View source for Seven and a Half Lessons About the Brain

== 1/2. Your Brain is Not For Thinking ==
* During the Cambrian period (500m ya), something new and significant appeared on the evolutionary scene: hunting. Somewhere, somehow, one creature became able to sense the presence of another creature and deliberately ate it. Animals had gobbled one another before, but now the eating was more purposeful. Hunting didn't require a brain, but it was a big step toward developing one.
* Creatures who could better sense their surroundings were more likely to survive and thrive. The amphioxus may have been a master of its environment, but it couldn't sense that it had an environment. These new animals could.
* Once creatures could sense at a distance and make more sophisticated movements, evolution favored those who perform these tasks efficiently. If they chased a meal but moved too slowly, something else caught the meal and ate it first. If they burned up energy fleeing from a potential threat that never arrived, they wasted resources that they might have needed later. Energy efficiency was the key to survival.
* When it came to body budgeting, prediction beat reaction. A creature that prepared its movement before the predator struck was more likely to be around tomorrow than a creature that awaited a predator's pounce. Creatures that predicted correctly most of the time, or made nonfatal mistakes and learned from them, did well. those that frequently predicted poorly, missed threats, or false-alarmed about threats that never materialized didn't do so well. They explored their environment less, foraged less, and were less likely to reproduce.
* The scientific name for body budgeting is allostasis. It means automatically predicting and preparing to meet the body's needs before they arise.
* The value of any movement is intimately bound up with body budgeting by allostasis.
* Newer animals developed intricate internal systems, like a cardiovascular system with a heart that pumps blood, a respiratory system that takes in oxygen and eliminates carbon dioxide, and an adaptable immune system that fights infection. Systems like these made body budgeting much more challenging, less like a single bank account and more like the accounting department of a sizable company. These complex bodies needed something more than a handful of cells to ensure that water and blood and salt and oxygen and glucose and cortisol and sex hormones and dozens of other resources were all regulated well to keep a body running efficiently. They needed a command center. A brain.
* Human brains efficiently supervise over 600 muscles in motion, balances dozens of different hormones, pumps blood  at a rate of 2k gallons per day, regulates the energy of billions of brain cells, digests food, excretes waste, and fights illness, all of it nonstop for approx 72yrs.
* Your body budget is like thousands of financial accounts in a giant multinational corporation, and you have a brain that's up to the task. And all your body budgeting takes place in a massively complicated world made even more challenging by the other brains-in-bodies that you share it with.
* Your brain's most important job is not rationality, emotion, imagination, creativity, or empathy. It is to control your body - manage allostasis - by predicting energy needs before they arise so you can efficiently make worthwhile movements and survive.
* Your brain's most important job is not thinking. It's running a little worm body that has become very, very complicated.
== 1. You Have One Brain (Not Three) ==
* The triune brain idea says that the human brain is make up of three layers:
** The deepest layer, the lizard brain, is for surviving.
** The middle layer, the limbic system, is for feeling
** The outermost layer, the neocortex, is for thinking.
*It is one of the most successful and widespread errors in all of science. By the 1990s, experts had completely rejected the idea of a three-layered brain.
*It turns out that as brains become larger over evolutionary time, they reorganize.
*Scientists have recently discovered that the brains of all mammals are built from a single manufacturing plan, and most likely, the brains of reptiles and other vertebrates follow that same plan.
*The biological building blocks are the same, what differs is the timing. For example, the stage that produces neurons for the cerebral cortex in humans runs for a shorter time in rodents and a much shorter time in lizards, so your cerebral cortex is large, a mouse's is smaller, and an iguana's is tiny (or possibly non-existant).
*If a monkey's brain could grow to human size, its cerebral cortex would be the same size as ours. Elephants have much more cerebral cortex than we do, but so would an elephant-sized human brain.
*The real story is that during the course of evolution, certain genes mutated to cause particular stages of brain development to run for longer or shorter times, producing a brain with proportionally bigger or smaller parts.
*Your brain is not more evolved than a rat or lizard brain, just differently evolved.
*What we call mental illnesses may be rational body-budgeting for the short term that's out of sync with the immediate environment, the needs of other people, or your own best interests down the road.
*Rational behavior, therefore, means making a good body-budgeting investment in a given situation.
== 2. Your Brain is a Network ==
* Your brain network is always on. Your neurons never just sit around waiting for something in the outside world to make them fire. Instead, all of your neurons chat constantly with one another through their wiring. Their communications may become stronger or weaker depending on what's happening in the world and in your body, but the conversation never stops, until your die.
* Communication in your brain is a balancing act between speed and cost. Each neuron directly passes information to just a few thousand other neurons and receives information from a few thousand other neurons and receives information from a few thousand others, give or take, yielding over 500 tn neuron-to-neuron connections.
* Your brain network is organized much like the global air travel network. Its neurons are grouped into clusters that are like airports. Most of the connections in and out of a cluster are local, so, like an airport, the cluster serves mostly local traffic. In addition, some clusters serve as hubs for communication. They are densely connected to many other clusters, and some of their axons reach far across the brain and act as long-distance connections. Brain hubs, like airport hubs, make a complicated system efficient. They allow most neurons to participate globally even as they focus more locally. Hubs form the backbone of communication throughout the brain.
