Professor Paul Bloom:
We’re going to begin the class proper, Introduction to
Psychology, with a discussion about the brain.
And, in particular, I want to lead off the class
with an idea that the Nobel Prize winning biologist,
Francis Crick, described as “The Astonishing
Hypothesis.” And The Astonishing Hypothesis
is summarized like this. As he writes,
The Astonishing Hypothesis is that:
You, your joys and your sorrows, your memories and your
ambitions, your sense of personal identity and free will
are in fact no more than the behavior of a vast assembly of
nerve cells and their associated molecules.
As Lewis Carroll’s Alice might have phrased it,
“you’re nothing but a pack of neurons.”
It is fair to describe this as astonishing.
It is an odd and unnatural view and I don’t actually expect
people to believe it at first. It’s an open question whether
you’ll believe it when this class comes to an end,
but I’d be surprised if many of you believe it now.
Most people don’t. Most people,
in fact, hold a different view. Most people are dualists.
Now, dualism is a very different doctrine.
It’s a doctrine that can be found in every religion and in
most philosophical systems throughout history.
It was very explicit in Plato, for instance.
But the most articulate and well-known defender of dualism
is the philosopher Rene Descartes,
and Rene Descartes explicitly asked a question,
“Are humans merely physical machines,
merely physical things?” And he answered, “no.”
He agreed that animals are machines.
In fact, he called them “beast machines” and said animals,
nonhuman animals are merely robots, but people are
different. There’s a duality of people.
Like animals, we possess physical material
bodies, but unlike animals, what we are is not physical.
We are immaterial souls that possess physical bodies,
that have physical bodies, that reside in physical bodies,
that connect to physical bodies.
So, this is known as dualism because the claim is,
for humans at least, there are two separate things;
there’s our material bodies and there’s our immaterial minds.
Now, Descartes made two arguments for dualism.
One argument involved observations of a human action.
So, Descartes lived in a fairly sophisticated time,
and his time did have robots. These were not electrical
robots, of course. They were robots powered by
hydraulics. So, Descartes would walk around
the French Royal Gardens and the French Royal Gardens were set up
like a seventeenth-century Disneyland.
They had these characters that would operate according to water
flow and so if you stepped on a certain panel,
a swordsman would jump out with a sword.
If you stepped somewhere else, a bathing beauty would cover
herself up behind some bushes. And Descartes said,
“Boy, these machines respond in certain ways to certain actions
so machines can do certain things and,
in fact,” he says, “our bodies work that way too.
If you tap somebody on the knee, your leg will jump out.
Well, maybe that’s what we are.” But Descartes said that can’t
be because there are things that humans do that no machine could
ever do. Humans are not limited to
reflexive action. Rather, humans are capable of
coordinated, creative, spontaneous things.
We can use language, for instance,
and sometimes my use of language can be reflexive.
Somebody says, “How are you?” And I say, “I am fine.
How are you?” But sometimes I could say what
I choose to be, “How are you?”
“Pretty damn good.” I can just choose.
And machines, Descartes argued,
are incapable of that sort of choice.
Hence, we are not mere machines. The second argument is,
of course, quite famous and this was the method.
This he came to using the method of doubt.
So, he started asking himself the question,
“What can I be sure of?” And he said,
“Well, I believe there’s a God, but honestly,
I can’t be sure there’s a God. I believe I live in a rich
country but maybe I’ve been fooled.”
He even said, “I believe I have had friends
and family but maybe I am being tricked.
Maybe an evil demon, for instance,
has tricked me, has deluded me into thinking I
have experiences that aren’t real.”
And, of course, the modern version of this is
The Matrix. The idea of The Matrix is
explicitly built upon Cartesian–Descartes’ worries
about an evil demon. Maybe everything you’re now
experiencing is not real, but rather is the product of
some other, perhaps malevolent, creature.
Descartes, similarly, could doubt he has a body.
In fact, he noticed that madmen sometimes believe they have
extra limbs or they believe they’re of different sizes and
shapes than they really are and Descartes said,
“How do I know I’m not crazy? Crazy people don’t think
they’re crazy so the fact that I don’t think I’m crazy doesn’t
mean I’m not crazy. How do I know,” Descartes said,
“I’m not dreaming right now?” But there is one thing,
Descartes concluded, that he cannot doubt,
and the answer is he cannot doubt that he is himself
thinking. That would be self-refuting.
And so, Descartes used the method of doubt to say there’s
something really different about having a body that’s always
uncertain from having a mind. And he used this argument as a
way to support dualism, as a way to support the idea
that bodies and minds are separate.
