Understanding Brain Complexity and Growth

The brain is wider than the sky, for put them side by side, the one the other will contain with ease, and you beside. The brain is deeper than the sea, for hold them blue to blue. The one the other will absorb, as sponges, buckets do. The brain is just the weight of God, for heft them pound for pound, and they will differ if they do. A syllable from sound. A baby's brain. Less than one pound of gelatinous tissue. And within its milky, convoluted folds, a universe of meaning. Emotions, ideas, memories, dreams, all will somehow find a home here, evolving and changing over a lifetime. The ultimate machine and the ultimate source of everything. We understand the world the way we do because of the brains we have. We will understand the brain itself the way we will because of the brains we have. Brain is the most complex thing on earth. Even the brain of a baby is wildly complicated. A piece of the brain the size of a grain of rice contains about 10,000 nerve cells just in that little piece you can just imagine how many pieces you have in your head within that 10,000 nerve cells each nerve cell can make anywhere between one to ten thousand connections with other nerve cells So there are something like a trillion connections. It's almost overwhelming to think about the whole thing. If you think about how the whole brain and nervous system gets assembled, you know, you just want to throw up your hands and say, it's way too complicated, we're never going to understand it. The brain is the seat of our consciousness, of who we are. And in understanding where it comes from, we understand where we come from. Elizabeth Traphagen was born less than two weeks ago, three months before she was expected, three months before she was ready to meet the world. She was 28 weeks and six days. She weighed three pounds and she was 14 inches long. It was somewhat frightening not knowing what a preemie would look like. It's something you don't expect. You're suddenly in this medical world rather than the world of taking your baby home and trying to figure out how to dress it and change its diaper. Elizabeth is a healthy, premature baby. Her lungs actively suck in the air. Her heart beats on its own. But the one organ central to all the others is not fully prepared. Her brain. The miracle technologies of modern medicine can help keep Elizabeth alive. But 12 critical weeks of brain development must now continue outside the protective walls of the womb. When the baby comes out of the womb, everything changes. Suddenly light, suddenly sharp sounds. The brain reacts to the stimulation. It can't filter, it can't stop, it can't shut it out. They survive and make the best of it. Yet what's the cost? The brain of a baby born three months later. premature is vulnerable many precious weeks of development still remain billions of brain cells are not done forging links with billions of other brain cells Eventually, there will be trillions and trillions of connections between cells, charged with electrical pulses rippling like lightning storms across the hills and valleys of the brain's deeply furrowed tissue. Every cell in its place, every link between cells carefully organized. Nothing random, nothing arbitrary. What we would really love to understand is how the brain during development generates millions and millions of neurons, sends them to the right position in the brain, and then somehow instructs each of those individual nerve cells to form very very specific connections with one another. You can think about development like a play. A play that follows a script that is written down by the genetic code, but it has no director, it has no producer, and it has a bunch of actors that have never spoken their lines before. Despite all this, you pull the play off. To me, that's a miracle. Egg and sperm, their union forms a single cell, which will divide and divide and divide again. Within three weeks the multiplying cells have curled into a quivering oval ball. Inside lies a cluster of cells that have begun to fold themselves into the shape of a garden hose. The neural tube. From the bottom will come the spinal cord. From the top, The brain. Here lies the primitive beginning of all our thoughts and feelings. By four weeks, just as a woman is discovering she is pregnant, the first brain cells, the neurons, are already forming at an astonishing rate. 500,000 neurons every minute. Neurons that will never reproduce themselves. and rarely be replaced. And that's amazing, because if you think about it, most cells in your body turn over. If you think about your skin, you're constantly, it's sort of disgusting, you're constantly sloughing off dead skin cells. And someone calculated once that if you look at the turnover of skin across a lifetime, you're probably generating and shedding about 90 pounds of skin. So most cells in the body do their thing. And then they die and they're replaced. Neurons are born in fetal life, and then those very cells are the ones that are still functioning all the way into old age. As the tiny fetus grows, the neurons make their way out from inside the neural tube to build the brain, layer upon layer, like an onion. The neurons follow a cellular pathway as if they were traveling down a highway. They just grab hold of supporting cells called glia and propel themselves along. They put their nucleus in the back of the cell which makes them sort of fat in the back and then they hold on to the guide wire this glial fiber. So it's kind of like an inchworm as it moves along and each little cell goes all by itself. in what is a very, very vulnerable process. No other kind of cell has to do that. It's just an amazing thing. Neurons travel in waves, millions every day embarking on a daunting expedition that scientists call migration. It's an amazing phenomenon because it's as if they're going across the country, I mean, in terms of the distances relative to their size. They're making a huge odyssey through all kinds of foreign territory. And the most amazing thing about this migration is that they generally do it without mistakes. They're following cues along the way that are telling them to do it. ...telling them exactly where to go. For years, scientists wondered how the migrating neurons find their place in the brain. Do the neurons simply travel in herds, gliding down a glial highway which takes them to their final destination? Or do neurons do their own driving? Each neuron genetically programmed to fulfill its own predetermined purpose. We used to think that migration was just like delivering cells out a conveyor belt. And you just dump out the cells at the end. But now we know that's not the case. There's evidence that shows that... young neurons have an idea about where they're migrating to and that they can recognize their position within the brain. In her laboratory at Stanford University, neurobiologist Susan McConnell devised a series of experiments to track the destiny of a migrating neuron. Neurons are born from the division of stem cells, the seeds from which the tissues of the body grow. Some stem cells can transform themselves into any kind of cell blood, skin, heart, bone, or brain cell. McConnell took a descendant of a stem cell, and before it morphed into a neuron, transplanted it into a developing brain. Then watched it migrate. She found that the fate of the soon-to-become neuron was determined by the neurons that were its neighbors. It traveled beside them and took on the same function they did. That cell is plastic. It's still listening to signals from the outside. It gets the instructions from the new neighbors, and it resets its fate. It says, yeah, sure, I can do that too. But when McConnell transplanted a neuron, it was true to its own genetic destiny. It followed its own path and took on an entirely different function from the cells surrounding it. What this result tells us is that by the time a young neuron begins its migration, it has already received instructions about what to become. It knows! It goes into a new environment, and even though everyone else in the brain, all these other young neurons, are going to position A, it says, no, no, I'm supposed to go to position B, and that's exactly what it does. By 24 weeks... The vital organs of the fetus are well formed. The primitive heart can beat on its own. The once powerless lungs