Ep75 "How do you decide?" (Part 1)

When you make a decision about what food to order, what's happening in your brain? How do you clinch long-term decisions, like hitting the gym instead of doomscrolling? And what does any of this have to do with the ancient Greeks, alien hand syndrome, and constraining a president who wants to launch a nuclear bomb? Join Eagleman this week and next to discover how your brain weighs alternatives and nails down decisions.

Episode Transcript

Speaker 1 (00:05):
When you're trying to choose which ice cream flavor to get,
what's actually happening in your brain? How do you decide?
It seems pretty easy, but that's only if you don't
see the storms of activity lighting up the brain. And
how do you make long term decisions like that You're
not going to eat the ice cream at all, but
instead you're going to eat some broccoli. And what does

(00:27):
any of this have to do with the ancient Greeks,
or what alien hand syndrome is, or what the rules
should be around how the president can launch the nuclear bomb.
Welcome to Inner Cosmos with me David Eagleman. I'm a
neuroscientist and author at Stanford and in these episodes we

(00:49):
dive deeply into our three pound universe to uncover some
of the most surprising aspects of our lives. Today's episode
and next week's is about decision making. Although you generally
feel like you're just moving through a day, decision making

(01:11):
lies at the heart of everything we do. The complexity
of the world presents itself to us, and we are
constantly weighing alternatives. If you couldn't do that, you couldn't
navigate the now, and you couldn't plan out your future.
So by having a richer understanding of how choices battle

(01:31):
it out in the brain, we can learn how to
make better decisions for ourselves. And, as we're going to
see next week, because this is a two partern, we'll
even see how we can use this to build a
better criminal justice system. So let's start at the very beginning.
Should you choose the taco or the brito? Should you
go for that T shirt or a more formal shirt.

(01:53):
Should you take care of this email first or that
bill payment first? Do you feel like the mint, chocolate
chip or cookies and cream? On any day, you're making
one thousand little decisions, which phone calls to make, which
shooes to wear, whether to take the shorter path or
the faster path, how exactly you should answer a question,

(02:14):
what you should agree to on your schedule tomorrow. This,
it turns out, is one of the most central things
the brain does, make decisions. Your brain is a decision
making machine. It takes the complexity of the world and
it squeezes things down to single decisions. So how do
brains do this? Now? When economists and psychologists first started

(02:38):
looking at this question, they assumed that we humans act rationally.
The idea is we look at our options, we add
up the pros and cons, and we make the optimal decision.
That's not necessarily how it goes with our brains. And
in this episode and the next one, we're going to
get a really good understanding why. So let's get going

(02:58):
with these drawing where there are two ways to interpret
the same image. You've probably seen these things. If you
look at the picture one way, it looks like a rabbit,
and if you keep staring at it you can see
that suddenly it looks like a duck. So you probably
saw this when you were a kid, But just in
case you didn't, I'm putting it on the show notes
at eagleman dot com slash podcast. The point is the

(03:22):
image is what we call perceptually by stable, which is
just a way of saying that when you stare at
the picture, your brain can make one interpretation of what
you're seeing or the other interpretation, and it switches back
and forth. You see the rabbit and then the duck,
and then the rabbit and then the duck. The critical
thing to appreciate is that nothing on the page changes,

(03:44):
so the only thing that's changing is something inside your brain.
So some years ago I collaborated with my neurosurgery colleagues
to study this sort of thing. Now, neuroscience, what I
do is pretty different from brain surgery what a neurosurgeon does,
but happily we tend to be friends and we can
often help each other. So I accompanied surgeries while my

(04:05):
colleagues were operating on people's brains. And you may know,
one of the incredible things about neurosurgery is that you
can do this while a patient is awake and talking
to you. And this is because you can put little
electrodes these are small metal wires into the brain and
the brain has no pain receptors, so it doesn't hurt.

