The Brain: The Story of You

by David Eagleman

Baby animals develop quickly because their brains are wiring up according to a largely preprogrammed routine.

Instead of arriving with everything wired up – let’s call it “hardwired” – a human brain allows itself to be shaped by the details of life experience.

Which synapses stay and which go? When a synapse successfully participates in a circuit, it is strengthened; in contrast, synapses weaken if they aren’t useful, and eventually they are eliminated.

If developing brains are not given the proper, “expected” environment – one in which a child is nurtured and looked after – the brain will struggle to develop normally.

A mature pleasure-seeking system coupled with an immature orbitofrontal cortex means that teens are not only emotionally hypersensitive, but also less able to control their emotions than adults.

tectonic

After learning The Knowledge, the hippocampuses of London cab drivers visibly changed shape – reflecting their improved skills of spatial navigation.

It’s not just illness or chemicals that change us: from the movies we watch to the jobs we work, everything contributes to a continual reshaping of the neural networks we summarize as us. So who exactly are you? Is there anyone down deep, at the core?

Your memory of an event is represented by the unique constellation of cells involved in the details you experience.

So a single event may be perceived somewhat differently by you at different stages in your life.

To imagine tomorrow’s experience at the beach, the hippocampus, in particular, plays a key role in assembling an imagined future by recombining information from our past.

Keeping a busy lifestyle into old age benefits the brain.

The participants with diseased neural tissue – but no cognitive symptoms – have built up what is known as “cognitive reserve”. As areas of brain tissue have degenerated, other areas have been well exercised, and therefore have compensated or taken over those functions. The more we keep our brains cognitively fit – typically by challenging them with difficult and novel tasks, including social interaction – the more the neural networks build new roadways to get from A to B.

Think of the brain like a toolbox. If it’s a good toolbox, it will contain all the tools you need to get a job done. If you need to disengage a bolt, you might fish out a ratchet; if you don’t have access to the ratchet, you’ll pull out a wrench; if the wrench is missing you might try a pair of pliers. It’s the same concept in a cognitively fit brain: even if many pathways degenerate because of disease, the brain can retrieve other solutions.

Consciousness emerges when neurons are coordinating with one another in complex, subtle, mostly independent rhythms. In slow-wave sleep, neurons are more synchronized with one another, and consciousness is absent.

So who you are depends on what your neurons are up to, moment by moment.

Imagine I were to take a piece of cloth, put some colored pigments on it, and display it to your visual system. Is that likely to trigger memories and fire up your imagination? Well, probably not, because it’s just a piece of cloth, right? But now imagine that those pigments on a cloth are arranged into a pattern of a national flag. Almost certainly that sight will trigger something for you – but the specific meaning is unique to your history of experiences. You don’t perceive objects as they are. You perceive them as you are.

And because the physical stuff is constantly changing, we are too. We’re not fixed. From cradle to grave, we are works in progress. Your interpretation of physical objects has everything to do with the historical trajectory of your brain – and little to do with the objects themselves. These two rectangles contain nothing but arrangements of color. A dog would appreciate no meaningful difference between them. Whatever reaction you have to these is all about you, not them.

gone. To synchronize the incoming information from the senses, the cost is that our conscious awareness lags behind the physical world. That’s the unbridgeable gap between an event occurring and your conscious experience of it.

So at any moment, what we experience as seeing relies less on the light streaming into our eyes, and more on what’s already inside our heads.

So why does the world appear stable to you when you’re looking at it? Why doesn’t it appear as jerky and nauseating as the poorly filmed video? Here’s why: your internal model operates under the assumption that the world outside is stable. Your eyes are not like video cameras – they simply venture out to find more details to feed into the internal model. They’re not like camera lenses that you’re seeing through; they’re gathering bits of data to feed the world inside your skull.

We tracked eye movements as volunteers looked at The Unexpected Visitor, a painting by Ilya Repin. The white streaks show where their eyes went. Despite the coverage with eye movements, they retained almost none of the detail.

So why doesn’t the brain give us the full picture? Because brains are expensive, energy-wise. Twenty percent of the calories we consume are used to power the brain. So brains try to operate in the most energy-efficient way possible, and that means processing only the minimum amount of information from our senses that we need to navigate the world.

