The Brain

In the brain’s microscopically small circuitry is etched the history and future of our species.

All the experiences in your life – from single conversations to your broader culture – shape the microscopic details of your brain. Neurally speaking, who you are depends on where you’ve been. Your brain is a relentless shape-shifter, constantly rewriting its own circuitry – and because your experiences are unique, so are the vast, detailed patterns in your neural networks. Because they continue to change your whole life, your identity is a moving target; it never reaches an endpoint.

Only a couple of decades ago it was thought that brain development was mostly complete by the end of childhood. But we now know that the process of building a human brain takes up to twenty-five years.

Hormones coursing around our bodies cause obvious physical changes as we take on the appearance of adults – but out of sight our brains are undergoing equally monumental changes. These changes profoundly color how we behave and react to the world around us.

medial prefrontal cortex (mPFC). This region becomes active when you think about your self – and especially the emotional significance of a situation to your self.

Beyond social awkwardness and emotional hypersensitivity, the teen brain is set up to take risks. Whether it’s driving fast or sexting naked photos, risky behaviors are more tempting to the teen brain than to the adult brain. Much of that has to do with the way we respond to rewards and incentives. As we move from childhood into adolescence, the brain shows an increasing response to rewards in areas related to pleasure seeking (one such area is called the nucleus accumbens). In teens, the activity here is as high as it is in adults. But here’s the important fact: activity in the orbitofrontal cortex – involved in executive decision making, attention, and simulating future consequences – is still about the same in teens as it is in children. 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.

who we are as a teenager is not simply the result of a choice or an attitude; it is the product of a period of intense and inevitable neural change.

By the time we’re twenty-five years of age, the brain transformations of childhood and adolescence are finally over. The tectonic shifts in our identity and personality have ended, and our brain appears to now be fully developed. You might think that who we are as adults is now fixed in place, immoveable. But it’s not: in adulthood our brains continue to change. Something that can be shaped – and can hold that shape – is what we describe as plastic. And so it is with the brain, even in adulthood: experience changes it, and it retains the change.

When one of the most famous brains of the twentieth century was examined, Albert Einstein’s brain did not reveal the secret of his genius. But it did show that the brain area devoted to his left fingers had expanded – forming a giant fold in his cortex called the Omega sign, shaped like the Greek symbol O – all thanks to his less commonly known passion for playing the violin. This fold becomes enlarged in experienced violin players, who intensively develop fine dexterity with the fingers of their left hand. Piano players, in contrast, develop an Omega sign in both hemispheres, as they use both hands in fine, detailed movements.

everything you’ve experienced has altered the physical structure of your brain – from the expression of genes to the positions of molecules to the architecture of neurons.

Your family of origin, your culture, your friends, your work, every movie you’ve watched, every conversation you’ve had – these have all left their footprints in your nervous system. These indelible, microscopic impressions accumulate to make you who you are, and to constrain who you can become.

Whitman’s request was granted. After an autopsy, the pathologist reported that Whitman had a small brain tumor. It was about the size of a nickel, and it was pressing against a part of his brain called the amygdala, which is involved in fear and aggression. This small amount of pressure on the amygdala led to a cascade of consequences in Whitman’s brain, resulting in him taking actions that would otherwise be completely out of character. His brain matter had been changing, and who he was changed with it.

Consider the ingestion of drugs or alcohol. Particular kinds of epilepsy make people more religious. Parkinson’s disease often makes people lose their faith, while the medication for Parkinson’s can often turn people into compulsive gamblers. 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?

Our brains and bodies change so much during our life that – like a clock’s hour hand – it’s difficult to detect the changes. Every four months your red blood cells are entirely replaced, for instance, and your skin cells are replaced every few weeks. Within about seven years every atom in your body will be replaced by other atoms. Physically, you are constantly a new you. Fortunately, there may be one constant that links all these different versions of your self together: memory. Perhaps memory can serve as the thread that makes you who you are. It sits at the core of your identity, providing a single, continuous sense of self.

The enemy of memory isn’t time; it’s other memories.

So not only was it possible to implant false new memories in the brain, but people embraced and embellished them, unknowingly weaving fantasy into the fabric of their identity.

