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(2010-02-07 21:56:01)


     Professor Paul Bloom: We're going to begin the class proper, Introduction to Psychology, with a discussion about the brain. And, in particular, I want to lead off the class with an idea that the Nobel Prize winning biologist, Francis Crick, described as "The Astonishing Hypothesis." And The Astonishing Hypothesis is summarized like this. As he writes, The Astonishing Hypothesis is that:


    You, your joys and your sorrows, your memories and your ambitions, your sense of personal identity and free will are in fact no more than the behavior of a vast assembly of nerve cells and their associated molecules. As Lewis Carroll's Alice might have phrased it, "you're nothing but a pack of neurons."


   It is fair to describe this as astonishing. It is an odd and unnatural view and I don't actually expect people to believe it at first. It's an open question whether you'll believe it when this class comes to an end, but I'd be surprised if many of you believe it now. Most people don't. Most people, in fact, hold a different view. Most people are dualists. Now, dualism is a very different doctrine. It's a doctrine that can be found in every religion and in most philosophical systems throughout history. It was very explicit in Plato, for instance.


  But the most articulate and well-known defender of dualism is the philosopher Rene Descartes, and Rene Descartes explicitly asked a question, "Are humans merely physical machines, merely physical things?" And he answered, "no." He agreed that animals are machines. In fact, he called them "beast machines" and said animals, nonhuman animals are merely robots, but people are different. There's a duality of people. Like animals, we possess physical material bodies, but unlike animals, what we are is not physical. We are immaterial souls that possess physical bodies, that have physical bodies, that reside in physical bodies, that connect to physical bodies. So, this is known as dualism because the claim is, for humans at least, there are two separate things; there's our material bodies and there's our immaterial minds.


Now, Descartes made two arguments for dualism. One argument involved observations of a human action. So, Descartes lived in a fairly sophisticated time, and his time did have robots. These were not electrical robots, of course. They were robots powered by hydraulics. So, Descartes would walk around the French Royal Gardens and the French Royal Gardens were set up like a seventeenth-century Disneyland. They had these characters that would operate according to water flow and so if you stepped on a certain panel, a swordsman would jump out with a sword. If you stepped somewhere else, a bathing beauty would cover herself up behind some bushes. And Descartes said, "Boy, these machines respond in certain ways to certain actions so machines can do certain things and, in fact," he says, "our bodies work that way too. If you tap somebody on the knee, your leg will jump out. Well, maybe that's what we are." But Descartes said that can't be because there are things that humans do that no machine could ever do. Humans are not limited to reflexive action. Rather, humans are capable of coordinated, creative, spontaneous things. We can use language, for instance, and sometimes my use of language can be reflexive. Somebody says, "How are you?" And I say, "I am fine. How are you?" But sometimes I could say what I choose to be, "How are you?" "Pretty damn good." I can just choose. And machines, Descartes argued, are incapable of that sort of choice. Hence, we are not mere machines.'


   The second argument is, of course, quite famous and this was the method. This he came to using the method of doubt. So, he started asking himself the question, "What can I be sure of?" And he said, "Well, I believe there's a God, but honestly, I can't be sure there's a God. I believe I live in a rich country but maybe I've been fooled." He even said, "I believe I have had friends and family but maybe I am being tricked. Maybe an evil demon, for instance, has tricked me, has deluded me into thinking I have experiences that aren't real." And, of course, the modern version of this is The Matrix.



The idea of The Matrix is explicitly built upon Cartesian--Descartes' worries about an evil demon. Maybe everything you're now experiencing is not real, but rather is the product of some other, perhaps malevolent, creature. Descartes, similarly, could doubt he has a body. In fact, he noticed that madmen sometimes believe they have extra limbs or they believe they're of different sizes and shapes than they really are and Descartes said, "How do I know I'm not crazy? Crazy people don't think they're crazy so the fact that I don't think I'm crazy doesn't mean I'm not crazy. How do I know," Descartes said, "I'm not dreaming right now?" But there is one thing, Descartes concluded, that he cannot doubt, and the answer is he cannot doubt that he is himself thinking. That would be self-refuting. And so, Descartes used the method of doubt to say there's something really different about having a body that's always uncertain from having a mind. And he used this argument as a way to support dualism, as a way to support the idea that bodies and minds are separate. And so he concluded, "I knew that I was a substance, the whole essence or nature of which is to think, and that for its existence, there is no need of any place nor does it depend on any material thing. That is to say, the soul by which I am, when I am, is entirely distinct from body."