are now prepared to fill with air. And the brain has nearly its full complement of billions and billions of neurons. Reaching out to each other, building connections with mind-boggling speed. Nearly two million every second, until the brain has become a tightly packed network of trillions of criss-crossing wires. with more connections than stars in the sky. You can imagine the size of the wiring problem. So how is that problem solved? How is that achieved during development? How is it that each one of those trillion connections is made appropriately? You might think, oh, what a mess. It's just going to be a jumble of connections and wires all over the place. But in fact, the nervous system... Seems to have a strategy. The strategy is in the genes. The brain begins to wire itself by following a precisely specified genetic blueprint. The connections are following very defined rules. You know, go out of the eye, turn right at the optic chiasm, cross the chiasm, head toward the lateral geniculate nucleus. Grow into the lateral geniculate nucleus. Don't grow into the medial geniculate nucleus because that's an auditory structure. So you can imagine the first stage of brain wiring is kind of like solving the problem of connecting phones in New York to phones in Boston. Making sure that you're making connections between Boston and New York and not Boston and Washington, D.C. And that's all specified genetically. Now then there's a second phase of brain wiring. Let's say you want to place a phone call to your grandmother in New York, and you want that phone to ring, you know, on Park Avenue and 47th or whatever. You don't want the phone to ring up at the Waldorf Astoria. Okay, how do you get that precise phone to ring? That's the second phase of... If you place a phone call to your grandmother early in development, her phone will ring, but so will a lot of other phones. So there are a lot of connections that are made. If the connections are correct and being used, they get strengthened. If they're not being used, or they're only being used occasionally, they're lost. We could call it use it or lose it. So the fetal brain is really a dynamic structure that's constantly... changing in response to this process of strengthening appropriate connections and pruning inappropriate connections. Getting the circuits all tuned up takes a long time so it can't happen overnight because you have literally billions of connections to check. When a child is born prematurely, the process is only partly over. So a huge amount of brain wiring is having to happen in the nursery. At Brigham and Women's Hospital in Boston, two-week-old Elizabeth Traphagen, born three months premature, must cope with the world before her brain is ready. For more than two decades, developmental psychologist Haidelise Ahls has been studying preemies like Elizabeth to learn how their fragile brains, accustomed to the muffled darkness of the womb, adapt to the dazzle and buzz of the world. How does the difference of inputs, of sound, of light shape how the brain grows itself? All those cells haven't yet laid down their... They're connective tissue. They're telephone wires, if you will, but it's much more active than that. It's like a wire that grows itself. So it's dynamic. It's biological. It's not like the heart. hardware in your computer that you put in but it depends on what it's experiencing on the way it grows thanks to the technological wonders of the modern intensive care unit most premature babies survive nearly half will have difficulties later in life difficulty paying attention difficulty learning they will have trouble with planning imposing structure prioritizing as they grow up they appear as very bright children and they are yet they can't hold their own in the second grade classroom and her research team believe that the glare and clamor of the intensive care unit itself is part of the problem. In the early days, just having these children survive was a miracle. We referred to children who made it on their own as miracle babies. Now miracles are becoming more common. In fact, it's more or less an expectation that a premature infant will live. Then we've discovered that that may not be enough. We've got to go astray. step further and ask ourselves despite our very best efforts medically they aren't quite comparable to full-term infants why this premature birth shaped the brain in ways that nature never intended for the next eight years Elizabeth will be part of an unprecedented study EEGs will record her brain's electrical impulses. Magnetic resonance images reveal her brain's ...hidden structures. Yeah, it's bright in here for you. I know. We may be able to do something about that. Elizabeth doesn't know it yet, but Haidelise Ahls has now become part of her life. The brain is faced with more challenges than the brain would be faced in the womb. In the womb she doesn't get food directly into her stomach. She gets food via the digestive system of the mother. And she isn't lying in a bed. She has all that support. And she doesn't have to breathe on her own. The mother's whole body takes care of it. The preterm can see, they hear, yet they can't manage themselves in the same way that a full-term child does. Can I move you a little bit? That's too bad. They will be much more hypersensitive, more easily overstimulated. Few impressions can be managed easily. They all go in and flood. So you have these big overreactive responses that cost the baby tremendously. So then you say, well, can I do something about it? I think I can't really see where you are. How are you doing there? I can't see your face. Can you see your face? Yeah, I can see. Is he okay? All right. Your nose isn't covered up or anything, so... Okay, here. Make it warm again. OZ has demonstrated that a carefully controlled environment tuned to a preemie's special needs will help them better manage the world around them as they grow. Elizabeth has spent her short life in an intensive care unit specially designed by ALS. Everything is gentle and slow, trying to be quiet with the baby. Trying to emulate the womb where she'd hear muffled sounds and it'd be dark. And then the skin-to-skin contact. She can hear my heart and that she's close to me. And it's nice because she does seem to recognize me. She settles down and finds her spot and settles in. And that's a great feeling when you're leaving her care up to people who are much more qualified for most of her daily life. It's nice to know that she knows who Mom is. The mother or father can do so much better in helping her be relaxed. The mother has the baby on the breast. That's what the brain, that's what the body of the baby, the nervous system, has been promised. The womb, the breast, the closeness of holding, the body of the parent, and the family, the social group that makes that family feel confident. Elizabeth was strong enough to go home when she was six weeks old. Now it's up to her parents to continue the gentle care begun in the hospital. Welcome home. She'll be going back to see Dr. Ahles in two months. Just after she was supposed to have been born. ALS wants to compare Elizabeth's brain to the brains of other premature babies. Premies who spent the first days of their lives in a standard hospital intensive care unit. Will the special treatment Elizabeth received make a difference? How much influence does the world around her have on the world around us? have on the developing brain? To help answer that question, neuroscientists turned to a small animal, immortalized in a portrait by Leonardo da Vinci, over 500 years ago. The ferret. The most fundamental question in understanding how the brain develops has to be the interaction between nature and nurture. We know that the brain has different areas that do different things, such as the visual cortex at the back of the brain. or the auditory cortex in the middle of the brain. How do these areas get to be where they are and how do they do what they end up doing in the adult? How plastic is the brain? How flexible? Can nurture trump what nature intended? In a series of elegant experiments, neuroscientist Muriganka Sir restructured the brains of newborn ferrets. In the normal ferret, light striking the eye creates electrical waves that travel to the visual cortex. Suhr rewired the ferret's brain, hooking up the eyes to the auditory cortex, showering