November 17, 2025 • 45 mins
What do propaganda posters have in common across nation and time, and how is that related to the medial prefrontal cortex? What is behind repeating cycles of societal polarization? What does any of this have to do with the American Civil War, hippies vs soldiers, border ruffians vs free-staters, hanging chads, Pearl Harbor, and why education can serve as an immune response to mind viruses?
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Speaker 1 (00:05):
What does political polarization have to do with the brain.
How does an understanding of the medial prefrontal cortex tell
us about what propaganda posters have in common across nation
and time. What does any of this have to do
with the Civil War or hippies versus soldiers, or border
(00:27):
ruffians versus free staters or barbarians, or hanging chads or
pearl harbor, or the shadows side of oxytocin, And why
education can serve as an immune response to mind viruses.
Welcome to Inner Cosmos with me David Eagleman. I'm a
(00:49):
neuroscientist and author at Stanford and in these episodes we
sail deeply into our three pound universe to understand why
and how our lives look the way they do. Today's
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episode is one of a couple I'm making on the
topic of neuropolitics. We are in a polarized era, and
when I look around, I see a primate brain doing
lots of things that primate brains do. So today I'm
going to talk about polarization, and in the next episode,
I'm going to talk about all the good news, which
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is the flexibility of the brain and what hopes we
might have to get ourselves out of polarization. I'm also
going to do another episode about all the other aspects
of the bigger picture that I'm calling neuropolitics, which is
the way that the circuitry of our brains leads us
to the kind of political viewpoints we have, and why
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we often have a difficult time understanding one another and
why societies fracture along particular lines. Okay, so when I
think about America, the polarization is high, and this feeling
we all have is of course easily quantified. As one example,
you can look at the numbers about how many times
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you have congressmen voting across the aisle. When a society
is very polarized, like it is now, people hold on
tight to their team. I'm very interested in viewing this
all from the perspective of the brain, but first I
need to do some table setting. A lot of people
assert that our polarization has everything to do with social media.
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I'm interested in the roles that social media plays, but
I do need to say that I don't think it
serves by itself as much of an explanation for our polarization. Why,
because we've been exactly this polarized many many times before,
all before the Internet was even a twinkle in anybody's eyes. So,
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for example, America in the late nineteen sixties was very polarized.
This was easily seen on the streets, in living rooms,
on television screens. The Vietnam War split the nation. You
had young people marching against it, while others saw opposition
as unpatriotic and dangerous. The Civil rights movement was reshaping
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laws and culture, and that was going too fast for
some and too slow for others. Generational divides ran deep.
Parents who had lived through World War Two and fought
in it struggled to understand their children's embrace of counterculture
and long hair and psychedelic music and radical politics. The
assassinations of Martin Luther King and Senator Robert F. Kennedy,
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the urban riots, what happened Kent State. All of these
moments reinforced the sense that Americans were not living in
one shared country, but in different realities. Trust in government
plummeted with Watergate in the nineteen seventies, and that further
hardened the feeling that institutions could no longer be trusted.
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It was a time when the nation's social fabrics seemed
to be tearing and when, much like today, people questioned
whether their neighbors were even living in the same world
that they were. And of course that was just one
of many polarized eras in this country. The most obvious
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one began in the eighteen forties and led to the
Civil War. The divide over slavery and states rights sharpened
decade by decade, inflamed by the Missouri Compromised, the Kansas
Nebraska Act, the dread Scott decision. You can see the
way that newspapers and churches and politicians increasingly spoke in
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absolutist terms, and by the way violence erupted well before
the war did. From eighteen fifty four to fifty nine
in the Kansas territory, you had pro slavery border Ruffians
and the anti slavery free Staters, and they would make
raids back and forth, committing assaults and murders, each retaliating
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for the last. There were at least fifty six political
killings during that time, and by the next year, eighteen sixty,
the election of Abraham Lincoln prompted Southern states to secede
and Civil War followed. Okay, so that was a really
grim outcome with seven hundred thousand people killed. But there
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have been many, many other periods of polarization that somehow
had their day, and then the temperature went down without
war for different reasons, and we're going to dive into
that next week. For example, in the eighteen seventies, a
decade after the Civil War, polarization grew again around rapid industrialization.
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You had labor strikes and violent clashes like the Haymarket
riot and the Pullman strike. You had class resentment between
robber barons and workers. And what you can see then
as now is that newspapers and politicians portrayed opponents as
existential threats to the American way of life. Then in
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the nineteen tens and twenties, polarization happened again. World War
I and its aftermath split Americans over issues of free
speech and loyalty and communism. The first Red Scare was
concerned about anarchists and labor organizers who were depicted as
dangerous reds. There were mass arrests and deportations, and this
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deepened divides, and simultaneously there was a surgeon racial violence.
The summer of nineteen nineteen saw dozens of race riots
and the rise of the Second Ku Klux Klan, which
polarized communities along racial and religious and immigrant lines. Then
by the Late Night Seen twenties and nineteen thirties, you
had the Great Depression, the economic collapse that sparked really
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fierce battles over the role of government. FDR's New Deal
was hailed as salvation by some and it was condemned
as socialism by others. Far left and far right groups
clashed bitterly. And it was also the case that the
country was polarized over whether America should intervene in Europe
as fascism rose, until the attack on Pearl Harbor, which
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temporarily united public opinion. Okay, then I already mentioned the
polarization of the civil rights movement Vietnam era. So let's
jump to the culture wars of the nineteen eighties and nineties.
Some of you might even recall the Reagan era, where
the country saw sharp divides over taxation and welfare, and
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abortion and feminism and gay rights. These were the so
called culture wars, which pitted conservatives and evangelicals against progressives
in battles over school curricula and art and family values.
And again you could measure this with polarization in Congress
steadily growing. Finally, some of you may even remember the
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contested two thousand election of Bush versus Gore. Again, this
was still pre social media, and the whole race came
down to just the state of Florida, where Bush seemed
to lead by a few hundred votes out of six
million cast there, and officials tried to figure out voter
intent involving hanging chads, which were in completely punched paper ballots,
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and pregnant chads, which were paper ballots that were dimpled. Anyway,
this spun all the way up to the Supreme Court,
who finally ruled the electoral vote in favor of Bush,
even though Gore had received five hundred thousand more popular
votes nationwide. Now, not all my listeners were alive or
watching the news at that time, but boy, that was
a really highly polarized time as well. Then you had
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nine to eleven, which brought the nation together. But then
over some years the Iraq War started to sharpen those
divides again. Now you might be tempted to say, well,
it's worse than ever now because of social media filter bubbles,
but I just want to remind us all that echo
chambers are the oldest story of humankind. We are more
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comfortable with people who agree with us and see the
world from our angle now. I often hear people say
things like, yes, but we only had a few news
sources back in the day, so everyone was pinned to
the same truth. Walter Kronkite or whoever. This is a
seductive idea, but it's not true. People got some of
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their info from Kronkite, but also from the newsletters they
subscribe to in their physical mailbox, and also from all
their friends and neighbors and co workers. And when people
would have dinners together or chat in the breakroom or
drink beers in their backyard with their friends, that's when
they would really come to consensus agreement about what was
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happening in the world. Just to jump back to the
Vietnam era, do you think the hippies and the returning
soldiers were sitting down and watching Walter Cronkite and saying, ah, okay,
I see the truth. There's no problem. We all agree now.
So any reading of history shows that polarization is depressingly
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a recurring pattern. Each cycle takes a different shape, whether
that's slavery or labor or immigration, or race or culture
or war. But the common thread is the part I
want to zoom in on. When people begin to see
each other not as neighbors with families and mortgages and
lives and desires for a better life, but as existential threats.
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When that happens, the brain circuitry involved in empathy, in
understanding another person's hopes and dreams, the activity in those
circuits dials down, and the social fabric begins to frame.
