Livewired by David Eagleman (Book Summary + Infographic)

This is a book summary of Livewired: The Inside Story of the Ever-Changing Brain by David Eagleman (Amazon).

Quick Housekeeping:

All content in quotation marks is from the author (content not in quotations is paraphrased).
All content is organized into my own themes (not necessarily the author’s chapters).
Emphasis has been added in bold for readability/skimmability.

Book Summary Contents:

Mother Nature, Genetics, & DNA
Birth, Childhood, & Environment
Neurons
Plasticity, & Livewiring (+ Infographic)
Body & Senses
Energy & Change
Relevance & Reward
Memory & Learning
Self & Thinking

**The Ever-Changing Brain: Livewired by David Eagleman (Book Summary)**

Mother Nature, Genetics, & DNA

“It’s a great trick on the part of Mother Nature, allowing the brain to learn languages, ride bicycles, and grasp quantum physics, all from the seeds of a small collection of genes. Our DNA is not a blueprint; it is merely the first domino that kicks off the show.”

Mother Nature:

“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.”

Unpacking a brain:

“Mother Nature’s strategy of unpacking a brain relies on proper world experience. Without it, the brain becomes malformed and pathological. Like a tree that needs nutrient-rich soil to arborize, a brain requires the rich soil of social and sensory interaction.”

Driving the available machinery & designing new devices/input channels:

“Mother Nature has the freedom to experiment with outlandish plug-and-play motor devices. Whether fingers, flappers, or fins; whether two legs, four legs, or eight; whether hands or talons or wings—the fundamental principles of brain operation don’t need to be redesigned each time. The motor system simply figures out how to drive the available machinery.”
“One of the great tricks of nature: to tap into new energy sources from the world, it is not required to redesign the brain from scratch each time. Instead, she only needs to design new peripheral devices.”
“Mother Nature can build new senses simply by building new peripherals. In other words, once she has figured out the operating principles of the brain, she can tinker around with different sorts of input channels to pick up on different energy sources from the world.”
“Your brain doesn’t know, and it doesn’t care, where the data come from. Whatever information comes in, it just works out how to leverage it … It just sucks up the available signals and determines—nearly optimally—what it can do with them. And that strategy, I propose, frees up Mother Nature to tinker around with different sorts of input channels.”
“Mother Nature figured out not only how to build an eye but also how to adjust its circuitry on the fly so it can operate differently in various contexts—all to make the best use of what’s available. It’s infotropic (infotropism is the hypothesis that neural circuitry constantly shifts to maximize the amount of information it can extract from the environment … The brain maximizes its resources to interpret whatever data flows in).”

Evolution and mutations:

“In evolutionary time, random mutations introduce strange new sensors, and the recipient brains simply figure out how to exploit them. Once the principles of brain operation have been established, nature can simply worry about designing new sensors.”
“A livewired brain does not need to be swapped out for each genetic change to the body plan. It adjusts itself. And that’s how evolution can so effectively shape animals to fit any habitat. Whether hooves or toes are appropriate to the environment, fins or forearms, or trunks or tails or talons, Mother Nature doesn’t have to do anything extra to make the new animal operate correctly. Evolution really couldn’t work any other way: it simply would not operate quickly enough unless body-plan changes were easy to deploy and brain changes followed without difficulty.”
“Exceptionally useful programs get burned down all the way to the level of the DNA. Consider instincts—the inborn behaviors we don’t have to learn. These come about via plasticity on a longer timescale: the Darwinian plasticity of species. By natural selection over millennia, those with instincts that favor survival and reproduction tend to multiply.”

Genetics & DNA:

“How does the massively complicated brain, with its eighty-six billion neurons, get built from such a small recipe book (~20,000 genes)? The answer pivots on a clever strategy implemented by the genome: build incompletely and let world experience refine.”

“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.”
“All genes aren’t equal. Genes unpack in an exquisitely precise order, with the expression of one triggering the expression of the next ones in a sophisticated algorithm of feedback and feedforward.”
“Despite some genetic pre-specification, nature’s approach to growing a brain relies on receiving a vast set of experiences, such as social interaction, conversation, play, exposure to the world, and the rest of the landscape of normal human affairs. The strategy of interaction with the world allows the colossal machinery of the brain to take shape from a relatively small set of instructions.”
“If DNA were the only thing that mattered, there would be no particular reason to build meaningful social programs to pour good experiences into children and protect them from bad experiences.”