the hearing parts of the brain with electric waves generated by the light. We reasoned that if we can make the eyes to be able to see, visual inputs from the eye go to the auditory cortex that normally processes hearing. Would the hearing cortex now become like a visual cortex or a seeing cortex if it grew up? with vision rather than with audition. Would the hearing cortex now come to have the same circuits and connections that mark the visual cortex? If it doesn't, then nature or the genetic endowment is of the essence. If it does, then the inputs are important or nurture is important and the animal would see. By recording a series of images directly from the brains of his rewired ferrets, Sir provided evidence that the ferrets could see. With normal ferrets, the activity of the neurons in the visual cortex takes on a characteristic pinwheel shape. With the rewired ferrets, the auditory cortex describes a similar pinwheel design. The brain has been transformed, but not entirely. Instead of 20-20 vision, they will have, let's say, 20-60 vision, meaning that they see at 20 feet what a normal ferret would see at 60 feet. The characteristic pinwheel is still there, but it is less orderly. Slurred. Environment shapes the brain, but can't completely change genetic destiny. Our experiments demonstrate beautifully, I think, the interaction of nature and nurture. I believe that the environment writes on a developing brain, but does not write on a blank slate. There is a structure that comes about due to genes, which then is influenced further by the environment that the brain is developing in. Our experiments provide very clear evidence of the remarkable plasticity of the brain. Three weeks after the day she was supposed to have been born, Elizabeth's parents brought her back to see Haidel Isals at Children's Hospital in Boston. Does the brain's remarkable plasticity make preemies like Elizabeth especially vulnerable? Does an intensive care unit that mimics the womb have a demonstrable effect on the brain? Once again, Al's observed Elizabeth carefully. Elizabeth, my beautiful girl. Did we wake you up out of your sleep? Paige? That was great. The toy really captured our attention. She just brightened right up to it. And her eyebrows up and her eyes curious and her face shaped forward. And she followed very smoothly in all directions and up and... to the side and in the full arc. So that's wonderful for just about three weeks after due date. And she did very nicely with the light. So although that kept coming, she shut it. with just a little bit of breathing adjustment on her part in terms of her strength and all her reflex repertoire. She's symmetrical, she's strong, and she came to alertness. I mean, she's really come together. It's impressive. So overall, you've done a remarkable job in supporting her. It's not trivial. Elizabeth appeared to be doing well, but she was enlisted in another round of tests to learn if her behavior corresponded to measurable changes in her brain. No one has really done this before. It's only been recently that we've had the experience to say, is it possible that our intervention may actually be visible in terms of a change in physical development of brain parameters? Can we actually see it in the brain? It's still too early to draw conclusions. But we do know something about Elizabeth. Pictures from the MRI reveal normal brain maturation. And as for the results of her EEG... Oh, she's surpassed, caught up and surpassed what I would expect. It's a very nice, normal, exemplary, full-term EEG that I could put in a textbook as an example. To what can we attribute this? This will be the result of our study. As scientists, we have to be very cautious not to over-interpret individual cases. It's entirely possible that her improvement was through her own internal fortitude. that we were bit players in this great game of glowing up. On the other hand, we might have been very crucial. And we'll never know, because we can't wind the clock back and not do the intervention on her. So what we have to do is have a population where there is no intervention population with an intervention and compare them as a group. There will always be a star in the non-intervening group who comes through well and there will always be someone that we just couldn't help. But on the average is what we're looking for and that's what the scientific method is all about. Whatever the reason, Elizabeth is improving every day. Hi. Hi. Hi, how's my girl? And for her parents, that's enough. There's a great possibility for Elizabeth to have normal brain development. And that's just such a huge gift. My hope when she was born was that by the time she reached kindergarten age, people, she would just blend in with her class. But there seems to be a very good chance that on her first birthday, she will be starting to toddle like any other one-year-old, and that would be great. Premature or full term, every baby is faced with the same challenge. Wash and novel sights and sounds babies must begin to learn how to navigate a roiling sea of sensations There's a huge task in organizing the world it must be difficult, but the babies seem to do it They act like little scientists. They actively explore and construct a view of the world. And in that sense, they are parallel to what we as scientists do our entire lives and what all of us do as we try to negotiate a very complicated world that's constantly under change. Babies are exquisitely sensitive. A newborn can identify his mother's whispered coos, respond to the fragrance of her body, and the sweet taste of her milk, even recognize her face. When you're holding your baby and rocking him in your arms and peering down at him, your face happens to be the distance that babies like to look at most of all. And in fact, even by two days of age, a newborn baby can recognize his mother from sight alone. Now that's quite a remarkable ability for a baby that has a poorly developed eye and for a baby that has a poorly developed brain. Vision is the last of the senses to develop. With an immature eye sending wobbly signals to a still developing brain, it's no surprise that a baby looks out on a different world than an adult. What the baby is seeing then we think looks something like a faded photograph. If you take a photograph and sort of fade it out so that it's all washed out, and if you're looking at the faded photograph through a tube, then that is what the world would look like to a newborn baby. The fact that the baby doesn't see very well, in a sense, is very good for an immature brain. And that's because this immature brain cannot handle excess stimulation. So what the eye is doing is dampening down. that external stimulation making it something that the brain can handle much better but it's also important to remember that no matter how dampened down that stimulation is that's going into this very immature brain that stimulation is critical what happens if the brain doesn't get the stimulation it needs what if light falls upon the eye but never reaches its destination Holly McMillan is just five weeks old, a healthy, normal baby. But her right eye is clouded by a faulty lens, a cataract that must be removed at once, or she will never see like a normal child. On the day that she was born, we noticed that her eye, her right eye, didn't open as wide as her left eye. But in my family, I have a sister and my father that have an eye that's a little bit, just a little bit smaller than the other, so we didn't really think anything of it. But we were informed that we would have to have surgery to remove the lens. And what we hear, the sooner the better for the surgery, so hopefully it's soon enough. Basically this is, after all our discussions that we had before, this is the final form that just gives me permission to go ahead and do the right eye. Oh, I won't forget. For a baby, it's really urgent that we get in there. Because if a baby... has a cataract there the images that are supposed to be getting in those images which are critical for the brain to be able to develop its vision those images aren't getting there and as a result the brain is not getting the opportunity to experience vision and go through its normal visual development which allows it to eventually create the healthy normal vision that we all know when grandma has a cataract all of her connections