Читать книгу Livewired - David Eagleman - Страница 8

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THE DELICATE PINK MAGISTERIUM

Imagine this: instead of sending a four-hundred-pound rover vehicle to Mars, we merely shoot over to the planet a single sphere, one that can fit on the end of a pin. Using energy from sources around it, the sphere divides itself into a diversified army of similar spheres. The spheres hang on to each other and sprout features: wheels, lenses, temperature sensors, and a full internal guidance system. You’d be gobsmacked to watch such a system discharge itself.

But you only need to go to any nursery to see this unpacking in action. You’ll see wailing babies who began as a single, microscopic, fertilized egg and are now in the process of emancipating themselves into enormous humans, replete with photon detectors, multi-jointed appendages, pressure sensors, blood pumps, and machinery for metabolizing power from all around them.

But this isn’t even the best part about humans; there’s something more astonishing. Our machinery isn’t fully preprogrammed, but instead shapes itself by interacting with the world. As we grow, we constantly rewrite our brain’s circuitry to tackle challenges, leverage opportunities, and understand the social structures around us.

Our species has successfully taken over every corner of the globe because we represent the highest expression of a trick that Mother Nature discovered: don’t entirely pre-script the brain; instead, just set it up with the basic building blocks and get it into the world. The bawling baby eventually stops crying, looks around, and absorbs the world around it. It molds itself to the surroundings. It soaks up everything from local language to broader culture to global politics. It carries forward the beliefs and biases of those who raise it. Every fond memory it possesses, every lesson it learns, every drop of information it drinks—all these fashion its circuits to develop something that was never preplanned, but instead reflects the world around it.

This book will show how our brains incessantly reconfigure their own wiring, and what that means for our lives and our futures. Along the way, we’ll find our story illuminated by many questions: Why did people in the 1980s (and only in the 1980s) see book pages as slightly red? Why is the world’s best archer armless? Why do we dream each night, and what does that have to do with the rotation of the planet? What does drug withdrawal have in common with a broken heart? Why is the enemy of memory not time but other memories? How can a blind person learn to see with her tongue or a deaf person learn to hear with his skin? Might we someday be able to read the rough details of someone’s life from the microscopic structure etched in their forest of brain cells?

THE CHILD WITH HALF A BRAIN

While Valerie S. was getting ready for work, her three-year-old son, Matthew, collapsed on the floor.¹ He was unarousable. His lips turned blue.

Valerie called her husband in a panic. “Why are you calling me?” he bellowed. “Call the doctor!”

A trip to the emergency room was followed by a long aftermath of appointments. The pediatrician recommended Matthew have his heart checked. The cardiologist outfitted him with a heart monitor, which Matthew kept unplugging. All the visits surfaced nothing in particular. The scare was a one-off event.

Or so they thought. A month later, while he was eating, Matthew’s face took on a strange expression. His eyes became intense, his right arm stiffened and straightened up above his head, and he remained unresponsive for about a minute. Again Valerie rushed him to the doctors; again there was no clear diagnosis.

Then it happened again the next day.

A neurologist hooked up Matthew with a cap of electrodes to measure his brain activity, and that’s when he found the telltale signs of epilepsy. Matthew was put on seizure medications.

The medications helped, but not for long. Soon Matthew was having a series of intractable seizures, separated from one another first by an hour, then by forty-five minutes, then by thirty minutes—like the shortening durations between a woman’s contractions during labor. After a time he was suffering a seizure every two minutes. Valerie and her husband, Jim, hurried Matthew to the hospital each time such a series began, and he’d be housed there for days to weeks. After several stints of this routine, they would wait until his “contractions” had reached the twenty-minute mark and then call ahead to the hospital, climb in the car, and get Matthew something to eat at McDonald’s on the way there.

Matthew, meanwhile, labored to enjoy life between seizures.

The family checked into the hospital ten times each year. This routine continued for three years. Valerie and Jim began to mourn the loss of their healthy child—not because he was going to die, but because he was no longer going to live a normal life. They went through anger and denial. Their normal changed. Finally, during a three-week hospital stay, the neurologists had to allow that this problem was bigger than they knew how to handle at the local hospital.