Now, I said before that this is common sense and I want to illustrate the common sense nature of this in a few ways. One thing is our dualism is enmeshed in our language. So, we have a certain mode of talking about things that we own or things that are close to us – my arm, my heart, my child, my car – but we also extend that to my body and my brain. We talk about owning our brains as if we're somehow separate from them. Our dualism shows up in intuitions about personal identity. And what this means is that common sense tells us that somebody can be the same person even if their body undergoes radical and profound changes. The best examples of this are fictional. So, we have no problem understanding a movie where somebody goes to sleep as a teenager and wakes up as Jennifer Garner, as an older person. Now, nobody says, "Oh, that's a documentary. I believe that thoroughly true" but at the same time nobody, no adult, no teenager, no child ever leaves and says, "I'm totally conceptually confused." Rather, we follow the story. We can also follow stories which involve more profound transformations as when a man dies and is reborn into the body of a child.

  现在,我先声明这是一般的意义并且我想用一些方法说明一般的意义。一项要说明的是我们的二元论是用我们自己的语言表达的。所以,我们有一种特定的方法来讨论我们拥有的事情或与我们接近的事情-我的手臂,我的心脏,我的孩子,我的汽车-但是我们也把这延伸到了我的身体和我的大脑,我们讨论我们拥有我们自己的大脑就象某种程度上我们与之分离。我们的二元论表明个人身份的直觉。这就意味着一般意义告诉我们某些人能够是同一个人尽管他们的身体经历了激烈的和复杂的变化。这最好的例子是这些是虚构的。所以,我们毫无问题的理解这部电影某人睡觉时象个年轻人而醒来时是Jennifer Garner,是一个长大的人。现在,无人说:“哦,这是文件。我相信完全真实但是在同一时间无人,无成年人,无年青人,无儿童离开,并且说,“我完全概念地困惑了”当然,我们追随了这个故事。我们也可以追寻这个故事.这包括了更复杂的转生,一个人死了并且在投身为儿童的身体。




Now, you might have different views around--People around this room will have different views as to whether reincarnation really exists, but we can imagine it. We could imagine a person dying and then reemerging in another body. This is not Hollywood invention. One of the great short stories of the last century begins with a sentence by Franz Kafka: "As Gregor Samsa woke one morning from uneasy dreams, he found himself transformed in his bed into a gigantic insect." And again, Kafka invites us to imagine waking up into a body of a cockroach and we can. This is also not modern. Hundreds of years before the birth of Christ, Homer described the fate of the companions of Odysseus who were transformed by a witch into pigs. Actually, that's not quite right. She didn't turn them into pigs. She did something worse. She stuck them in the bodies of pigs. They had the head and voice and bristles and body of swine but their minds remained unchanged as before, so they were penned there weeping. And we are invited to imagine the fate of again finding ourselves in the bodies of other creatures and, if you can imagine this, this is because you are imagining what you are as separate from the body that you reside in.


We allow for the notion that many people can occupy one body. This is a mainstay of some slapstick humor including the classic movie, All of Me--Steve Martin and Lily Tomlin – highly recommended. But many people think this sort of thing really happens. One analysis of multiple personality disorder is that you have many people inside a single body fighting it out for control. Now, we will discuss multiple personality disorder towards the end of the semester and it turns out things are a good deal more complicated than this, but still my point isn't about how it really is but how we think about it. Common sense tells us you could have more than one person inside a single body. This shows up in a different context involving exorcisms where many belief systems allow for the idea that people's behavior, particularly their evil or irrational behavior, could be because something else has taken over their bodies.