And so he concluded, “I knew that I was a substance,
the whole essence or nature of which is to think,
and that for its existence, there is no need of any place
nor does it depend on any material thing.
That is to say, the soul by which I am,
when I am, is entirely distinct from body.”
Now, I said before that this is common sense and I want to
illustrate the common sense nature of this in a few ways.
One thing is our dualism is enmeshed in our language.
So, we have a certain mode of talking about things that we own
or things that are close to us – my arm,
my heart, my child, my car – but we also extend
that to my body and my brain. We talk about owning our brains
as if we’re somehow separate from them.
Our dualism shows up in intuitions about personal
identity. And what this means is that
common sense tells us that somebody can be the same person
even if their body undergoes radical and profound changes.
The best examples of this are fictional.
So, we have no problem understanding a movie where
somebody goes to sleep as a teenager and wakes up as
Jennifer Garner, as an older person.
Now, nobody says, “Oh, that’s a documentary.
I believe that thoroughly true” but at the same time nobody,
no adult, no teenager, no child ever leaves and says,
“I’m totally conceptually confused.”
Rather, we follow the story. We can also follow stories
which involve more profound transformations as when a man
dies and is reborn into the body of a child.
Now, you might have different views around–People around this
room will have different views as to whether reincarnation
really exists, but we can imagine it.
We could imagine a person dying and then reemerging in another
body. This is not Hollywood invention.
One of the great short stories of the last century begins with
a sentence by Franz Kafka: “As Gregor Samsa woke one
morning from uneasy dreams, he found himself transformed in
his bed into a gigantic insect.” And again, Kafka invites us to
imagine waking up into a body of a cockroach and we can.
This is also not modern. Hundreds of years before the
birth of Christ, Homer described the fate of the
companions of Odysseus who were transformed by a witch into
pigs. Actually, that’s not quite
right. She didn’t turn them into pigs.
She did something worse. She stuck them in the bodies of
pigs. They had the head and voice and
bristles and body of swine but their minds remained unchanged
as before, so they were penned there weeping.
And we are invited to imagine the fate of again finding
ourselves in the bodies of other creatures and,
if you can imagine this, this is because you are
imagining what you are as separate from the body that you
reside in. We allow for the notion that
many people can occupy one body. This is a mainstay of some
slapstick humor including the classic movie,
All of Me–Steve Martin and Lily Tomlin – highly
recommended. But many people think this sort
of thing really happens. One analysis of multiple
personality disorder is that you have many people inside a single
body fighting it out for control.
Now, we will discuss multiple personality disorder towards the
end of the semester and it turns out things are a good deal more
complicated than this, but still my point isn’t about
how it really is but how we think about it.
Common sense tells us you could have more than one person inside
a single body. This shows up in a different
context involving exorcisms where many belief systems allow
for the idea that people’s behavior,
particularly their evil or irrational behavior,
could be because something else has taken over their bodies.
Finally, most people around the world, all religions and most
people in most countries at most times,
believe that people can survive the destruction of their bodies.
Now, cultures differ according to the fate of the body.
Some cultures have the body going to–sorry–the fate of the
soul. Some cultures have you going to
Heaven or descending to Hell. Others have you occupying
another body. Still, others have you
occupying an amorphous spirit world.
But what they share is the idea that what you are is separable
from this physical thing you carry around.
And the physical thing that you carry around can be destroyed
while you live on. These views are particularly
common in the United States. In one survey done in Chicago a
few years ago, people were asked their
religion and then were asked what would happen to them when
they died. Most people in the sample were
Christian and about 96% of Christians said,
“When I die I’m going to go to Heaven.”
Some of the sample was Jewish. Now, Judaism is actually a
religion with a less than clear story about the afterlife.
Still, most of the subjects who identified themselves as Jewish
said when they die they will go to Heaven.
Some of the sampled denied having any religion at all–said
they have no religion at all. Still, when these people were
asked what would happen when they would die,
most of them answered, “I’m going to go to Heaven.”
So, dualism is emmeshed. A lot rests on it but,
as Crick points out; the scientific consensus now is
that dualism is wrong. There is no “you” separable or
separate from your body. In particular,
there is no “you” separable from your brain.
To put it the way cognitive scientists and psychologists and
neuroscientists like to put it, “the mind is what the brain
does.” The mind reflects the workings
of the brain just like computation reflects the working
of a computer. Now, why would you hold such an
outrageous view? Why would you reject dualism in
favor of this alternative? Well, a few reasons.
One reason is dualism has always had its problems.
