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02 Foundations: This is Your Brain基础原理:这是你的大脑

2011-3-27 13:26| 发布者: spybot| 查看: 3478| 评论: 0|原作者: spybot


Professor Paul Bloom: We're going to begin the class proper,Introduction to Psychology, with a discussion about the brain. And, inparticular, I want to lead off the class with an idea that the NobelPrize winning biologist, Francis Crick, described as "The AstonishingHypothesis." And The Astonishing Hypothesis is summarized like this. Ashe writes, The Astonishing Hypothesis is that:
You, your joys and your sorrows, your memories and yourambitions, your sense of personal identity and free will are in fact nomore than the behavior of a vast assembly of nerve cells and theirassociated 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 andunnatural view and I don't actually expect people to believe it atfirst. It's an open question whether you'll believe it when this classcomes 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. Mostpeople are dualists. Now, dualism is a very different doctrine. It's adoctrine that can be found in every religion and in most philosophicalsystems throughout history. It was very explicit in Plato, forinstance.
But the most articulate and well-known defender of dualism is thephilosopher Rene Descartes, and Rene Descartes explicitly asked aquestion, "Are humans merely physical machines, merely physicalthings?" And he answered, "no." He agreed that animals are machines. Infact, he called them "beast machines" and said animals, nonhumananimals are merely robots, but people are different. There's a dualityof people. Like animals, we possess physical material bodies, butunlike animals, what we are is not physical. We are immaterial soulsthat possess physical bodies, that have physical bodies, that reside inphysical bodies, that connect to physical bodies. So, this is known asdualism because the claim is, for humans at least, there are twoseparate things; there's our material bodies and there's our immaterialminds.
Now, Descartes made two arguments for dualism. One argument involvedobservations of a human action. So, Descartes lived in a fairlysophisticated time, and his time did have robots. These were notelectrical robots, of course. They were robots powered by hydraulics.So, Descartes would walk around the French Royal Gardens and the FrenchRoyal Gardens were set up like a seventeenth-century Disneyland. Theyhad these characters that would operate according to water flow and soif you stepped on a certain panel, a swordsman would jump out with asword. If you stepped somewhere else, a bathing beauty would coverherself up behind some bushes. And Descartes said, "Boy, these machinesrespond in certain ways to certain actions so machines can do certainthings and, in fact," he says, "our bodies work that way too. If youtap somebody on the knee, your leg will jump out. Well, maybe that'swhat we are." But Descartes said that can't be because there are thingsthat humans do that no machine could ever do. Humans are not limited toreflexive action. Rather, humans are capable of coordinated, creative,spontaneous things. We can use language, for instance, and sometimes myuse of language can be reflexive. Somebody says, "How are you?" And Isay, "I am fine. How are you?" But sometimes I could say what I chooseto be, "How are you?" "Pretty damn good." I can just choose. Andmachines, 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 themethod. This he came to using the method of doubt. So, he startedasking 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 aGod. I believe I live in a rich country but maybe I've been fooled." Heeven said, "I believe I have had friends and family but maybe I ambeing tricked. Maybe an evil demon, for instance, has tricked me, hasdeluded me into thinking I have experiences that aren't real." And, ofcourse, the modern version of this is The Matrix.
The idea of The Matrix is explicitly built uponCartesian--Descartes' worries about an evil demon. Maybe everythingyou're now experiencing is not real, but rather is the product of someother, perhaps malevolent, creature. Descartes, similarly, could doubthe has a body. In fact, he noticed that madmen sometimes believe theyhave extra limbs or they believe they're of different sizes and shapesthan 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 thinkI'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, Descartesconcluded, that he cannot doubt, and the answer is he cannot doubt thathe is himself thinking. That would be self-refuting. And so, Descartesused the method of doubt to say there's something really differentabout having a body that's always uncertain from having a mind. And heused this argument as a way to support dualism, as a way to support theidea that bodies and minds are separate. And so he concluded, "I knewthat I was a substance, the whole essence or nature of which is tothink, and that for its existence, there is no need of any place nordoes it depend on any material thing. That is to say, the soul by whichI am, when I am, is entirely distinct from body."
