one
mapping between molecules and behavior. And this is what we're
going to dig into in the next episode. But despite
(38:14):
this complexity, we can conclude that your world is directly
tied to your biology. If there could even exist something
like a soul, we'd have to conclude at minimum that
it is tangled irreversibly with the molecular and cellular details.
Whatever else might be going on with our mysterious existence.
(38:36):
The fact is that your essence is irreversibly yoked to
your biology.
Speaker 1 (38:42):
That is beyond doubt.
Speaker 2 (38:45):
So join me next week for part two, when we're
going to go to the next level and reveal some surprises.
Speaker 1 (38:56):
To find out more and to share your thoughts, head over.
Speaker 2 (38:59):
To egoman dot com slash podcasts. Send me an email
at podcasts at eagleman dot com with questions or discussions,
and I'll be making episodes in which I address those
until next time. I'm David Eagleman, and this is Inner Cosmos.
Host
David Eagleman
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