Livewired. David Eagleman

that shape. This is how the material we call plastic gets its name: we mold bowls, toys, and phones with it, and the material doesn’t melt uselessly back to its original form. And so it is with the brain: experience changes it, and it retains the change.

      “Brain plasticity” (also called neuroplasticity) is the term we use in neuroscience. But I’ll use that term only sparingly in this book, because it sometimes risks missing the target. Whether intentionally or not, “plasticity” suggests that the key idea is to mold something once and keep it that way forever: to shape the plastic toy and never change it again. But that’s not what the brain does. It carries on remolding itself throughout your life.

      Think of a developing city, and note the way it grows, optimizes, and responds to the world around it. Observe where the city builds its truck stops, how it crafts its immigration policies, how it modifies its education and legal systems. A city is always in flux. A city is not designed by urban planners and then immobilized like a plastic ornament. It incessantly develops.

      Just like cities, brains never reach an end point. We spend our lives blossoming toward something, even as the target moves. Consider the feeling of stumbling on a diary entry that you wrote many years ago. It represents the thinking, opinions, and viewpoint of someone who was a bit different from who you are now, and that previous person can sometimes border on the unrecognizable. Despite having the same name and the same early history, in the years between inscription and interpretation the narrator has altered.

      The word “plastic” can be stretched to fit this notion of ongoing change, and to keep ties to the existing literature I’ll use the term occasionally.⁷ But the days of being impressed by plastic molding may be past us. Our goal here is to understand how this living system operates, and for that I’ll coin a term that better captures the point: “livewired.” As we’ll see, it becomes impossible to think about the brain as divisible into layers of hardware and software. Instead, we’ll need the concept of liveware to grasp this dynamic, adaptable, information-seeking system.

      To appreciate the power of a self-configuring organ, let’s return to Matthew’s story. After the removal of an entire hemisphere of his brain, he was incontinent, couldn’t walk, and couldn’t speak. His parents’ worst fears had materialized.

      But with daily physical therapy and language therapy, he was slowly able to relearn language. His acquisition followed the same stages as an infant: first one word, then two, then small phrases.

      Three months later, he was developmentally appropriate—right back where he was supposed to be.

      Now, many years later, Matthew cannot use his right hand well, and he walks with a slight limp.⁸ But he otherwise lives a normal life with little indication that he’s been through such an extraordinary adventure. His long-term memory is excellent. He went to college for three semesters, but because of difficulty taking notes with his right hand, he quit to work at a restaurant. There he answers phones, takes care of customer service, serves dishes, and covers just about any job that needs to be done. People who meet him have no suspicion that he is missing half of his brain. As Valerie puts it, “If they didn’t know, they wouldn’t know.”

      How could such a major neural obliteration go unnoticed?

      Here’s how: the remainder of Matthew’s brain dynamically rewired to take over the missing functions. The blueprints of his nervous system adjusted themselves to occupy a smaller piece of real estate—encompassing the fullness of life with half the machinery. You couldn’t slice out half the electronics from your smartphone and hope to still make a call, because hardware is fragile. Liveware endures.

      In 1596, the Flemish cartographer Abraham Ortelius pored over a map of the earth and had a revelation: the Americas and Africa looked as if they could fit together like puzzle pieces. The match seemed clear, but he had no good idea about what had “torn them apart.” By 1912, the German geophysicist Alfred Wegener conjectured the notion of continental drift: although the continents had previously been assumed to be immutable in their locations, perhaps they were floating around like mammoth lily pads. The drift is slow (continents waft at the same rate your fingernails grow), but a million-year movie of the globe would reveal the landmasses as part of a dynamic, flowing system, redistributing according to rules of heat and pressure.

      Like the globe, the brain is a dynamic, flowing system, but what are its rules? The number of scientific papers on brain plasticity has bloomed into the hundreds of thousands. But even today, as we stare at this strange pink self-configuring material, there is no overarching framework that tells us why and how the brain does what it does. This book lays out that framework, allowing us to better understand who we are, how we came to be, and where we’re going.

      Once we get in the mode of thinking about livewiring, our current hardwired machines seem hopelessly inadequate for our future. After all, in traditional engineering, everything important is carefully designed. When a car company remodels the chassis of a vehicle, it spends months producing the engine to fit. But imagine changing the bodywork any way you’d like and letting the engine reconfigure itself to match. As we’ll see, once we understand the principles of livewiring, we can draft off Mother Nature’s genius to fabricate new machines: devices that dynamically determine their own circuitry by optimizing themselves to their inputs and learning from experience.

      The thrill of life is not about who we are but about who we are in the process of becoming. Similarly, the magic of our brain lies not in its constituent elements but in the way those elements unceasingly reweave themselves to form a dynamic, electric, living fabric.

      Just a handful of pages into this book, your brain has already changed: these symbols on the page have orchestrated millions of tiny changes across the vast seas of your neural connections, crafting you into someone just slightly different than you were at the beginning of the chapter.

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      JUST ADD WORLD

      HOW TO GROW A GOOD BRAIN

      Brains are not born into the world as blank slates. Instead, they arrive pre-equipped with expectations. Consider the birth of a baby chicken: moments after hatching, it wobbles around on its little legs and can clumsily run and dodge. In its environment, it simply doesn’t have time to spend months or years learning how to move around.

      Human infants, as well, come to the table with a good deal of preprogramming. Take the fact that we come pre-equipped to absorb language. Or that babies will mimic an adult sticking out her tongue, a feat requiring a sophisticated ability to translate vision into motor action.¹ Or that fibers from your eye don’t need to learn how to find their targets deep in the brain; they simply follow molecular cues and hit their goal—every time. For all this sort of hardwiring, we can thank our genes.

      But genetic hardwiring does not provide the whole story, especially for humans. The system’s organization is too complex, and the genes are far too few. Even when you take into account the slicing and dicing that produces many different flavors of the same gene, the number of neurons and their connections vastly outstrips the number of genetic combinations.

      So we know that the details of brain wiring involve more than the genetics. And two centuries ago, thinkers began to correctly suspect that the details of experience carried importance. In 1815, the physiologist Johann Spurzheim proposed that the brain, like the muscles, could be increased by exercise: his idea was that blood carried with it the nutrition for growth and that it was “carried in greater abundance to the parts which are excited.”² By 1874, Charles Darwin wondered if this basic idea might explain why rabbits in the wild had larger brains than domestic rabbits: he suggested that the wild hares were forced to use their wits and senses more than the domesticated ones and that the size of their brains followed.³

      In the 1960s, researchers began to study in earnest whether the brain could change in measurable ways as