Now, I said before that this is common sense and I want toillustrate the common sense nature of this in a few ways. One thing isour dualism is enmeshed in our language. So, we have a certain mode oftalking about things that we own or things that are close to us – myarm, my heart, my child, my car – but we also extend that to my bodyand my brain. We talk about owning our brains as if we're somehowseparate from them. Our dualism shows up in intuitions about personalidentity. And what this means is that common sense tells us thatsomebody can be the same person even if their body undergoes radicaland profound changes. The best examples of this are fictional. So, wehave no problem understanding a movie where somebody goes to sleep as ateenager 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 everleaves and says, "I'm totally conceptually confused." Rather, we followthe story. We can also follow stories which involve more profoundtransformations as when a man dies and is reborn into the body of achild.
Now, you might have different views around--People around this roomwill have different views as to whether reincarnation really exists,but we can imagine it. We could imagine a person dying and thenreemerging in another body. This is not Hollywood invention. One of thegreat short stories of the last century begins with a sentence by FranzKafka: "As Gregor Samsa woke one morning from uneasy dreams, he foundhimself transformed in his bed into a gigantic insect." And again,Kafka invites us to imagine waking up into a body of a cockroach and wecan. This is also not modern. Hundreds of years before the birth ofChrist, Homer described the fate of the companions of Odysseus who weretransformed by a witch into pigs. Actually, that's not quite right. Shedidn't turn them into pigs. She did something worse. She stuck them inthe bodies of pigs. They had the head and voice and bristles and bodyof swine but their minds remained unchanged as before, so they werepenned there weeping. And we are invited to imagine the fate of againfinding ourselves in the bodies of other creatures and, if you canimagine this, this is because you are imagining what you are asseparate from the body that you reside in.
We allow for the notion that many people can occupy one body. Thisis 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 analysisof multiple personality disorder is that you have many people inside asingle body fighting it out for control. Now, we will discuss multiplepersonality disorder towards the end of the semester and it turns outthings are a good deal more complicated than this, but still my pointisn't about how it really is but how we think about it. Common sensetells us you could have more than one person inside a single body. Thisshows up in a different context involving exorcisms where many beliefsystems allow for the idea that people's behavior, particularly theirevil or irrational behavior, could be because something else has takenover their bodies.
Finally, most people around the world, all religions and most peoplein most countries at most times, believe that people can survive thedestruction of their bodies. Now, cultures differ according to the fateof the body. Some cultures have the body going to--sorry--the fate ofthe soul. Some cultures have you going to Heaven or descending to Hell.Others have you occupying another body. Still, others have youoccupying an amorphous spirit world. But what they share is the ideathat what you are is separable from this physical thing you carryaround. And the physical thing that you carry around can be destroyedwhile you live on.
These views are particularly common in the United States. In onesurvey done in Chicago a few years ago, people were asked theirreligion and then were asked what would happen to them when they died.Most people in the sample were Christian and about 96% of Christianssaid, "When I die I'm going to go to Heaven." Some of the sample wasJewish. Now, Judaism is actually a religion with a less than clearstory about the afterlife. Still, most of the subjects who identifiedthemselves as Jewish said when they die they will go to Heaven. Some ofthe sampled denied having any religion at all--said they have noreligion at all. Still, when these people were asked what would happenwhen they would die, most of them answered, "I'm going to go toHeaven."
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 scientistsand psychologists and neuroscientists like to put it, "the mind is whatthe brain does." The mind reflects the workings of the brain just likecomputation reflects the working of a computer. Now, why would you holdsuch an outrageous view? Why would you reject dualism in favor of thisalternative? Well, a few reasons. One reason is dualism has always hadits problems. For one thing, it's a profoundly unscientific doctrine.We want to know as curious people how children learn language, what wefind attractive or unattractive, and what's the basis for mentalillness. And dualism simply says, "it's all nonphysical, it's part ofthe ether," and hence fails to explain it.
