One of the things that this brain development has to do is to send long fibers from one place to another. So the basic structure of a neuron typically, is the cell body located here and then some long fiber that goes out and makes a connection someplace else. This is written in the instructions of the DNA, where they're supposed to go. Now you may recall that the brain has lots and lots of neurons in it and from the time of conception until the time of birth, about a million new neurons are developed every minute of that nine month period. They have to find their way to the proper location and in that process, there's some competition involved. You've all been engaged in a similar competition, in the past week or so, when you went onto your computer and tried to target courses for the spring semester. In many cases, you would find out that you got there a little bit too late and it had turned from from green to red. That's kind of a bummer and the same thing happens with neurons. When you have instructions in the DNA that says you need to go from here to here and make a connection, when that connection is made, it's sort of a handshake type of agreement between both the sending cell and the receiving cell and they say okay, good, this is going to work. Now some other neuron from that same region comes up here and sorry, there's no place to connect. This is worse than having a course close because a cell dies, if it doesn't make the connection. To accommodate that, we have something called programmed cell death. Programmed cell death, where cells are supposed to die. So the way this works is that by the time you were born, you had created a million or so neurons every minute during gestation period and by the time you were born, about half of all the neurons formed in your brain had died. They had died, and there's a good reason for that and it kind of goes back to what may be an apocryphal story, or it may not be, but supposedly, someone once asked Michelangelo how you could start out with a big block of marble and end up with this beautiful statue of The David? He replied that it's really very simple. You just take a hammer and chisel and you chip away all the parts that don't look like David and then you have the statue, that's kind of what happens during brain development. You have a whole bunch of neurons being developed going out trying to find locations, and if they don't look like this final product, they don't look like the blueprint, they shrivel up and die. I have a little jar of rice here, it's the cheap stuff, small grain, white rice that's probably not even good for you but anyway, you all know what rice looks like even if you can't see this. How many grains of rice do you suppose might be in here? There's no prize but feel free to guess. What do you think? You. >> [INAUDIBLE] >> How many? Five hundred? >> Five hundred. Anybody else? Take another guess. How about you, what do you think? >> Nine hundred. How about you? Two hundred. >> You guys are so, so wrong, there are 5,000 grains of rice in here. Now, let me say that it's about 5,000, I didn't count out 5,000 grains of rice and put them in here but I did very carefully measure a couple of teaspoons, and so this is close to 5,000 grains of rice. Now the brain. Has that many neurons in it, give or take. See different estimates but about 500 billion. Now the only other place you see these kinds of numbers is with national debt. >> [LAUGH] >> We don't understand that any better than we understand the brain but I want to give to you some sort of a feeling, since we don't understand those numbers, some sort of a feeling for how big the brain is. If you take these 5,000 and then figure out how big the container would have to be to hold this many, i.e., how big our head would have to be if our neurons were the size of grains of rice. We'd have a lot of trouble fitting through doorways because if you get that number of grains of rice, and start pouring them in to the football stadium, by the time you get to that number, you will have filled that stadium higher than you're head. The brain is huge and each of these neurons may have as many as 1,000 interconnections with other neurons. Carl Sagan, whom you've saw in a video a few weeks back, wasn't afraid of big numbers and he made the calculation that if you look at all the synapses in the brain and consider the possibility that they could be either active or inactive, how many states of the brain could you have, just viewing the brain as a computer? The number of different states that the brain could be in is way, way, way larger then the number of electrons and protons and other elemental units in the entire known universe So, what that means is that this big, gooey disk drive, I guess you might call it, is perfectly capable of holding all of your memories, all of your language. All of the things that you will learn in your college education, your love for your grandmother, your contempt for the neighbor's cat, it's all in there and there's plenty of room left over. So we end up as they told us with a structure that is breathtaking in its complexity yet frugal in its variability so we can perhaps begin to understand some of the aspects of this brain. Now I've talked to you a couple of times, about MacLean's triune brain. The reptilian brain serves basic functions. The more complicated old mammalian brain in the new mammalian brain, which in us looks like this, with all of it's wrinkles in the cortex. The reason why the cortex is wrinkled is because it has a lot of things that it has to do. And if you look at the cortex with a microphone, no, you use a microscope, actually. It works better than a microphone to look at the cortex. If you look at it with a microscope you will see that it's a highly structured set of cells that are in layers and communicate with each other up and down the layers. If you were to take this cortex, if you were able to take the cortex and spread it out, smooth out the wrinkles, it would be about the size of a queen size bed sheet. Not nearly that thick. But it's a big sheet-like structure. And if you want to get it inside a human skull, what do you have to do? You have to just stuff it in there, and it ends up being wrinkled like this. So it's just a big surface area. And so we have this amazing structure, layered structure where things get added. Starting out, evolutionarily with some pretty simple stuff and adding layer after layer after layer of more complicated things on top of it that, of course, allow us to do more and more complicated things. And when you look at that. When you look at the brain, you have to just think that such a grand orchestration could not have occurred by accident. It's one of the things that the naysayers will say, you can't get this by accident. But, the fact of the matter is, we kind of did. With the two basic rules, natural variability and natural selection, That slowly, slowly, slowly built up to this complicated structure. Now I've got an image of a watch or a clock there. And here's an important thing to know about