So what does the world outside your head really “look” like? Not only is there no color, there’s also no sound: the compression and expansion of air is picked up by the ears, and turned into electrical signals. The brain then presents these signals to us as mellifluous tones and swishes and clatters and jangles. Reality is also odorless: there’s no such thing as smell outside our brains. Molecules floating through the air bind to receptors in our nose and are interpreted as different smells by our brain. The real world is not full

Every time I meet someone who has this kind of experience, it’s a reminder that from person to person – and from brain to brain – our internal experience of reality can be somewhat different.

Believing what our brains tell us

sporadically

It was about chemical imbalances in her brain that subtly changed the pattern of signals. A slightly different pattern, and one can suddenly be trapped inside a reality in which strange and impossible things unfold. When Elyn was inside a schizophrenic episode, it never struck her that something was strange. Why? Because she believed the narrative told by the sum of her brain chemistry.

cognizant.

reality is a narrative played out inside the sealed auditorium of the cranium.

In threatening situations, an area of the brain called the amygdala kicks into high gear, commandeering the resources of the rest of the brain and forcing everything to attend to the situation at hand. When the amygdala is in play, memories are laid down with far more detail and richness than under normal circumstances; a secondary memory system has been activated. After all, that’s what memory is for: keeping track of important events, so that if you’re ever in a similar situation, your brain has more information to try to survive. In other words, when things are life-threateningly scary, it’s a good time to take notes.

Your brain serves up a narrative – and each of us believes whatever narrative it tells. Whether you’re falling for a visual illusion, or believing the dream you happen to be trapped in, or experiencing letters in color, or accepting a delusion as true during an episode of schizophrenia, we each accept our realities however our brains script them.

Despite the feeling that we’re directly experiencing the world out there, our reality is ultimately built in the dark, in a foreign language of electrochemical signals. The activity churning across vast neural networks gets turned into your story of this, your private experience of the world: the feeling of this book in your hands, the light in the room, the smell of roses, the sound of others speaking.

So what is reality? It’s like a television show that only you can see, and you can’t turn it off. The good news is that it happens to be broadcasting the most interesting show you could ask for: edited, personalized, and presented just for you.

This is your brain on flow. Dean tries not to think while he climbs without a rope. Conscious interference would worsen his performance.

The deep caverns of the unconscious

He became convinced that the conscious mind is the tip of the iceberg of our mental processes, while the much larger part of what drives our thoughts and behaviors lies hidden from view. Freud suggested that the mind is like an iceberg, the majority of it hidden from our awareness.

We mostly walk around in our own mental worlds, passing strangers in the street without registering any details about them. But when something

goals. Consciousness is the system that has this unique vantage point, one that no other subsystem of the brain has. And for this reason, it can play the role of arbiter of the billions of interacting elements, subsystems and burnt-in processes. It can make plans and set goals for the system as a whole.

Even after an experimenter manipulates a choice by stimulating the brain, participants often claim that their decision was freely chosen.

The power of now So we’ve seen how values get attached to different options. But there’s a twist that often gets in the way of good decision making: options right in front of us tend to be valued higher than those

we merely simulate. The thing that trips up good decision making about the future is the present. In 2008, the US economy took a sharp downturn. At the heart of the trouble was the simple fact that many homeowners had over-borrowed. They had taken out loans that offered wonderfully low interest rates for a period of a few years. The problem occurred at the end of the trial period, when the rates went up. At the higher rates, many homeowners found themselves unable to make the payments. Close to a million homes went into foreclosure, sending shockwaves through the economy of the planet. What did this disaster have to do with competing networks in the brain? These subprime loans allowed people to obtain a nice house now, with the high rates deferred until later. As such, the offer perfectly appealed to the neural networks that desire instant gratification – that is, those networks that want things now. Because the seduction of the immediate satisfaction pulls so strongly on our decision making, the housing bubble can be understood not simply as an economic phenomenon, but also as a neural one. The pull of the now wasn’t just about the people borrowing, of course, but also the lenders who were getting rich, right now, by offering loans that weren’t going to get paid. They rebundled the loans and sold them off. Such practices are unethical, but the temptation proved too enticing to many thousands. This now-versus-the-future battle doesn’t just apply to housing bubbles, it cuts...

inspiration from a man who lived 3,000 years ago.

So willpower isn’t something that we just exercise – it’s something we deplete.

nuanced

burgeoning

incarceration

relapse

hamstrung

Although you have a single identity, you’re not of a single mind: instead, you are a collection of many competing drives. By understanding how choices battle it out in the brain, we can learn to make better decisions for ourselves, and for our society.