More specifically, dualists like Descartes struggle to explain how aphysical body connects to an immaterial soul. What's the conduit? Howcould this connection be made? After all, Descartes knew full well thatthere is such a connection. Your body obeys your commands. If you bangyour toe or stub your toe you feel pain. If you drink alcohol itaffects your reasoning, but he could only wave his hands as to how thisphysical thing in the world could connect to an immaterial mind.
Descartes, when he was alive, was reasonable enough concluding thatphysical objects cannot do certain things. He was reasonable enough inconcluding, for instance, as he did, that there's no way a merelyphysical object could ever play a game of chess because--and that sucha capacity is beyond the capacity of the physical world and hence youhave to apply--you have to extend the explanation to an immaterial soulbut now we know--we have what scientists call an existence proof. Weknow physical objects can do complicated and interesting things. Weknow, for instance, machines can play chess. We know machines canmanipulate symbols. We know machines have limited capacities to engagein mathematical and logical reasoning, to recognize things, to dovarious forms of computations, and this makes it at least possible thatwe are such machines. So you can no longer say, "Look. Physical thingsjust can't do that" because we know physical things can do a lot andthis opens up the possibility that humans are physical things, inparticular, that humans are brains.
Finally, there is strong evidence that the brain is involved inmental life. Somebody who hold a--held a dualist view that said thatwhat we do and what we decide and what we think and what we want areall have nothing to do with the physical world, would be embarrassed bythe fact that the brain seems to correspond in intricate and elaborateways to our mental life. Now, this has been known for a long time.Philosophers and psychologists knew for a long time that gettingsmacked in the head could change your mental faculties; that diseaseslike syphilis could make you deranged; that chemicals like caffeine andalcohol can affect how you think. But what's new is we can now indifferent ways see the direct effects of mental life.
Somebody with a severe and profound loss of mental faculties--thedeficit will be shown correspondingly in her brain. Studies usingimaging techniques like CAT scans, PET, and fMRI, illustrate thatdifferent parts of the brain are active during different parts ofmental life. For instance, the difference between seeing words, hearingwords, reading words and generating words can correspond to differentaspects of what part of your brain is active. To some extent, if we putyou in an fMRI scanner and observed what you're doing in real time, bylooking at the activity patterns in your brain we can tell whether youare thinking about music or thinking about sex. To some extent we cantell whether you're solving a moral dilemma versus something else. Andthis is no surprise if what we are is the workings of our physicalbrains, but it is extremely difficult to explain if one is adualist.
Now, so what you have is--the scientific consensus is that all ofmental life including consciousness and emotions and choice andmorality are the products of brain activities. So, you would expectthat when you rip open the skull and look at the brain; you'd seesomething glorious, you'd see – I don't know – a big, shiny thing withglass tubes and blinding lights and sparks and wonderful colors. Andactually though, the brain is just disgusting. It looks like an oldmeat loaf. It's gray when you take it out of the head. It's called graymatter but that's just because it's out of the head. Inside the headit's bright red because it's pulsing with blood. It doesn't even tastegood. Well, has anybody here ever eaten brain? It's good with creamsauce 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 anotherargument Descartes could have made that's a lot less subtle than theones he did make, which is "That thing responsible for free will andlove and consciousness? Ridiculous." What I want to do, and what thegoal of neuroscience is, is to make it less ridiculous, to try toexplain 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 butit's something we'll continue to discuss throughout the course as wetalk about different aspects of mental life. What I want to do thoughnow 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 andbigger and bigger – talk about how the small part of the brain, theneurons, the basic building blocks of thought, combine to other mentalstructures and into different subparts of the brain and finally to thewhole thing.
So, one of the discoveries of psychology is that the basic unit ofthe brain appears to be the neuron. The neuron is a specific sort ofcell and the neuron has three major parts, as you could see illustratedhere [pointing to the slide]. Neurons actually look quite differentfrom one another but this is a typical one. There are the dendrites –these little tentacles here. And the dendrites get signals from otherneurons. Now, these signals can be either excitatory, which is thatthey raise the likelihood the neuron will fire, or inhibitory in thatthey lower the likelihood that the neuron will fire. The cell body sumsit up and you could view it arithmetically. The excitatory signals arepluses, the inhibitory ones are minuses. And then if you get a certainnumber, plus 60 or something, the neuron will fire and it fires alongthe axon, the thing to the right. The axon is much longer than thedendrites and, in fact, some axons are many feet long. There's an axonleading from your spinal cord to your big toe for instance. [theclassroom lights accidentally go off] It is so shocking the lights goout.