We’re all susceptible to this memory manipulation – even Loftus herself. As it turns out, when Elizabeth was a child, her mother had drowned in a swimming pool. Years later, a conversation with a relative brought out an extraordinary fact: that Elizabeth had been the one to find her mother’s body in the pool. That news came as a shock to her; she hadn’t known that, and in fact she didn’t believe it. But, she describes, “I went home from that birthday and I started to think: maybe I did. I started to think about other things that I did remember – like when the firemen came, they gave me oxygen. Maybe I needed the oxygen ’cause I was so upset that I found the body?” Soon, she could visualize her mother in the swimming pool. But then her relative called to say he had made a mistake. It wasn’t the young Elizabeth after all who had found the body. It had been Elizabeth’s aunt. And that’s how Loftus had the opportunity to experience what it was like to possess her own false memory, richly detailed and deeply felt.

Our past is not a faithful record. Instead it’s a reconstruction, and sometimes it can border on mythology. When we review our life memories, we should do so with the awareness that not all the details are accurate. Some came from stories that people told us about ourselves; others were filled in with what we thought must have happened. So if your answer to who you are is based simply on your memories, that makes your identity something of a strange, ongoing, mutable narrative.

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. Each of us is on our own trajectory – steered by our genes and our experiences – and as a result every brain has a different internal life. Brains are as unique as snowflakes.

As your trillions of new connections continually form and re-form, the distinctive pattern means that no one like you has ever existed, or will ever exist again. The experience of your conscious awareness, right now, is unique to you. And because the physical stuff is constantly changing, we are too. We’re not fixed. From cradle to grave, we are works in progress.

Our perception of reality has less to do with what’s happening out there, and more to do with what’s happening inside our brain.

There are a hundred billion neurons in the human brain, and each neuron sends tens or hundreds of electrical pulses to thousands of other neurons every second of your life.

Everything you experience – every sight, sound, smell – rather than being a direct experience, is an electrochemical rendition in a dark theater.

One of neuroscience’s unsolved puzzles is known as the “binding problem”: how is the brain able to produce a single, unified picture of the world, given that vision is processed in one region, hearing in another, touch in another, and so on? While the problem is still unsolved, the common currency among neurons – as well as their massive interconnectivity – promises to be at the heart of the solution.

Vision isn’t about photons that can be readily interpreted by the visual cortex. Instead it’s a whole body experience. The signals coming into the brain can only be made sense of by training, which requires cross-referencing the signals with information from our actions and sensory consequences. It’s the only way our brains can come to interpret what the visual data actually means.

When babies hit the bars of their cribs and chew their toes and play with their blocks, they’re not simply exploring – they’re training up their visual systems.

But here’s where it gets strange. We’ve just seen that the brain processes sounds more quickly than sights. And yet take a careful look at what happens when you clap your hands in front of you. Try it. Everything seems synchronized. How can that be, given that sound is processed more quickly? What it means is that your perception of reality is the end result of fancy editing tricks: the brain hides the difference in arrival times.

What it serves up as reality is actually a delayed version. Your brain collects up all the information from the senses before it decides upon a story of what happens.

you collect up all the signals first, so that everything seems synchronized. The strange consequence of all this is that you live in the past. By the time you think the moment occurs, it’s already long 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.

Completely isolated from the outside world, with no sound and no light, Luke’s eyes and ears were completely starved of input. But his mind didn’t abandon the notion of an outside world. It just continued to make one up.

In fact, the brain generates its own reality, even before it receives information coming in from the eyes and the other senses. This is known as the internal model.

The thalamus simply reports on differences between what the eyes are reporting, and what the brain’s internal model has predicted. In other words, what gets sent back to the visual cortex is what fell short in the expectation (also known as the “error”): the part that wasn’t predicted away.

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.

And of course you don’t have to go far to find your own sensory deprivation chamber. Every night when you go to sleep you have full, rich, visual experiences. Your eyes are closed, but you enjoy the lavish and colorful world of your dreams, believing the reality of every bit of it.

Instead of using your senses to constantly rebuild your reality from scratch every moment, you’re comparing sensory information with a model that the brain has already constructed: updating it, refining it, correcting it. Your brain is so expert at this task that you’re normally unaware of it.

This isn’t a failure of the brain. It doesn’t try to produce a perfect simulation of the world. Instead, the internal model is a hastily drawn approximation – as long as the brain knows where to go to look for the finer points, more details are added on a need-to-know basis.