So the family took an air ambulance flight from their home in Albuquerque, New Mexico, to Johns Hopkins hospital in Baltimore. It was here, in the pediatric intensive care unit, that they came to understand that Matthew had Rasmussen’s encephalitis, a rare, chronic inflammatory disease. The problem with the disease is that it affects not just a small bit of the brain but an entire half. Valerie and Jim explored their options and were alarmed to learn there was only one known treatment for Matthew’s condition: a hemispherectomy, or the surgical removal of an entire half of the brain. “I can’t tell you anything the doctors said after that,” Valerie told me. “One just shuts down, like everyone’s talking a foreign language.”

Valerie and Jim tried other approaches, but they proved fruitless. When Valerie called Johns Hopkins hospital to schedule the hemispherectomy some months later, the doctor asked her, “Are you sure?”

“Yes,” she said.

“Can you look in the mirror every day and know you’ve chosen what you’ve needed to do?”

Valerie and Jim couldn’t sleep beneath the crushing anxiety. Could Matthew survive the surgery? Was it even possible to live with half of the brain missing? And even if so, would the removal of one hemisphere be so debilitating as to offer Matthew a life on terms not worth taking?

But there were no more options. A normal life couldn’t be lived in the shadow of multiple seizures each day. They found themselves weighing Matthew’s assured disadvantages against an uncertain surgical outcome.

Matthew’s parents flew him to the hospital in Baltimore. Under a small child-sized mask, Matthew drifted away into the anesthesia. A blade carefully opened a slit in his shaved scalp. A bone drill cut a circular burr hole in his skull.

Working patiently over the course of several hours, the surgeon removed half of the delicate pink material that underpinned Matthew’s intellect, emotion, language, sense of humor, fears, and loves. The extracted brain tissue, useless outside its biological milieu, was banked in small containers. The empty half of Matthew’s skull slowly filled up with cerebrospinal fluid, appearing in neuroimaging as a black void.²

Half of Matthew’s brain was surgically removed.

In the recovery room, his parents drank hospital coffee and waited for Matthew to open his eyes. What would their son be like now? Who would he be with only half a brain?

Of all the objects our species has discovered on the planet, nothing rivals the complexity of our own brains. The human brain consists of eighty-six billion cells called neurons: cells that shuttle information rapidly in the form of traveling voltage spikes.³ Neurons are densely connected to one another in intricate, forest-like networks, and the total number of connections between the neurons in your head is in the hundreds of trillions (around 0.2 quadrillion). To calibrate yourself, think of it this way: there are twenty times more connections in a cubic millimeter of cortical tissue than there are human beings on the entire planet.

But it’s not the number of parts that make a brain interesting; it’s the way those parts interact.

In textbooks, media advertisements, and popular culture, the brain is typically portrayed as an organ with different regions dedicated to specific tasks. This area here exists for vision, that swath there is necessary for knowing how to use tools, this region becomes active when resisting candy, and that spot lights up when mulling over a moral conundrum. All the areas can be neatly labeled and categorized.

But that textbook model is inadequate, and it misses the most interesting part of the story. The brain is a dynamic system, constantly altering its own circuitry to match the demands of the environment and the capabilities of the body. If you had a magical video camera with which to zoom in to the living, microscopic cosmos inside the skull, you would witness the neurons’ tentacle-like extensions grasping around, feeling, bumping against one another, searching for the right connections to form or forgo, like citizens of a country establishing friendships, marriages, neighborhoods, political parties, vendettas, and social networks. Think of the brain as a living community of trillions of intertwining organisms. Much stranger than the textbook picture, the brain is a cryptic kind of computational material, a living three-dimensional textile that shifts, reacts, and adjusts itself to maximize its efficiency. The elaborate pattern of connections in the brain—the circuitry—is full of life: connections between neurons ceaselessly blossom, die, and reconfigure. You are a different person than you were at this time last year, because the gargantuan tapestry of your brain has woven itself into something new.

When you learn something—the location of a restaurant you like, a piece of gossip about your boss, that addictive new song on the radio—your brain physically changes. The same thing happens when you experience a financial success, a social fiasco, or an emotional awakening. When you shoot a basketball, disagree with a colleague, fly into a new city, gaze at a nostalgic photo, or hear the mellifluous tones of a beloved voice, the immense, intertwining jungles of your brain work themselves into something slightly different from what they were a moment before. These changes sum up to our memories: the outcome of our living and loving. Accumulating over minutes and months and decades, the innumerable brain changes tally up to what we call you.

Or at least the you right now. Yesterday you were marginally different. And tomorrow you’ll be someone else again.