Surrounded--Surrounding--To complete a mechanical metaphor thatwould have led Descartes to despair--[the classroom lights turn on]Thank you, Koleen. Surrounding the axon is a myelin sheath, which isactually just insulation. It helps the firing work quicker. So, hereare some facts about neurons. There are a lot of them – about onethousand billion of them – and each neuron can be connected to aroundthousands, perhaps tens of thousands, other neurons. So, it's anextraordinarily complicated computing device. Neurons come in threeflavors. There are sensory neurons, which take information from theworld so as you see me, for instance, there are neurons firing fromyour retina sending signals to your brain. There are motor neurons. Ifyou decide to raise your hand, those are motor neurons telling themuscles what to do. And there are interneurons which connect the two.And basically, the interneurons do the thinking. They make theconnection between sensation and action.
It used to be believed, and it's the sort of thing I would--when Itaught this course many years ago I would lecture on--that neurons donot grow back once you lose them. You never get them back. This isactually not true. There are parts of the brain in which neurons canre-grow.
One interesting thing about neurons is a neuron is like a gun. Iteither fires or it doesn't. It's all or nothing. If you squeeze thetrigger of a gun really hard and really fast, it doesn't fire anyfaster or harder than if you just squeezed it gently. Now, this seemsto be strange. Why? How could neurons be all or nothing when sensationis very graded? If somebody next to you pushed on your hand--the degreeof pushing--you'd be able to notice it. It's not either pushing or notpushing. You can--Degrees of pushing, degrees of heat, degrees ofbrightness. And the answer is, although neurons are all or nothing,there are ways to code intensity. So, one simple way to code intensityis the number of neurons firing; the more neurons the more intense.Another way to increase intensity is the frequency of firing. So, I'lljust use those two. The first one is the number of neurons firing. Thesecond one is the frequency of firing in that something is more intenseif it's "bang, bang, bang, bang, bang, bang" then [louder] "bang, bang,bang" and these are two ways through which neurons encodeintensity.
Now, neurons are connected and they talk to one another and it usedto be thought they were tied to one another like a computer, like youtake wires and you connect wires to each other, you wrap them aroundand connect them. It turns out this isn't the case. It turns out thatneurons relate to one another chemically in a kind of interesting way.Between any neurons, between the axon of one neuron and the dendrite ofanother, there's a tiny gap. The gap could be about one ten-thousandthsof a millimeter wide. This infinitesimal gap--and this gap is known asa synapse--and what happens is when a neuron fires, an axon sendschemicals shooting through the gap. These chemicals are known asneurotransmitters and they affect the dendrites. So, neuronscommunicate to one another chemically. These--Again, the chemicalscould excite the other neuron (excitatory) bring up the chances it willfire, or inhibit the other neuron (inhibitory).
Now, neurotransmitters become interesting because a lot ofpsychopharmacology, both of the medical sort and the recreational sort,consists of fiddling with neurotransmitters and so you could see thisthrough some examples. There are two sorts of ways you could fiddlewith neurotransmitters, and correspondingly two sorts of drugs. Thereare agonists. And what an agonist does is increases the effect ofneurotransmitters, either by making more neurotransmitters or stoppingthe cleanup of neurotransmitters, or in some cases by faking aneurotransmitter, by mimicking its effects. Then, there are antagoniststhat slow down the amount of neurotransmitters, either because theydestroy neurotransmitters or they make it hard to create more. Or insome cases they go to the dendrite of the neuron and they kind of put apaste over it so that the neurotransmitters can't connect. And it'sthrough these clever ways that neurons can affect your mental life.