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.

We think of color as a fundamental quality of the world around us. But in the outside world, color doesn’t actually exist. When electromagnetic radiation hits an object, some of it bounces off and is captured by our eyes. We can distinguish between millions of combinations of wavelengths – but it is only inside our heads that any of this becomes color. Color is an interpretation of wavelengths, one that only exists internally. And it gets stranger, because the wavelengths we’re talking about involve only what we call “visible light”, a spectrum of wavelengths that runs from red to violet. But visible light constitutes only a tiny fraction of the electromagnetic spectrum – less than one ten-trillionth of it. All the rest of the spectrum – including radio waves, microwaves, X-rays, gamma rays, cell phone conversations, wi-fi, and so on – all of this is flowing through us right now, and we’re completely unaware of it. This is because we don’t have any specialized biological receptors to pick up on these signals from other parts of the spectrum. The slice of reality that we can see is limited by our biology.

Each creature picks up on its own slice of reality. In the blind and deaf world of the tick, the signals it detects from its environment are temperature and body odor. For bats, it’s the echolocation of air compression waves. For the black ghost knifefish, its experience of the world is defined by perturbations in electrical fields. These are the slices of their ecosystem that they can detect. No one is having an experience of the objective reality that really exists; each creature perceives only what it has evolved to perceive. But presumably, every creature assumes its slice of reality to be the entire objective 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 of rich sensory events; instead, our brains light up the world with their own sensuality.

Synesthesia is a condition in which senses (or in some cases concepts) are blended. There are many different kinds of synesthesia. Some taste words. Some see sounds as colors. Some hear visual motion. About 3% of the population has some form of synesthesia.

Schizophrenia is a disorder of her brain function, causing her to hear voices, or see things others don’t see, or believe that other people are reading her thoughts.

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.

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.

For every situation with multiple witnesses, different brains are having different private subjective experiences. With seven billion human brains wandering the planet (and trillions of animal brains), there’s no single version of reality. Each brain carries its own truth. 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.

The intricate details of our most basic movements are animated by trillions of calculations, all buzzing along at a spatial scale smaller than you can see, and a complexity scale beyond what you can comprehend. We have yet to build robots that scratch the edges of human performance. And while a supercomputer racks up enormous energy bills, our brains work out what to do with baffling efficiency, using about the energy of a 60-watt light bulb.

German physiologist and psychiatrist Hans Berger recorded the first human EEG in 1924, and researchers in the 1930s and 1940s identified several different types of brain waves: Delta waves (below 4 Hz) occur during sleep; Theta waves (4–7 Hz) are associated with sleep, deep relaxation, and visualization; Alpha waves (8–13 Hz) occur when we are relaxed and calm; Beta waves (13–38 Hz) are seen when we are actively thinking and problem solving. Other ranges of brain waves have been identified as important since then, including Gamma waves (39–100 Hz) which are involved in concentrated mental activity, such as reasoning and planning.

As a skill becomes hardwired, it sinks below the level of conscious control. At that point, we can perform a task automatically and without thinking about it – that is, without conscious awareness.

During flow, the brain enters a state of hypofrontality, meaning that parts of the prefrontal cortex temporarily become less active. These are areas involved in abstract thinking, planning into the future, and concentrating on one’s sense of self.

It’s often the case that consciousness is best left at the sidelines – and for some types of tasks, there’s really no choice, because the unconscious brain can perform at speeds that the conscious mind is too slow to keep up with.

your unconscious brain has been working on those ideas – consolidating memories, trying out new combinations, evaluating the consequences – for hours or months before the idea rises to your awareness and you declare, “I just thought of something!”

Sigmund Freud entered medical school in Vienna in 1873, and specialized in neurology. When he opened his private practice for the treatment of psychological disorders, he realized that often his patients had no conscious knowledge of what was driving their behavior. Freud’s insight was that much of their behavior was a product of unseen mental processes. This simple idea transformed psychiatry, ushering in a new way of understanding human drives and emotions.

Freud suggested that the mind is like an iceberg, the majority of it hidden from our awareness.

Our brains constantly pull information from the environment and use it to steer our behavior, but often the influences around us are not recognized.

In their book Nudge, Richard Thaler and Cass Sunstein laid out an approach to improving “decisions about health, wealth, and happiness” by playing to the brain’s unconscious networks. A small nudge in our environment can change our behavior and decision making for the better, without us being aware of it.