Birth, Childhood, & Environment

“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.”

Birth:

“Human infants 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. 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.”
“Brains are not born into the world as blank slates. Instead, they arrive pre-equipped with expectations.”
“For humans at birth, the brain is remarkably unfinished, and interaction with the world is necessary to complete it.”
“Human babies are born with few built-in skills and a great deal of plasticity, while adults have mastered specific tasks at the expense of flexibility. There’s a trade-off between adaptability and efficiency: as your brain gets good at certain jobs, it becomes less able to tackle others.”
“Preserving total flexibility would retain the helplessness of an infant.”
“The human brain arrives in the world unfinished. Proper development requires proper input. The brain absorbs experience to unpack its programs, and only during a rapidly closing window of time. Once the window is missed, it is difficult or impossible to reopen.”
“There’s a critical window for proper input from the world.”

Childhood & Environment:

“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 pre-planned, but instead reflects the world around it.”

Environment & world interaction:

“Neuronal networks require interaction with the world for their proper development.”
“Brains require the right kind of environment if they are to correctly develop.”
“The flexibility of the brain allows the events in your life to stitch themselves directly into the neural fabric.”
“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.”
“The fine structure of the brain reflects the environment to which it is exposed. World experience modulates almost every measurable detail of the brain, from the molecular scale to overall brain anatomy.”

Childhood experiences:

“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.”
“Brains are most flexible at the beginning, in a window of time known as the sensitive period. As this period passes, the neural geography becomes more difficult to change.”
“The ability to learn language, possess vision, interact socially, walk normally, and have normal neurodevelopment is limited to the years of young childhood. After a certain point, these abilities are lost. The brain needs to experience the proper input within the right window to achieve its most useful connectivity.”
“Early experience becomes foundational. It develops into the architecture upon which everything subsequent is built. Everything new is understood through the filter of the old.”
“The normal development of the brain can been derailed by severe social deprivation.”
“A child raised without human interaction does not grow up to walk, speak, write, lecture, and thrive.”
“Brain changes are driven by the difference between the internal model and what happens in the world. Thus, brains shift only when something is unpredicted. As you age and figure out the rules of the world—from the expectations of your home life to behavior in your social circles to the foods you prefer—your brain becomes less challenged with novel stimulation, and therefore more settled into place.”
“The brain’s solidification reflects its success in understanding the world. Neural networks lock themselves more deeply into place not because of fading function, but instead because they have had success in figuring things out. So would you really want the plasticity of a child again? Although having a sponge-like brain that absorbs everything sounds appealing, the game of life is largely about figuring out the rules. What we lose in modifiability we gain in expertise. Our hard-won networks of association may not be fully correct or even internally consistent, but they add up to life experience, know-how, and an approach to the world.”
“The differences between a baby and an adult are easy to see, but the neural transition from one to the other does not happen in a smooth line. Instead, it is like a door that swings closed. Once it shuts, large-scale change is over.”
“A fact of life: to get good at one thing is to close the door on others. Because you possess only a single life, what you devote yourself to sends you down particular roads, while the other paths will forever remain untrodden by you. Thus, I began this book with one of my favorite quotations from the philosopher Martin Heidegger: ‘Every man is born as many men and dies as a single one.'”

Neurons

“The human brain consists of eighty-six billion cells called neurons: cells that shuttle information rapidly in the form of traveling voltage spikes. 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) … 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.”

Pathways, Maps, & Territories:

“In the young neighborhood of a new brain, nerves coming from the body to the brain branch out broadly. But they set down permanent roots in places where they fire in close timing with other neurons. Because of the synchrony, they strengthen their bonds … A neuron normally grows like a branched tree, allowing it to connect to other neurons. In an enriched environment, branches grow more lavishly. In a deprived environment, branches shrivel.”