(04:25):
The patient can't feel that. Now, why does the brain
have no pain receptors. It's generally because nothing ever touches
your brain. Your brain, which is about the consistency of jello,
is well protected in the thick plates of the skull,
so evolutionarily, there was no point in developing pain receptors
in the brain anyway. As a consequence, a neurosurgeon only

(04:47):
needs to use local anesthesia when making a cut on
the scalp, and then they drill a burhole into the skull,
and once the brain is exposed, you can poke things
into the tissue while you and the patient are having
a conversation about what it's like and what you find
there is that this empire of eighty six billion neurons

(05:08):
is constantly storming with activity. Every neuron in your head
is having these little spikes of electrical voltage known as
action potentials, and every neuron is firing off some tens
or hundreds of these spikes every second of your life.
Every idea you've ever had, every memory you can ever recollect,

(05:28):
every choice that you've ever contemplated, is written in the
language of these tiny, mysterious spikes. And using a very
very tiny electrode think of a super small wire that
you just push into the brain, you can eavesdrop on
these spikes. Now, let's call the patient on the table, Marcia.

(05:48):
So Marcia is wide awake and talking to me, and
I can show her this bistable picture of the rabbit
duck and ask her to tell me what she sees. Now,
the moment that Marcia switches to rabbit or duck, her
brain has made a decision. A decision doesn't have to
be conscious in this case, it's a perceptual decision by

(06:11):
her visual system, and the mechanics of this switchover are
totally hidden under the hood. Now, what's interesting is that
in theory, a brain should be able to see both
the rabbit and the duck at the same time, but
in reality, brains don't do that. What brains do is
they take ambiguous data and they make a choice. In

(06:33):
this case, it eventually remakes the choice, and it might
switch back and forth over and over. But the point
is that our brains are always crushing ambiguity down to
a choice. So when Marsha's brain lands on the interpretation
that the drawing is of a duck or a rabbit,
we can listen through the electrode to the responses from

(06:53):
a small number of neurons these cells in her brain.
Some neurons shift to a higher rate of activity while
other neurons slow down their activity. And that happens right

(07:15):
when Marcia says, oh, now I see it as a duck,
and then when she says, oh, now it's a rabbit again,
the neurons are changing their activity. Now, the neurons we
happen to be eavesdropping on are not by themselves responsible
for the perceptual change. Instead, they're operating in concert with
billions of other neurons. So the changes we're listening to

(07:37):
are just pieces of this massive changing pattern taking hold
across large swaths of brain territory. But the idea is
that when one pattern wins out over the other in
Marcia's brain, a decision has been landed upon. Now it's
a rabbit. Now it's a duck. Now. Just as a

(07:58):
side note, it's not always about the neurons speeding up
or slowing down their spikes. Sometimes neurons change their pattern
of activity in more subtle ways. They become synchronized or
desynchronized with other neurons even while they're maintaining their original pace.
Now here's the thing. Although we can look at this
in Marsha's brain and correlate the changes with seeing the

(08:20):
rabbit or the duck, the thing to appreciate is that
your brain makes thousands of decisions every day of your life,
and that dictates your experience of the world. What are
you gonna wear today, who are you going to text today,
How are you going to interpret what was meant by
that email? Are you going to exercise today? Or are
you gonna eat that bag of chips or pass it up.

(08:41):
We don't typically chew on it, but these small decisions
underlie every action we take. Who you are emerges from
the brain wide battles for dominance that rage in your
skull every moment of your life. So listening to that
neural activity in Marsha's head, it's impossible not to be

(09:09):
in awe because this is what every decision in the
history of our species sounded like. Every marriage proposal, every
declaration of war, every leap of imagination, every mission launched
into the unknown, every act of kindness, every lie, every breakthrough,
every decisive moment. It all happened right here in the

(09:33):
darkness of the skull, emerging from patterns of activity in
networks of biological cells. So let's take a closer look
at what's happening behind the scenes during a decision. So
imagine you're making a simple choice. You're standing in the
drinksisle at the store, and you're trying to decide between

(09:53):
two flavors of sports strength that you like equally. So
you're looking at lemon and blueberry. Now from on the outside,
someone's looking at you standing in the aisle. It doesn't
look like you're doing much. You're simply stuck there in
the aisle, looking back and forth between these two options.
But inside your brain, a simple choice like this has
unleashed a hurricane of activity. Now keep in mind that