* Hub damage is associated with depression, schizophrenia, dyslexia, chronic pain, dementia, Parkinson's disease, and other disorders. Hubs are points of vulnerability because they are points of efficiency - they make it possible to run a human brain in a human body without depleting the body budget.
* Neuromodulators and neurotransmitters together allow your brain's single structure to take on trillions of different patterns of activity.
* Overall, no neuron has a single psychological function, though a neuron may be more likely to contribute to some functions than others.
* It's also the case that different groups of neurons can produce the same result. This is called degeneracy. (Degeneracy is the ability of elements that are structurally different to perform the same function or yield the same output.)
* Complexity - The brain's ability to configure itself into an enormous number of distinct neural patterns by combining bits and pieces of old patterns it has made before. The result is a brain that runs its body efficiently in a world full of constantly changing situations by recalling patterns that helped in the past and generating new ones to try.
* When existing brain parts become more flexible, the result is much more complexity than we get by accumulating new parts. Meatloaf Brain and Pocketknife Brain may have some advantages, but a brain with high complexity beats them both.
* Brains of higher complexity can remember more. A brain doesn't store memories like files on a computer - it reconstructs them on demand with electricity and swirling chemicals. We call this process remembering but it's really assembling. A complex brain can assemble many more memories than either Meatloaf Brain or Pocketknife Brain could. And each time you have the same memory, your brain may have assembled it with a different collection of neurons (that's degeneracy).
* Your brain network may even extend, surprisingly, into your gut and intestines, where scientists have found microbes that communicate with your brain via neurotransmitters.
== 3. Little Brains Wire Themselves to Their World ==
* Little human brains are born under construction. They don't take on their full adult structure and function until they finish their principal wiring, a process that takes about 25 years.
* The distinction between nature and nurture is illusory. To a remarkable extent, a baby's genes are guided and regulated by the surrounding environment. The brain areas that are most centrally involved in vision, for example, develop normally after birth only if a baby's retinas are regularly exposed to light. An infant's brain also learns to locate sounds in the world based on the specific shape of the baby's ear. To make matters even stranger, a baby's body requires some additional genes that sneak in from the outside world. These tiny visitors travel inside of bacteria and other critters and affect the brain in ways that scientists are only beginning to understand.
* Tuning and pruning:
** Tuning means strengthening the connections between neurons, particularly connections that are used frequently or are important for budgeting the resources of your body. Neurons that fire together, wire together.
** Pruning means that less-used connections weaken and die off. If you don't use it, you lose it. A human embryo creates twice as many neurons as an adult brain needs, and infant neurons are quite a bit bushier than neurons in an adult brain. Unused connections are helpful at the outset. They enable a brain to tailor itself to diverse environments. But over the longer term, unused connections are a burden, metabolically speaking - they don't contribute anything worthwhile, so it's a waste of energy for the brain to maintain them.
*Caregivers regulate the baby's physical environment and therefore her body budget by feeding her, setting sleep times, and wrapping her in blankets and cuddles. These actions help the baby's brain maintain its body budget, so her internal systems operate efficiently and she stays alive and healthy.
*In general, toddlers learn to tend their own body budgets better when their caregivers create learning opportunities for them instead of hovering and taking care of their every need. A big challenge of parenting is knowing when to step in and when to step back.
*Newborn brains don't know what's important and what's not, so they cannot focus as adults do. They still lack the wiring that narrows their lantern of attention into a spotlight.
*Little by little, sharing attention teaches an infant which parts of the environment matter and which parts don't. The infant brain is then able to construct its own environment of what is relevant to its body budget and what can be ignored. Scientists call this environment a niche. Every animal has a niche, and it creates that niche as it sense the world, makes worthwhile movements, and regulates its body budget.
*Adult humans have a gigantic niche, perhaps the largest of any creature. Your niche extends far beyond your immediate surroundings to include events around the world, past, present, and future.
*Sounds that are frequent cause certain neural connections to be tuned, and the baby's brain starts to treat those sounds as part of its niche. Sounds that are rare are treated as noise to be ignored, and eventually, related neural connections fall out of use and are pruned away.
*Little brains require a social world in order to develop typically. If these needs aren't met, things can go terribly wrong.
*When it comes to the brain, simple distinctions like nature vs nurture are alluring but not realistic. We have the kind of nature that requires nurture. Your genes require a physical and social environment - a niche filled with other humans who shared your infant gaze, spoke to you with intent, set your sleep schedule, and controlled your body temperature - in order to produce a finished brain.
== 4. Your Brain Predicts (Almost) Everything You Do ==
* Your brain combines information from outside and inside your head to produce everything you see, hear, smell, taste, and feel.
* Inside your skull, without your awareness, billions of your neurons are trying to give these lines and blobs (from The Ultimate Droodles Compendium) meaning. Your brain is searching through a lifetime of past experiences, issuing thousands of guesses at once, weighing probabilities, trying to answer the question What are these wavelengths of light most like? And it's all happening faster than you can snap your fingers.