By the way, I just want to flag a point
that I'm going to explore next week, which is that
most historians interested in this topic linger on how societies
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fall into polarization, but my main interest nowadays is how
they crawl back out. So next week I'm going to
examine the factors that seem to pull societies back from
the brink, because with all those eras that I just named,
we went to actual war only once, and with all
the other periods, we managed to pull ourselves back onto
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a straight road. Sometimes this is because of external factors
and sometimes because of internal work, And this is all
what we're going to address next week. Okay, So now
I want to return to the particular issue for today,
which is how our brains operate with in and out
groups and what the brain is capable of when it's
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pushed in the wrong direction. So let's start in nineteen
ninety four in Rwanda. The radio was on in homes
and shops and bars, and the message that pours out
every day is relentless. The Tutsis are cockroaches. They must
be crushed. This was literally the language in this framework.
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The Tutsi were not citizens or neighbors or people with
families and histories and memories, but they were cockroaches. The
more often this message was repeated, the more it carved
itself into people's brains, and eventually the machetes got unsheathed,
neighbors turned on neighbors. In one hundred days, half a
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million people were killed. And the part that is frankly
terrifying is that when you think about genocide, you might
think this gets driven by soldiers or politicians, but that's
not what was going on here. The engine of what
happened in Rwanda was regular people who to neighbors who
had lived side by side with the Tutsi for generations.
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That is the power of dehumanization. Once someone is no
longer perceived as human, the neural breaks come off. Now,
it would be comforting if we could view Rwanda as
a tragic anomaly, but it's not. History gives us no
shortage of examples of this very same principle. In Nazi Germany,
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the Jewish community was depicted in newspapers like their Sturmer,
as rodents swarming through sewers. They were painted as vermin
to be exterminated. And this is precisely the cognitive space
that you need to get into if you actually want
to murder your former friends and neighbors. And by the way,
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it's not just the Hutu and the Nazis, but everyone
does it. So during World War Two, American propaganda posters
portrayed the Japanese with distorted faces and thick glasses and
clawed fingers crouched like apes. The caption was this is
the enemy. And this is the same across history. If
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we step back into the world of ancient Rome, you'll
see that outsiders were called barbarians. The word comes from
the Greek barbaros, which was a mocking sound meant to
imitate the noise of foreign languages. Bar barbar Originally, it
didn't have a negative connotation. But pretty quickly the terms
meaning shifted from outsider to a pejorative for being savage
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or uncivilized. And this was because to Roman ears, outsiders
had meaningless babbel and increasingly reviewed like animals. The Romans
often described enemies as wild or beasts. Julius Caesar characterized
the Galls and Germans as quote, living like animals. Tacitus
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described the Britons as quote savages who live like beasts
in the forests. So across continents and centuries, the pattern
is exactly the same. When societies prepare for conflict, they
sharpen their words, and the words are designed for the
simple task of stripping away the humanity of the other side.
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Now why does this work so well? Why are animal
metaphors so effective. It's because they reach down into the
neural machinery and turn a dial. Under normal circumstances, when
you look at someone else and another person, you have
regions of the brain that allow you to imagine their
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inner life. Specifically, a region behind your forehead called the
medial prefrontal cortex gets involved when you consider that this
person has thoughts and feelings and plans and fears. That's
what lights up when you see someone else as a
human reaching out to deal with a bicycle or a
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chair or a coffee machine. This area does not become active.
It's only active when you're dealing with a human, when
you're doing what researchers call a social cognition task. But
some years ago, my colleagues Lasana Harris and Susan Fiske
at Princeton wanted to see if the amount this area
is active depends on what you think about a particular group.
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So they put people in the brain scanner fMRI, and
they showed them photographs of business people and athletes and
the elderly, and nurses, and drug addicts and people who
were homeless. And here's what they found. While some pictures,
like wealthy people, triggered envy, this social region, the medial
prefrontal cortex was still active. Other photos, let's say a
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very elderly people, triggered emotions of pity, and this social
region was still active. But when the brain looked at
pictures and felt discussed, like for pictures of homeless people
or drug addicts at rock bottom, the brain viewed them
not as humans with minds, but more like objects. That
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is the humanization, your brain decides, and this is essentially
all subconsciously that this person does not count as another mind.
This person is neurally speaking, less than human. And by
the way, I'm linking all the relevant studies to the
show notes, I encourage you to check those out. So
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let's return to propaganda. When some group of people is
portrayed as cockroaches or rats or babbling animal, barbarians, or
a virus or a robot or whatever, the social cognition
regions like the medial prefrontal cortex get dialed down. The
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brain no longer treats this other group as people with
a mind. Instead, people of that group become more like objects.
And when these circuits are not steering your decisions, violence
becomes psychologically easier. As an example, unless you are a vegetarian,
you don't really mind murdering a big, beautiful animal like
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a cow or a bowl, because you want that burger,
and that animal is just an animal to your mind,
it's not a human, and so your medial prefrontal cortex
is less active when you look at that cow, and
so you can take a knife to its throat without
that keeping you up at night, and that ease of killing.
Maybe it bothers you a little, but not enough to
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stop doing it. That's what we see throughout history, over
and over, people murdering their neighbors after a sufficient amount
of messaging telling them that their neighbors aren't really humans.
They are less than humans, they're more like cows or worse,
they carry pestilence and they're dangerous. Now, next month, I'm
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going to have a colleague of mine on the podcast
who pioneered a lot of these studies, Lassana Harris, So
we'll go into more detail about the prefrontal cortex then,
But for today, I just want to make it crystal
clear that this dehumanization is the oldest trick in the
playbook of propaganda. Dehumanizing another group doesn't have to be
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about making watertight arguments for convincing people with data. It
can simply be about bypassing reason entirely and tampering directly
with the machinery of social cognition. It's really important to
understand that this is a vulnerability built into the human brain.
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When the wind blows hard enough, the flame of your
social empathy gets blown out. So when we look at
Rwanda or Nazi Germany or America during wartime, we're seeing
a basic lesson about the architecture of our own We're
seeing how fragile our humanizing can be and how dangerous
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it is when pundits and politicians and online influencers lay
their hands on the dials. Now, before I go on,
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I want to make really clear why I'm devoting a
lot of my efforts to this sort of research is
because I think we can solve this, at least mostly,
and part of this comes down to education as a population.
If we can learn to recognize the tricks of the
trade of propaganda, that renders those tricks mostly impotent. Just
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imagine that all the schools in the nation spent just
fifteen minutes teaching what I just told you. Then the
next time a student see some TikTokers say oh, those
people are like animals, or that group is a disease
that's infecting our country, a light bulb goes on in
our kids' minds and they say, wait a minute, we've
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heard that before. That kind of simple recognition is ninety
percent of the game. That recognition turns all of us
from passive receivers into active listeners. Having knowledge about this
topic about how dehumanization works in the brain. Is the
difference between catching the contagion of hate and mounting an
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immune response against it. So now let's turn to a
related issue, one which is equally important to the story,
and again is deeply embedded in our brains, And that's
our predilection for in groups and outgroups. We are fundamentally
very tribal. We see this in so many ways, and
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sometimes it doesn't matter, like which football team you root for,
but when when it comes to politics, it carries cognitive consequences.
You end up feeling certain that your side of the
political aisle generally has the right idea and the other
half of the nation who knows what's infected their brains.
And I just want to be crystal clear that it
doesn't matter which side of the aisle you're on, you
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are likely to genuinely feel this about the other side,
and you'll feel like if they would only listen to
you and stop being so misinformed or stubborn or wrongheaded,
everyone would fundamentally come to agree with you. Now, if
we want to understand why humans divide so easily into
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in and out groups, we have to return to our brains,
in our psychologies, because long before Instagram or cable news,
or long before propaganda ministries and political campaigns, and even
long before there were even such things as nations, we
were wired for us versus them. If you picture the
world of our ancestors, you had small bands of maybe
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one hundred or so hunter gatherers traveling together, depending on
each other for survival. These were people who shared food,
raised children, collectively, hunted side by side, defended one another
when predators or rivals approached. In that world, there wasn't
anything abstract about belonging. To be inside the group was life.