“Brains begin with many possible routes through the neural networks; with time, the practiced pathways become difficult to exit. Unused paths become thinned away. Neurons that can’t find success with the world eventually fold up shop and commit suicide. Through decades of experience, the brain comes to physically represent the environment, and your decisions follow the remaining, hard-paved paths. The upside is that you end up with lightning-fast ways of solving problems. The downside is that it’s harder to attack problems with wild unstructured inventiveness. Beyond the diminishing optionality in the pathways, there is a second reason that older brains are less flexible: when they change, they do so only in small spots.”
“Baby brains modify across vast territories. Using broadcast systems like acetylcholine, infants transmit announcements throughout the brain, allowing pathways and connections to modify. Their brains are changeable everywhere, slowly coming into focus like a Polaroid photograph. An adult brain changes only little bits at a time. It keeps most of its connections locked into place, to hold on to what has been learned, and only small areas are made flexible via a combination lock of the right neurotransmitters.”
“Neural maps are not predefined by a genetic urban planning commission. Instead, whatever real estate is available gets used and filled.”
“The brain matures like the planet. Through years of border disputes, neural maps become increasingly solidified.”
“An older brain cannot easily reassign settled territories for new tasks, while a brain at the dawn of its wars can still reimagine its maps.”
“In an adult … the system has less flexibility to rewrite its manifest.”
“The older the brain, the less flexible it is for redeployment.”
“Maintaining territory in the brain is activity-dependent: preserving ground requires constant vigor. As inputs diminish, neurons change their connections until they find where the action is.”
“Maintaining territory requires constant input to the individual neurons: when effort slows, they seek to switch teams to the active inputs.”
“The cartography of the brain constantly shifts to best represent the incoming data.”
“Neural redeployment replaces the old paradigm of predetermined brain areas with something more flexible. Territory can be reassigned to different tasks. There is nothing special about visual cortex neurons, for example … These exact same neurons can process other types of information in the sightless.”
“Atypical feats can be accomplished when the brain devotes an unusually large swath of its real estate to one task (such as memorization, or visual analysis, or puzzles). But these human superpowers come at the expense of other tasks among which brains normally divide their territory, such as all the subtasks that add up to reliable social skills.”

When there is less territory available:

“What happens when disease, surgery, or brain damage result in less available territory? Just as with neighboring countries, there are two possibilities. The brain might leave out the parts of the map corresponding to the missing tissue, or the brain might squish the original map on a smaller piece of real estate.”
“Brain tissue rewired itself to maintain business as usual, even when the territory was radically changed … The cerebral maps rewired themselves onto half the previous real estate while retaining their relationships, tasks, and functions.”

Survival, Competition, & War:

“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.”

“Neurons live their lives in a perpetual state of looking for their right place. They put out feelers. If they’re getting a good response, they keep it going. If they get the cold shoulder, they try their luck nearby with other neurons. At some point, if they’re getting no positive feedback, they get the message that they simply don’t belong.”
“In embryonic development, the trajectory from a webbed hand to clearly defined fingers depends on sculpting away cells, not adding them. The same principles apply to sculpting the brain. During development, 50 percent more neurons than needed are produced. Massive die-off is standard operating procedure.”
“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.”
“The constant fight for territory in the brain is a survival-of-the-fittest competition: each synapse, each neuron, each population, is fighting for resources. As the border wars are fought, the maps shift in such a way that the goals most important to the organism are always reflected in the structure of the brain.”
“It can appear that its maps are stable simply because they are perfectly balanced in their counterforces. The brain gives the illusion that it is settled into stillness, but the principles of competition poise it on the hair-trigger edge of change. Don’t let the calm fool you: neural networks appear settled only because every region is trapped in a cold war, tightly wound, ready to compete for the future borders of the internal globe.”
“We are livewired creatures. Neurons in the brain (and more generally, all cells in the body) are locked in a battle for survival, and sometimes that fever pitch of competition will tip into pathology. Some mutations can give a slight advantage to a cell in this environment—but at the cost of tipping the whole system into a death spiral.”
“Although we typically think of neurons cooperating happily, we can also view them as being locked in chronic battle. Instead of transmitting information to one another, they’re spitting on each other. Through this lens, what we witness in active brain tissue is the competition among billions of individual agents, each of whom is battling for resources and trying to stay alive.”
“There is competition at small levels, and we get emergent properties (stretching, shrinking, sharing) at higher levels. As the local wars rage through a lifetime, the brain’s maps are redrawn. And this is because each neuron confronts the same challenge as the urban drug dealer: find an open niche, and then spend all your time defending it. The constant fight for territory in the brain is live-or-die: each neuron spends its life fighting for resources so it can survive.”