(10:17):
by itself, no single neuron has much influence. But each
neuron is connected to thousands of others, and they in
turn connect to thousands of others and so on. In
this massive, loopy, intertwining network, they're all releasing chemicals that
excite or depress each other. Within this web, a particular

(10:37):
constellation of neurons represents the Lemon drink, and this pattern
is formed from neurons that mutually excite each other. Now
they're not necessarily next to each other. They might span
distant brain regions involved in smell and taste, and vision
and your unique history of memories involving lemons sports strengths.

(10:58):
Each of these neurons by itself has very little to
do with lemon. In fact, each neuron plays many different
roles at different times in ever shifting coalitions. But when
these neurons all become active collectively at the same time
in this particular arrangement, that's the Lemons sports drink. To
your brain. So as you're standing in front of the drinks,

(11:21):
this federation of neurons eagerly communicates with one another, like
the way that dispersed individuals link online. Now, these neurons
aren't acting alone in their electioneering. At the same time,
the competing possibility the blueberry flavored drink is represented by
its own neural coalition, and thousands or millions of neurons

(11:43):
there are talking with each other and trying to get
the vote out. Now, each coalition lemon and blueberry, tries
to gain the upper hand by intensifying its own activity
and suppressing the others. Neural populations compete against one another,
just like police parties struggle for dominance. They fight it
out until one of them triumphs in this winner take

(12:07):
all competition, and whichever network wins defines what you do next. Now,

(12:28):
this is what is so cool about brains as compared
to let's say, are digital computers. The brain is a
machine that runs on conflict between different possibilities, and all
these possibilities are always trying to outcompete the others, and
there are always multiple options. Even after you've selected the

(12:48):
lemon or the blueberry drink, you find yourself in a
new conflict. Should I drink the whole thing right now?
Part of you feels like it's a good idea to
make sure you have plenty of hydration, And at the
same time, part of you he recognizes that it's very
sugary and you don't want to do too much of that.
And part of you also knows you're going to have
to go to the bathroom soon if you drink the

(13:09):
whole thing. So whether you polish off the whole drink
now or save some for later is simply a matter
of the way that the infighting goes as a result
of the ongoing conflict in the brain. You can argue
with yourself, you can curse it yourself, you can cajole yourself.
But who exactly is talking with whom? It's all you,

(13:29):
but it's different parts of you now. As I said,
we're not usually aware of these internal conflicts, but sometimes
we can use simple tasks to bring this to the surface.
For example, there was a simple psychological task introduced in
the nineteen thirties, which we call the Stroop task, and
it's very easy. All you do is you look at

(13:49):
a word printed on a page, and the word might
be in red ink or blue, or green or yellow,
and all you need to do is say the color
of the ink. So if I show you the word
garage and the ink is yellow, all you do is
you say yellow. Now that sounds very easy to do,
But the trick is that the words I show you
might themselves be color words. Like I show you the

(14:12):
letters R, E, D, but the ink is in green.
So when you see this, you're supposed to shout out green,
but it proves very difficult. Or I show you the
word purple written in yellow ink, or the word blue
written in red ink. Check out some examples on the
show notes. Now, the instructions are very easy. All you're

(14:34):
supposed to do is say the color of the ink.
So why is the stroop task so hard? It's because
one network in your brain has the task of identifying
the color of the ink and putting a name to it.
But at the same time, you have competing networks in
your brain that are responsible for reading words. And these
are so proficient that word reading has become a deeply

(14:56):
ingrained automatic process. And so you can feel the strugg
as these systems contend with each other and to get
the right answer. You have to actively suppress the strong
impulse to read the word in favor of really concentrating
on the ink color. So with a simple task like this,
you can directly experience the conflict. But most of the

(15:18):
time things are running so smoothly under the hood that
you don't even realize that you have all these competing networks.
And it's only under very special circumstances that it can
become easy for us to witness in another person the
internal conflict between the different parts of the brain. So
this can happen when a person has a particular kind