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To be outside might mean death, so you had to
be sensitive to this distinction. Our brains carry this inheritance,
and we are natural born categorizers. We draw circles around
us with them on the outside, and once that circle
is drawn, things inside feel safer and more trustworthy, and
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things outside feel riskier and more dangerous. So there was
a good experiment on this in the nineteen seventies. The
psychologist Henry Tefel wanted to know how little it would
take to spark the tribal machinery, so he brought in
volunteers and showed them slides of dots on a screen,
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and he asked them to estimate how many dots there were. Then,
with a straight face, Taefel divided them into two groups,
overestimators and underestimators, and that was it. It was just
a label that represented a meaningless categorization. And yet right
away people started favoring their own side. They gave more
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rewards to fellow overestimators or to fellow underestimators, and not
to the other side. They rated their own group as
more likable and more trustworthy. The thing I want you
to note here is that there was no deep history
or ideology here. This was just about dots on a
slide and more specifically belonging to one team or the other.
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So the brain doesn't require a grand narrative to polarize,
It doesn't need centuries of grievance. It just needs a category.
And once the category is there, the neural machinery of
favoritism for your group weres to life and seeing the
out group as fully human. That dials down. And even
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earlier experiment on this was from nineteen fifty four. This
was called the robbers Cave experiment. The psychologist Muzifer Sharif
recruited two groups of eleven year old boys and took
them to a summer camp in Oklahoma. Yeah, for the
first week, the groups didn't even know the other existed.
Each built their own identity. One group called itself the Rattlers,
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the other the Eagles. They made flags, they sang songs,
they created rituals, and then once those identities had formed,
Sharif brought the two groups together and set them into competition.
There was baseball and tugawar and treasure hunts and so on,
and Sharif watched as things spiraled turned into food fights.
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Food fights escalated into raids on each other's cabins. Cabin
raids escalated into rocks hurled across the camp, and by
the end the hostility was so intense that the researchers
had to physically intervene to keep the boys safe. What's
so striking about this is how quickly it happened. These
were boys who had no prior grudges, no ideological differences.
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The researchers manufactured a divide out of thin air, and
the brains tribal machinery did the rest. And I wish
this only said something about psychology labs or summer camps,
but of course, we see the same story everywhere in
our society. So first let's take something that's not so terrible.
We see tribalism on full display every weekend in sports stadiums. Sports,
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in a way are our culture's safe tribalism. They let
us channel our loyalty and hostility into arbitrary groups. So
it's Yeas versus Red Sox, or Manchester United versus Liverpool,
or Cowboys versus forty nine ers. People chant, they paint
their faces, they wave flags, they curse at their rivals,
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and for a few hours they experience the same surge
of in group bonding that once held hunter gatherer bands together,
and when the game ends, most fans go home without bloodshed.
Sports give us the thrill of us versus them in
a contained, ritualized form. They act like a lightning rod,
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grounding tribal energy, so it doesn't always arc into violence.
But outside the stadium, when the same circuitry is recruited
for politics, religion, race, the consequences aren't so harmless because
then the stakes are higher and the hostility doesn't turn
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off when the whistle blows. So here's what the neurosigence
shows us about this. The amigdala, which we often think
of as a detector of fear, is also a sentinel
for otherness. It flares up when we see faces from
outside our group. The salience network orients our attention to
those differences, telling the brain this matters. Watch closely. Meanwhile,
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the chemicals involved in bonding, like oxytocin. These surge up
when we're with our in group, rewarding us for loyalty,
for cooperation, for connection. It feels good to be with us,
which by implication, makes them feel even more alien. Okay, Now,
when we're talking about summer camps or sports, that's one thing.
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But now take tribal categories and add decades or centuries
of history and culture, and toss in some ideology, whether
political or religious or whatever. Then the effect really deepens.
So my lab Ryan is study on this. Imagine yourself
lying on back in a brain imaging machine fMRI. You
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see a screen with six people's hands on it, and
the computer goes around and randomly picks one of the hands.
Then you see that hand get stabbed with a syringe needle.
Now your brain has a very fast and low level response.
A network of areas comes online and we summarize that
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as the pain matrix. This is the same set of
areas that would come online if your hand was getting stabbed.
But the interesting part is that this is not your hand.
You're watching someone else's hand get stabbed. And this is
the neural basis of empathy. You see something happen to
someone else, but your brain runs a simulation about how
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that must feel and how that would hurt. Okay, but
now the experiment changes. We add a one word label
to each hand Christian, Jewish, Muslim, Hindu, scientologist to atheists,
and now you watch the computer pick one of these
hands at random and get stabbed. And the question is
does your brain care more when it is a member
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of your in group and doesn't care less when the
hand is labeled as any one of your outgroups? And
that is precisely what happens. We tested over one hundred
people of all different faiths, including atheists, and that's the
clear picture. When the suffering belongs to a hand labeled
as your group, the pain matrix has a big response,
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But when the very same pain is inflicted on a
member of an outgroup, those circuits dim The response is weaker,
so your brain distributes empathy unequally. It follows the boundaries
of us and them. Other colleagues of might have found
exactly the same pattern. For example, my colleague Tanya Singer,
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she studied this with soccer fans. She recruited diehard supporters
of teams and put them into brains scanners and showed
them videos of fans receiving painful shocks. Sometimes it was
fellow fans, sometimes it was rival fans, and when their
own teams fans suffered, these empathy circuits came online. But
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when the rival fans took the same shock, there was
less of a response, and in some brains something even
more surprising appeared, which was activity in the reward circuits.
The suffering of rivals didn't just fail to evoke empathy,
it evoked pleasure. So when we talk about polarization, we're
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talking about deep circuits firing in the brain, circuits designed
long ago for survival and small tribes. And these circuits
are fast and automatic and they run reliably under the hood.
So when we look at all these studies together, from
the circuits that involved looking at fellow humans to the
circuits that come online when we watch other people and
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pain when you put all these studies together, it's clear
that empathy is not a light that shines equally on everyone.
It depends on who is in your in groups and
who in your outgroups. Now, I want to point out
two more related aspects of polarization that I think are
often left out of the conversation. The first has to
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do with identity and the second with belonging. So let's
start with identity. In twenty sixteen, Jonas Kaplan and Sam
Harris invited people to participate in an fMRI study, so
people would lie down in the brain scanner and see
statements about politics. Some of the statements were neutral, but
others directly contradicted the participants' core political beliefs. What happened
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was that the amygdala and the insula lit up. And
these are the same regions we see when the body
feels physically threatened. In other words, when people encountered ideas
that clashed with their politics, their brains reacted as though
under siege. But this is another way. Someone disagreeing with
your politics is not experienced as oh, that's interesting, you
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have a different opinion. It's experienced as something analogous to
you are attacking me. When political belief is wired into
the same threat circuitry as our sense of self. Then
it's no surprise that debate becomes combat or that political
disagreement is perceived as aggression. It is no wonder that
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arguments get so heated at the dinner table. It's no
wonder that threads on social media devolve into shouting matches.
From the point of view of the brain, in these situations,
people feel like they're in danger. When some people say
things like words are violence, that squelch is meaningful thinking
and is quite frankly spineless. But when I saw this
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study some years ago, I thought, ah, okay, that's why
they're saying it. This is no defense of shutting down
free speech, but it sheds light on why people deep
down really want to maintain free speech for their side
but shut it down for the other side. So this
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is a very important issue about how beliefs become identity.
You always see this in the language that we use.