between eye and brain have ...been formed years ago and they remain stable over time. So even if they're not used, they don't go away. But when your child has a cataract, it's the use it or lose it game that's being played during development. It's still a period of decision making and pruning of connections. In fact, even just one or two months of missing visual experience from birth can have permanent consequences. on the way that brain is wired up and on what that brain can do later on. See you soon, okay? Take good care of yourself. Excuse me. Okay, so there's the cataract right there inside the eye. I've just got a little bit of piece left here that I need to get rid of. Thank you. Now we're just going to slip this in. In the old days we used to do this under general anesthesia, but the nice thing about this lens is that it allows us to do it this way. Within a week of the operation, Holly's eye has healed, and Dr. Levin inserts a contact lens, which Holly will need for the rest of her life. her life. For the first time Holly's right eye is sending clear images to her brain. The key is if you just put your hand right underneath it you can feel the eyeball underneath, you'll be fine. All of a sudden it's as if the eye was open to the brain. It's the same as if the baby came out of the dark jet black womb and all of a sudden opened their eyes in a delivery room somewhere. But Holly's vision is still in danger. For at least five years, until her visual development stabilizes, she will have to wear a patch for most of her waking hours over her good left eye, or else her brain will never learn to use the right eye to see. If the good eye was not patched, there is no point in... having the surgery at all there's no point in having the contact lens you have this weak eye that has to fight for cortical connections with a totally normal strong good eye and that totally normal strong good eye if allowed will take over all the brain space leave nothing for the deprived eye and the deprived eye will get weaker and weaker sounds a little counterintuitive patching the good eye should cause the same problem that the cataract did but in fact it doesn't and we really don't understand why that is and you can patch that good eye intensely and virtually never see any adverse effect of that that's one of our mysteries now daddy if you'll just shut your eyes as I show you you each one of these cards. Holly's cataract has been removed. But how well can Holly see? Okay, we got one beautiful look over there. Just minutes after Holly receives her contact lens, psychologist Terry Lewis examines her vision by watching whether a finely calibrated series of patterns captures her attention. You can't play the game with your eyes closed. We find that even with intention, we can't see. minutes of first being able to see the baby can see as well as a normal newborn that tells us that the brain can mature up to some point without any visual experience up to the newborn levels because certainly there's no visual experience while the baby's in utero although cataract babies like Holly see as well as newborn babies they don't see as well as babies their own age but they catch up quickly it's shocking how quickly vision improves after that contact lens is put in. We found that within one hour we have a significant improvement. in how well the babies can see now why this is so exciting is because it tells us that although the brain is no better than that of a normal newborn in the absence of visual experience once it gets that visual experience it's ready to go it's champing at the bit because that first little bit even that first hour of visual experience is going to send that brain into action faster than it would in normal development. In a series of carefully controlled studies comparing normal babies to cataract babies, Lewis has found that as cataract babies grow, their vision continues to improve until they reach their first birthday. The children do begin falling behind after a year, but on average with early treatment and complying with doctor's instructions, the eye can end up being a totally good functioning eye. It has been seven months since Holly's surgery, and her parents have been diligently patching her good eye. Let's see how you're doing this time. Holly, here we go. Are you ready? Looking at me. That's a good girl. That was a nice, good look for me. Holly's vision is improving. Her cataract was removed early, in time for her developing brain to learn to see. Hello, Holly. The visual tapestry of the world will be fully hers for the rest of her life. Good girl. Yes, that was really good looking. When we are babies, our brains are more open to the shaping hand of experience than any time in our lives. In response to the demands of the world, the baby's brain sculpts itself. I think the brain of a baby is like a work in progress. We're not really building circuits from scratch anymore, we've done that. But now a baby's experience with the environment can refine the circuit and influence which connections are stabilized and which connections are lost. We really think of brain development as a continuum. Although large sections of wiring are permanent, development doesn't stop. It's not over. It keeps on going as we grow older. It doesn't ever stop. And in fact, at the end of this program, your brain is going to be different from the way it was in the beginning because you've learned something and remembered something, hopefully. Or you've forgotten. But whatever you've done, it's different from the way it was before. Our brains are plastic. As babies grow and develop, their brains adapt to the world with a flexibility that is the hallmark of being human. There's great mystery left. Our memories and our hopes and our aspirations. and who we love and all of that is in there, encoded in the circuits. And we only have the barest beginnings of an understanding about how all of these things really work. The brain is just the weight of God. For heft them pound for pound, and they will differ, if they do, as syllable from sound. Join us for the next four episodes of The Secret Life of the Brain and follow the brain's remarkable journey through a lifetime. Childhood can be one of the most wonderful periods of all of life because we have everything to discover. The child's brain and the miracle of language. Ooh, bubbles! How does a child learn to talk? No, it's my way too. How about this one? And to read? Aaaaaah! What happens if something goes wrong? I have this, um, this thing in my brain that's called dyslexia. We clap our hands in the sanctuary. We clap our hands. Adolescence is the last great time of enormous brain change and brain development. The teenage brain is vulnerable to the dangers of drugs. I'm an addict, and I need help. And the chaos of schizophrenia. I spent 19 years with the same personality. all of a sudden it was taken away. We are not thinking machines, we are feeling machines that think. The adult brain, a fragile balance between thinking and feeling. Why do we have these emotions? What are they for? There's no empathy or sympathy. He just can't get that feeling. Deadness, terror, distorted time. I did not want to live. One weekend our daughter was here and he walked into the kitchen and he said, who are you? In its final decades the brain is faced with a new set of challenges. 63 years old and can't tie your own shoes? Isn't that ridiculous? But it marshals surprising powers of renewal. What makes the engine go desire, desire, desire? Take a 3D animated tour of the brain at PBS online. Find brain teasers, take a cognitive test and more at PBS.org. Major funding for The Secret Life of the Brain is provided by the National Science Foundation, America's investment in the future. Funding is also provided by... At Pfizer, we're spending nearly $5 billion looking for the cures of the future. We have 12,000 scientists and health experts who firmly believe the only thing incurable is our passion. Pfizer. Life is our life's work. The Medtronic Foundation, on behalf of Medtronic. Providing lifelong solutions for people with chronic disease. Medtronic. When life depends on medical technology. The Park Foundation. Dedicated to education and quality television. The Dana Foundation. The Corporation for Public Broadcasting and by contributions to your PBS station from viewers like you. Thank you.