So, for instance, there is a drug known as Curare and Curare is anantagonist. It's a very particular sort of antagonist. It blocks motorneurons from affecting muscle fibers. What this does then is itparalyzes you because your motor neurons--You send the command to yourarm to stand, to lift up. It doesn't work. You send the command to yourleg to move. It doesn't work. The motor neurons are deactivated andthen, because the way you breathe is through motor neurons, you thendie.
There's alcohol. Alcohol is inhibitory. Now, this may be puzzling topeople. It's mildly paradoxical because you may be thinking, "alcoholis not inhibitory. On the contrary, when I drink a lot of alcohol Ilose my inhibitions and become a more fun person. I become moreaggressive and more sexually vibrant and simply more beautiful. And soin what way is alcohol inhibitory?" Well, the answer is it inhibits theinhibitory parts of your brain. So, you have parts of your brain thatare basically telling you now, largely in the frontal lobes, thatare--"Okay. Keep your pants on. Don't hit me, buddy. Don't use badwords." Alcohol relaxes, shuts down those parts of the brain. If youtake enough alcohol, it then goes down to inhibit the excitatory partsof your brain and then you fall on the floor and pass out.
Amphetamines increase the amount of arousal. In particular, theyincrease the amount of norepinephrine, a neurotransmitter that'sresponsible for just general arousal. And so, amphetamines includedrugs like "speed" and "coke." There are--Prozac works on serotonin.When we discuss clinical psychology and depression we'll learn theextent to which neurotransmitter disorders are implicated in certaindisorders 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 helpalleviate depression. Parkinson's disease is a disease involvingdestruction of motor control and loss of motor control, difficultymoving. And one factor in Parkinson's is too little of aneurotransmitter known as dopamine. The drug L-DOPA increases thesupply of dopamine and so there is something to alleviate, at leasttemporarily, the symptoms of Parkinson's.
So, you have neurons and they're clustered together and they fireand they communicate to one another. So, how does this all work to giverise 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 acomputer, like a PC or a Mac or something like that, but we know thiscan't be true. It can't be true because there's two ways in which thebrain is better than a computer. For one thing, the brain is highlyresistant to damage. If you have a laptop and I persuade you to open itup 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 mentalfunctioning. To some interesting sense, there's some sort of damageresistance built in to the brain that allows different parts of thebrain to take over if some parts are damaged.
A second consideration is the brain is extremely fast. Your computerworks on wires and electricity but your brain uses tissue and tissue isextremely slow. The paradox then is how do you create such a fastcomputer with such slow stuff? And you can't. If the brain was wired uplike a personal computer, it would take you four hours to recognize aface but, in fact, we could do things extremely quickly. So, thequestion then is how is the brain wired up? And the answer is, unlikemanys, unlike commercially generated computers, the brain works throughparallel processing, massively parallel distributed processing.
There's a whole lot of research and this is research, some of whichtakes place outside psychology departments and in engineeringdepartments and computer science departments, trying to figure out howa computer can do the same things brains can do. And one way people dothis is they take a hint from nature and they try to constructmassively distributed networks to do aspects of reasoning. So, there'sa very simple computational network. That is interesting because itkind of looks to some extent like the way neurons look and this isoften known as neural networks. And people who study this often claimto be studying neural network modeling to try to build smart machinesby modeling them after brains. And in the last 20 years or so, this hasbeen a huge and vibrant area of study where people are trying to wireup machines that can do brain-like things from components that look alot like neurons and are wired up together as neurons are. Oneconsideration in all of this is that this is a very young field andnobody knows how to do it yet. There is no machine yet that canrecognize faces or understand sentences at the level of a two-year-oldhuman. There is no machine yet that can do just about anything peoplecan do in an interesting way. And this is, in part, because the humanbrain is wired up in an extraordinarily more complicated way than anysort of simple neural network. This is a sort of schematic diagram –you're not responsible for this – of parts of the visual cortex, andthe 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 blocksof the brain – neurons. We've then talked about how neurons cancommunicate to one another; then, [we] turned to how neurons are wiredup together. Now let's talk a little bit about different parts of thebrain. Now, there's some things you don't actually need your brain todo. The study of what you don't need your brain to do has often drawnupon this weird methodology where--This was actually done in France alot where they would decapitate people and when--After they decapitatedpeople, psychologists would rush to the body of the headless person andsort of just test out reflexes and stuff like that. It's kind ofgruesome but we know there are some things you don't need your brainfor.