People will say things like as a conservative or as
a progressive, I believe, and the signals that what we're
about to hear has elements of a self definition. It's
embedded in their identity. And when identity is threatened people
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double down. In fact, a bunch of studies show that
when deeply held beliefs are challenged, people often emerge even
more convinced of their beliefs. This is a cognitive bias
called the backfire effect, in which a person's beliefs become
more entrenched and stronger when presented with evidence that contradicts them.
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And it's precisely because it's a form of defense against
a personal attack. Now, this hopefully makes it clear why
facts alone so rarely change minds. Present somebody with evidence
that contradicts their worldview, and you might expect to see curiosity,
but we rarely see that. We see resistance. The brain
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is protecting what it perceives as the self. Now, just
to be clear, this isn't about laughing at other people's foibles.
We've all felt this ourselves at some level. Really, think
about a time when someone questioned something that you felt
was core to who you are. Maybe it was your
religious beliefs, or your political stance, or something about your
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country of origin or whatever. Chances are, your body reacted.
Maybe you had a quickening heart rate or a flush
of heat, or a tightening in your chest. Your threat
circuits were activated. Your amigdala and insula were firing. Your
brain was preparing to defend itself. Now, not all beliefs
(36:15):
are fused with identity. If someone challenges your belief about
the best way to fix the car engine or which
restaurant has the best tacos, you might say, okay, cool,
I'll think about that. That's a belief floating freely. It's
not attached to your selfhood. But if someone challenges your
belief about your values, your tribe, your politics, that's more
(36:37):
fused with your identity, and you are more likely to
defend that with vim and vigor. Now, one of the
dangers about a period of high polarization is that more
and more beliefs become fused with who you are, so
it pretty quickly reaches beyond people disagreeing about academic theories,
of taxation or healthcare. The political disagreements get bundled up
(37:02):
with identities. Who you vote for, where you live, what
media you consume, what brands you buy. A red baseball
cap or a rainbow flag can suggest to you things
about a person's politics before a single word is spoken.
There's also a psychological comfort infused identity, which brings us
(37:23):
to the second point. It tells you who you are,
and it tells you who your people are. In other words,
while it's often tempting to think about polarization as something
about social media and news stations, underneath all of that
there's another angle which is belonging. For example, I mentioned
earlier the hormone oxytocin. This is often called the love
(37:46):
hormone or the bonding hormone, and that's because it surges
when we hug, when we kiss, when we fall in love,
and more generally, it helps bond groups together. It strengthens
trust between friends. If you could bottle the warmth of
human closeness, oxytocin would be one of the main ingredients.
(38:08):
But there's a dark side to the oxytocin story because
other research has shown that it increases empathy and generosity selectively.
What it does is it sharpens the line between us
and them. So, for example, in one experiment, participants were
given oxytocin and then they played a little economics game
(38:30):
with each other where they're making trades, and what happens
is that when they have this extra oxytocin, people become
more generous towards members of their own group, but less
generous toward outsiders. The same chemical that makes them extend
kindness to their in group members turns them against their outgroup.
(38:52):
It's like you've only got so much ability to bond
and that all gets funneled to your tribe. And oxytocin
is one of several chemicals involved. You've heard of dopamine,
which is involved in the reward system. The research shows
that dopamine release is higher when we cooperate with in
group members. Same thing happens with serotonin, which helps regulate
(39:15):
feelings of trust and belonging. You've also got endorphins, which
flow during synchronized activities that you do with an in group,
and this, I suspect is why rituals matter so much.
I devoted episode fifty four to this question of why
armies march in step, or why religious congregations chant together,
(39:37):
or why sports fans do things in unison. Synchronized movement
and shared rhythms amplify endorphin release, creating a larger sense
of us. So collectively, these are the biological undercurrents of
human connection, and they have evolved to feel good to us.
(39:58):
We like to be coordinate with our in groups, but
The problem is that the stronger the US, the sharper
than them. All you have to do is study any
war period or even just highly polarized period to see
that the stronger the in group bond, the more ferocious
the outgroup hatred. So all this is to say, part
(40:21):
of why polarization can feel so intoxicating is that it's
not just the anger or outrage piece. It's equally the
belonging piece to be part of aside to march and
step with others, to chant the same slogans, to share
the same memes. That is rewarding to the brain and
(40:42):
even in some ways addictive. So I've told you several
different aspects of polarization, from dehumanization to propaganda, to in
groups and outgroups, to issues of identity and belonging. But
this was all table setting because what I really want
to do is pose the critical question and what do
we do about all this? If we understand something about
(41:04):
the neuroscience that leads to polarization, can we use this
same knowledge to do something about it. That's what part
two of this podcast is going to be next week.
But there's one piece that I want to flag again,
which is education. To my mind. The most important thing
we can do is teach people about what's going on
(41:25):
at the intersection of brains and politics, because that's the
only way we don't fall for it every time. We
need to be able to recognize when language collapses humans
into pests, or when headlines portray opponents as monsters, or
when memes strip away complexity in favor of ridicule. People,
(41:50):
especially young people, need to be able to recognize when
these ancient levers are being pulled. Why because propaganda is
never going going away. As long as we have brains
that can be polarized, there will be people who try
to exploit that for whatever reasons, their own beliefs, or
they realize it's working to give them power, or it
(42:13):
gives them a solid sense of belonging. Whatever the reason,
people will always pull these tricks. And the best defense,
possibly the only defense, is simply awareness. To understand how
these tricks work, so we can recognize them from a
mile away. That way we can at least resist the poll. So,
(42:35):
in closing today, where does this leave us? My position
here is that you can't explain polarization only in terms
of social media or which party is winning the election.
We also have to understand the brains that we are
all yoked with. We began with cockroaches on the Rwandan radio,
rats and Nazi cartoons, apes and American posters. We saw
(42:59):
how quickly the brain can dial down empathy when the
right metaphors are deployed. We follow the circuitry into the lab,
where empathy surges for in groups but dims for rivals.
We saw children at summer camp turn into enemies in
a manner of hours. We traced the pull of identity,
the power of disgust, and the shadow side of the
(43:23):
hormones and chemicals that bond us. The end result is
that our threat circuitry is like a smoke detector set
on high sensitivity. It goes off at the faintest whiff,
even when there's no fire. And we've seen how history,
again and again has weaponized these vulnerabilities of the brain.
(43:44):
But this is all just laying the foundation, and now
we're ready to see next week. My argument that this
is not destiny. The challenge for us is not to
abolish tribalism, because I'm not sure that we can, but
instead to channel it, to find out that let us
experience belonging without dehumanization generally to expand the circle of
(44:07):
who counts as us, and I'll explain how we can
do that, and to learn to recognize the tricks of dehumanization,
because somehow every generation falls for them anew like it's
the first time. We now have more educational firepower than
we've ever had in global history, and it's time to
make sure everyone knows the tricks of the trade so
(44:30):
we can have some immunity against them. When we understand
the neuroscience of polarization, we have the opportunity to derive
a little bit of hope because the same brains that
divide us under different conditions can unite us. The key
thing about the brain is that it's live wired. It's
always adapting, it's always reshaping its circuitry. So what we'll
(44:53):
see next week is that even when tribalism mutes empathy,
shared goals and cooperation can reignite it. And where propaganda
can dimn humanness perspective, taking can light it up again
to see how we might build a better world. Please
join me next week for part two. Go to Eagleman
(45:18):
dot com slash podcast for more information and to find
further reading. Join the weekly discussions on my substack and
check out Subscribe to Inner Cosmos on YouTube for videos
of each episode and to leave comments until next time.
I'm David Eagleman and this is Inner Cosmos.
What does political polarization have to do with the brain.
How does an understanding of the medial prefrontal cortex tell
us about what propaganda posters have in common across nation
and time. What does any of this have to do
with the Civil War or hippies versus soldiers, or border
(00:27):
ruffians versus free staters or barbarians, or hanging chads or
pearl harbor, or the shadows side of oxytocin, And why
education can serve as an immune response to mind viruses.