For one thing, it’s a profoundly unscientific
doctrine. We want to know as curious
people how children learn language, what we find
attractive or unattractive, and what’s the basis for mental
illness. And dualism simply says,
“it’s all nonphysical, it’s part of the ether,” and
hence fails to explain it. More specifically,
dualists like Descartes struggle to explain how a
physical body connects to an immaterial soul.
What’s the conduit? How could this connection be
made? After all, Descartes knew full
well that there is such a connection.
Your body obeys your commands. If you bang your toe or stub
your toe you feel pain. If you drink alcohol it affects
your reasoning, but he could only wave his
hands as to how this physical thing in the world could connect
to an immaterial mind. Descartes, when he was alive,
was reasonable enough concluding that physical objects
cannot do certain things. He was reasonable enough in
concluding, for instance, as he did, that there’s no way
a merely physical object could ever play a game of chess
because–and that such a capacity is beyond the capacity
of the physical world and hence you have to apply–you have to
extend the explanation to an immaterial soul but now we
know–we have what scientists call an existence proof.
We know physical objects can do complicated and interesting
things. We know, for instance,
machines can play chess. We know machines can manipulate
symbols. We know machines have limited
capacities to engage in mathematical and logical
reasoning, to recognize things,
to do various forms of computations,
and this makes it at least possible that we are such
machines. So you can no longer say, “Look.
Physical things just can’t do that” because we know physical
things can do a lot and this opens up the possibility that
humans are physical things, in particular,
that humans are brains. Finally, there is strong
evidence that the brain is involved in mental life.
Somebody who hold a–held a dualist view that said that what
we do and what we decide and what we think and what we want
are all have nothing to do with the physical world,
would be embarrassed by the fact that the brain seems to
correspond in intricate and elaborate ways to our mental
life. Now, this has been known for a
long time. Philosophers and psychologists
knew for a long time that getting smacked in the head
could change your mental faculties;
that diseases like syphilis could make you deranged;
that chemicals like caffeine and alcohol can affect how you
think. But what’s new is we can now in
different ways see the direct effects of mental life.
Somebody with a severe and profound loss of mental
faculties–the deficit will be shown correspondingly in her
brain. Studies using imaging
techniques like CAT scans, PET, and fMRI,
illustrate that different parts of the brain are active during
different parts of mental life. For instance,
the difference between seeing words, hearing words,
reading words and generating words can correspond to
different aspects of what part of your brain is active.
To some extent, if we put you in an fMRI
scanner and observed what you’re doing in real time,
by looking at the activity patterns in your brain we can
tell whether you are thinking about music or thinking about
sex. To some extent we can tell
whether you’re solving a moral dilemma versus something else.
And this is no surprise if what we are is the workings of our
physical brains, but it is extremely difficult
to explain if one is a dualist. Now, so what you have is–the
scientific consensus is that all of mental life including
consciousness and emotions and choice and morality are the
products of brain activities. So, you would expect that when
you rip open the skull and look at the brain;
you’d see something glorious, you’d see – I don’t know –
a big, shiny thing with glass tubes and blinding lights and
sparks and wonderful colors. And actually though,
the brain is just disgusting. It looks like an old meat loaf.
It’s gray when you take it out of the head.
It’s called gray matter but that’s just because it’s out of
the head. Inside the head it’s bright red
because it’s pulsing with blood. It doesn’t even taste good.
Well, has anybody here ever eaten brain? It’s good with cream sauce but
everything’s good with cream sauce.
So, the question is, “How can something like this
give rise to us?” And you have to have some
sympathy for Descartes. There’s another argument
Descartes could have made that’s a lot less subtle than the ones
he did make, which is “That thing
responsible for free will and love and consciousness?
Ridiculous.” What I want to do,
and what the goal of neuroscience is,
is to make it less ridiculous, to try to explain how the brain
works, how the brain can give rise to thought,
and what I want to do today is take a first stab at this
question but it’s something we’ll continue to discuss
throughout the course as we talk about different aspects of
mental life. What I want to do though now is
provide a big picture. So, what I want to do is start
off small, with the smallest interesting part of the brain
and then get bigger and bigger and bigger – talk about how
the small part of the brain, the neurons,
the basic building blocks of thought, combine to other mental
structures and into different subparts of the brain and
finally to the whole thing. So, one of the discoveries of
psychology is that the basic unit of the brain appears to be
the neuron. The neuron is a specific sort
of cell and the neuron has three major parts, as you could see
illustrated here. Neurons actually look quite
different from one another but this is a typical one.
There are the dendrites – these little tentacles here.
And the dendrites get signals from other neurons.