You don't need your brain for newborn 禁用词语ing, limb flexation inwithdrawal from pain. Your limbs will pull back even if your head isgone. Erection of the penis can be done without a brain. Vomiting alsois done without a brain. Oh. I need a volunteer. Very simple. This willnot involve any of--excellent--any of the above. Could you stand upjust--Okay. This is a new shirt so I want to stay away. Just--No. Thisis--If you'll hold out your hand and--one hand flat. [The student holdshis hand out flat] Excellent. [Professor Paul Bloom raises a book abovethe student's hand] That's the textbook, 5th edition. Now. [ProfessorPaul Bloom drops the book onto the student's hand. After succumbing tothe 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 noticeis this hit and this hand went back up. This is something automatic,instinctive, and does not require your brain. So your brain isn'tneeded for everything.
What does your brain do? Well, some things that your brain doesinvolve very low-level internal structures. And these are calledsubcortical structures because they're below the cortex. They'reunderneath the cortex. So, for instance, what we have here [gesturingtoward the slides] is a diagram of the brain. The way to read thisdiagram is it's as if it were my brain and I am facing this way. Myhead 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 areillustrated here. The medulla, for instance, is responsible for heartrate and respiration. It's very deep within the brain and if it getsdamaged you could--you are likely to die. The cerebellum is responsiblefor body balance and muscular coordination. And to give you, again, afeeling for the complexity of these systems, the cerebellum containsapproximately 30 billion neurons. The hypothalamus is responsible herefor feeding, hunger, thirst, and to some extent sleep. And here is thesame brain parts in close-up.
Now, all of these parts of the brains are essential and many of themare implicated in interesting psychological processes but where theaction is is the cortex. Isn't this beautiful? The cortex is the outerlayer and the outer layer is all crumpled up. Do you ever wonder whyyour brain looks wrinkled? That's because it's all crumpled. If youtook out somebody's cortex and flattened it out, it would be two feetsquare, sort of like a nice--like a rug. And the cortex is where allthe neat stuff takes place. Fish don't have any of that, so no offenseto fish but it's--fish don't have much of a mental life. Reptiles andbirds have a little bit about it--of it--and primates have a lot andhumans have a real lot. Eighty percent of the volume of our brain,about, is cortex. And the cortex can be broken up into different partsor lobes. There is the--And, again, this is facing in profile forward.There is the frontal lobe, easy to remember. This part in front, theparietal 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, theright half, everything's duplicated with some slight and subtledifferences. What's really weird--One really weird finding about theselobes is that they include topological maps. They include maps of yourbody. There is a cartoon which actually illustrates a classicexperiment by some physiologists who for some reason had a dog's brainopened up and started shocking different parts of the brain. You coulddo brain surgery while fully conscious because the brain itself has nosense organs to it. And it turns out that the dog--When they zappedpart of its brain, its leg would kick up.
And it took Dr. Penfield at McGill University to do the same thingwith people. So, they were doing some brain surgery. He had a littleelectrical thing just on--I don't know how he thought to do this. Hestarted zapping it and "boom." The person--Parts of their body wouldmove. More than that, when he zapped other parts of the brain, peoplewould claim to see colors. And he zapped other parts of the brain;people would claim to hear sounds; and other parts of the brain, peoplewould claim to experience touch. And through his research and otherresearch, 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 thesort up on the left and the sensory cortex of the sort that you couldsee on the right and if you--and you could tell what's what by openingup the brain and shocking different parts and those parts wouldcorrespond to the parts of the body shown in the diagram there.