Welcome to Inner Cosmos with me David Eagleman. I'm a
(00:49):
neuroscientist and author at Stanford and in these episodes we
sail deeply into our three pound universe to understand why
and how our lives look the way they do. Today's
(01:16):
episode is one of a couple I'm making on the
topic of neuropolitics. We are in a polarized era, and
when I look around, I see a primate brain doing
lots of things that primate brains do. So today I'm
going to talk about polarization, and in the next episode,
I'm going to talk about all the good news, which
(01:37):
is the flexibility of the brain and what hopes we
might have to get ourselves out of polarization. I'm also
going to do another episode about all the other aspects
of the bigger picture that I'm calling neuropolitics, which is
the way that the circuitry of our brains leads us
to the kind of political viewpoints we have, and why
(01:59):
we often have a difficult time understanding one another and
why societies fracture along particular lines. Okay, so when I
think about America, the polarization is high, and this feeling
we all have is of course easily quantified. As one example,
you can look at the numbers about how many times
(02:21):
you have congressmen voting across the aisle. When a society
is very polarized, like it is now, people hold on
tight to their team. I'm very interested in viewing this
all from the perspective of the brain, but first I
need to do some table setting. A lot of people
assert that our polarization has everything to do with social media.
(02:43):
I'm interested in the roles that social media plays, but
I do need to say that I don't think it
serves by itself as much of an explanation for our polarization. Why,
because we've been exactly this polarized many many times before,
all before the Internet was even a twinkle in anybody's eyes. So,
(03:05):
for example, America in the late nineteen sixties was very polarized.
This was easily seen on the streets, in living rooms,
on television screens. The Vietnam War split the nation. You
had young people marching against it, while others saw opposition
as unpatriotic and dangerous. The Civil rights movement was reshaping
(03:28):
laws and culture, and that was going too fast for
some and too slow for others. Generational divides ran deep.
Parents who had lived through World War Two and fought
in it struggled to understand their children's embrace of counterculture
and long hair and psychedelic music and radical politics. The
assassinations of Martin Luther King and Senator Robert F. Kennedy,
(03:52):
the urban riots, what happened Kent State. All of these
moments reinforced the sense that Americans were not living in
one shared country, but in different realities. Trust in government
plummeted with Watergate in the nineteen seventies, and that further
hardened the feeling that institutions could no longer be trusted.
(04:12):
It was a time when the nation's social fabrics seemed
to be tearing and when, much like today, people questioned
whether their neighbors were even living in the same world
that they were. And of course that was just one
of many polarized eras in this country. The most obvious
(04:33):
one began in the eighteen forties and led to the
Civil War. The divide over slavery and states rights sharpened
decade by decade, inflamed by the Missouri Compromised, the Kansas
Nebraska Act, the dread Scott decision. You can see the
way that newspapers and churches and politicians increasingly spoke in
(04:54):
absolutist terms, and by the way violence erupted well before
the war did. From eighteen fifty four to fifty nine
in the Kansas territory, you had pro slavery border Ruffians
and the anti slavery free Staters, and they would make
raids back and forth, committing assaults and murders, each retaliating
(05:16):
for the last. There were at least fifty six political
killings during that time, and by the next year, eighteen sixty,
the election of Abraham Lincoln prompted Southern states to secede
and Civil War followed. Okay, so that was a really
grim outcome with seven hundred thousand people killed. But there
(05:37):
have been many, many other periods of polarization that somehow
had their day, and then the temperature went down without
war for different reasons, and we're going to dive into
that next week. For example, in the eighteen seventies, a
decade after the Civil War, polarization grew again around rapid industrialization.
(05:58):
You had labor strikes and violent clashes like the Haymarket
riot and the Pullman strike. You had class resentment between
robber barons and workers. And what you can see then
as now is that newspapers and politicians portrayed opponents as
existential threats to the American way of life. Then in
(06:20):
the nineteen tens and twenties, polarization happened again. World War
I and its aftermath split Americans over issues of free
speech and loyalty and communism. The first Red Scare was
concerned about anarchists and labor organizers who were depicted as
dangerous reds. There were mass arrests and deportations, and this
(06:41):
deepened divides, and simultaneously there was a surgeon racial violence.
The summer of nineteen nineteen saw dozens of race riots
and the rise of the Second Ku Klux Klan, which
polarized communities along racial and religious and immigrant lines. Then
by the Late Night Seen twenties and nineteen thirties, you
had the Great Depression, the economic collapse that sparked really
(07:06):
fierce battles over the role of government. FDR's New Deal
was hailed as salvation by some and it was condemned
as socialism by others. Far left and far right groups
clashed bitterly. And it was also the case that the
country was polarized over whether America should intervene in Europe
as fascism rose, until the attack on Pearl Harbor, which
(07:29):
temporarily united public opinion. Okay, then I already mentioned the
polarization of the civil rights movement Vietnam era. So let's
jump to the culture wars of the nineteen eighties and nineties.
Some of you might even recall the Reagan era, where
the country saw sharp divides over taxation and welfare, and
(07:49):
abortion and feminism and gay rights. These were the so
called culture wars, which pitted conservatives and evangelicals against progressives
in battles over school curricula and art and family values.
And again you could measure this with polarization in Congress
steadily growing. Finally, some of you may even remember the
(08:10):
contested two thousand election of Bush versus Gore. Again, this
was still pre social media, and the whole race came
down to just the state of Florida, where Bush seemed
to lead by a few hundred votes out of six
million cast there, and officials tried to figure out voter
intent involving hanging chads, which were in completely punched paper ballots,
(08:34):
and pregnant chads, which were paper ballots that were dimpled. Anyway,
this spun all the way up to the Supreme Court,
who finally ruled the electoral vote in favor of Bush,
even though Gore had received five hundred thousand more popular
votes nationwide. Now, not all my listeners were alive or
watching the news at that time, but boy, that was
a really highly polarized time as well. Then you had
(08:58):
nine to eleven, which brought the nation together. But then
over some years the Iraq War started to sharpen those
divides again. Now you might be tempted to say, well,
it's worse than ever now because of social media filter bubbles,
but I just want to remind us all that echo
chambers are the oldest story of humankind. We are more
(09:19):
comfortable with people who agree with us and see the
world from our angle now. I often hear people say
things like, yes, but we only had a few news
sources back in the day, so everyone was pinned to
the same truth. Walter Kronkite or whoever. This is a
seductive idea, but it's not true. People got some of
(09:42):
their info from Kronkite, but also from the newsletters they
subscribe to in their physical mailbox, and also from all
their friends and neighbors and co workers. And when people
would have dinners together or chat in the breakroom or
drink beers in their backyard with their friends, that's when
they would really come to consensus agreement about what was
(10:05):
happening in the world. Just to jump back to the
Vietnam era, do you think the hippies and the returning
soldiers were sitting down and watching Walter Cronkite and saying, ah, okay,
I see the truth. There's no problem. We all agree now.
So any reading of history shows that polarization is depressingly
(10:27):
a recurring pattern. Each cycle takes a different shape, whether
that's slavery or labor or immigration, or race or culture
or war. But the common thread is the part I
want to zoom in on. When people begin to see
each other not as neighbors with families and mortgages and
lives and desires for a better life, but as existential threats.
(10:52):
When that happens, the brain circuitry involved in empathy, in
understanding another person's hopes and dreams, the activity in those
circuits dials down, and the social fabric begins to frame.
By the way, I just want to flag a point
that I'm going to explore next week, which is that
most historians interested in this topic linger on how societies
(11:14):
fall into polarization, but my main interest nowadays is how
they crawl back out. So next week I'm going to
examine the factors that seem to pull societies back from
the brink, because with all those eras that I just named,
we went to actual war only once, and with all
the other periods, we managed to pull ourselves back onto
(11:36):
a straight road. Sometimes this is because of external factors
and sometimes because of internal work, And this is all
what we're going to address next week. Okay, So now
I want to return to the particular issue for today,
which is how our brains operate with in and out
groups and what the brain is capable of when it's
(11:57):
pushed in the wrong direction. So let's start in nineteen
ninety four in Rwanda. The radio was on in homes
and shops and bars, and the message that pours out
every day is relentless. The Tutsis are cockroaches. They must
be crushed. This was literally the language in this framework.