* Artwork, particularly abstract art, is made possible because the human brain constructs what it experiences. When you view a cubist painting by Picasso and see recognizable human figures, that happens only because you have memories of human figures that help your brain make sense of the abstract elements. 
* Marcel Duchamp: "An artist does only 50% of the work in creating art. The remaining 50% is in the viewer's brain. (the "beholder's share").
* You don't sense with your sensory organs. You sense with your brain.
* If the stuff inside and outside your head doesn't match then sometimes the inside stuff prevails.
* Neuroscientists like to say that your day-to-day experience is a carefully controlled hallucination, constrained by the world and your body but ultimately constructed by your brain.
* So, your brain issues predictions and checks them against the sense data coming from the world and your body... If your brain has predicted well, then your neurons are already firing in a pattern that matches the incoming sense data. That means this sense data itself has no further use beyond confirming your brain's predictions. What you see, hear, smell, and taste in the world and feel in your body in that moment are completely constructed in your head. By prediction, your brain has efficiently prepared you to act.
* Brains aren't wired for accuracy. They're wired to keep us alive.
* You and I seem to sense first and act second. You see an enemy and raise your rifle. But in your brain, sensing actually comes second. Your brain is wired to prepare for action first... and making body-budgeting changes to support that movement.
* It's impossible to change your past, but right now, with some effort, you can change how your brain will predict in the future. You can invest a little time and energy to try new activities. Everything you lean today seeds your brain to predict differently tomorrow.
* Everyone who's ever learned a skill, whether it's driving a car or tying a shoe, know that things that require effort today become automatic tomorrow with enough practice. They're automatic because your brain has tuned and pruned itself to make different predictions that launch different actions. As a consequence, you experience yourself and the world around you differently. That is a form of free will, or at least something we can arguably call free will. We can choose what we expose ourselves to.
* With practice, you can make some automatic behaviors more likely than others and have more control over your future actions and experiences than you might think.
* Sometimes we're responsible for things not because they're our fault, but because we're the only ones who can change them.
* When you were a child, your caregivers tended the environment that wired your brain. They created your niche. You didn't choose that niche - you were a baby. So you're not responsible for your early wiring.
== 5. Your Brain Secretly Works with Other Brains ==
* Some brains are more attentive to the people around them, and others less so, but everybody has somebody. (Even psychopaths are dependent on other people, just in a really unfortunate way.) Ultimately, your family, friends, neighbors, and even strangers contribute to your brain's structure and function and help your brain keep your body humming along.
* It's metabolically costly for a brain to deal with things that are hard to predict. No wonder people create so-called echo chambers, surrounding themselves with news and views that reinforce what they already believe - it reduces the metabolic cost and unpleasantness of learning something new. Unfortunately, it also reduces the odds of learning something that might change a person's mind.
* Why do the words you encounter have such wide-ranging effects inside you? Because many brain regions that process language also control the inside of your body, including major organs and systems that support your body budget. These brain regions, which are in what scientists call the "language network" guide your hear rate up and down. They adjust the glucose entering your bloodstream to fuel your cells. They change the flow of chemicals that support your immune system. The power of words is not a metaphor. It's in your brain wiring.
* Words, then, are tools for regulating human bodies. Other people's words have a direct effect on your brain activity and your bodily systems, and your words have that same effect on other people. Whether you intend that effect is irrelevant. It's how we're wired.
* A long period of chronic stress can harm a human brain. Scientific studies are absolutely clear on this point. When you're on the receiving end of ongoing insults and threats, for example, studies show that you're more likely to get sick.
* The best thing for your nervous system is another human. The worst thing for your nervous system is another human. This situation leads us to a fundamental dilemma of the human condition. Your brain needs other people in order to keep your body alive and healthy, and at the same time, many cultures strongly value individual rights and freedoms. Dependence and freedom are naturally in conflict. How, then, can we best respect and cultivate individual rights when we are social animals who regulate one another's nervous systems to survive.
== 6. Brains Make More than One Kind of Mind ==
* A mind is something that emerges from a transaction between your brain and your body while they are surrounded by other brains-in-bodies that are immersed in a physical world and constructing a social world.
* We come into the world with a basic brain plan that can be wired in a variety of ways to construct different kinds of minds.
* If we all had the same kind of mind - if there were only one human nature - then when disaster struck, we might become extinct.
* As far as I can tell, the human mind has no universal defining features. 
* An especially useful feature of the mind, and one of the closest things we have to a universal mental feature, is mood - the general sense of feeling that comes from your body. Scientists call it affect. Feelings of affect range from pleasant to unpleasant, from idle to activated. Affect is not emotion; your brain produces affect all the time, whether you're emotional or not and whether you notice it or not.
* Affect is the source of all your joys and sorrows. It makes some things profound or sacred to you and other things trivial or vile.
* In the midst of all the activity going on inside you, something miraculous happens. Your brain summarizes what's going on with your body in the moment, and you feel that summary as affect.
* A particularly challenging way to modify a mind is by moving it to another culture.
== 7. Our Brains Can Create Reality ==
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== Epilogue ==
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