Now, two things to notice about these maps. The first is they'retopographical and what this means is that if two parts of the--twoparts are close together on the body, they'll be close together on thebrain. So, your tongue is closer to your jaw than it is to your hip inthe 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 thebrain does not correspond to the size of the body part in the realworld. Rather, what determines the size in the brain is the extent towhich either they have motor command over it or sensory control. So,there's a whole lot of sensory organs, for instance, focused along yourtongue, and that's why that's so big, and an enormous amount on yourface but your shoulder isn't even--doesn't even make it on therebecause, 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 yoursensory body.
Now, so, you have these maps in your head but the thing to realizeis--And these maps are part of your cortex, but the things to realizeis that's an important part of what goes on in your brain but less thanone quarter of the cortex contains these maps or projection areas. Therest 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 moreand more to other things. So, how do we figure out what the other partsof the brain do? Well, there's all sorts of methods. Typically, theseare 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 knowwhich part of your brain is responsible for language, you could putsomebody into a scanner and have them exposed to language or do alinguistic task or talk or something and then see what parts of theirbrain are active.
Another way to explore what the brain does is to consider whathappens to people when very bad things happen to their brain. And thesebad things could happen through lesions, through tumors, throughstrokes, through injury. For the most part, neuropsychologists don'tlike helmet laws. Neuropsychologists love when motorcyclists drivewithout helmets because through their horrible accidents we gain greatinsights into how the brain works. And the logic is if you findsomebody--Crudely, if you find somebody with damage to this part of thebrain right here and that person can't recognize faces for instance,there's some reason to believe that this part of the brain is relatedto face recognition.
And so, from the study of brain damage and the study of--we can gainsome understanding of what different parts of the brain do. And so,people study brain damages--brain damage that implicates motor controlsuch as apraxia. And what's interesting about apraxia is it's notparalysis. Somebody with apraxia can move, do simple movements justfine but they can't coordinate their movements. They can't do somethinglike wave goodbye or light a cigarette.
There is agnosia and agnosia is a disorder which isn't blindnessbecause the person could still see perfectly well. Their eyes areintact but rather what happens in agnosia is they lose the ability torecognize certain things. Sometimes this is described as psychicblindness. And so, they may get visual agnosia and lose the ability torecognize objects. They may get prosopagnosia and lose the ability torecognize faces. There are disorders of sensory neglect, some famousdisorders. Again, it's not paralysis, it's not blindness, but due tocertain 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 leftside of the world. And these cases are so interesting I want to devotesome chunk to a class in the next few weeks to discussing them.
There are disorders of language like aphasia. The classic case wasdiscovered by Paul Broca in 1861. A patient who had damage to part ofhis brain and can only say one word, "tan," and the person would say,"tan, tan, tan, tan," and everything else was gone. There's otherdisorders of language such as receptive aphasia where the person couldspeak very fluently but the words don't make any sense and they can'tunderstand anybody else. Other disorders that we'll discuss later oninclude acquired psychopathy, where damage to parts of your brain,particularly related to the frontal lobes, rob you of the ability totell right from wrong.
The final--I want to end--We're talking about neurons, connectionbetween neurons, how neurons are wired up, the parts of the brain, whatthe different parts do. I want to end by talking about the two halvesof 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, itwould look pretty symmetrical, but it actually is not. There are actualdifferences between the right hemisphere and the left hemisphere. Howmany people here are right-handed? How many people here areleft-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 often people, have language in your left hemisphere. And, in fact, we'regoing to be talking about right-handed people for the most part, makinggeneralizations in what I'll talk about now. Those of you who areleft-handed are more complicated. Some of you have language in yourright 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 tolose half your brain, the other half can actually do a lot but somethings are more prevalent and more powerful in one part of the brainthan the other. And I want to show you a brief film clip from"Scientific American" that illustrates the differences between thehemispheres, but before doing that, I want to provide some introductoryfacts. Some functions are lateralized. So, typically, language in theleft. Again, this is a right-handed centric thing but if you'reright-handed – language on the left, math and music on the right. Thereis a crossover and this is important when we think about the studiesthat will follow but the crossover is that everything you see in theleft visual field goes to the right side of your brain; everything inthe right visual field goes to the left side of the brain, andsimilarly, there's a crossover in action. So, your right hemispherecontrols the left side of the body. Your left hemisphere controls theright side of the body. Now, finally, the two halves are connected.They're connected by this huge web called the corpus callosum. And I'mjust going to skip this because the movie illustration will go throughsome 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 onthe two halves of the brain. The only flaw in this movie is people arejust extremely pleased with themselves, so you have to ignore thatwhile 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 themesthat are discussed in detail in the Gray book, concerning thelateralization of different parts of different mental capacities, somein the left hemisphere, some in the right hemisphere. But it alsoserves as a useful methodological development, which is a niceillustration as to how looking at people who are incredibly unusual,such as this man who had his brain bisected so his left hemisphere andhis right hemisphere don't communicate with one another--how looking atsuch people, such extreme cases, can provide us with some understandingof how we normally do things. And this, again, is a theme we'll returnto throughout the course.