Finally, most people around the world, all religions and most people in most countries at most times, believe that people can survive the destruction of their bodies. Now, cultures differ according to the fate of the body. Some cultures have the body going to--sorry--the fate of the soul. Some cultures have you going to Heaven or descending to Hell. Others have you occupying another body. Still, others have you occupying an amorphous spirit world. But what they share is the idea that what you are is separable from this physical thing you carry around. And the physical thing that you carry around can be destroyed while you live on.


These views are particularly common in the United States. In one survey done in Chicago a few years ago, people were asked their religion and then were asked what would happen to them when they died. Most people in the sample were Christian and about 96% of Christians said, "When I die I'm going to go to Heaven." Some of the sample was Jewish. Now, Judaism is actually a religion with a less than clear story about the afterlife. Still, most of the subjects who identified themselves as Jewish said when they die they will go to Heaven. Some of the sampled denied having any religion at all--said they have no religion at all. Still, when these people were asked what would happen when they would die, most of them answered, "I'm going to go to Heaven."


So, dualism is emmeshed. A lot rests on it but, as Crick points out; the scientific consensus now is that dualism is wrong. There is no "you" separable or separate from your body. In particular, there is no "you" separable from your brain. To put it the way cognitive scientists and psychologists and neuroscientists like to put it, "the mind is what the brain does." The mind reflects the workings of the brain just like computation reflects the working of a computer. Now, why would you hold such an outrageous view? Why would you reject dualism in favor of this alternative? Well, a few reasons. One reason is dualism has always had its problems. For one thing, it's a profoundly unscientific doctrine. We want to know as curious people how children learn language, what we find attractive or unattractive, and what's the basis for mental illness. And dualism simply says, "it's all nonphysical, it's part of the ether," and hence fails to explain it.


More specifically, dualists like Descartes struggle to explain how a physical body connects to an immaterial soul. What's the conduit? How could this connection be made? After all, Descartes knew full well that there is such a connection. Your body obeys your commands. If you bang your toe or stub your toe you feel pain. If you drink alcohol it affects your reasoning, but he could only wave his hands as to how this physical thing in the world could connect to an immaterial mind.

Descartes, when he was alive, was reasonable enough concluding that physical objects cannot do certain things. He was reasonable enough in concluding, for instance, as he did, that there's no way a merely physical object could ever play a game of chess because--and that such a capacity is beyond the capacity of the physical world and hence you have to apply--you have to extend the explanation to an immaterial soul but now we know--we have what scientists call an existence proof. We know physical objects can do complicated and interesting things. We know, for instance, machines can play chess. We know machines can manipulate symbols. We know machines have limited capacities to engage in mathematical and logical reasoning, to recognize things, to do various forms of computations, and this makes it at least possible that we are such machines. So you can no longer say, "Look. Physical things just can't do that" because we know physical things can do a lot and this opens up the possibility that humans are physical things, in particular, that humans are brains.


Finally, there is strong evidence that the brain is involved in mental life. Somebody who hold a--held a dualist view that said that what we do and what we decide and what we think and what we want are all have nothing to do with the physical world, would be embarrassed by the fact that the brain seems to correspond in intricate and elaborate ways to our mental life. Now, this has been known for a long time. Philosophers and psychologists knew for a long time that getting smacked in the head could change your mental faculties; that diseases like syphilis could make you deranged; that chemicals like caffeine and alcohol can affect how you think. But what's new is we can now in different ways see the direct effects of mental life.


Somebody with a severe and profound loss of mental faculties--the deficit will be shown correspondingly in her brain. Studies using imaging techniques like CAT scans, PET, and fMRI, illustrate that different parts of the brain are active during different parts of mental life. For instance, the difference between seeing words, hearing words, reading words and generating words can correspond to different aspects of what part of your brain is active. To some extent, if we put you in an fMRI scanner and observed what you're doing in real time, by looking at the activity patterns in your brain we can tell whether you are thinking about music or thinking about sex. To some extent we can tell whether you're solving a moral dilemma versus something else. And this is no surprise if what we are is the workings of our physical brains, but it is extremely difficult to explain if one is a dualist.