A syllable from sound. A baby's brain. Less than one pound of gelatinous tissue.

And within its milky, convoluted folds, a universe of meaning. Emotions, ideas, memories, dreams, all will somehow find a home here, evolving and changing over a lifetime. The ultimate machine and the ultimate source of everything.

We understand the world the way we do because of the brains we have. We will understand the brain itself the way we will because of the brains we have. Brain is the most complex thing on earth. Even the brain of a baby is wildly complicated.

A piece of the brain the size of a grain of rice contains about 10,000 nerve cells just in that little piece you can just imagine how many pieces you have in your head within that 10,000 nerve cells each nerve cell can make anywhere between one to ten thousand connections with other nerve cells So there are something like a trillion connections. It's almost overwhelming to think about the whole thing. If you think about how the whole brain and nervous system gets assembled, you know, you just want to throw up your hands and say, it's way too complicated, we're never going to understand it. The brain is the seat of our consciousness, of who we are.

And in understanding where it comes from, we understand where we come from. Elizabeth Traphagen was born less than two weeks ago, three months before she was expected, three months before she was ready to meet the world. She was 28 weeks and six days.

She weighed three pounds and she was 14 inches long. It was somewhat frightening not knowing what a preemie would look like. It's something you don't expect.

You're suddenly in this medical world rather than the world of taking your baby home and trying to figure out how to dress it and change its diaper. Elizabeth is a healthy, premature baby. Her lungs actively suck in the air. Her heart beats on its own. But the one organ central to all the others is not fully prepared.

Her brain. The miracle technologies of modern medicine can help keep Elizabeth alive. But 12 critical weeks of brain development must now continue outside the protective walls of the womb.

When the baby comes out of the womb, everything changes. Suddenly light, suddenly sharp sounds. The brain reacts to the stimulation.

It can't filter, it can't stop, it can't shut it out. They survive and make the best of it. Yet what's the cost? The brain of a baby born three months later. premature is vulnerable many precious weeks of development still remain billions of brain cells are not done forging links with billions of other brain cells Eventually, there will be trillions and trillions of connections between cells, charged with electrical pulses rippling like lightning storms across the hills and valleys of the brain's deeply furrowed tissue.

Every cell in its place, every link between cells carefully organized. Nothing random, nothing arbitrary. What we would really love to understand is how the brain during development generates millions and millions of neurons, sends them to the right position in the brain, and then somehow instructs each of those individual nerve cells to form very very specific connections with one another.

You can think about development like a play. A play that follows a script that is written down by the genetic code, but it has no director, it has no producer, and it has a bunch of actors that have never spoken their lines before. Despite all this, you pull the play off. To me, that's a miracle.

Egg and sperm, their union forms a single cell, which will divide and divide and divide again. Within three weeks the multiplying cells have curled into a quivering oval ball. Inside lies a cluster of cells that have begun to fold themselves into the shape of a garden hose.

The neural tube. From the bottom will come the spinal cord. From the top, The brain.

Here lies the primitive beginning of all our thoughts and feelings. By four weeks, just as a woman is discovering she is pregnant, the first brain cells, the neurons, are already forming at an astonishing rate. 500,000 neurons every minute.

Neurons that will never reproduce themselves. and rarely be replaced. And that's amazing, because if you think about it, most cells in your body turn over. If you think about your skin, you're constantly, it's sort of disgusting, you're constantly sloughing off dead skin cells. And someone calculated once that if you look at the turnover of skin across a lifetime, you're probably generating and shedding about 90 pounds of skin.

So most cells in the body do their thing. And then they die and they're replaced. Neurons are born in fetal life, and then those very cells are the ones that are still functioning all the way into old age.

As the tiny fetus grows, the neurons make their way out from inside the neural tube to build the brain, layer upon layer, like an onion. The neurons follow a cellular pathway as if they were traveling down a highway. They just grab hold of supporting cells called glia and propel themselves along.

They put their nucleus in the back of the cell which makes them sort of fat in the back and then they hold on to the guide wire this glial fiber. So it's kind of like an inchworm as it moves along and each little cell goes all by itself. in what is a very, very vulnerable process. No other kind of cell has to do that.

It's just an amazing thing. Neurons travel in waves, millions every day embarking on a daunting expedition that scientists call migration. It's an amazing phenomenon because it's as if they're going across the country, I mean, in terms of the distances relative to their size. They're making a huge odyssey through all kinds of foreign territory. And the most amazing thing about this migration is that they generally do it without mistakes.

They're following cues along the way that are telling them to do it. ...telling them exactly where to go. For years, scientists wondered how the migrating neurons find their place in the brain. Do the neurons simply travel in herds, gliding down a glial highway which takes them to their final destination?

Or do neurons do their own driving? Each neuron genetically programmed to fulfill its own predetermined purpose. We used to think that migration was just like delivering cells out a conveyor belt.

And you just dump out the cells at the end. But now we know that's not the case. There's evidence that shows that... young neurons have an idea about where they're migrating to and that they can recognize their position within the brain. In her laboratory at Stanford University, neurobiologist Susan McConnell devised a series of experiments to track the destiny of a migrating neuron.

Neurons are born from the division of stem cells, the seeds from which the tissues of the body grow. Some stem cells can transform themselves into any kind of cell blood, skin, heart, bone, or brain cell. McConnell took a descendant of a stem cell, and before it morphed into a neuron, transplanted it into a developing brain. Then watched it migrate.

She found that the fate of the soon-to-become neuron was determined by the neurons that were its neighbors. It traveled beside them and took on the same function they did. That cell is plastic.

It's still listening to signals from the outside. It gets the instructions from the new neighbors, and it resets its fate. It says, yeah, sure, I can do that too.

But when McConnell transplanted a neuron, it was true to its own genetic destiny. It followed its own path and took on an entirely different function from the cells surrounding it. What this result tells us is that by the time a young neuron begins its migration, it has already received instructions about what to become.

It knows! It goes into a new environment, and even though everyone else in the brain, all these other young neurons, are going to position A, it says, no, no, I'm supposed to go to position B, and that's exactly what it does. By 24 weeks... The vital organs of the fetus are well formed.

The primitive heart can beat on its own. The once powerless lungs are now prepared to fill with air. And the brain has nearly its full complement of billions and billions of neurons. Reaching out to each other, building connections with mind-boggling speed.

Nearly two million every second, until the brain has become a tightly packed network of trillions of criss-crossing wires. with more connections than stars in the sky. You can imagine the size of the wiring problem. So how is that problem solved?