(15:39):
of epilepsy, where the epileptic seizures spread from one hemisphere
to the other. In these cases, some patients have undergone
what is called a split brain surgery, which the brain's
two hemispheres get surgically disconnected from each other. So normally
your two hemispheres are connected by a super highway of

(16:00):
nerves called the corpus colosum, and this allows the right
and left halves to coordinate and to work in concert. So,
for example, if you are feeling chilly, both of your
hands cooperate. One holds your jacket hem while the other
tugs up the zipper. But When the corpus closum gets cut,
the two hemispheres aren't talking anymore, and you can get

(16:23):
a very wild and haunting clinical condition that's called alien
hand syndrome. So the two hands can act with totally
different intentions. So a person with a severed corpus colosum
begins to zip up a jacket with one hand and
the other hand the alien hand suddenly grabs the zipper

(16:43):
and pulls it back down. Or the person might reach
for a piece of pizza with one hand and their
other hand leaps into action to slap the first hand.
The normal conflict running in the brain now comes to
the surface because the two hemispheres are now acting independently
of one another. They're not working things out under the

(17:04):
hood anymore. Alien hand syndrome typically fades in the weeks
after surgery, as the two halves of the brain take
advantage of any remaining connections to start coordinating again. But
what it reminds us is that even when we think
we're being single minded, our actions result from these immense
battles that continually rise and fall in the darkness of

(17:29):
the cranium. Now to appreciate some of the major competing
systems in your brain. Consider a philosophy experiment known as
the trolley dilemma. I spoke about this once about sixty
episodes ago, but if you haven't heard this one, it
paints an important point. So here's how it goes. A
trolley is barreling down a train track and you are

(17:51):
a bystander, and you notice that there are four workers
who are doing repairs down the track, and you realize
that they are going to get it and killed by
this trolley. Then you notice that there's a lever right
near you, and if you pull this lever, that'll divert
the trolley onto a parallel track. But wait a minute.

(18:11):
You realize that there's one worker on that track, and
if you pull the lever, that one worker will get killed.
So here's the question. Do you let four people get
killed or do you pull the lever so that only
one person is killed. When people are asked what they
would do in this scenario, almost everyone pulls the lever.
After all, it's better than only one person gets killed

(18:32):
rather than four, right, But now consider a slightly different scenario.
In the second scenario begins with the same premise that
trolley is barreling down the track and four workers are
going to get killed. But this time you're standing on
a bridge that goes over the tracks, and you notice
that there's a large man standing on the bridge watching

(18:53):
the birds. And you realize that if you push him off,
he'll land right on the track and his body will
be sufficient to stop the trolley and save the four workers.
So do you push him off? In this second scenario?
Almost no one I talk with is willing to push
the man. Why not? Well, when I ask them, they

(19:14):
give answers like that would be murder and that would
just be wrong. But wait, isn't it the same equation?
In both cases? The question is would you trade one
life for four? So why do the results come out
so differently in the second scenario. Ethicists have addressed this
problem from many angles, but brain imaging has been able

(19:36):
to provide a fairly straightforward answer to the brain. The
first scenario about pulling the lever, that's just a math problem.
The dilemma activates regions that are involved in solving logical problems.
But in the second scenario, where you have to physically
interact with the man and push him to his death,

(19:56):
that recruits additional networks. Into the decision. Now you have
the involvement of brain regions involved in emotion. In this
second scenario, you're caught in a conflict between two systems
that have very different opinions. Your rational networks tell you
that one death is better than four, but your emotional
networks trigger this gut feeling that murdering a bystander is wrong.