LIFE’S OTHER SECRET

In 1953, Francis Crick burst into the Eagle and Child pub. He announced to the startled swillers that he and James Watson had just discovered the secret of life: they had deciphered the double-helical structure of DNA. It was one of the great pub-crashing moments of science.

But it turns out that Crick and Watson had discovered only half the secret. The other half you won’t find written in a sequence of DNA base pairs, and you won’t find it written in a textbook. Not now, not ever.

Because the other half is all around you. It is every bit of experience you have with the world: the textures and tastes, the caresses and car accidents, the languages and love stories.⁴

To appreciate this, imagine you were born thirty thousand years ago. You have exactly your same DNA, but you slide out of the womb and open your eyes onto a different time period. What would you be like? Would you relish dancing in pelts around the fire while marveling at stars? Would you bellow from a treetop to warn of approaching saber-toothed tigers? Would you be anxious about sleeping outdoors when rain clouds bloomed overhead?

Whatever you think you’d be like, you’re wrong. It’s a trick question.

Because you wouldn’t be you. Not even vaguely. This caveman with identical DNA might look a bit like you, as a result of having the same genomic recipe book. But the caveman wouldn’t think like you. Nor would the caveman strategize, imagine, love, or simulate the past and future quite as you do.

Why? Because the caveman’s experiences are different from yours. Although DNA is a part of the story of your life, it is only a small part. The rest of the story involves the rich details of your experiences and your environment, all of which sculpt the vast, microscopic tapestry of your brain cells and their connections. What we think of as you is a vessel of experience into which is poured a small sample of space and time. You imbibe your local culture and technology through your senses. Who you are owes as much to your surroundings as it does to the DNA inside you.

Contrast this story with a Komodo dragon born today and a Komodo dragon born thirty thousand years ago. Presumably it would be more difficult to tell them apart by any measure of their behavior.

What’s the difference?

Komodo dragons come to the table with a brain that unpacks to approximately the same outcome each time. The skills on their résumé are mostly hardwired (eat! mate! swim!), and these allow them to fill a stable niche in the ecosystem. But they’re inflexible workers. If they were airlifted from their home in southeastern Indonesia and relocated to snowy Canada, there would soon be no more Komodo dragons.

In contrast, humans thrive in ecologies around the globe, and soon enough we’ll be off the globe. What’s the trick? It’s not that we’re tougher, more robust, or more rugged than other creatures: along any of these measures, we lose to almost every other animal. Instead, it’s that we drop into the world with a brain that’s largely incomplete. As a result, we have a uniquely long period of helplessness in our infancy. But that cost pays off, because our brains invite the world to shape them—and this is how we thirstily absorb our local languages, cultures, fashions, politics, religions, and moralities.

Dropping into the world with a half-baked brain has proven a winning strategy for humans. We have outcompeted every species on the planet: covering the landmass, conquering the seas, and bounding onto the moon. We have tripled our life spans. We compose symphonies, erect skyscrapers, and measure with ever-increasing precision the details of our own brains. None of those enterprises were genetically encoded.

At least they weren’t encoded directly. Instead, our genetics bring about a simple principle: don’t build inflexible hardware; build a system that adapts to the world around it. Our DNA is not a fixed schematic for building an organism; rather, it sets up a dynamic system that continually rewrites its circuitry to reflect the world around it and to optimize its efficacy within it.

Think about the way a schoolchild will look at a globe of the earth and assume there is something fundamental and unchanging about the country borders. In contrast, a professional historian understands that country borders are functions of happenstance and that our story could have been run with slight variations: a would-be king dies in infancy, or a corn pestilence is avoided, or a warship sinks and a battle tips the other way. Small changes would cascade to yield different maps of the world.

And so it goes with the brain. Although a traditional textbook drawing suggests that neurons in the brain are happily packed next to one another like jelly beans in a jar, don’t let the cartoon fool you: neurons are locked in competition for survival. Just like neighboring nations, neurons stake out their territories and chronically defend them. They fight for territory and survival at every level of the system: each neuron and each connection between neurons fights for resources. As the border wars rage through the lifetime of a brain, maps are redrawn in such a way that the experiences and goals of a person are always reflected in the brain’s structure. If an accountant drops her career to become a pianist, the neural territory devoted to her fingers will expand; if she becomes a microscopist, her visual cortex will develop higher resolution for the small details she seeks; if she becomes a perfumer, her brain regions assigned to smell will enlarge.

