Subtitles section Play video Print subtitles This machine, which we all have residing in our skulls, reminds me of an aphorism, of a comment of Woody Allen to ask about what is the very best thing to have within your skull. And it's this machine. And it's constructed for change. It's all about change. It confers on us the ability to do things tomorrow that we can't do today, things today that we couldn't do yesterday. And of course it's born stupid. The last time you were in the presence of a baby -- this happens to be my granddaughter, Mitra. Isn't she fabulous? (Laughter) But nonetheless when she popped out despite the fact that her brain had actually been progressing in its development for several months before on the basis of her experiences in the womb -- nonetheless she had very limited abilities, as does every infant at the time of normal, natural full-term birth. If we were to assay her perceptual abilities, they would be crude. There is no real indication that there is any real thinking going on. In fact there is little evidence that there is any cognitive ability in a very young infant. Infants don't respond to much. There is not really much of an indication in fact that there is a person on board. (Laughter) And they can only in a very primitive way, and in a very limited way control their movements. It would be several months before this infant could do something as simple as reach out and grasp under voluntary control an object and retrieve it, usually to the mouth. And it will be some months beforeward, and we see a long steady progression of the evolution from the first wiggles, to rolling over, and sitting up, and crawling, standing, walking, before we get to that magical point in which we can motate in the world. And yet, when we look forward in the brain we see really remarkable advance. By this age the brain can actually store. It has stored, recorded, can fastly retrieve the meanings of thousands, tens of thousands of objects, actions, and their relationships in the world. And those relationships can in fact be constructed in hundreds of thousands, potentially millions of ways. By this age the brain controls very refined perceptual abilities. And it actually has a growing repertoire of cognitive skills. This brain is very much a thinking machine. And by this age there is absolutely no question that this brain, it has a person on board. And in fact at this age it is substantially controlling its own self-development. And by this age we see a remarkable evolution in its capacity to control movement. Now movement has advanced to the point where it can actually control movement simultaneously, in a complex sequence, in complex ways as would be required for example for playing a complicated game, like soccer. Now this boy can bounce a soccer ball on his head. And where this boy comes from, Sao Paulo, Brazil, about 40 percent of boys of his age have this ability. You could go out into the community in Monterey, and you'd have difficulty finding a boy that has this ability. And if you did he'd probably be from Sao Paulo. (Laughter) That's all another way of saying that our individual skills and abilities are very much shaped by our environments. That environment extends into our contemporary culture, the thing our brain is challenged with. Because what we've done in our personal evolutions is build up a large repertoire of specific skills and abilities that are specific to our own individual histories. And in fact they result in a wonderful differentiation in humankind, in the way that, in fact, no two of us are quite alike. Every one of us has a different set of acquired skills and abilities that all derive out of the plasticity, the adaptability of this really remarkable adaptive machine. In an adult brain of course we've built up a large repertoire of mastered skills and abilities that we can perform more or less automatically from memory, and that define us as acting, moving, thinking creatures. Now we study this, as the nerdy, laboratory, university-based scientists that we are, by engaging the brains of animals like rats, or monkeys, or of this particularly curious creature -- one of the more bizarre forms of life on earth -- to engage them in learning new skills and abilities. And we try to track the changes that occur as the new skill or ability is acquired. In fact we do this in individuals of any age, in these different species -- that is to say from infancies, infancy up to adulthood and old age. So we might engage a rat, for example, to acquire a new skill or ability that might involve the rat using its paw to master particular manual grasp behaviors just like we might examine a child and their ability to acquire the sub-skills, or the general overall skill of accomplishing something like mastering the ability to read. Or you might look in an older individual who has mastered a complex set of abilities that might relate to reading musical notation or performing the mechanical acts of performance that apply to musical performance. From these studies we defined two great epochs of the plastic history of the brain. The first great epoch is commonly called the "Critical Period." And that is the period in which the brain is setting up in its initial form its basic processing machinery. This is actually a period of dramatic change in which it doesn't take learning, per se, to drive the initial differentiation of the machinery of the brain. All it takes for example in the sound domain, is exposure to sound. And the brain actually is at the mercy of the sound environment in which it is reared. So for example I can