How is that achieved during development? How is it that each one of those trillion connections is made appropriately? You might think, oh, what a mess.

It's just going to be a jumble of connections and wires all over the place. But in fact, the nervous system... Seems to have a strategy.

The strategy is in the genes. The brain begins to wire itself by following a precisely specified genetic blueprint. The connections are following very defined rules.

You know, go out of the eye, turn right at the optic chiasm, cross the chiasm, head toward the lateral geniculate nucleus. Grow into the lateral geniculate nucleus. Don't grow into the medial geniculate nucleus because that's an auditory structure. So you can imagine the first stage of brain wiring is kind of like solving the problem of connecting phones in New York to phones in Boston. Making sure that you're making connections between Boston and New York and not Boston and Washington, D.C. And that's all specified genetically.

Now then there's a second phase of brain wiring. Let's say you want to place a phone call to your grandmother in New York, and you want that phone to ring, you know, on Park Avenue and 47th or whatever. You don't want the phone to ring up at the Waldorf Astoria. Okay, how do you get that precise phone to ring?

That's the second phase of... If you place a phone call to your grandmother early in development, her phone will ring, but so will a lot of other phones. So there are a lot of connections that are made.

If the connections are correct and being used, they get strengthened. If they're not being used, or they're only being used occasionally, they're lost. We could call it use it or lose it. So the fetal brain is really a dynamic structure that's constantly...

changing in response to this process of strengthening appropriate connections and pruning inappropriate connections. Getting the circuits all tuned up takes a long time so it can't happen overnight because you have literally billions of connections to check. When a child is born prematurely, the process is only partly over.

So a huge amount of brain wiring is having to happen in the nursery. At Brigham and Women's Hospital in Boston, two-week-old Elizabeth Traphagen, born three months premature, must cope with the world before her brain is ready. For more than two decades, developmental psychologist Haidelise Ahls has been studying preemies like Elizabeth to learn how their fragile brains, accustomed to the muffled darkness of the womb, adapt to the dazzle and buzz of the world.

How does the difference of inputs, of sound, of light shape how the brain grows itself? All those cells haven't yet laid down their... They're connective tissue.

They're telephone wires, if you will, but it's much more active than that. It's like a wire that grows itself. So it's dynamic. It's biological.

It's not like the heart. hardware in your computer that you put in but it depends on what it's experiencing on the way it grows thanks to the technological wonders of the modern intensive care unit most premature babies survive nearly half will have difficulties later in life difficulty paying attention difficulty learning they will have trouble with planning imposing structure prioritizing as they grow up they appear as very bright children and they are yet they can't hold their own in the second grade classroom and her research team believe that the glare and clamor of the intensive care unit itself is part of the problem. In the early days, just having these children survive was a miracle.

We referred to children who made it on their own as miracle babies. Now miracles are becoming more common. In fact, it's more or less an expectation that a premature infant will live. Then we've discovered that that may not be enough.

We've got to go astray. step further and ask ourselves despite our very best efforts medically they aren't quite comparable to full-term infants why this premature birth shaped the brain in ways that nature never intended for the next eight years Elizabeth will be part of an unprecedented study EEGs will record her brain's electrical impulses. Magnetic resonance images reveal her brain's ...hidden structures.

Yeah, it's bright in here for you. I know. We may be able to do something about that. Elizabeth doesn't know it yet, but Haidelise Ahls has now become part of her life.

The brain is faced with more challenges than the brain would be faced in the womb. In the womb she doesn't get food directly into her stomach. She gets food via the digestive system of the mother.

And she isn't lying in a bed. She has all that support. And she doesn't have to breathe on her own.

The mother's whole body takes care of it. The preterm can see, they hear, yet they can't manage themselves in the same way that a full-term child does. Can I move you a little bit? That's too bad.

They will be much more hypersensitive, more easily overstimulated. Few impressions can be managed easily. They all go in and flood.

So you have these big overreactive responses that cost the baby tremendously. So then you say, well, can I do something about it? I think I can't really see where you are.

How are you doing there? I can't see your face. Can you see your face?

Yeah, I can see. Is he okay? All right. Your nose isn't covered up or anything, so... Okay, here.

Make it warm again. OZ has demonstrated that a carefully controlled environment tuned to a preemie's special needs will help them better manage the world around them as they grow. Elizabeth has spent her short life in an intensive care unit specially designed by ALS.

Everything is gentle and slow, trying to be quiet with the baby. Trying to emulate the womb where she'd hear muffled sounds and it'd be dark. And then the skin-to-skin contact. She can hear my heart and that she's close to me.

And it's nice because she does seem to recognize me. She settles down and finds her spot and settles in. And that's a great feeling when you're leaving her care up to people who are much more qualified for most of her daily life. It's nice to know that she knows who Mom is.

The mother or father can do so much better in helping her be relaxed. The mother has the baby on the breast. That's what the brain, that's what the body of the baby, the nervous system, has been promised. The womb, the breast, the closeness of holding, the body of the parent, and the family, the social group that makes that family feel confident. Elizabeth was strong enough to go home when she was six weeks old.

Now it's up to her parents to continue the gentle care begun in the hospital. Welcome home. She'll be going back to see Dr. Ahles in two months.

Just after she was supposed to have been born. ALS wants to compare Elizabeth's brain to the brains of other premature babies. Premies who spent the first days of their lives in a standard hospital intensive care unit. Will the special treatment Elizabeth received make a difference? How much influence does the world around her have on the world around us?

have on the developing brain? To help answer that question, neuroscientists turned to a small animal, immortalized in a portrait by Leonardo da Vinci, over 500 years ago. The ferret. The most fundamental question in understanding how the brain develops has to be the interaction between nature and nurture.

We know that the brain has different areas that do different things, such as the visual cortex at the back of the brain. or the auditory cortex in the middle of the brain. How do these areas get to be where they are and how do they do what they end up doing in the adult? How plastic is the brain?

How flexible? Can nurture trump what nature intended? In a series of elegant experiments, neuroscientist Muriganka Sir restructured the brains of newborn ferrets.

In the normal ferret, light striking the eye creates electrical waves that travel to the visual cortex. Suhr rewired the ferret's brain, hooking up the eyes to the auditory cortex, showering the hearing parts of the brain with electric waves generated by the light. We reasoned that if we can make the eyes to be able to see, visual inputs from the eye go to the auditory cortex that normally processes hearing. Would the hearing cortex now become like a visual cortex or a seeing cortex if it grew up? with vision rather than with audition.