Now, so what you have is--the scientific consensus is that all of mental life including consciousness and emotions and choice and morality are the products of brain activities. So, you would expect that when you rip open the skull and look at the brain; you'd see something glorious, you'd see – I don't know – a big, shiny thing with glass tubes and blinding lights and sparks and wonderful colors. And actually though, the brain is just disgusting. It looks like an old meat loaf. It's gray when you take it out of the head. It's called gray matter but that's just because it's out of the head. Inside the head it's bright red because it's pulsing with blood. It doesn't even taste good. Well, has anybody here ever eaten brain? It's good with cream sauce but everything's good with cream sauce.


So, the question is, "How can something like this give rise to us?" And you have to have some sympathy for Descartes. There's another argument Descartes could have made that's a lot less subtle than the ones he did make, which is "That thing responsible for free will and love and consciousness? Ridiculous." What I want to do, and what the goal of neuroscience is, is to make it less ridiculous, to try to explain how the brain works, how the brain can give rise to thought, and what I want to do today is take a first stab at this question but it's something we'll continue to discuss throughout the course as we talk about different aspects of mental life. What I want to do though now is provide a big picture. So, what I want to do is start off small, with the smallest interesting part of the brain and then get bigger and bigger and bigger – talk about how the small part of the brain, the neurons, the basic building blocks of thought, combine to other mental structures and into different subparts of the brain and finally to the whole thing.


So, one of the discoveries of psychology is that the basic unit of the brain appears to be the neuron. The neuron is a specific sort of cell and the neuron has three major parts, as you could see illustrated here [pointing to the slide]. Neurons actually look quite different from one another but this is a typical one. There are the dendrites – these little tentacles here. And the dendrites get signals from other neurons. Now, these signals can be either excitatory, which is that they raise the likelihood the neuron will fire, or inhibitory in that they lower the likelihood that the neuron will fire. The cell body sums it up and you could view it arithmetically. The excitatory signals are pluses, the inhibitory ones are minuses. And then if you get a certain number, plus 60 or something, the neuron will fire and it fires along the axon, the thing to the right. The axon is much longer than the dendrites and, in fact, some axons are many feet long. There's an axon leading from your spinal cord to your big toe for instance. [the classroom lights accidentally go off] It is so shocking the lights go out.


Surrounded--Surrounding--To complete a mechanical metaphor that would have led Descartes to despair--[the classroom lights turn on] Thank you. Surrounding the axon is a myelin sheath, which is actually just insulation. It helps the firing work quicker. So, here are some facts about neurons. There are a lot of them – about one thousand billion of them – and each neuron can be connected to around thousands, perhaps tens of thousands, other neurons. So, it's an extraordinarily complicated computing device. Neurons come in three flavors. There are sensory neurons, which take information from the world so as you see me, for instance, there are neurons firing from your retina sending signals to your brain. There are motor neurons. If you decide to raise your hand, those are motor neurons telling the muscles what to do. And there are interneurons which connect the two. And basically, the interneurons do the thinking. They make the connection between sensation and action.


It used to be believed, and it's the sort of thing I would--when I taught this course many years ago I would lecture on--that neurons do not grow back once you lose them. You never get them back. This is actually not true. There are parts of the brain in which neurons can re-grow.

One interesting thing about neurons is a neuron is like a gun. It either fires or it doesn't. It's all or nothing. If you squeeze the trigger of a gun really hard and really fast, it doesn't fire any faster or harder than if you just squeezed it gently. Now, this seems to be strange. Why? How could neurons be all or nothing when sensation is very graded? If somebody next to you pushed on your hand--the degree of pushing--you'd be able to notice it. It's not either pushing or not pushing. You can--Degrees of pushing, degrees of heat, degrees of brightness. And the answer is, although neurons are all or nothing, there are ways to code intensity. So, one simple way to code intensity is the number of neurons firing; the more neurons the more intense. Another way to increase intensity is the frequency of firing. So, I'll just use those two. The first one is the number of neurons firing. The second one is the frequency of firing in that something is more intense if it's "bang, bang, bang, bang, bang, bang" then [louder] "bang, bang, bang" and these are two ways through which neurons encode intensity.