(20:21):
You're now dealing with these competing drives, with the end
result that your decision is likely to change entirely from
the first scenario. Now, the trolley dilemma sheds light on

(20:48):
real world situations. Just think of modern warfare, which has
become more like pulling the lever rather than pushing the
man off the bridge. When a person pushed which is
the button to launch a long range missile, it involves
only the networks involved in logical problems. Operating a drone

(21:09):
can become like a video game. Cyber attacks reconsequences at
a distance, So the rational networks are at work here,
but not necessarily the emotional networks. The detached nature of
distance warfare reduces internal conflict, and it makes this easier
to wage. So in the nineteen sixties there was a

(21:30):
military thinker who suggested that the button to launch nuclear
missiles should be implanted in the chest of the president's
best friend. That way, if the president chooses to launch nukes,
he'd have to inflict physical violence on his friend first,
he'd have to tear him open, and that consideration would

(21:52):
recruit emotional networks into the decision. After all, the world
would not be better if we all behaved like row
robots when making life and death decisions. Unchecked reason can
be dangerous. Our emotions are actually a powerful and often
insightful constituency, and we'd be remiss to exclude them from

(22:14):
the parliamentary voting. Although the neuroscience is new, this intuition
about having different drives has a long history. The ancient
Greeks suggested that we should think of our lives like
we are charioteers trying to hold on to two horses.
We've got the horse of reason and the horse of passion,
and each horse pulls slightly off center in opposite directions,

(22:38):
and your job is to keep control of both horses,
keeping yourself moving down the middle of the road. So
I've asserted that emotions are really important and we shouldn't
try to be like mister Spock. But I want to
double click on that claim, and the way we can
do that is by seeing what happens when a person
loses the capacity to include emotions in decision making. So

(23:03):
let's take someone like Hammy Myers, who I filmed in
my television show called The Brain. Cammy is a former
engineer and some years ago she got into a motorcycle
accident and the consequence was damaged to her orbitofrontal cortex,
which is the region just above the orbits of the eyes. Now,
this is a critical region to integrate signals streaming in

(23:26):
from the body, Signals that tell the rest of the
brain what state her body is in. Is she hungry,
is she nervous? Is she excited? Is she embarrassed? Is
she thirsty? Is she joyful? Now? The interesting thing is
that Cammy doesn't look like someone who has suffered a
traumatic brain injury. But if you were to spend even

(23:48):
five minutes with her, you would detect there's a problem
with her ability to deal with decision making. So let's
say you say, hey, do you want the lemon drinker
the blueberry? And she can describe all the pros and
the cons while the lemon drinks a little more sour,
but the blueberry has more sugar, and so on. But

(24:08):
she can't actually decide. She can't finalize a choice. Even
the simplest situations leave her mired and indecision why. It's
because she can no longer read her body's emotional summaries,
and as a result, decisions become incredibly difficult for her.
In other words, because of her brain injury, no particular

(24:32):
choice is now tangibly different from any other choice, and
without decision making, very little gets done. Tammy reports she
often spends all day on the sofa, So her brain
injury tells us something crucial about decision making. It's easy
to think about the brain commanding the body from on high,
but in fact, the brain is in constant feedback with

(24:56):
the body. The physical signals from the body give a
quick summary of what's going on and what to do
about it. To land on a choice, the body and
the brain have to be in close communication, and for
that you need the orbit or frontal cortex. Now you can,
of course understand this in your own life. Consider a
situation like this. You get a package misdelivered to your door,

(25:19):
but it belongs to your next door neighbors. So you
go over to deliver it to them, But as you
approach their gate, their dog growls and bares its teeth.
So do you open the gate and press on to
their front door? Your knowledge of the statistics of dog attacks,
that's not the deciding factor here. Instead, the dog's threatening

(25:42):
posture triggers a set of physiologic responses in your body.
You get an increased heart rate, you get a tightening
of the gut, a tensing of the muscles, you get
pupil dilation, changes in blood hormones, opening of sweat glands,
and so on. And all these responses are automatic and unconscious.
So in this moment, standing there with your hand on

(26:05):
their fence latch, there are a lot of external details
you could assess, like what's the color difference between the
dog's ears and nose, But your brain doesn't care about that.
Way your brain really needs to know right now is
whether you should face the dog or deliver the package.
Another way, the state of your body helps you in

(26:26):
this task. It serves as a summary of the situation.
Your physiological signature can be thought of as a low
resolution headline like this is bad or this is no problem,
and that helps your brain decide what to do next.
Most situations involve too many details to compute a purely

(26:48):
logical decision. To guide the process, we need these abridged summaries.
I am safe here, I am in danger here. The
physiological state of the body maintains this instant two way
dialogue with the brain, and every day we read the
states of our bodies like this. But in most situations,

(27:08):
our physiologic signals are more subtle and so we aren't
aware of them. But these signals are crucial to steering
the decisions we have to make. So consider being in
a restaurant. This is the kind of place which leaves
TAMMI paralyzed within decision. Do I want an appetizer, which one?
What kind of salad dressing? Which dessert should I order?