“implicit egotism”, which describes our attraction to things that remind us of ourselves.

When psychologist John Jones and his colleagues looked at the marriage registers in Georgia and Florida they discovered that more married couples than expected shared the same first initial.

None of the men explicitly noted anything about women’s pupil sizes – and presumably none of the men knew that dilated eyes are a biological sign of female arousal. But their brains knew it.

Really, this is how love often goes. You find yourself more attracted to some people over others, and it’s generally not possible to put your finger on precisely why. Presumably there is a why; you just don’t have access to it.

The job of this organ is to gather information about the world and steer your behavior appropriately. It doesn’t matter if your conscious awareness is involved or not. And most of the time it’s not. Most of the time you are not aware of the decisions being made on your behalf.

We mostly walk around in our own mental worlds, passing strangers in the street without registering any details about them. But when something challenges our unconscious expectations, conscious attention comes online to try to build a rapid model of what’s happening.

In terms of the brain, consciousness is a way for billions of cells to see themselves as a unified whole, a way for a complex system to hold up a mirror to itself.

The conscious mind excels at telling itself the narrative of being in control.

Our brains are like this ping pong ball tank, but massively more complex. You might be able to fit a few hundred ping pong balls in a tank, but your skull houses trillions of times more interactions than the tank, and it goes on bouncing throughout every second of your lifetime. And from those innumerable exchanges of energy, your thoughts, feelings, and decisions emerge.

our lives are steered by forces far beyond our capacity for awareness or control.

Because the brain has no pain receptors, a patient can be awake during a surgery.

Who you are emerges from the brain-wide battles for dominance that rage in your skull every moment of your life.

Unlike computers, the brain runs on conflict between different possibilities, all of which try to out-compete the others.

As a treatment for certain forms of epilepsy, some patients undergo “split-brain” surgery, in which the brain’s two hemispheres are disconnected from each other. Normally the two hemispheres are connected by a super-highway of nerves called the corpus callosum, and this allows the right and left halves to coordinate and work in concert.

when the corpus callosum is severed, a remarkable and haunting clinical condition can emerge: alien hand syndrome. The two hands can act with totally different intentions:

The trolley dilemma. When people are asked what they would do in this scenario, almost everyone pulls the lever. After all, it’s far better that only one person is killed rather than four, right?

Our rational networks tell us that one death is better than four, but our emotional networks trigger a gut feeling that murdering the bystander is wrong.

The detached nature of distance warfare reduces internal conflict, making it easier to wage.

The ancient Greeks suggested that we should think of our lives like chariots. We are charioteers trying to hold two horses: the white horse of reason and the black horse of passion. Each horse pulls off-center, in opposite directions. Your job is to keep control of both horses, navigating down the middle of the road.

Emotions do more than add richness to our lives – they’re also the secret behind how we navigate what to do next at every moment.

It’s easy to think about the brain commanding the body from on high – but in fact the brain is in constant feedback with the body.

To land on a choice, the body and the brain have to be in close communication.

Your physiological signature can be thought of as a low-resolution headline: “this is bad” or “this is no problem.” And that helps your brain decide what to do next.

The physiological state of the body maintains a constant two-way dialog with the brain.

You don’t just extract the data from the soup cans, you feel the data.

Earlier, when you were deciding between the mint and lemon yogurt, there was a battle between networks. The physiological states from your body were the key things that helped tip that battle, that allowed one network to win over another.

Because the conscious mind has low bandwidth, you don’t typically have full access to the bodily signals that tip your decisions; most of the action in your body lives far below your awareness.

As Read Montague points out, “sharks don’t go on hunger strikes”: the rest of the animal kingdom only chases its basic needs, while only humans regularly override those needs in deference to abstract ideals.

Time travel is something the human brain does relentlessly. When faced with a decision, our brains simulate different outcomes to generate a mockup of what our future might be. Mentally, we can disconnect from the present moment and voyage to a world that doesn’t yet exist.

Like all animals in the animal kingdom, we can’t just wander around hoping to randomly discover what results in future reward and what doesn’t.

There’s a tiny, ancient system in the brain whose mission is to keep updating your assessments of the world. This system is made of tiny groups of cells in your midbrain that speak in the language of a neurotransmitter called dopamine.