(12:20):
The Tutsi were not citizens or neighbors or people with
families and histories and memories, but they were cockroaches. The
more often this message was repeated, the more it carved
itself into people's brains, and eventually the machetes got unsheathed,
neighbors turned on neighbors. In one hundred days, half a
(12:41):
million people were killed. And the part that is frankly
terrifying is that when you think about genocide, you might
think this gets driven by soldiers or politicians, but that's
not what was going on here. The engine of what
happened in Rwanda was regular people who to neighbors who
had lived side by side with the Tutsi for generations.
(13:03):
That is the power of dehumanization. Once someone is no
longer perceived as human, the neural breaks come off. Now,
it would be comforting if we could view Rwanda as
a tragic anomaly, but it's not. History gives us no
shortage of examples of this very same principle. In Nazi Germany,
(13:28):
the Jewish community was depicted in newspapers like their Sturmer,
as rodents swarming through sewers. They were painted as vermin
to be exterminated. And this is precisely the cognitive space
that you need to get into if you actually want
to murder your former friends and neighbors. And by the way,
(13:49):
it's not just the Hutu and the Nazis, but everyone
does it. So during World War Two, American propaganda posters
portrayed the Japanese with distorted faces and thick glasses and
clawed fingers crouched like apes. The caption was this is
the enemy. And this is the same across history. If
(14:10):
we step back into the world of ancient Rome, you'll
see that outsiders were called barbarians. The word comes from
the Greek barbaros, which was a mocking sound meant to
imitate the noise of foreign languages. Bar barbar Originally, it
didn't have a negative connotation. But pretty quickly the terms
meaning shifted from outsider to a pejorative for being savage
(14:35):
or uncivilized. And this was because to Roman ears, outsiders
had meaningless babbel and increasingly reviewed like animals. The Romans
often described enemies as wild or beasts. Julius Caesar characterized
the Galls and Germans as quote, living like animals. Tacitus
(14:55):
described the Britons as quote savages who live like beasts
in the forests. So across continents and centuries, the pattern
is exactly the same. When societies prepare for conflict, they
sharpen their words, and the words are designed for the
simple task of stripping away the humanity of the other side.
(15:18):
Now why does this work so well? Why are animal
metaphors so effective. It's because they reach down into the
neural machinery and turn a dial. Under normal circumstances, when
you look at someone else and another person, you have
regions of the brain that allow you to imagine their
(15:41):
inner life. Specifically, a region behind your forehead called the
medial prefrontal cortex gets involved when you consider that this
person has thoughts and feelings and plans and fears. That's
what lights up when you see someone else as a
human reaching out to deal with a bicycle or a
(16:02):
chair or a coffee machine. This area does not become active.
It's only active when you're dealing with a human, when
you're doing what researchers call a social cognition task. But
some years ago, my colleagues Lasana Harris and Susan Fiske
at Princeton wanted to see if the amount this area
is active depends on what you think about a particular group.
(16:27):
So they put people in the brain scanner fMRI, and
they showed them photographs of business people and athletes and
the elderly, and nurses, and drug addicts and people who
were homeless. And here's what they found. While some pictures,
like wealthy people, triggered envy, this social region, the medial
prefrontal cortex was still active. Other photos, let's say a
(16:50):
very elderly people, triggered emotions of pity, and this social
region was still active. But when the brain looked at
pictures and felt discussed, like for pictures of homeless people
or drug addicts at rock bottom, the brain viewed them
not as humans with minds, but more like objects. That
(17:12):
is the humanization, your brain decides, and this is essentially
all subconsciously that this person does not count as another mind.
This person is neurally speaking, less than human. And by
the way, I'm linking all the relevant studies to the
show notes, I encourage you to check those out. So
(17:35):
let's return to propaganda. When some group of people is
portrayed as cockroaches or rats or babbling animal, barbarians, or
a virus or a robot or whatever, the social cognition
regions like the medial prefrontal cortex get dialed down. The
(17:56):
brain no longer treats this other group as people with
a mind. Instead, people of that group become more like objects.
And when these circuits are not steering your decisions, violence
becomes psychologically easier. As an example, unless you are a vegetarian,
you don't really mind murdering a big, beautiful animal like
(18:19):
a cow or a bowl, because you want that burger,
and that animal is just an animal to your mind,
it's not a human, and so your medial prefrontal cortex
is less active when you look at that cow, and
so you can take a knife to its throat without
that keeping you up at night, and that ease of killing.
Maybe it bothers you a little, but not enough to
(18:39):
stop doing it. That's what we see throughout history, over
and over, people murdering their neighbors after a sufficient amount
of messaging telling them that their neighbors aren't really humans.
They are less than humans, they're more like cows or worse,
they carry pestilence and they're dangerous. Now, next month, I'm
(19:03):
going to have a colleague of mine on the podcast
who pioneered a lot of these studies, Lassana Harris, So
we'll go into more detail about the prefrontal cortex then,
But for today, I just want to make it crystal
clear that this dehumanization is the oldest trick in the
playbook of propaganda. Dehumanizing another group doesn't have to be
(19:24):
about making watertight arguments for convincing people with data. It
can simply be about bypassing reason entirely and tampering directly
with the machinery of social cognition. It's really important to
understand that this is a vulnerability built into the human brain.
(19:44):
When the wind blows hard enough, the flame of your
social empathy gets blown out. So when we look at
Rwanda or Nazi Germany or America during wartime, we're seeing
a basic lesson about the architecture of our own We're
seeing how fragile our humanizing can be and how dangerous
(20:06):
it is when pundits and politicians and online influencers lay
their hands on the dials. Now, before I go on,
(20:29):
I want to make really clear why I'm devoting a
lot of my efforts to this sort of research is
because I think we can solve this, at least mostly,
and part of this comes down to education as a population.
If we can learn to recognize the tricks of the
trade of propaganda, that renders those tricks mostly impotent. Just
(20:52):
imagine that all the schools in the nation spent just
fifteen minutes teaching what I just told you. Then the
next time a student see some TikTokers say oh, those
people are like animals, or that group is a disease
that's infecting our country, a light bulb goes on in
our kids' minds and they say, wait a minute, we've
(21:12):
heard that before. That kind of simple recognition is ninety
percent of the game. That recognition turns all of us
from passive receivers into active listeners. Having knowledge about this
topic about how dehumanization works in the brain. Is the
difference between catching the contagion of hate and mounting an
(21:36):
immune response against it. So now let's turn to a
related issue, one which is equally important to the story,
and again is deeply embedded in our brains, And that's
our predilection for in groups and outgroups. We are fundamentally
very tribal. We see this in so many ways, and
(21:56):
sometimes it doesn't matter, like which football team you root for,
but when when it comes to politics, it carries cognitive consequences.
You end up feeling certain that your side of the
political aisle generally has the right idea and the other
half of the nation who knows what's infected their brains.
And I just want to be crystal clear that it
doesn't matter which side of the aisle you're on, you
(22:19):
are likely to genuinely feel this about the other side,
and you'll feel like if they would only listen to
you and stop being so misinformed or stubborn or wrongheaded,
everyone would fundamentally come to agree with you. Now, if
we want to understand why humans divide so easily into
(22:40):
in and out groups, we have to return to our brains,
in our psychologies, because long before Instagram or cable news,
or long before propaganda ministries and political campaigns, and even
long before there were even such things as nations, we
were wired for us versus them. If you picture the
world of our ancestors, you had small bands of maybe
(23:03):
one hundred or so hunter gatherers traveling together, depending on
each other for survival. These were people who shared food,
raised children, collectively, hunted side by side, defended one another
when predators or rivals approached. In that world, there wasn't
anything abstract about belonging. To be inside the group was life.