Would the hearing cortex now come to have the same circuits and connections that mark the visual cortex? If it doesn't, then nature or the genetic endowment is of the essence. If it does, then the inputs are important or nurture is important and the animal would see.

By recording a series of images directly from the brains of his rewired ferrets, Sir provided evidence that the ferrets could see. With normal ferrets, the activity of the neurons in the visual cortex takes on a characteristic pinwheel shape. With the rewired ferrets, the auditory cortex describes a similar pinwheel design.

The brain has been transformed, but not entirely. Instead of 20-20 vision, they will have, let's say, 20-60 vision, meaning that they see at 20 feet what a normal ferret would see at 60 feet. The characteristic pinwheel is still there, but it is less orderly. Slurred. Environment shapes the brain, but can't completely change genetic destiny.

Our experiments demonstrate beautifully, I think, the interaction of nature and nurture. I believe that the environment writes on a developing brain, but does not write on a blank slate. There is a structure that comes about due to genes, which then is influenced further by the environment that the brain is developing in.

Our experiments provide very clear evidence of the remarkable plasticity of the brain. Three weeks after the day she was supposed to have been born, Elizabeth's parents brought her back to see Haidel Isals at Children's Hospital in Boston. Does the brain's remarkable plasticity make preemies like Elizabeth especially vulnerable? Does an intensive care unit that mimics the womb have a demonstrable effect on the brain? Once again, Al's observed Elizabeth carefully.

Elizabeth, my beautiful girl. Did we wake you up out of your sleep? Paige?

That was great. The toy really captured our attention. She just brightened right up to it. And her eyebrows up and her eyes curious and her face shaped forward. And she followed very smoothly in all directions and up and...

to the side and in the full arc. So that's wonderful for just about three weeks after due date. And she did very nicely with the light. So although that kept coming, she shut it.

with just a little bit of breathing adjustment on her part in terms of her strength and all her reflex repertoire. She's symmetrical, she's strong, and she came to alertness. I mean, she's really come together.

It's impressive. So overall, you've done a remarkable job in supporting her. It's not trivial. Elizabeth appeared to be doing well, but she was enlisted in another round of tests to learn if her behavior corresponded to measurable changes in her brain.

No one has really done this before. It's only been recently that we've had the experience to say, is it possible that our intervention may actually be visible in terms of a change in physical development of brain parameters? Can we actually see it in the brain? It's still too early to draw conclusions.

But we do know something about Elizabeth. Pictures from the MRI reveal normal brain maturation. And as for the results of her EEG... Oh, she's surpassed, caught up and surpassed what I would expect.

It's a very nice, normal, exemplary, full-term EEG that I could put in a textbook as an example. To what can we attribute this? This will be the result of our study. As scientists, we have to be very cautious not to over-interpret individual cases.

It's entirely possible that her improvement was through her own internal fortitude. that we were bit players in this great game of glowing up. On the other hand, we might have been very crucial.

And we'll never know, because we can't wind the clock back and not do the intervention on her. So what we have to do is have a population where there is no intervention population with an intervention and compare them as a group. There will always be a star in the non-intervening group who comes through well and there will always be someone that we just couldn't help. But on the average is what we're looking for and that's what the scientific method is all about.

Whatever the reason, Elizabeth is improving every day. Hi. Hi. Hi, how's my girl? And for her parents, that's enough.

There's a great possibility for Elizabeth to have normal brain development. And that's just such a huge gift. My hope when she was born was that by the time she reached kindergarten age, people, she would just blend in with her class. But there seems to be a very good chance that on her first birthday, she will be starting to toddle like any other one-year-old, and that would be great.

Premature or full term, every baby is faced with the same challenge. Wash and novel sights and sounds babies must begin to learn how to navigate a roiling sea of sensations There's a huge task in organizing the world it must be difficult, but the babies seem to do it They act like little scientists. They actively explore and construct a view of the world. And in that sense, they are parallel to what we as scientists do our entire lives and what all of us do as we try to negotiate a very complicated world that's constantly under change. Babies are exquisitely sensitive.

A newborn can identify his mother's whispered coos, respond to the fragrance of her body, and the sweet taste of her milk, even recognize her face. When you're holding your baby and rocking him in your arms and peering down at him, your face happens to be the distance that babies like to look at most of all. And in fact, even by two days of age, a newborn baby can recognize his mother from sight alone.

Now that's quite a remarkable ability for a baby that has a poorly developed eye and for a baby that has a poorly developed brain. Vision is the last of the senses to develop. With an immature eye sending wobbly signals to a still developing brain, it's no surprise that a baby looks out on a different world than an adult. What the baby is seeing then we think looks something like a faded photograph.

If you take a photograph and sort of fade it out so that it's all washed out, and if you're looking at the faded photograph through a tube, then that is what the world would look like to a newborn baby. The fact that the baby doesn't see very well, in a sense, is very good for an immature brain. And that's because this immature brain cannot handle excess stimulation. So what the eye is doing is dampening down.

that external stimulation making it something that the brain can handle much better but it's also important to remember that no matter how dampened down that stimulation is that's going into this very immature brain that stimulation is critical what happens if the brain doesn't get the stimulation it needs what if light falls upon the eye but never reaches its destination Holly McMillan is just five weeks old, a healthy, normal baby. But her right eye is clouded by a faulty lens, a cataract that must be removed at once, or she will never see like a normal child. On the day that she was born, we noticed that her eye, her right eye, didn't open as wide as her left eye.

But in my family, I have a sister and my father that have an eye that's a little bit, just a little bit smaller than the other, so we didn't really think anything of it. But we were informed that we would have to have surgery to remove the lens. And what we hear, the sooner the better for the surgery, so hopefully it's soon enough. Basically this is, after all our discussions that we had before, this is the final form that just gives me permission to go ahead and do the right eye. Oh, I won't forget.

For a baby, it's really urgent that we get in there. Because if a baby... has a cataract there the images that are supposed to be getting in those images which are critical for the brain to be able to develop its vision those images aren't getting there and as a result the brain is not getting the opportunity to experience vision and go through its normal visual development which allows it to eventually create the healthy normal vision that we all know when grandma has a cataract all of her connections between eye and brain have ...been formed years ago and they remain stable over time. So even if they're not used, they don't go away.