It is only from a dispassionate distance that the brain gives the illusion of a globe with predestined and definitive borders.

The brain distributes its resources according to what’s important, and it does so by implementing do-or-die competition among all the parts that make it up. This basic principle will illuminate several questions we’ll encounter shortly: Why do you sometimes feel as though your cell phone just buzzed in your pocket, only to discover it’s on the table? Why does the Austrian-born actor Arnold Schwarzenegger have a thick accent when he speaks American English, while the Ukrainian-born actress Mila Kunis has none? Why is a child with autistic savant syndrome able to solve a Rubik’s Cube in forty-nine seconds but unable to hold a normal conversation with a peer? Can humans leverage technology to build new senses, thus gaining a direct perception of infrared light, global weather patterns, or the stock market?

IF YOU’RE MISSING THE TOOL, CREATE IT

At the end of 1945, Tokyo found itself in a bind. Through the period that spanned the Russo-Japanese War and two world wars, Tokyo had devoted forty years of intellectual resources to military thinking. This had equipped the nation with talents best suited for only one thing: more warfare. But atomic bombs and the fatigue of combat had abated its appetite for conquest in Asia and the Pacific. War was over. The world had changed, and the Japanese nation was going to have to change with it.

But change invited a difficult question: What would they do with their vast numbers of military engineers who, since the dawn of the century, had been trained to produce better weaponry? These engineers simply didn’t mesh with Japan’s newly discovered desire for tranquility.

Or so it seemed. But over the next few years, Tokyo shifted its social and economic landscape by redeploying its engineers toward new assignments. Thousands were tasked with building the high-speed bullet train known as the Shinkansen.⁵ Those who had previously designed aerodynamic navy aircraft now crafted streamlined railcars. Those who had worked on the Mitsubishi Zero fighter plane now devised wheels, axles, and railing to ensure the bullet train could operate safely at high speeds.

Tokyo shaped its resources to better match its external environment. It beat its swords into plowshares. It altered its machinery to match the demands of the present.

Tokyo did what brains do.

The brain chronically adjusts itself to reflect its challenges and goals. It molds its resources to match the requirements of its circumstance. When it doesn’t possess what it needs, it sculpts it.

Why is that a good strategy for the brain? After all, human-built technology has been very successful, and we use an entirely different strategy there. We build fixed hardware devices with software programs to neatly accomplish what we need. What would be the advantage of melting the distinction between those layers so that the machinery is constantly redesigned by the running of the programs?

The first advantage is speed.⁶ You type rapidly on your laptop because you don’t have to think about the details of your fingers’ positions, aims, and goals. It all just proceeds on its own, seemingly magically, because typing has become part of your circuitry. By reconfiguring the neural wiring, tasks like this become automatized, allowing fast decisions and actions. Millions of years of evolution didn’t presage the arrival of written language, much less a keyboard, and yet our brains have no trouble taking advantage of the innovations.

Compare this with hitting the correct keys on a musical instrument you’ve never played before. For these sorts of untrained tasks, you rely on conscious thinking, and that is comparably quite slow. This speed difference between amateurism and expertise is why a leisure soccer player constantly has the ball stolen. In contrast, the experienced player reads the signals of his opponents, capers with fancy footwork, and shoots the ball with high precision. Unconscious actions are more rapid than conscious deliberation. Plows farm faster than swords.

The second advantage of specializing the machinery for important tasks is energy efficiency. The newbie soccer player simply doesn’t understand how all the movement of the field fits together, while the pro can manipulate the game play in multiple ways to score a goal. Whose brain is more active? You might guess it’s the high-scoring expert—because he understands the structure of the game and is zipping through possibilities, decisions, and intricate moves. But that would be the wrong guess. The expert’s brain has developed neural circuitry specific to soccer, allowing him to make his moves with surprisingly little brain activity. In a sense, the expert has made himself one with the game. In contrast, the amateur’s brain is on fire with activity. He’s trying to figure out which movements matter. He’s entertaining multiple interpretations of the situation and trying to determine which, if any, are correct.

As a result of burning soccer into the circuitry, the pro’s performance is both fast and efficient. He’s optimized his internal wiring for that which is important in his outside world.

AN EVER-CHANGING SYSTEM

The concept of a system that can be changed by external events—and keep its new shape—led the American psychologist William James to coin the term “plasticity.” A plastic object is one that can be shaped, and it can hold 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.