(23:26):
To be outside might mean death, so you had to
be sensitive to this distinction. Our brains carry this inheritance,
and we are natural born categorizers. We draw circles around
us with them on the outside, and once that circle
is drawn, things inside feel safer and more trustworthy, and
(23:49):
things outside feel riskier and more dangerous. So there was
a good experiment on this in the nineteen seventies. The
psychologist Henry Tefel wanted to know how little it would
take to spark the tribal machinery, so he brought in
volunteers and showed them slides of dots on a screen,
(24:09):
and he asked them to estimate how many dots there were. Then,
with a straight face, Taefel divided them into two groups,
overestimators and underestimators, and that was it. It was just
a label that represented a meaningless categorization. And yet right
away people started favoring their own side. They gave more
(24:31):
rewards to fellow overestimators or to fellow underestimators, and not
to the other side. They rated their own group as
more likable and more trustworthy. The thing I want you
to note here is that there was no deep history
or ideology here. This was just about dots on a
slide and more specifically belonging to one team or the other.
(24:54):
So the brain doesn't require a grand narrative to polarize,
It doesn't need centuries of grievance. It just needs a category.
And once the category is there, the neural machinery of
favoritism for your group weres to life and seeing the
out group as fully human. That dials down. And even
(25:17):
earlier experiment on this was from nineteen fifty four. This
was called the robbers Cave experiment. The psychologist Muzifer Sharif
recruited two groups of eleven year old boys and took
them to a summer camp in Oklahoma. Yeah, for the
first week, the groups didn't even know the other existed.
Each built their own identity. One group called itself the Rattlers,
(25:39):
the other the Eagles. They made flags, they sang songs,
they created rituals, and then once those identities had formed,
Sharif brought the two groups together and set them into competition.
There was baseball and tugawar and treasure hunts and so on,
and Sharif watched as things spiraled turned into food fights.
(26:02):
Food fights escalated into raids on each other's cabins. Cabin
raids escalated into rocks hurled across the camp, and by
the end the hostility was so intense that the researchers
had to physically intervene to keep the boys safe. What's
so striking about this is how quickly it happened. These
were boys who had no prior grudges, no ideological differences.
(26:26):
The researchers manufactured a divide out of thin air, and
the brains tribal machinery did the rest. And I wish
this only said something about psychology labs or summer camps,
but of course, we see the same story everywhere in
our society. So first let's take something that's not so terrible.
We see tribalism on full display every weekend in sports stadiums. Sports,
(26:50):
in a way are our culture's safe tribalism. They let
us channel our loyalty and hostility into arbitrary groups. So
it's Yeas versus Red Sox, or Manchester United versus Liverpool,
or Cowboys versus forty nine ers. People chant, they paint
their faces, they wave flags, they curse at their rivals,
(27:11):
and for a few hours they experience the same surge
of in group bonding that once held hunter gatherer bands together,
and when the game ends, most fans go home without bloodshed.
Sports give us the thrill of us versus them in
a contained, ritualized form. They act like a lightning rod,
(27:33):
grounding tribal energy, so it doesn't always arc into violence.
But outside the stadium, when the same circuitry is recruited
for politics, religion, race, the consequences aren't so harmless because
then the stakes are higher and the hostility doesn't turn
(27:54):
off when the whistle blows. So here's what the neurosigence
shows us about this. The amigdala, which we often think
of as a detector of fear, is also a sentinel
for otherness. It flares up when we see faces from
outside our group. The salience network orients our attention to
those differences, telling the brain this matters. Watch closely. Meanwhile,
(28:20):
the chemicals involved in bonding, like oxytocin. These surge up
when we're with our in group, rewarding us for loyalty,
for cooperation, for connection. It feels good to be with us,
which by implication, makes them feel even more alien. Okay, Now,
when we're talking about summer camps or sports, that's one thing.
(28:42):
But now take tribal categories and add decades or centuries
of history and culture, and toss in some ideology, whether
political or religious or whatever. Then the effect really deepens.
So my lab Ryan is study on this. Imagine yourself
lying on back in a brain imaging machine fMRI. You
(29:03):
see a screen with six people's hands on it, and
the computer goes around and randomly picks one of the hands.
Then you see that hand get stabbed with a syringe needle.
Now your brain has a very fast and low level response.
A network of areas comes online and we summarize that
(29:23):
as the pain matrix. This is the same set of
areas that would come online if your hand was getting stabbed.
But the interesting part is that this is not your hand.
You're watching someone else's hand get stabbed. And this is
the neural basis of empathy. You see something happen to
someone else, but your brain runs a simulation about how
(29:46):
that must feel and how that would hurt. Okay, but
now the experiment changes. We add a one word label
to each hand Christian, Jewish, Muslim, Hindu, scientologist to atheists,
and now you watch the computer pick one of these
hands at random and get stabbed. And the question is
does your brain care more when it is a member
(30:09):
of your in group and doesn't care less when the
hand is labeled as any one of your outgroups? And
that is precisely what happens. We tested over one hundred
people of all different faiths, including atheists, and that's the
clear picture. When the suffering belongs to a hand labeled
as your group, the pain matrix has a big response,
(30:31):
But when the very same pain is inflicted on a
member of an outgroup, those circuits dim The response is weaker,
so your brain distributes empathy unequally. It follows the boundaries
of us and them. Other colleagues of might have found
exactly the same pattern. For example, my colleague Tanya Singer,
(30:53):
she studied this with soccer fans. She recruited diehard supporters
of teams and put them into brains scanners and showed
them videos of fans receiving painful shocks. Sometimes it was
fellow fans, sometimes it was rival fans, and when their
own teams fans suffered, these empathy circuits came online. But
(31:16):
when the rival fans took the same shock, there was
less of a response, and in some brains something even
more surprising appeared, which was activity in the reward circuits.
The suffering of rivals didn't just fail to evoke empathy,
it evoked pleasure. So when we talk about polarization, we're
(31:38):
talking about deep circuits firing in the brain, circuits designed
long ago for survival and small tribes. And these circuits
are fast and automatic and they run reliably under the hood.
So when we look at all these studies together, from
the circuits that involved looking at fellow humans to the
circuits that come online when we watch other people and
(32:00):
pain when you put all these studies together, it's clear
that empathy is not a light that shines equally on everyone.
It depends on who is in your in groups and
who in your outgroups. Now, I want to point out
two more related aspects of polarization that I think are
often left out of the conversation. The first has to
(32:20):
do with identity and the second with belonging. So let's
start with identity. In twenty sixteen, Jonas Kaplan and Sam
Harris invited people to participate in an fMRI study, so
people would lie down in the brain scanner and see
statements about politics. Some of the statements were neutral, but
others directly contradicted the participants' core political beliefs. What happened
(32:46):
was that the amygdala and the insula lit up. And
these are the same regions we see when the body
feels physically threatened. In other words, when people encountered ideas
that clashed with their politics, their brains reacted as though
under siege. But this is another way. Someone disagreeing with
your politics is not experienced as oh, that's interesting, you
(33:09):
have a different opinion. It's experienced as something analogous to
you are attacking me. When political belief is wired into
the same threat circuitry as our sense of self. Then
it's no surprise that debate becomes combat or that political
disagreement is perceived as aggression. It is no wonder that
(33:31):
arguments get so heated at the dinner table. It's no
wonder that threads on social media devolve into shouting matches.
From the point of view of the brain, in these situations,
people feel like they're in danger. When some people say
things like words are violence, that squelch is meaningful thinking
and is quite frankly spineless. But when I saw this
(33:53):
study some years ago, I thought, ah, okay, that's why
they're saying it. This is no defense of shutting down
free speech, but it sheds light on why people deep
down really want to maintain free speech for their side
but shut it down for the other side. So this
(34:26):
is a very important issue about how beliefs become identity.
