Introduction to Psychology: Lecture 2 Transcript
January 22, 2007
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 [pointing to the slide].
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. [the classroom lights accidentally go off] It is so shocking the
lights go out.
Surrounded--Surrounding--To complete a mechanical metaphor that would have led
Descartes to despair--[the classroom lights turn on] 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. Why? 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
[louder] "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, [we] 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. [The student
holds his hand out flat] Excellent. [Professor Paul Bloom raises a book above
the student's hand] That's the textbook, 5th edition. Now. [Professor Paul Bloom
drops the book onto the student's hand. After succumbing to the weight of the
book the student's hand automatically raises back up] Perfect. 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 [gesturing toward the slides] 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 [gesturing toward the slide]. 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 is an excellent summary of a discussion of Michael Gazzaniga, who's one of
the world's top neuroscientists and the leading expert on the two halves of the
brain. The only flaw in this movie is people are just extremely pleased with
themselves, so you have to ignore that while watching it. Is that working? Do
you people hear it?
[Professor Bloom plays a short video clip]
Now, I'll end on that happy note. 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 [pointing at a picture on the slide]
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 [pointing at a
another picture on the slide] 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 psychology. Alternatively, 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.
Source: http://oyc.yale.edu/yale/psychology/introduction-to-psychology/content/transcripts/transcript02.html