When there’s a mismatch between your expectation and your reality, this midbrain dopamine system broadcasts a signal that re-evaluates the price point. This signal tells the rest of the system whether things turned out better than expected (an increased burst of dopamine) or worse (a decrease in dopamine). That prediction error signal allows the rest of the brain to adjust its expectations to try to be closer to reality next time.

The dopamine acts as an error corrector: a chemical appraiser that always works to make your appraisals as updated as they can be. That way, you can prioritize your decisions based on your optimized guesses about the future.

Dopamine-releasing neurons involved in decision making are concentrated into tiny regions of the brain called the ventral tegmental area and the substantia nigra. Despite their small sizes, they have a wide reach, broadcasting updates when the predicted value of a choice turns out to be too high or too low.

Ulysses contract.

The key to the Ulysses contract is recognizing that we are different people in different contexts. To make better decisions, it’s important not only to know yourself but all of your selves.

A study in 2011 analyzed a thousand rulings from judges, and found it likely wasn’t about any of those factors. It was mostly about hunger. Just after the parole board had enjoyed a food break, a prisoner’s chance of parole rose to its highest point of 65%. But a prisoner seen towards the end of a session had the lowest chances: just a 20% likelihood of a favorable outcome.

Some psychologists describe this effect as “ego-depletion,” meaning that higher-level cognitive areas involved in executive function and planning (for example, the prefrontal cortex) get fatigued.

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

The dorsolateral prefrontal cortex becomes active when dieters choose the healthier food options in front of them, or when people choose to forego a small reward now for a better outcome later.

monogamy – bonding and staying with a single partner.

In one recent study, men who were in love with their female partners were given a small dose of extra oxytocin. They were then asked to rate the attractiveness of different women. With the extra oxytocin, the men found their partners more attractive – but not other women. In fact, the men kept a bit more physical distance from an attractive female research associate in the study. Oxytocin increased bonding to their partner.

After all, from an evolutionary perspective, we might expect that a male shouldn’t want monogamy if his biological mandate is to spread his genes as widely as possible. But for the survival of the children, having two parents around is better than one. This simple fact is so important that the brain possesses hidden ways to influence your decision making on this front.

At the extreme, we can end up as slaves to the immediate cravings of our impulses.

A few decades ago, 38,000 Americans were in prison for drug-related offenses. Today, it’s half a million.

The US has more people in prison for drug-related crimes than the European Union has prisoners.

The difficulty with drug supply is that it’s like a water balloon: if you push it down in one place, it comes up somewhere else. Instead of attacking supply, the better strategy is to address demand. And drug demand is in the brain of the addict.

In laboratory experiments, rats will self-administer drugs, continually hitting the delivery lever at the expense of food and drink. The rats aren’t doing that because of finances or social coercion. They’re doing it because the drugs tap into fundamental reward circuitry in their brains. The drugs effectively tell the brain that this decision is better than all the other things it could be doing. Other brain networks may join the battle, representing all the reasons to resist the drug. But in an addict, the craving network wins. The majority of drug addicts want to quit but find themselves unable. They end up becoming slaves to their impulses.

Drug addiction is a problem for millions of people. But prisons aren’t the place to solve the problem. Equipped with an understanding of how human brains actually make decisions, we can develop new approaches beyond punishment.

One such place is Mendota Juvenile Treatment Center in Madison, Wisconsin. Many of the twelve to seventeen-year-olds at Mendota have committed crimes that might otherwise qualify them for life in prison. Here, it qualifies them for admission. For many of the children, this is their last chance. The program started in the early 1990s to provide a new approach to working with youths the system had given up on. The program pays particular attention to their young, developing brains. As we saw in Chapter 1, without a fully developed prefrontal cortex, decisions are often made impulsively, without meaningful consideration of future consequences.

Mendota is an experiment in alternatives. Although societies possess deeply ingrained impulses for punishment, a different kind of criminal justice system – one with a closer relationship to the neuroscience of decisions – can be imagined.

Decision making lies at the heart of everything: who we are, what we do, how we perceive the world around us.

Normal brain function depends on the social web around us. Our neurons require other people’s neurons to thrive and survive.

Brains have traditionally been studied in isolation, but that approach overlooks the fact that an enormous amount of brain circuitry has to do with other brains.