Now, these signals can be either excitatory,
which is that they raise the likelihood the neuron will fire,
or inhibitory in that they lower the likelihood that the
neuron will fire. The cell body sums it up and
you could view it arithmetically.
The excitatory signals are pluses, the inhibitory ones are
minuses. And then if you get a certain
number, plus 60 or something, the neuron will fire and it
fires along the axon, the thing to the right.
The axon is much longer than the dendrites and,
in fact, some axons are many feet long.
There’s an axon leading from your spinal cord to your big toe
for instance. It is so shocking the lights go
complete a mechanical metaphor that would have led Descartes to
despair– Thank you, Koleen.
Surrounding the axon is a myelin sheath,
which is actually just insulation.
It helps the firing work quicker.
So, here are some facts about neurons.
There are a lot of them – about one thousand billion of
them – and each neuron can be connected to around thousands,
perhaps tens of thousands, other neurons.
So, it’s an extraordinarily complicated computing device.
Neurons come in three flavors. There are sensory neurons,
which take information from the world so as you see me,
for instance, there are neurons firing from
your retina sending signals to your brain.
There are motor neurons. If you decide to raise your
hand, those are motor neurons telling the muscles what to do.
And there are interneurons which connect the two.
And basically, the interneurons do the
thinking. They make the connection
between sensation and action. It used to be believed,
and it’s the sort of thing I would–when I taught this course
many years ago I would lecture on–that neurons do not grow
back once you lose them. You never get them back.
This is actually not true. There are parts of the brain in
which neurons can re-grow. One interesting thing about
neurons is a neuron is like a gun.
It either fires or it doesn’t. It’s all or nothing.
If you squeeze the trigger of a gun really hard and really fast,
it doesn’t fire any faster or harder than if you just squeezed
it gently. Now, this seems to be strange.
How could neurons be all or nothing when sensation is very
graded? If somebody next to you pushed
on your hand–the degree of pushing–you’d be able to notice
it. It’s not either pushing or not
pushing. You can–Degrees of pushing,
degrees of heat, degrees of brightness.
And the answer is, although neurons are all or
nothing, there are ways to code intensity.
So, one simple way to code intensity is the number of
neurons firing; the more neurons the more
intense. Another way to increase
intensity is the frequency of firing.
So, I’ll just use those two. The first one is the number of
neurons firing. The second one is the frequency
of firing in that something is more intense if it’s “bang,
bang, bang, bang, bang, bang” then “bang,
bang, bang” and these are two ways through which neurons
encode intensity. Now, neurons are connected and
they talk to one another and it used to be thought they were
tied to one another like a computer,
like you take wires and you connect wires to each other,
you wrap them around and connect them.
It turns out this isn’t the case.
It turns out that neurons relate to one another chemically
in a kind of interesting way. Between any neurons,
between the axon of one neuron and the dendrite of another,
there’s a tiny gap. The gap could be about one
ten-thousandths of a millimeter wide.
This infinitesimal gap–and this gap is known as a
synapse–and what happens is when a neuron fires,
an axon sends chemicals shooting through the gap.
These chemicals are known as neurotransmitters and they
affect the dendrites. So, neurons communicate to one
another chemically. These–Again,
the chemicals could excite the other neuron (excitatory) bring
up the chances it will fire, or inhibit the other neuron
(inhibitory). Now, neurotransmitters become
interesting because a lot of psychopharmacology,
both of the medical sort and the recreational sort,
consists of fiddling with neurotransmitters and so you
could see this through some examples.
There are two sorts of ways you could fiddle with
neurotransmitters, and correspondingly two sorts
of drugs. There are agonists.
And what an agonist does is increases the effect of
neurotransmitters, either by making more
neurotransmitters or stopping the cleanup of
neurotransmitters, or in some cases by faking a
neurotransmitter, by mimicking its effects.
Then, there are antagonists that slow down the amount of
neurotransmitters, either because they destroy
neurotransmitters or they make it hard to create more.
Or in some cases they go to the dendrite of the neuron and they
kind of put a paste over it so that the neurotransmitters can’t
connect. And it’s through these clever
ways that neurons can affect your mental life. So, for instance,
there is a drug known as Curare and Curare is an antagonist.
It’s a very particular sort of antagonist.
It blocks motor neurons from affecting muscle fibers.
What this does then is it paralyzes you because your motor
neurons–You send the command to your arm to stand,
to lift up. It doesn’t work.
You send the command to your leg to move.
It doesn’t work. The motor neurons are
deactivated and then, because the way you breathe is
through motor neurons, you then die.