But when your child has a cataract, it's the use it or lose it game that's being played during development. It's still a period of decision making and pruning of connections. In fact, even just one or two months of missing visual experience from birth can have permanent consequences.

on the way that brain is wired up and on what that brain can do later on. See you soon, okay? Take good care of yourself. Excuse me. Okay, so there's the cataract right there inside the eye.

I've just got a little bit of piece left here that I need to get rid of. Thank you. Now we're just going to slip this in. In the old days we used to do this under general anesthesia, but the nice thing about this lens is that it allows us to do it this way. Within a week of the operation, Holly's eye has healed, and Dr. Levin inserts a contact lens, which Holly will need for the rest of her life.

her life. For the first time Holly's right eye is sending clear images to her brain. The key is if you just put your hand right underneath it you can feel the eyeball underneath, you'll be fine. All of a sudden it's as if the eye was open to the brain. It's the same as if the baby came out of the dark jet black womb and all of a sudden opened their eyes in a delivery room somewhere.

But Holly's vision is still in danger. For at least five years, until her visual development stabilizes, she will have to wear a patch for most of her waking hours over her good left eye, or else her brain will never learn to use the right eye to see. If the good eye was not patched, there is no point in... having the surgery at all there's no point in having the contact lens you have this weak eye that has to fight for cortical connections with a totally normal strong good eye and that totally normal strong good eye if allowed will take over all the brain space leave nothing for the deprived eye and the deprived eye will get weaker and weaker sounds a little counterintuitive patching the good eye should cause the same problem that the cataract did but in fact it doesn't and we really don't understand why that is and you can patch that good eye intensely and virtually never see any adverse effect of that that's one of our mysteries now daddy if you'll just shut your eyes as I show you you each one of these cards.

Holly's cataract has been removed. But how well can Holly see? Okay, we got one beautiful look over there. Just minutes after Holly receives her contact lens, psychologist Terry Lewis examines her vision by watching whether a finely calibrated series of patterns captures her attention. You can't play the game with your eyes closed.

We find that even with intention, we can't see. minutes of first being able to see the baby can see as well as a normal newborn that tells us that the brain can mature up to some point without any visual experience up to the newborn levels because certainly there's no visual experience while the baby's in utero although cataract babies like Holly see as well as newborn babies they don't see as well as babies their own age but they catch up quickly it's shocking how quickly vision improves after that contact lens is put in. We found that within one hour we have a significant improvement.

in how well the babies can see now why this is so exciting is because it tells us that although the brain is no better than that of a normal newborn in the absence of visual experience once it gets that visual experience it's ready to go it's champing at the bit because that first little bit even that first hour of visual experience is going to send that brain into action faster than it would in normal development. In a series of carefully controlled studies comparing normal babies to cataract babies, Lewis has found that as cataract babies grow, their vision continues to improve until they reach their first birthday. The children do begin falling behind after a year, but on average with early treatment and complying with doctor's instructions, the eye can end up being a totally good functioning eye.

It has been seven months since Holly's surgery, and her parents have been diligently patching her good eye. Let's see how you're doing this time. Holly, here we go.

Are you ready? Looking at me. That's a good girl.

That was a nice, good look for me. Holly's vision is improving. Her cataract was removed early, in time for her developing brain to learn to see.

Hello, Holly. The visual tapestry of the world will be fully hers for the rest of her life. Good girl. Yes, that was really good looking. When we are babies, our brains are more open to the shaping hand of experience than any time in our lives.

In response to the demands of the world, the baby's brain sculpts itself. I think the brain of a baby is like a work in progress. We're not really building circuits from scratch anymore, we've done that. But now a baby's experience with the environment can refine the circuit and influence which connections are stabilized and which connections are lost.

We really think of brain development as a continuum. Although large sections of wiring are permanent, development doesn't stop. It's not over. It keeps on going as we grow older.

It doesn't ever stop. And in fact, at the end of this program, your brain is going to be different from the way it was in the beginning because you've learned something and remembered something, hopefully. Or you've forgotten. But whatever you've done, it's different from the way it was before.

Our brains are plastic. As babies grow and develop, their brains adapt to the world with a flexibility that is the hallmark of being human. There's great mystery left. Our memories and our hopes and our aspirations.

and who we love and all of that is in there, encoded in the circuits. And we only have the barest beginnings of an understanding about how all of these things really work. The brain is just the weight of God.

For heft them pound for pound, and they will differ, if they do, as syllable from sound. Join us for the next four episodes of The Secret Life of the Brain and follow the brain's remarkable journey through a lifetime. Childhood can be one of the most wonderful periods of all of life because we have everything to discover.

The child's brain and the miracle of language. Ooh, bubbles! How does a child learn to talk? No, it's my way too. How about this one?

And to read? Aaaaaah! What happens if something goes wrong? I have this, um, this thing in my brain that's called dyslexia.

We clap our hands in the sanctuary. We clap our hands. Adolescence is the last great time of enormous brain change and brain development.

The teenage brain is vulnerable to the dangers of drugs. I'm an addict, and I need help. And the chaos of schizophrenia.

I spent 19 years with the same personality. all of a sudden it was taken away. We are not thinking machines, we are feeling machines that think. The adult brain, a fragile balance between thinking and feeling. Why do we have these emotions?

What are they for? There's no empathy or sympathy. He just can't get that feeling.

Deadness, terror, distorted time. I did not want to live. One weekend our daughter was here and he walked into the kitchen and he said, who are you?

In its final decades the brain is faced with a new set of challenges. 63 years old and can't tie your own shoes? Isn't that ridiculous? But it marshals surprising powers of renewal.

What makes the engine go desire, desire, desire? Take a 3D animated tour of the brain at PBS online. Find brain teasers, take a cognitive test and more at PBS.org. Major funding for The Secret Life of the Brain is provided by the National Science Foundation, America's investment in the future.

Funding is also provided by... At Pfizer, we're spending nearly $5 billion looking for the cures of the future. We have 12,000 scientists and health experts who firmly believe the only thing incurable is our passion.

Pfizer. Life is our life's work. The Medtronic Foundation, on behalf of Medtronic. Providing lifelong solutions for people with chronic disease. Medtronic.

When life depends on medical technology. The Park Foundation. Dedicated to education and quality television.

The Dana Foundation. The Corporation for Public Broadcasting and by contributions to your PBS station from viewers like you. Thank you.

Transcript for:Understanding Brain Complexity and Growth

Transcript for:
Understanding Brain Complexity and Growth