Our social skills are deeply rooted in our neural circuitry – and understanding this circuitry is the basis of a young field of study called social neuroscience.

This penchant to assign intention to non-human characters was highlighted in a short film made in 1944 by psychologists Fritz Heider and Marianne Simmel.

From time immemorial, people have watched the flights of birds, the movement of stars, the swaying of trees, and invented stories about them, interpreting them as having intention.

even as babies, we come equipped with social antennae for feeling our way through the world. The brain comes with inborn instincts to detect who’s trustworthy, and who isn’t.

Autism is a neurodevelopmental disorder which affects 1% of the population. Although it’s established that both genetic and environmental causes underpin its development, the number of individuals diagnosed with autism has been on the rise in recent years, with little to no evidence explaining this increase.

In autism, this brain activity is not seen as strongly – and this is paralleled by diminished social skills.

Dr. Alvaro Pascual-Leone was using transcranial magnetic stimulation (TMS) to assess how activity in one area of the brain affected activity in another area.

This is the Botulinum toxin, derived from a bacterium, and it’s commonly marketed under the brand name Botox. When injected into facial muscles, it paralyzes them and thereby reduces wrinkling.

We showed Botox users the same set of photos. Their facial muscles showed less mirroring on our electromyogram. No surprise there – their muscles have been purposely weakened.

Imagine that someone stabs your hand with a syringe needle. There’s no single place in the brain where that pain is processed. Instead, the event activates several different areas of the brain, all operating in concert. This network is summarized as the pain matrix.

watching someone else in pain and being in pain use the same neural machinery. This is the basis of empathy.

The pain matrix is the name given to a set of areas that become active when you are in pain. Most of these areas also become active when you watch someone else in pain.

To empathize with another person is to literally feel their pain. You run a compelling simulation of what it would be like if you were in that situation. Our capacity for this is why stories – like movies and novels – are so absorbing and so pervasive across human culture.

From an evolutionary point of view, empathy is a useful skill: by gaining a better grasp of what someone is feeling, it gives a better prediction about what they’ll do next.

We can’t help but simulate others, connect with others, care about others, because we’re hardwired to be social creatures.

Solitary confinement is illegal in many jurisdictions, precisely because observers have long recognized the damage caused by stripping away one of the most vital aspects of a human life: interaction with others.

The philosopher Martin Heidegger suggested that it is difficult to speak of a person “being”, instead we are typically “being in the world.”

She found something remarkable: when the volunteers were left out of the game, areas involved in their pain matrix became active. Not getting the ball might seem insignificant, but to the brain social rejection is so meaningful that it hurts, literally.

Social pain – such as that resulting from exclusion – activates the same brain regions as physical pain.

“kin selection”. This means that I care not only about myself, but also others with whom I share genetic material,

“group selection”. Here’s the concept: if a group is composed entirely of people who cooperate, everyone in the group will be better off for it.

Together, the members of a group can help each other to survive. They’re safer, more productive, and better able to overcome challenges. This drive to bond with others is called eusociality (eu is Greek for good), and it provides a glue, irrespective of kinship, that allows the building of tribes, groups, and nations.

This has allowed human populations to thrive across the planet, and to build societies and civilizations – feats that individuals, no matter how fit, could never pull off in isolation.

Real progress is only possible with alliances that become confederations, and our eusociality is one of the major factors in the richness and complexity of our modern world.

Repeatedly, all across the globe, groups of people inflict violence on other groups, even those that are defenceless and pose no direct threat. The year 1915 saw the systematic killing of over a million Armenians by the Ottoman Turks. In the Nanking massacre of 1937, the Japanese invaded China and killed hundreds of thousands of unarmed civilians. In 1994, in a period of one hundred days, the Hutus in Rwanda killed 800,000 Tutsis, largely with machetes.

Syndrome E is characterized by a diminished emotional reactivity, which allows repetitive acts of violence.

Instead, a perpetrator’s choices are now fueled by parts of the brain that underpin logic and memory and reasoning and so on, but not the networks that involve emotional consideration of what it is like to be someone else.

People are no longer using the emotional systems that under normal circumstances steer their social decision making.

people’s brains showed a larger empathic response when they saw someone in their ingroup in pain, and less of a response when it was a member of one of their outgroups.