Plasticity & Livewiring

“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. 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.”

Plasticity:

“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 … 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.”

plasticity emerges from a struggle for survival of the parts of the system (compete or die).
plasticity exists throughout the brain at every level (all the forms of plasticity interact with one another, and the power of the system emerges from the layers operating in concert).
plastic changes are distributed along a time spectrum (not simply stored as all-or-none changes).
different areas of the brain operate on different schedules of plasticity / not all brain regions are equally plastic in terms of how flexibly they begin and how long they retain their adaptability (some neural networks are unyielding, while others are highly pliable; some sensitive periods are brief, while others are long; sensitive periods are different for different tasks of the brain).
the degree of plasticity in a brain region reflects how much its data change (or are likely to change) in the outside world (if the incoming data are unwavering, the system hardens around them; if the data are constantly changing, the system remains flexible; as a result, stable data solidify first).
lock down stable information (some parts of the brain are more flexible than others, depending on the input).
plasticity declines with age, but across the brain it declines differently, steeply or shallowly, depending on its function (there’s no single answer to whether the brain is plastic as we get older; it depends on what brain area we’re talking about).
although brain plasticity diminishes over the years, it is still present (neural reconfiguration is an ongoing process that lasts through our lives: we form new ideas, accumulate fresh information, and remember people and events).

Livewiring:

“Livewiring is more than a jaw-dropping curiosity of nature; it is the fundamental trick that allows for memory, flexible intelligence, and civilizations … 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.”

the elaborate pattern of connections in the brain—the circuitry—is full of life (connections between neurons ceaselessly blossom, die, and reconfigure).
the brain is a dynamic system that chronically reflects the world, wraps around the inputs, adjusts itself to its challenges and goals (constantly altering its own circuitry to match the demands of the environment and the capabilities of the body; it molds its resources to match the requirements of its circumstance; when it doesn’t possess what it needs, it sculpts it).
drive any machinery and move toward the data (brains learn to control whatever body plan they discover themselves inside of; brains leverage whatever information streams in; the brain builds an internal model of the world, and adjusts whenever predictions are incorrect).
brains never reach an end point (we spend our lives blossoming toward something, even as the target moves).

7 Principles of Livewiring:

Body & Senses

“Your three pounds of brain tissue are not directly hearing or seeing any of the world around you. Instead, your brain is locked in a crypt of silence and darkness inside your skull. All it ever sees are electrochemical signals that stream in along different data cables. That’s all it has to work with.”

Body:

“The brain contains a map of the body because of a simple rule that governs how individual brain cells make connections with one another: neurons that are active close in time to one another tend to make and maintain connections between themselves. That’s how a map of the body emerges in the darkness.”

“Brains are not predefined for particular bodies, but instead adapt themselves to move, interact, and succeed. And this isn’t simply about the body you’re born in, but about whatever opportunities might come along.”
“The brain’s map is flexibly defined by active inputs from the body. When the body changes, the homunculus follows.”
“The brain adapts to the body plan. When a hand is amputated, neighboring cortical territories move in to usurp the hand’s previously held territory (cortical reorganization: unused cortex is taken over by competing neighborhoods.)”
“The maps come to reflect the current form of the body.”
“When a part of the body no longer sends information, it loses territory.”
“The map congeals naturally from interaction with the world, with adjacent areas of the body staking out adjoining representations in the brain.”
“There’s a much higher receptor density in the fingers, lips, and genitals, and lower resolution in, say, the torso and thighs. The areas that send the most information win the largest representation.”
“Changes to sensory inputs (as with amputation or blindness or deafness) lead to massive cortical reorganization. The brain’s maps are not genetically pre-scripted but instead molded by the input. They are experience-dependent. They are an emergent property of local border competitions rather than the result of a prespecified global plan. Because neurons that fire together wire together, co-activation establishes neighboring representations in the brain. No matter the shape of your body, it will naturally end up mapped on the brain’s surface.”
“The motor areas optimize themselves to drive the available machinery.”
“The brain gracefully determines how best to drive the machinery in which it finds itself embedded.”

