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.