There’s alcohol. Alcohol is inhibitory.
Now, this may be puzzling to people.
It’s mildly paradoxical because you may be thinking,
“alcohol is not inhibitory. On the contrary,
when I drink a lot of alcohol I lose my inhibitions and become a
more fun person. I become more aggressive and
more sexually vibrant and simply more beautiful.
And so in what way is alcohol inhibitory?”
Well, the answer is it inhibits the inhibitory parts of your
brain. So, you have parts of your
brain that are basically telling you now, largely in the frontal
lobes, that are–“Okay. Keep your pants on.
Don’t hit me, buddy. Don’t use bad words.”
Alcohol relaxes, shuts down those parts of the
brain. If you take enough alcohol,
it then goes down to inhibit the excitatory parts of your
brain and then you fall on the floor and pass out.
Amphetamines increase the amount of arousal.
In particular, they increase the amount of
norepinephrine, a neurotransmitter that’s
responsible for just general arousal.
And so, amphetamines include drugs like “speed” and “coke.”
There are–Prozac works on serotonin.
When we discuss clinical psychology and depression we’ll
learn the extent to which neurotransmitter disorders are
implicated in certain disorders like depression.
And one problem is that – for depression – is that there’s
too little of a neurotransmitter known as serotonin.
Prozac makes serotonin more prevalent and so in some extent
might help alleviate depression. Parkinson’s disease is a
disease involving destruction of motor control and loss of motor
control, difficulty moving. And one factor in Parkinson’s
is too little of a neurotransmitter known as
dopamine. The drug L-DOPA increases the
supply of dopamine and so there is something to alleviate,
at least temporarily, the symptoms of Parkinson’s.
So, you have neurons and they’re clustered together and
they fire and they communicate to one another.
So, how does this all work to give rise to creatures who could
do interesting things like talk and think?
Well, again, it used to be believed that the
brain is wired up like a computer,
like a PC or a Mac or something like that, but we know this
can’t be true. It can’t be true because
there’s two ways in which the brain is better than a computer.
For one thing, the brain is highly resistant
to damage. If you have a laptop and I
persuade you to open it up for me and I take the pliers and
kind of snip just about anywhere,
your laptop will be destroyed but the brain is actually more
resilient. You can take a lot of brain
damage and still preserve some mental functioning.
To some interesting sense, there’s some sort of damage
resistance built in to the brain that allows different parts of
the brain to take over if some parts are damaged.
A second consideration is the brain is extremely fast.
Your computer works on wires and electricity but your brain
uses tissue and tissue is extremely slow.
The paradox then is how do you create such a fast computer with
such slow stuff? And you can’t.
If the brain was wired up like a personal computer,
it would take you four hours to recognize a face but,
in fact, we could do things extremely quickly.
So, the question then is how is the brain wired up?
And the answer is, unlike manys,
unlike commercially generated computers, the brain works
through parallel processing, massively parallel distributed
processing. There’s a whole lot of research
and this is research, some of which takes place
outside psychology departments and in engineering departments
and computer science departments,
trying to figure out how a computer can do the same things
brains can do. And one way people do this is
they take a hint from nature and they try to construct massively
distributed networks to do aspects of reasoning.
So, there’s a very simple computational network.
That is interesting because it kind of looks to some extent
like the way neurons look and this is often known as neural
networks. And people who study this often
claim to be studying neural network modeling to try to build
smart machines by modeling them after brains.
And in the last 20 years or so, this has been a huge and
vibrant area of study where people are trying to wire up
machines that can do brain-like things from components that look
a lot like neurons and are wired up together as neurons are.
One consideration in all of this is that this is a very
young field and nobody knows how to do it yet.
There is no machine yet that can recognize faces or
understand sentences at the level of a two-year-old human.
There is no machine yet that can do just about anything
people can do in an interesting way.
And this is, in part, because the human
brain is wired up in an extraordinarily more complicated
way than any sort of simple neural network.
This is a sort of schematic diagram – you’re not
responsible for this – of parts of the visual cortex,
and the thing to realize about this is it’s extraordinarily
simplified. So, the brain is a complicated
system. Now, so, we’ve talked a little
bit about the basic building blocks of the brain – neurons.
We’ve then talked about how neurons can communicate to one
another; then, turned to how neurons are
wired up together. Now let’s talk a little bit
about different parts of the brain.
Now, there’s some things you don’t actually need your brain
to do. The study of what you don’t
need your brain to do has often drawn upon this weird
methodology where–This was actually done in France a lot
where they would decapitate people and when–After they
decapitated people, psychologists would rush to the
body of the headless person and sort of just test out reflexes
and stuff like that. It’s kind of gruesome but we
know there are some things you don’t need your brain for.