evolution, and it's easily overlooked because we kind of tend to take a teleological point of view and we kind of, it's easy to think that this human brain is the end product and that's what was in mind all along with a process of evolution to reach that. But no, that's not the way it works. It's not the was it has worked. If you could set the clock back 40,000 years, 40 million years, if you could just set the clock back to all of the conditions that were present at some previous time. Everything exactly the same as it was then and start the clock ticking again. Those two processes, natural variability and natural selection would work, but because of all of the random variations and the other things that could happen we would not end up with something that looks like this. It just absolutely would not look like this. It might be better. It might be worse but the rules that apply do not have that in mind. That's just what has happened. So one of the things that I want to talk about is the question, is the human brain special? I mean we think we're special And we view ourselves above all of the lower creatures and everything, and view ourselves as being specially creative and all sorts of high order things. So is there any reason to believe that the human brain is special in any way? I think we have to answer yes, that it is special. And it's not that our brain is just bigger, faster, sharper maybe than the brains of other creatures. Well what we are going to see are differences in process and plasticity. Process and plasticity that kind of move us off the charts in some ways from other creatures. We are a very visual organism. We kind of have that as our primary source of information as we go through our daily lives. So I want to talk a little bit about the visual system because it's probably easier for you to understand. And to give you a demonstration of how the human brain is very special indeed in the way we process visual information. Let's begin with the moth. You've probably all been out on a summer evening and seen a whole swarm of moths circling around the street light. You might have even wondered why they're doing that, or you might not of. It might just be something that seems a little bit curious. But back in the day when we hadn't messed things up quite so much, on this planet. Before Thomas Edison invented his famous light bulb and things like that. Life for the month was pretty easy. The moth would go out at night and pick out some light source, most likely the moon and the moon is over the moth's right wing here. And it goes out an goes to work and do whatever moths do and then turns around put the moon over the left wing. And comes back unerringly to home, works like a charm. But now when the moth goes out and sees the brightest object in the sky which is a street lamp, puts that over its right wing, it ends up with an ever decreasing spiral until it's going round and round and round and round, and usually dies there at the street light. Well that's kind of stupid isn't it? Why doesn't the moth just figure out that that's not an appropriate aid to navigation and do something different. Well, that's because the moth's brain is so small that you can't really see it with the naked eye. It can't really process that kind of information. There is a famous experiment that was done with frogs, entitled what the frog's eye tells the frog's brain. Basically these researchers monitored the fibers going in from the frog's eye to the frog's brain, and they found out that the frog has some pretty basic systems built into the eye of the frog. And one of them was just the ability to see a line of contrast and maintain its orientation, so it's really kind of a horizon detector, if you will. Just a simple system in the neurons that connect the visual receptors in the eye. The frog also has a dimming detector, so if the frog is sitting there on its lily pad or whatever and all of a sudden a shadow swoops across, it's a good chance that shadow might be some bird of prey like the green-backed heron, here holding a frog in its mouth. And the frog then has the opportunity to escape from that predator. And the one most famous, of course, is the frog's ability to see a small dark object that's moving and flip out its tongue and catch it for its lunch. If you give a frog a bowl full of freeze dried flies that are dead it will starve to death because it doesn't know how to eat, a fly that doesn't move. If you put that fly on a little string and wiggled it in front, it'll catch it and eat it. So some pretty basic simples that worked like a charm for the frog, and it's pretty much all taken care of in the eye, and the eye then tells the brain what's going on out there? Now let's move to the little chick. One of the things that a chick has to do right away after it hatches is learn to peck at seeds and eat. How good are they at that? Well, a psychologist asked that question and the way he asked it was to take a little block of paraffin and to anchor a seed in the middle of some seeds that were loose. Can't see that anchor very well, I'll put a little mark on it there. And on the first day or two, after the chick has hatched, it will peck all around that, not being terribly accurate in hitting that seed. But now look what happens after about a week, the chick has become a much better marksman, and has developed eye-beak coordination, and can just zero right in on that. Cool, and you can all imagine how the chick is doing that because you all have at one time or another done some sort of a target practice, whether it's a bean toss or a bow and arrow or whatever, and you get better at it through practice. Now look at this, Professor Hess put goggles on the little chick, and they're not just any ordinary goggles, they're goggles that shift the chick's vision about 15 degrees to one side. And now we'll put a little marker on it again, this is the target and the poor little chick with his vision shifted, pecks about 15 degrees off to the side all around out here where the seed isn't. And over the course of a week, and I know this is hard to get your head around, but over the course of the week the chick, just like it did up here, develops much better eye-beak coordination and is pecking in a very tight pattern, not where the seed is. And the chick will never learn to adjust its pecking. It's just the way the chick is wired up. If the vision is distorted and goes over here, then that's just the way it is and it doesn't have the capability of making that correction. Now you have all probably in one of your seventh grade science classes or something, seen the little demonstration where you plunge a yard stick into an aquarium and it looks like the stick bends where it goes into the water because of the different refractive indexes. And when you look at a fish in the water, where you see it is not where it is, and countless people who have decided they'd like to eat fish and want to spear them, have learned to throw the spear where the fish doesn't appear to be so they can have it for lunch. The chick can't do that.
