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  • 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 carbut 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 Tomlinhighly 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 biggertalk 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 out.

  • Surrounded--Surrounding--To 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 themand 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 thatfor

  • depressionis 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

  • diagramyou're not responsible for thisof

  • 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 brainneurons. 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. Now.

  • 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 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-handedlanguage 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 psychologyparticularly a

  • lot of neuroscience and cognitive psychologyis 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 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.

Professor Paul Bloom: We're going to begin the class

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B1 中級

2.基礎。這是你的大腦 (2. Foundations: This Is Your Brain)

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    CH 發佈於 2021 年 01 月 14 日
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