You don’t need your brain for newborn sucking,
limb flexation in withdrawal from pain.
Your limbs will pull back even if your head is gone.
Erection of the penis can be done without a brain.
Vomiting also is done without a brain.
Oh. I need a volunteer.
Very simple. This will not involve any
of–excellent–any of the above. Could you stand up just–Okay.
This is a new shirt so I want to stay away.
Just–No. This is–If you’ll hold out
your hand and–one hand flat. Excellent.
That’s the textbook, 5th edition.
What you’ll notice is–Thank you very much.
What you’ll notice is this hit and this hand went back up.
This is something automatic, instinctive,
and does not require your brain.
So your brain isn’t needed for everything.
What does your brain do? Well, some things that your
brain does involve very low-level internal structures.
And these are called subcortical structures because
they’re below the cortex. They’re underneath the cortex.
So, for instance, what we have here is a diagram
of the brain. The way to read this diagram is
it’s as if it were my brain and I am facing this way.
My head gets cut in half down here and then you could see the
brain. So, this is the front over here.
That’s the back. Some key parts are illustrated
here. The medulla,
for instance, is responsible for heart rate
and respiration. It’s very deep within the brain
and if it gets damaged you could–you are likely to die.
The cerebellum is responsible for body balance and muscular
coordination. And to give you,
again, a feeling for the complexity of these systems,
the cerebellum contains approximately 30 billion
neurons. The hypothalamus is responsible
here for feeding, hunger, thirst,
and to some extent sleep. And here is the same brain
parts in close-up. Now, all of these parts of the
brains are essential and many of them are implicated in
interesting psychological processes but where the action
is is the cortex. Isn’t this beautiful?
The cortex is the outer layer and the outer layer is all
crumpled up. Do you ever wonder why your
brain looks wrinkled? That’s because it’s all
crumpled. If you took out somebody’s
cortex and flattened it out, it would be two feet square,
sort of like a nice–like a rug.
And the cortex is where all the neat stuff takes place.
Fish don’t have any of that, so no offense to fish but
it’s–fish don’t have much of a mental life.
Reptiles and birds have a little bit about it–of it–and
primates have a lot and humans have a real lot.
Eighty percent of the volume of our brain, about,
is cortex. And the cortex can be broken up
into different parts or lobes. There is the–And,
again, this is facing in profile forward.
There is the frontal lobe, easy to remember.
This part in front, the parietal lobe,
the occipital lobe, and the temporal lobe.
And one theme we’re going to return to is–this is half the
brain. This is, in fact,
the left half of the brain. On the other half,
the right half, everything’s duplicated with
some slight and subtle differences.
What’s really weird–One really weird finding about these lobes
is that they include topological maps.
They include maps of your body. There is a cartoon which
actually illustrates a classic experiment by some physiologists
who for some reason had a dog’s brain opened up and started
shocking different parts of the brain.
You could do brain surgery while fully conscious because
the brain itself has no sense organs to it.
And it turns out that the dog–When they zapped part of
its brain, its leg would kick up.
And it took Dr. Penfield at McGill University
to do the same thing with people.
So, they were doing some brain surgery.
He had a little electrical thing just on–I don’t know how
he thought to do this. He started zapping it and
“boom.” The person–Parts of their body
would move. More than that,
when he zapped other parts of the brain, people would claim to
see colors. And he zapped other parts of
the brain; people would claim to hear
sounds; and other parts of the brain,
people would claim to experience touch.
And through his research and other research,
it was found that there are maps in the brain of the body.
There is a map in the motor part of the brain,
the motor cortex, of the sort up on the left and
the sensory cortex of the sort that you could see on the right
and if you–and you could tell what’s what by opening up the
brain and shocking different parts and those parts would
correspond to the parts of the body shown in the diagram there.
Now, two things to notice about these maps.
The first is they’re topographical and what this
means is that if two parts of the–two parts are close
together on the body, they’ll be close together on
the brain. So, your tongue is closer to
your jaw than it is to your hip in the body;
so too in both the motor cortex and the somatosensory cortex.
Also, you’ll notice that the size of the body part
represented in the brain does not correspond to the size of
the body part in the real world. Rather, what determines the
size in the brain is the extent to which either they have motor
command over it or sensory control.
So, there’s a whole lot of sensory organs,
for instance, focused along your tongue,
and that’s why that’s so big, and an enormous amount on your
face but your shoulder isn’t even–doesn’t even make it on
there because, although your shoulder might be
bigger than your tongue, there’s not much going on.