Now, neurons are connected and they talk to one another and it used to be thought they were tied to one another like a computer, like you take wires and you connect wires to each other, you wrap them around and connect them. It turns out this isn't the case. It turns out that neurons relate to one another chemically in a kind of interesting way. Between any neurons, between the axon of one neuron and the dendrite of another, there's a tiny gap. The gap could be about one ten-thousandths of a millimeter wide. This infinitesimal gap--and this gap is known as a synapse--and what happens is when a neuron fires, an axon sends chemicals shooting through the gap. These chemicals are known as neurotransmitters and they affect the dendrites. So, neurons communicate to one another chemically. These--Again, the chemicals could excite the other neuron (excitatory) bring up the chances it will fire, or inhibit the other neuron (inhibitory).


Now, neurotransmitters become interesting because a lot of psychopharmacology, both of the medical sort and the recreational sort, consists of fiddling with neurotransmitters and so you could see this through some examples. There are two sorts of ways you could fiddle with neurotransmitters, and correspondingly two sorts of drugs. There are agonists. And what an agonist does is increases the effect of neurotransmitters, either by making more neurotransmitters or stopping the cleanup of neurotransmitters, or in some cases by faking a neurotransmitter, by mimicking its effects. Then, there are antagonists that slow down the amount of neurotransmitters, either because they destroy neurotransmitters or they make it hard to create more. Or in some cases they go to the dendrite of the neuron and they kind of put a paste over it so that the neurotransmitters can't connect. And it's through these clever ways that neurons can affect your mental life.


So, for instance, there is a drug known as Curare and Curare is an antagonist. It's a very particular sort of antagonist. It blocks motor neurons from affecting muscle fibers. What this does then is it paralyzes you because your motor neurons--You send the command to your arm to stand, to lift up. It doesn't work. You send the command to your leg to move. It doesn't work. The motor neurons are deactivated and then, because the way you breathe is through motor neurons, you then die.


There's alcohol. Alcohol is inhibitory. Now, this may be puzzling to people. It's mildly paradoxical because you may be thinking, "alcohol is not inhibitory. On the contrary, when I drink a lot of alcohol I lose my inhibitions and become a more fun person. I become more aggressive and more sexually vibrant and simply more beautiful. And so in what way is alcohol inhibitory?" Well, the answer is it inhibits the inhibitory parts of your brain. So, you have parts of your brain that are basically telling you now, largely in the frontal lobes, that are--"Okay. Keep your pants on. Don't hit me, buddy. Don't use bad words." Alcohol relaxes, shuts down those parts of the brain. If you take enough alcohol, it then goes down to inhibit the excitatory parts of your brain and then you fall on the floor and pass out.


Amphetamines increase the amount of arousal. In particular, they increase the amount of norepinephrine, a neurotransmitter that's responsible for just general arousal. And so, amphetamines include drugs like "speed" and "coke." There are--Prozac works on serotonin. When we discuss clinical psychology and depression we'll learn the extent to which neurotransmitter disorders are implicated in certain disorders like depression. And one problem is that – for depression – is that there's too little of a neurotransmitter known as serotonin. Prozac makes serotonin more prevalent and so in some extent might help alleviate depression. Parkinson's disease is a disease involving destruction of motor control and loss of motor control, difficulty moving. And one factor in Parkinson's is too little of a neurotransmitter known as dopamine. The drug L-DOPA increases the supply of dopamine and so there is something to alleviate, at least temporarily, the symptoms of Parkinson's.

安非他命增加了兴奋的数量。特别的,他们增加了去甲肾上腺素的数量,神经递质起到了普通唤起的作用。因此,安非他命包括了可卡因和按非他命的药物。他们是-作用于血清素的百忧解。当我们讨论临床心理学的时候和我们要讨论的压抑时我们会学到神经递质的障碍与压抑这样疾病是有关的。一个问题是-压抑-就是血清素中的神经递质太少了。百忧解让血清素更多并且在某种程度上能减少压抑。帕金森病就是一种运动损坏和运动控制减少的疾病,很难行动。帕金森病的一个因素就是神经递质中的多巴胺过少的缘故。药物如 L-DOPA 增加了多巴胺的供应因此这可以使得帕金森症状某些症状减轻,至少是暂时的。



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