rear an animal in an environment in which there is meaningless dumb sound, a repertoire of sound that I make up, that I make, just by exposure, artificially important to the animal and its young brain. And what I see is that the animal's brain sets up its initial processing of that sound in a form that's idealized, within the limits of its processing achievements to represent it in an organized and orderly way. The sound doesn't have to be valuable to the animal: I could raise the animal in something that could be hypothetically valuable, like the sounds that simulate the sounds of a native language of a child. And I see the brain actually develop a processor that is specialized -- specialized for that complex array, a repertoire of sounds. It actually exaggerates their separateness of representation, in multi-dimensional neuronal representational terms. Or I can expose the animal to a completely meaningless and destructive sound. I can raise an animal under conditions that would be equivalent to raising a baby under a moderately loud ceiling fan, in the presence of continuous noise. And when I do that I actually specialize the brain to be a master processor for that meaningless sound. And I frustrate its ability to represent any meaningful sound as a consequence. Such things in the early history of babies occur in real babies. And they account for, for example the beautiful evolution of a language-specific processor in every normally developing baby. And so they also account for development of defective processing in a substantial population of children who are more limited, as a consequence, in their language abilities at an older age. Now in this early period of plasticity the brain actually changes outside of a learning context. I don't have to be paying attention to what I hear. The input doesn't really have to be meaningful. I don't have to be in a behavioral context. This is required so the brain sets up it's processing so that it can act differentially, so that it can act selectively, so that the creature that wears it, that carries it, can begin to operate on it in a selective way. In the next great epoch of life, which applies for most of life, the brain is actually refining its machinery as it masters a wide repertoire of skills and abilities. And in this epoch, which extends from late in the first year of life to death; it's actually doing this under behavioral control. And that's another way of saying the brain has strategies that define the significance of the input to the brain. And it's focusing on skill after skill, or ability after ability, under specific attentional control. It's a function of whether a goal in a behavior is achieved or whether the individual is rewarded in the behavior. This is actually very powerful. This lifelong capacity for plasticity, for brain change, is powerfully expressed. It is the basis of our real differentiation, one individual from another. You can look down in the brain of an animal that's engaged in a specific skill, and you can witness or document this change on a variety of levels. So here is a very simple experiment. It was actually conducted about five years ago in collaboration with scientists from the University of Provence in Marseilles. It's a very simple experiment where a monkey has been trained in a task that involves it manipulating a tool that's equivalent in its difficulty to a child learning to manipulate or handle a spoon. The monkey actually mastered the task in about 700 practice tries. So in the beginning the monkey could not perform this task at all. It had a success rate of about one in eight tries. Those tries were elaborate. Each attempt was substantially different from the other. But the monkey gradually developed a strategy. And 700 or so tries later the monkey is performing it flawlessly -- never fails. He's successful in his retrieval of food with this tool every time. At this point the task is being performed in a beautifully stereotyped way: very beautifully regulated and highly repeated, trial to trial. We can look down in the brain of the monkey. And we see that it's distorted. We can track these changes, and have tracked these changes in many such behaviors across time. And here we see the distortion reflected in the map of the skin surfaces of the hand of the monkey. Now this is a map, down in the surface of the brain, in which, in a very elaborate experiment we've reconstructed the responses, location by location, in a highly detailed response mapping of the responses of its neurons. We see here a reconstruction of how the hand is represented in the brain. We've actually distorted the map by the exercise. And that is indicated in the pink. We have a couple fingertip surfaces that are larger. These are the surfaces the monkey is using to manipulate the tool. If we look at the selectivity of responses in the cortex of the monkey, we see that the monkey has actually changed the filter characteristics which represents input from the skin of the fingertips that are engaged. In other words there is still a single, simple representation of the fingertips in this most organized of cortical areas of the surface of the skin of the body. Monkey has like you have. And yet now it's represented in substantially finer grain. The monkey is getting more detailed information from these surfaces. And that is an unknown -- unsuspected, maybe, by you -- part of acquiring the skill or ability. Now actually we've looked in several different cortical areas in the monkey learning this task. And each one of them changes in ways that are specific to the skill or ability.