(27:31):
Thousands of choices bear down on the restaurant goer, with
the end result that we spend hours of our lives
staring at menus, making our neural networks commit to one
decision over another. And although we don't commonly realize it,
our body helps us to navigate this boggling complexity. Take

(27:51):
the choice of which Italian dish are going to order?
There's too much data for you to grapple with. You
can think about calories or price, or salt content, taste
or whatever. There's lots of data to draw from here.
But if you were a robot, you'd be stuck here
all day trying to make your decision with no obvious
way to trade off. Which details matter more. To land

(28:13):
on a choice, you need a summary of some sort,
and that's what the feedback from your body gives you.
For example, thinking about your budget might make your palm sweat,
or you might salivate thinking about the last time you
consumed the angel hair pasta, or thinking about the excessive
creaminess of the alfredo might put a cramp in your intestines.

(28:34):
You simulate your experience with one pasta, and then you
simulate the next and the next, and your bodily experience
helps your brain to quickly place a value on the
first pasta offering, and another on the second pasta, and
on the third and so on, and this is what
allows you to tip the balance in one direction or another.

(28:55):
You don't just extract the data from the pasta descriptions,
you so feel the data. These emotional signatures are more
subtle than the ones related to facing down a barking dog.
But the idea is the same. Every choice that you
face is marked by a bodily signature, and that helps
you decide. Earlier, when I was deciding between the lemon

(29:20):
and the blueberry, exercise drink, I told you that there
was a battle between networks. The physiological states from my
body are the key things that help tip that battle,
that allow one network to win over another. But for Tammy,
because of her brain damage, she can't integrate her bodily
signals into her decision making, so she has no way

(29:42):
to rapidly compare the overall value between options. She has
no way to prioritize the dozens of details that she
can articulate. That's why Tammy stays on the soface so
much of the time. None of the choices in front
of her carry any particular emotional value. There's no way
to tip one network's campaign over any other, so the

(30:07):
debates in her neural parliament continue along in deadlock. Because
the conscious mind has low bandwidth, you don't typically have
full access to the bodily signals that tip your decisions.
Most of the action lives far below awareness. Nonetheless, these
signals can have far reaching consequences on the type of

(30:28):
person you are and who you'll become. So what we've
been introduced to today is this incredible thing that brains
do called decision making, where neurons consider options and things
are set up so that one coalition can smash everything
else down so you get to one outcome. And even
though we typically don't give it much consideration, decision making

(30:51):
lies at the heart of everything we do during a day.
Without the ability to consider alternatives and weigh them and
select one over others, the complexity of the world would
just paralyze us. And one of the lessons that surfaced
is that although you feel like you have a single identity,
you're not of a single mind. Instead, you're a collection

(31:13):
of many competing neural networks. You are, in a sense,
a machine built of conflict. So what we covered is
that every decision you make involves your past experiences stored
in the states of your body, as well as an
analysis of your presence situation. Do I have enough money
to buy X instead of Y? Is options Z available?

(31:35):
But there's one more part to the story of decisions,
perhaps the most important part of all, and that is
predictions about the future. And that is where we're going
to pick up next week. Until then, keep making good
decisions and I'll see you next time. Go to eagleman
dot com slash podcast for more information and to find

(31:58):
further reading, and send me an email at podcast at
eagleman dot com with questions or discussions, and check out
and subscribe to Inner Cosmos on YouTube for videos of
each episode and to leave comments. Until next time, I'm
David Eagleman, and you made the very nice decision to
join me here in the Inner Cosmos