This is generally the general introduction of the brain that Iwanted to provide, giving the framework for what I'll be talking aboutlater on throughout the course so that I might later on make referenceto neurons or neurotransmitters or the cortex or the left hemisphereand you'll sort of have the background to understand what I'm talkingabout. But I want to end this first real class with a bit of humilityas to what psychologists know and don't know. So, the idea behind a lotof psychology – particularly a lot of neuroscience and cognitivepsychology – is to treat the mind as an information processor, as anelaborate computer. And so, we study different problems likerecognizing faces or language or motor control or logic. The strategythen often is to figure out how, what sort of program can solve theseproblems and then we go on to ask, "How could this program beinstantiated in the physical brain?" So, we would solve--We studypeople 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 therestill remains what's sometimes called the "hard problem" ofconsciousness and this involves subjective experience. What's it like?So, my computer can play chess. My computer can recognize numbers. Itcan do math. And maybe it does it kind of the same way that I do it butmy computer doesn't have feelings in the same sense.
These are two classic illustrations. This [pointing at a picture onthe slide] is from a very old "Star Trek" episode. It illustratesangst. I think a starship's about to go into the sun or something. Andthat'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 giverise to consciousness and subjective experience?" And this is a deeppuzzle. And although some psychologists and philosophers think they'vesolved it, most of us are a lot more skeptical. Most of us think wehave so far to go before we can answer questions like Huxley'squestion. Huxley points out, "How it is that anything so remarkable asa state of consciousness comes about as a result of irritating nervoustissue, is just as unaccountable as the appearance of the Djinn…" – ofthe genie – "…when Aladdin rubs his lamp." It seems like magic that afleshy lump of gray, disgusting meat can give rise to thesefeelings.
The second bit of humility we'll end the class on is I am presentinghere, and I'll be presenting throughout this semester, what you cancall a mechanistic conception of mental life. I'm not going to betalking about how beautiful it is and how wonderful it is and howmysterious it is. Rather, I'm going to be trying to explain it. I'mgoing to be trying to explain fundamental aspects of ourselvesincluding questions like how do we make decisions, why do we love ourchildren, 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 moralsetting, we think in terms of free will and responsibility. If we'redriving and you cut me off, you chose to do that. It reflects badly onyou. If you save a life at risk to your own, you're--you deservepraise. You did something wonderful. It might be hard to mesh this withthe conception in which all actions are the result of neurochemicalphysical processes. It might also be hard to mesh a notion such as thepurported intrinsic value of people. And finally, it might be hard tomesh the mechanistic notion of the mind with the idea that people havespiritual value.
Faced with this tension, there are three possibilities. You mightchoose to reject the scientific conception of the mind. Many people do.You may choose to embrace dualism, reject the idea that the brain isresponsible for mental life, and reject the promise of a scientificpsychology. Alternatively, you might choose to embrace the scientificworldview and reject all these humanist values. And there are somephilosophers and psychologists who do just that, who claim that freewill and responsibility and spiritual value and intrinsic value are allillusions; they're pre-scientific notions that get washed away inmodern science or you could try to reconcile them. You could try tofigure out how to mesh your scientific view of the mind with thesehumanist values you might want to preserve. And this is an issue whichwe're going to return to throughout the course. Okay. I'll see you onWednesday.
[end of transcript]
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