Lasana Harris of the University of Leiden in Holland

Harris is looking for changes in the brain’s social network, in particular the medial prefrontal cortex (mPFC). This region becomes active when we’re interacting with, or thinking about, other people – but it’s not active when we’re dealing with inanimate objects, like a coffee mug.

Harris shows volunteers photographs of people from different social groups, for example, homeless people, or drug addicts. And he finds that the mPFC is less active when they look at a homeless person. It’s as though the person is more like an object.

The medial prefrontal cortex is involved in thinking about other people – at least, most other people.

As he puts it, by shutting down the systems that see the homeless person as a fellow human, one doesn’t have to experience the unpleasant pressures of feeling bad about not giving money. In other words, the homeless have become dehumanized: the brain is viewing them more like objects and less like people.

Dehumanization is a key component of genocide.

Genocide is only possible when dehumanization happens on a massive scale, and the perfect tool for this job is propaganda:

it keys right into the neural networks that understand other people, and dials down the degree to which we empathize with them.

One of the most important things we learn as humans is perspective taking.

When one is forced to understand what it’s like to stand in someone else’s shoes, it opens up new cognitive pathways.

Education plays a key role in preventing genocide. Only by understanding the neural drive to form ingroups and outgroups – and the standard tricks by which propaganda plugs into this drive – can we hope to interrupt the paths of dehumanization that end in mass atrocity.

The human body is a masterpiece of complexity and beauty – a symphony of forty trillion cells working in concert.

Over the last 100,000 years our species has been on quite a journey: we’ve gone from living as primitive hunter-gatherers surviving on scraps to a planet-conquering hyper-connected species that defines its own destiny.

The secret to understanding our success – and our future opportunity – is the brain’s tremendous ability to adjust, known as brain plasticity.

Brain plasticity is also the key to our future, because it opens the door to making modifications to our own hardware.

brain: it rewires itself to adjust to the inputs, outputs, and tasks at hand.

the brain is fundamentally unlike the hardware in our digital computers. Instead, it’s “liveware”. It reconfigures its own circuitry.

We come into the world with a standard set of basic senses: hearing, touch, sight, smell, and taste, along with other senses such as balance, vibration, and temperature. The sensors we have are the portals by which we pick up signals from our environment.

I think of our sensory portals as peripheral plug-and-play devices. The key is that the brain doesn’t know and doesn’t care where it gets the data.

The idea is that Mother Nature only needed to invent the principles of brain operation once – and then she was freed up to tinker with designing new input channels.

In this framework, evolution doesn’t need to continually redesign the brain, just the peripherals, and the brain figures out how to utilize them.

Snakes have heat sensors. The glass knifefish has electrosensors for interpreting changes in the local electrical field. Cows and birds have magnetite, with which they can orient themselves to the Earth’s magnetic field. Animals can see in ultraviolet; elephants can hear at very long distances, while dogs experience a richly scented reality.

The end result is that evolution has built a brain that can experience many different slices of reality.

The body we arrive with is really just the starting point for humanity. In the distant future, we won’t just be extending our physical bodies, but fundamentally our sense of self.

Our great-great-great-great-grandchildren may struggle to understand who we were, and what was important to us. At this moment in history, we may have more in common with our Stone Age ancestors than with our near-future descendants.

There will come a moment when all your neural activity will come to a halt, and then the glorious experience of being conscious will come to an end. It doesn’t matter who you know or what you do: this is the fate of all of us. In fact, it’s the fate of all life, but only humans are so unusually foresighted that we suffer over this knowledge.

For the past fifty years, the Alcor Life Extension Foundation has been developing technology they believe will allow people living today to enjoy a second life-cycle later. The organization currently stores 129 people in a deep freeze that halts their biological decay.

A person is declared legally dead when either his brain is clinically dead or his body has experienced irreversible cessation of respiration and circulation.

Biological death, on the other hand, happens in the absence of intervention, and involves the death of cells throughout the body: in the organs and in the brain, and means that the organs are no longer suitable for donation.

no one on the planet today knows how to successfully unfreeze and reanimate these frozen residents. But that’s not the point. The hope is that one day the technology will exist to carefully thaw – and then revive – the people in this community.

the sub-microscopically detailed structure of your brain contains all your knowledge and memories – so why couldn’t that book be decrypted?