Senses:

“Inputs to the brain—photons at the eyes, air compression waves at the ears, pressure on the skin—are all converted into the common currency of electrical signals. As long as the incoming spikes carry information that represents something important about the outside world, the brain will learn how to interpret it. The vast neural forests in the brain don’t care about the route by which the spikes entered.”

“Our eyes and our ears and our fingertips—are merely peripheral plug-and-play devices. You stick them in, and you’re good to go. The brain figures out what to do with the data that come in.”
“The fingertip or the eyeball is just the peripheral device that converts information from the outside world into spikes in the brain.”
“When inputs suddenly cease, sensory cortical areas do not lie fallow. Instead, they are invaded by their neighbors.”
“Brain regions care about solving certain types of tasks, irrespective of the sensory channel by which information arrives.”
“Whatever information the brain is fed, it will learn to adjust to it and extract what it can. As long as the data have a structure that reflects something important about the outside world, the brain will figure out how to decode it.”
“This is why the neocortex looks about the same everywhere: because it is the same. Any patch of cortex is pluripotent—meaning that it has the possibility to develop into a variety of fates, depending on what’s plugged into it.”
“The pattern of inputs determines the fate of the cortex. The brain dynamically wires itself to best represent (and eventually act upon) whatever data come swimming in.”
“The brain figures out how to extract shape information from incoming signals, regardless of the path by which those signals get into the inner sanctum of the skull—whether by sight, touch, or sound. The details of the detectors don’t matter. All that matters is the information they carry.”

Energy & Change

“Brains care about change. Just as in the Troxler effect, features that don’t change yield little information about the world. All the important information comes from things in flux … The strategy of ignoring the unchanging keeps the system poised to detect anything that moves or shifts or transforms.”

Energy:

“Your brain doesn’t want to pay the energy cost of spiking neurons, so the goal is to reconfigure the network to waste as little power as possible.“

“If a pattern streams in that is predictable—or even partially guessable—the system saves energy by structuring itself around that input so as not to be surprised by it. A quieter nervous system means fewer violations of expectations: things in the outside world are going approximately as forecast. In other words, an energy-conscious brain wants to predict away everything possible so that it can save its energy for just representing the unexpected. Silence is golden. While many neuroscientists think of activity in neurons as the representation of things in the world, it could turn out that the truth is exactly the opposite: spikes are the unpredicted, energy-expensive part. The representation of something totally expected would be nothing but a hush falling over the neuronal forest.”
“Your brain actively recalibrates, because that allows it to burn less energy. But there is an even deeper principle at work here. In the darkness of the skull, your brain is striving to build an internal model of the outside world.”
“Just as the plant seeks sunlight and the bacteria seeks sugar, the brain seeks information. It tries to constantly change its circuitry to maximize the data it can draw from the world. To that end, it builds an internal model of the outside, which equates to its predictions. If the world proceeds as expected, the brain saves energy.”

Change:

“Changes in the brain happen only when there’s a difference between what was expected and what actually happens.”

“Fundamentally, the brain is a prediction machine, and that is the driving engine behind its constant self-reconfiguration. By modeling the state of the world, the brain reshapes itself to have good expectations, and therefore to be maximally sensitive to the unexpected.”
“Your visual system is always seeking motion and change. Something fixed quickly becomes invisible. Good information is expected to update; things that do not change are ignored by the system.”
“The retina is blanketed by a meshwork of blood vessels. Because these sit between the world and our photoreceptors, we should see them superimposed on the visual scene. But the vessels’ pattern is stable, and hence carries no new information—and so our visual systems learn to ignore them completely.”
“Successful adaptation makes regularities invisible.”
“As activity passes through the brain, it changes the structure.”
“The nervous system must physically change itself to optimally reflect the world in which it’s embedded.”
“A general principle of reorganization is that the brain conceals a great many silent connections. These are normally inhibited and don’t contribute much of anything. But they’re available if needed in the future. Leveraging these, the brain can respond rapidly to changes in input. However, these silent connections are limited in number, and for longer, more widespread change a different approach is used: if short-term changes are found to be useful to the animal, then long-term changes (such as the sprouting of new synapses and growth of new axons) will eventually follow.”