You always see this in the language that we use.
People will say things like as a conservative or as
a progressive, I believe, and the signals that what we're
about to hear has elements of a self definition. It's
embedded in their identity. And when identity is threatened people
(34:49):
double down. In fact, a bunch of studies show that
when deeply held beliefs are challenged, people often emerge even
more convinced of their beliefs. This is a cognitive bias
called the backfire effect, in which a person's beliefs become
more entrenched and stronger when presented with evidence that contradicts them.
(35:10):
And it's precisely because it's a form of defense against
a personal attack. Now, this hopefully makes it clear why
facts alone so rarely change minds. Present somebody with evidence
that contradicts their worldview, and you might expect to see curiosity,
but we rarely see that. We see resistance. The brain
(35:32):
is protecting what it perceives as the self. Now, just
to be clear, this isn't about laughing at other people's foibles.
We've all felt this ourselves at some level. Really, think
about a time when someone questioned something that you felt
was core to who you are. Maybe it was your
religious beliefs, or your political stance, or something about your
(35:54):
country of origin or whatever. Chances are, your body reacted.
Maybe you had a quickening heart rate or a flush
of heat, or a tightening in your chest. Your threat
circuits were activated. Your amigdala and insula were firing. Your
brain was preparing to defend itself. Now, not all beliefs
(36:15):
are fused with identity. If someone challenges your belief about
the best way to fix the car engine or which
restaurant has the best tacos, you might say, okay, cool,
I'll think about that. That's a belief floating freely. It's
not attached to your selfhood. But if someone challenges your
belief about your values, your tribe, your politics, that's more
(36:37):
fused with your identity, and you are more likely to
defend that with vim and vigor. Now, one of the
dangers about a period of high polarization is that more
and more beliefs become fused with who you are, so
it pretty quickly reaches beyond people disagreeing about academic theories,
of taxation or healthcare. The political disagreements get bundled up
(37:02):
with identities. Who you vote for, where you live, what
media you consume, what brands you buy. A red baseball
cap or a rainbow flag can suggest to you things
about a person's politics before a single word is spoken.
There's also a psychological comfort infused identity, which brings us
(37:23):
to the second point. It tells you who you are,
and it tells you who your people are. In other words,
while it's often tempting to think about polarization as something
about social media and news stations, underneath all of that
there's another angle which is belonging. For example, I mentioned
earlier the hormone oxytocin. This is often called the love
(37:46):
hormone or the bonding hormone, and that's because it surges
when we hug, when we kiss, when we fall in love,
and more generally, it helps bond groups together. It strengthens
trust between friends. If you could bottle the warmth of
human closeness, oxytocin would be one of the main ingredients.
(38:08):
But there's a dark side to the oxytocin story because
other research has shown that it increases empathy and generosity selectively.
What it does is it sharpens the line between us
and them. So, for example, in one experiment, participants were
given oxytocin and then they played a little economics game
(38:30):
with each other where they're making trades, and what happens
is that when they have this extra oxytocin, people become
more generous towards members of their own group, but less
generous toward outsiders. The same chemical that makes them extend
kindness to their in group members turns them against their outgroup.
(38:52):
It's like you've only got so much ability to bond
and that all gets funneled to your tribe. And oxytocin
is one of several chemicals involved. You've heard of dopamine,
which is involved in the reward system. The research shows
that dopamine release is higher when we cooperate with in
group members. Same thing happens with serotonin, which helps regulate
(39:15):
feelings of trust and belonging. You've also got endorphins, which
flow during synchronized activities that you do with an in group,
and this, I suspect is why rituals matter so much.
I devoted episode fifty four to this question of why
armies march in step, or why religious congregations chant together,
(39:37):
or why sports fans do things in unison. Synchronized movement
and shared rhythms amplify endorphin release, creating a larger sense
of us. So collectively, these are the biological undercurrents of
human connection, and they have evolved to feel good to us.
(39:58):
We like to be coordinate with our in groups, but
The problem is that the stronger the US, the sharper
than them. All you have to do is study any
war period or even just highly polarized period to see
that the stronger the in group bond, the more ferocious
the outgroup hatred. So all this is to say, part
(40:21):
of why polarization can feel so intoxicating is that it's
not just the anger or outrage piece. It's equally the
belonging piece to be part of aside to march and
step with others, to chant the same slogans, to share
the same memes. That is rewarding to the brain and
(40:42):
even in some ways addictive. So I've told you several
different aspects of polarization, from dehumanization to propaganda, to in
groups and outgroups, to issues of identity and belonging. But
this was all table setting because what I really want
to do is pose the critical question and what do
we do about all this? If we understand something about
(41:04):
the neuroscience that leads to polarization, can we use this
same knowledge to do something about it. That's what part
two of this podcast is going to be next week.
But there's one piece that I want to flag again,
which is education. To my mind. The most important thing
we can do is teach people about what's going on
(41:25):
at the intersection of brains and politics, because that's the
only way we don't fall for it every time. We
need to be able to recognize when language collapses humans
into pests, or when headlines portray opponents as monsters, or
when memes strip away complexity in favor of ridicule. People,
(41:50):
especially young people, need to be able to recognize when
these ancient levers are being pulled. Why because propaganda is
never going going away. As long as we have brains
that can be polarized, there will be people who try
to exploit that for whatever reasons, their own beliefs, or
they realize it's working to give them power, or it
(42:13):
gives them a solid sense of belonging. Whatever the reason,
people will always pull these tricks. And the best defense,
possibly the only defense, is simply awareness. To understand how
these tricks work, so we can recognize them from a
mile away. That way we can at least resist the poll. So,
(42:35):
in closing today, where does this leave us? My position
here is that you can't explain polarization only in terms
of social media or which party is winning the election.
We also have to understand the brains that we are
all yoked with. We began with cockroaches on the Rwandan radio,
rats and Nazi cartoons, apes and American posters. We saw
(42:59):
how quickly the brain can dial down empathy when the
right metaphors are deployed. We follow the circuitry into the lab,
where empathy surges for in groups but dims for rivals.
We saw children at summer camp turn into enemies in
a manner of hours. We traced the pull of identity,
the power of disgust, and the shadow side of the
(43:23):
hormones and chemicals that bond us. The end result is
that our threat circuitry is like a smoke detector set
on high sensitivity. It goes off at the faintest whiff,
even when there's no fire. And we've seen how history,
again and again has weaponized these vulnerabilities of the brain.
(43:44):
But this is all just laying the foundation, and now
we're ready to see next week. My argument that this
is not destiny. The challenge for us is not to
abolish tribalism, because I'm not sure that we can, but
instead to channel it, to find out that let us
experience belonging without dehumanization generally to expand the circle of
(44:07):
who counts as us, and I'll explain how we can
do that, and to learn to recognize the tricks of dehumanization,
because somehow every generation falls for them anew like it's
the first time. We now have more educational firepower than
we've ever had in global history, and it's time to
make sure everyone knows the tricks of the trade so
(44:30):
we can have some immunity against them. When we understand
the neuroscience of polarization, we have the opportunity to derive
a little bit of hope because the same brains that
divide us under different conditions can unite us. The key
thing about the brain is that it's live wired. It's
always adapting, it's always reshaping its circuitry. So what we'll
(44:53):
see next week is that even when tribalism mutes empathy,
shared goals and cooperation can reignite it. And where propaganda
can dimn humanness perspective, taking can light it up again
to see how we might build a better world. Please
join me next week for part two. Go to Eagleman
(45:18):
dot com slash podcast for more information and to find
further reading. Join the weekly discussions on my substack and
check out Subscribe to Inner Cosmos on YouTube for videos
of each episode and to leave comments until next time.
I'm David Eagleman and this is Inner Cosmos.
Host
David Eagleman
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