In fact, if you draw a diagram of a person, what their body is
corresponding to the amount of somatosensory cortex,
you get something like that. That’s your sensory body. Now, so, you have these maps in
your head but the thing to realize is–And these maps are
part of your cortex, but the things to realize is
that’s an important part of what goes on in your brain but less
than one quarter of the cortex contains these maps or
projection areas. The rest is involved in
language and reasoning and moral thought and so on.
And, in fact, the proportion as you go from
rat, cat, and monkey, humans–less and less of it is
devoted to projection and there is more and more to other
things. So, how do we figure out what
the other parts of the brain do? Well, there’s all sorts of
methods. Typically, these are recent
imaging methods like CAT scan and PET scan and fMRI which,
as I said before, show parts of your brain at
work. If you want to know which part
of your brain is responsible for language, you could put somebody
into a scanner and have them exposed to language or do a
linguistic task or talk or something and then see what
parts of their brain are active. Another way to explore what the
brain does is to consider what happens to people when very bad
things happen to their brain. And these bad things could
happen through lesions, through tumors,
through strokes, through injury.
For the most part, neuropsychologists don’t like
helmet laws. Neuropsychologists love when
motorcyclists drive without helmets because through their
horrible accidents we gain great insights into how the brain
works. And the logic is if you find
somebody–Crudely, if you find somebody with
damage to this part of the brain right here and that person can’t
recognize faces for instance, there’s some reason to believe
that this part of the brain is related to face recognition.
And so, from the study of brain damage and the study of–we can
gain some understanding of what different parts of the brain do.
And so, people study brain damages–brain damage that
implicates motor control such as apraxia.
And what’s interesting about apraxia is it’s not paralysis.
Somebody with apraxia can move, do simple movements just fine
but they can’t coordinate their movements.
They can’t do something like wave goodbye or light a
cigarette. There is agnosia and agnosia is
a disorder which isn’t blindness because the person could still
see perfectly well. Their eyes are intact but
rather what happens in agnosia is they lose the ability to
recognize certain things. Sometimes this is described as
psychic blindness. And so, they may get visual
agnosia and lose the ability to recognize objects.
They may get prosopagnosia and lose the ability to recognize
faces. There are disorders of sensory
neglect, some famous disorders. Again, it’s not paralysis,
it’s not blindness, but due to certain parts of
your–of damaged parts of your brain,
you might lose, for instance,
the idea that there’s a left side of your body or a left side
of the world. And these cases are so
interesting I want to devote some chunk to a class in the
next few weeks to discussing them.
There are disorders of language like aphasia.
The classic case was discovered by Paul Broca in 1861.
A patient who had damage to part of his brain and can only
say one word, “tan,”
and the person would say, “tan, tan, tan,
tan,” and everything else was gone.
There’s other disorders of language such as receptive
aphasia where the person could speak very fluently but the
words don’t make any sense and they can’t understand anybody
else. Other disorders that we’ll
discuss later on include acquired psychopathy,
where damage to parts of your brain,
particularly related to the frontal lobes,
rob you of the ability to tell right from wrong.
The final–I want to end–We’re talking about neurons,
connection between neurons, how neurons are wired up,
the parts of the brain, what the different parts do.
I want to end by talking about the two halves of the brain and
ask the question, “How many minds do you have?”
Now, if you look at the brain–If you took the brain out
and held it up, it would look pretty
symmetrical, but it actually is not.
There are actual differences between the right hemisphere and
the left hemisphere. How many people here are
right-handed? How many people here are
left-handed? How many people here are sort
of complicated, ambidextrous,
don’t know, “bit of the right, bit of left” people?
Okay. Those of you who are
right-handed, which comprises about nine out
of ten people, have language in your left
hemisphere. And, in fact,
we’re going to be talking about right-handed people for the most
part, making generalizations in what I’ll talk about now.
Those of you who are left-handed are more
complicated. Some of you have language in
your right hemisphere, some in your left hemisphere,
some God knows where. It’s complicated.
Now, the idea is that some things are duplicated.
So, if you were to lose half your brain, the other half can
actually do a lot but some things are more prevalent and
more powerful in one part of the brain than the other.
And I want to show you a brief film clip from “Scientific
American” that illustrates the differences between the
hemispheres, but before doing that,
I want to provide some introductory facts.
Some functions are lateralized. So, typically,
language in the left. Again, this is a right-handed
centric thing but if you’re right-handed – language on the
left, math and music on the right.