Relevance & Reward

“The brain reorganizes its circuitry to optimize its representation of the world. So when we feed in new, useful data opportunities, the brain wraps itself around them. This comes with two stipulations to which we’ll return: the new data are best learned if they are tied to a user’s goals and yoked to his own actions.”

Relevance:

“Brains distribute their resources based on relevance.”

“The first solution to the stability/plasticity dilemma is to make sure the whole system isn’t changing at once. Instead, flexibility should turn on and off only in small spots, as steered by relevance.”
“The basis of behavioral improvement is not simply the repeated performance of a task; it also requires neuromodulatory systems to encode relevance.”
“What you spend your time on changes your brain. You’re more than what you eat; you become the information you digest.”
“Brain circuitry comes to reflect what you do … What you do over and over becomes reflected in the structure of the brain. And these changes involve much more than the motor cortex.”
“A brain’s goals play a critical role in how and when it changes.”

Reward:

“Reward is a powerful way to rewire the brain, but happily your brain doesn’t require cookies or cash for each modification. More generally, change is tied to anything that is relevant to your goals … When a task is roughly aligned with our larger goals, our brain circuitry comes to reflect it.”

“Your brain adjusts itself according to what you spend your time on, as long as those tasks have alignment with rewards or goals.”
“The brain fine-tunes its circuitry to maximize the data it streams from the world. The fine-tuning is helped along by rewards, which cause broadcasts throughout the circuitry to announce that something worked. In this way, with a minimum of preprogramming, the system works out how to optimize its interaction with the world.”
“Brains reflect not simply the outside world but more specifically your outside world.”
“The present maps of neural territory reflect the strategies that have won positive feedback.”
“Neurotransmitters (such as dopamine) are involved in the direction of change, encoding whether something was punishing or rewarding. Researchers all over the planet are still working to decipher the complex choreography of the neuromodulatory systems—but we know that collectively these chemical messengers allow reconfiguration in some areas while keeping the rest locked down.”

Memory & Learning

“Experiences turn into memories when they are germane to the life of the organism, and especially when connected to a high emotional state such as fear or pleasure. This reduces the chances of overwhelming a network, because not everything gets written down.”

Memory:

“French psychologist Théodule Ribot, who was struck by his observation that older memories are more stable than newer memories. This is known today as Ribot’s law.”

“Memory storage is not like a filing cabinet, but instead like distributed cloud computing.”
“The changes underlying memory are distributed widely over titanic numbers of neurons, synapses, molecules, and genes.”
“Context steers the correct path through the network.”
“Memory is a function of everything that has come before it.”
“Memory is not one thing, but instead comprises many different subtypes.”
“You can lose the ability to remember the narrative of your life, but this has no bearing on your ability to learn and remember new motor skills.”
“The brain doesn’t always hold memories in one place. Instead, it passes what it has learned to another area for more permanent storage.”
“The formation of new memories requires the hippocampus, but the memories are not stored permanently there. Instead, it passes along the learning to parts of the cortex, which hold the memory more permanently.”
“One proposal is that stable storage cannot be achieved the first time a pattern of activity goes through the cortex; instead, an area such as the hippocampus must reactivate the trace several times to lock the memory into the cortex. This framework suggests why the hippocampus is necessary to consolidate memory: it needs to replay the patterns to the cortex over and over. Once the memories are in the cortex, they gain stabilization with time.”
“If memories were simply retained in the fabric of synaptic weights, we’d have no reason to expect neurogenesis: the growth and insertion of new neurons. In fact, fresh neurons inserting themselves into the network would be expected to scramble up the delicate synaptic pattern. And yet there they are: a stream of new neurons being born in the hippocampus and trucking their way into the adult cortex. They’re not accidental; they can be pinned to memory formation.”

Learning:

“The brain is not simply a blank slate upon which the world scrawls all its stories. Instead, the brain comes pre-equipped for certain types of learning in particular types of situations.”

“When you learn something…your brain physically changes … The immense, intertwining jungles of your brain work themselves into something slightly different from what they were a moment before.”
“We know that when you learn a new fact—say, your new neighbor’s name—there are physical changes in the structure of your brain.”
“Instead of encoding pixels or transcripts, we encode stimuli with respect to other things we have learned, including concepts both physical and social. What we learn is represented in terms of what we already know.”
“New information builds upon the old, fitting into the constraints offered by previous experience.”
“With each new thing you learn, the better you’re able to absorb the next related fact.”
“The highest level—where the best learning occurs—is achieved when a student is invested, curious, interested. Through our modern lens, we would say that a particular formula of neurotransmitters is required for neural changes to take place, and that formula correlates with investment, curiosity, and interest.”
“Given how brains adapt and rewrite their wiring, a neuroscience-compatible classroom is one in which students drill into the vast sphere of human knowledge by following the paths of their individual passions.”
“All new ideas in your brain come from a mash-up of previously learned inputs, and today we get more new inputs than ever before. Children now live in a time unparalleled in richness: our knowledge sphere has exploded in diameter, and as it grows it offers more doors for entry. Young minds have the opportunity to cross-link facts from completely different domains to generate ideas that previous eras couldn’t have imagined.”
“The brain has to have different systems with different speeds of learning: one for the extraction of generalities in the environment (slow learning), and one for episodic memory (fast learning).”
“An active mental life, even in the very elderly, fosters new connections … Learning can happen at any age.”

Self & Thinking

“We generally go through life thinking there’s me and there’s the world. But, who you are emerges from everything you’ve interacted with: your environment, all of your experiences, your friends, your enemies, your culture, your belief system, your era—all of it. Although we value statements such as ‘he’s his own man’ or ‘she’s an independent thinker,’ there is in fact no way to separate yourself from the rich context in which you’re embedded. There is no you without the external. Your beliefs and dogmas and aspirations are shaped by it, inside and out, like a sculpture from a block of marble. Thanks to livewiring, each of us is the world.”

Self:

“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.”

“In ways we are still working to understand, the brain is stunningly gifted at taking in these signals and extracting patterns. To those patterns it assigns meaning. With the meaning you have subjective experience. The brain is an organ that converts sparks in the dark into the euphonious picture show of your world. All of the hues and aromas and emotions and sensations in your life are encoded in trillions of signals zipping in blackness, just as a beautiful screen saver on your computer screen is fundamentally built of zeros and ones.”
“Fundamentally, who you are is the sum total of your memory.”
“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.”
“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.”
“The thrill of life is not about who we are but about who we are in the process of becoming.”
“What you can control becomes the self, and what you cannot control has no relation to you.”
“How the brain determines selfhood: if I can control what it does, it is me.”
“Self-identity is surprisingly flexible. Researchers have been studying in recent years how taking on the face of a different person can enhance empathy.”
“Who we are depends on how the whole brain is wired. Tweak the body and you may tweak the person.”

Thinking:

“Constant testing of the world may also be how we learn to think.”

“From your brain’s point of view, thinking is remarkably similar to motor movements. The neural storm of activity that causes your arm to lift is much like the storm that causes you to think about what you should say to your depressed friend, or where your other sock might have disappeared to, or what you’re going to order for lunch.”
“Thinking a thought is like moving a limb; in the same way that our brains drive a kick, a lunge, or a grasp, it may be that thinking moves concepts around in thought space.”
“In other words, thinking is the act of pushing around concepts instead of coffee cups, notions instead of napkins. And this starts with the same sort of babbling: generating a thought and assessing the consequences. Some thoughts map well onto the world (if I pull this cord, the lawn mower will start), while others gain nothing (what would happen if I fling my pancake across the table?). Just like movements and speech, thoughts have to learn how to best operate in the world.”

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