There is a crossover and this is important when we think about
the studies that will follow but the crossover is that everything
you see in the left visual field goes to the right side of your
brain; everything in the right visual
field goes to the left side of the brain, and similarly,
there’s a crossover in action. So, your right hemisphere
controls the left side of the body.
Your left hemisphere controls the right side of the body.
Now, finally, the two halves are connected.
They’re connected by this huge web called the corpus callosum.
And I’m just going to skip this because the movie illustration
will go through some of this. This illustrates certain themes
that are discussed in detail in the Gray book,
concerning the lateralization of different parts of different
mental capacities, some in the left hemisphere,
some in the right hemisphere. But it also serves as a useful
methodological development, which is a nice illustration as
to how looking at people who are incredibly unusual,
such as this man who had his brain bisected so his left
hemisphere and his right hemisphere don’t communicate
with one another–how looking at such people,
such extreme cases, can provide us with some
understanding of how we normally do things.
And this, again, is a theme we’ll return to
throughout the course. This is generally the general
introduction of the brain that I wanted to provide,
giving the framework for what I’ll be talking about later on
throughout the course so that I might later on make reference to
neurons or neurotransmitters or the cortex or the left
hemisphere and you’ll sort of have the background to
understand what I’m talking about.
But I want to end this first real class with a bit of
humility as to what psychologists know and don’t
know. So, the idea behind a lot of
psychology – particularly a lot of neuroscience and
cognitive psychology – is to treat the mind as an information
processor, as an elaborate computer.
And so, we study different problems like recognizing faces
or language or motor control or logic.
The strategy then often is to figure out how,
what sort of program can solve these problems and then we go on
to ask, “How could this program be
instantiated in the physical brain?”
So, we would solve–We study people much as we’d study a
computer from an alien planet or something.
And I think–This strategy is one I’m very enthusiastic about
but there still remains what’s sometimes called the “hard
problem” of consciousness and this involves subjective
experience. What’s it like?
So, my computer can play chess. My computer can recognize
numbers. It can do math.
And maybe it does it kind of the same way that I do it but my
computer doesn’t have feelings in the same sense.
These are two classic illustrations.
This is from a very old “Star Trek” episode.
It illustrates angst. I think a starship’s about to
go into the sun or something. And that’s my older kid,
Max, who’s happy. And so the question is,
“How does a thing like that give rise to consciousness and
subjective experience?” And this is a deep puzzle.
And although some psychologists and philosophers think they’ve
solved it, most of us are a lot more skeptical.
Most of us think we have so far to go before we can answer
questions like Huxley’s question.
Huxley points out, “How it is that anything so
remarkable as a state of consciousness comes about as a
result of irritating nervous tissue,
is just as unaccountable as the appearance of the Djinn…” –
of the genie – “…when Aladdin rubs his lamp.”
It seems like magic that a fleshy lump of gray,
disgusting meat can give rise to these feelings.
The second bit of humility we’ll end the class on is I am
presenting here, and I’ll be presenting
throughout this semester, what you can call a mechanistic
conception of mental life. I’m not going to be talking
about how beautiful it is and how wonderful it is and how
mysterious it is. Rather, I’m going to be trying
to explain it. I’m going to be trying to
explain fundamental aspects of ourselves including questions
like how do we make decisions, why do we love our children,
what happens when we fall in love, and so on.
Now, you might find this sort of project in the end to be
repellant. You might worry about how this,
well, this meshes with humanist values.
For instance, when we deal with one another
in a legal and a moral setting, we think in terms of free will
and responsibility. If we’re driving and you cut me
off, you chose to do that. It reflects badly on you.
If you save a life at risk to your own, you’re–you deserve
praise. You did something wonderful.
It might be hard to mesh this with the conception in which all
actions are the result of neurochemical physical
processes. It might also be hard to mesh a
notion such as the purported intrinsic value of people.
And finally, it might be hard to mesh the
mechanistic notion of the mind with the idea that people have
spiritual value. Faced with this tension,
there are three possibilities. You might choose to reject the
scientific conception of the mind.
Many people do. You may choose to embrace
dualism, reject the idea that the brain is responsible for
mental life, and reject the promise of a scientific
you might choose to embrace the scientific worldview and reject
all these humanist values. And there are some philosophers
and psychologists who do just that, who claim that free will
and responsibility and spiritual value and intrinsic value are
all illusions; they’re pre-scientific notions
that get washed away in modern science or you could try to
reconcile them. You could try to figure out how
to mesh your scientific view of the mind with these humanist
values you might want to preserve.
And this is an issue which we’re going to return to
throughout the course. Okay.
I’ll see you on Wednesday.