The typical brain has about eighty-six billion neurons, each making about ten thousand connections. They connect in a very specific manner, unique to each person.

Your experiences, your memories, all the stuff that makes you you is represented by the unique pattern of the quadrillion connections between your brain cells. This pattern, far too large to comprehend, is summarized as your “connectome”.

Dr. Sebastian Seung at Princeton is working with his team to excavate the fine details of a connectome.

The alchemy of thought, of feeling, of awareness – this emerges from quadrillions of interactions between brain cells every second: the release of chemicals, the changes in the shapes of proteins, the traveling waves of electrical activity down the axons of neurons.

a team of researchers at the École polytechnique fédérale de Lausanne (EPFL) in Switzerland is working toward. Their goal is to deliver by 2023 a software and hardware infrastructure capable of running a whole human brain simulation.

The Human Brain Project: a large research team in Switzerland is compiling data from laboratories around the world – with the eventual goal of building a working simulation of a full brain.

computational hypothesis of the brain. The idea is that the neurons and synapses and other biological matter aren’t the critical ingredients: it’s the computations they happen to be implementing. It may be that what the brain physically is doesn’t matter, but instead what it does.

In theory, you might swap cells for circuitry, or oxygen for electricity: the medium doesn’t matter, provided that all the pieces and parts are connecting and interacting in the right way. In this way, we may be able to “run” a fully functioning simulation of you without a biological brain.

The computational hypothesis of the brain is just that – a hypothesis – one that we don’t yet know is true. After all, there may be something special and undiscovered about the biological wetware, and in that case we’re stuck with the biology we arrived with. However, if the computational hypothesis is correct, then a mind could live in a computer.

People have been trying for a long time to create machines that think. That line of research – artificial intelligence – has been around since at least the 1950s.

“Instead of trying to produce a program to simulate the adult mind, why not rather try to produce one which simulates the child’s?” – Alan Turing, 1950. There are twenty-nine identical iCubs in research labs all over the globe, each one part of a common platform that can merge their learning.

In the 1980s the philosopher John Searle came up with a thought experiment that gets right to the heart of this question. He called it the Chinese Room Argument.

In the Chinese Room thought experiment, a man in a booth follows instructions to manipulate symbols. This fools a native speaker into believing that the person in the booth speaks Chinese.

Searle argued this is just what is happening inside a computer. No matter how intelligent a program like iCub seems to be, it’s only following sets of instructions to spit out answers – manipulating symbols without ever really understanding what it’s doing.

With every attempt to simulate or create a human-like intelligence, we’re confronted by a central unsolved question of neuroscience: how does something as rich as the subjective feeling of being me – the sting of pain, the redness of red, the taste of grapefruit – arise from billions of simple brain cells running through their operations? After all, each brain cell is just a cell, following local rules, running its basic operations. By itself, it can’t do much. So how do billions of these add up to the subjective experience of being me?

In 1714, Gottfried Wilhelm Leibniz argued that matter alone could never produce a mind.

Leibniz was a German philosopher, mathematician, and scientist who is sometimes called “the last man who knew everything”.

Leibniz’s Mill. Imagine a large mill. If you were to walk around inside of it, you would see its cogs and struts and levers all moving, but it would be preposterous to suggest that the mill is thinking or feeling or perceiving. How could a mill fall in love or enjoy a sunset? A mill is just made of pieces and parts. And so it is with the brain, Leibniz asserted. If you could expand the brain to the size of a mill and stroll around inside it, you would only see pieces and parts. Nothing would obviously correspond to perception. Everything would simply be acting on everything else. If you wrote down every interaction, it wouldn’t be obvious where thinking and feeling and perceiving reside.

A mill has mechanically interacting pieces and parts, but one wouldn’t be tempted to propose that the mill thinks. So where does the magic occur in the brain, which is also made of pieces and parts?

With millions of members in a colony, leaf-cutter ants cultivate their own food. Just like humans, they’re farmers.

smaller worker ants take the pieces of leaves, chew them into smaller pieces, and use these as fertilizer to grow fungus in large underground “gardens”. The ants feed the fungus, and the fungus blossoms into small fruiting bodies which the ants later eat.

(The relationship has become so symbiotic that the fungus can no longer reproduce on its own; it relies entirely on the ants for its propagation.)

This phenomenon, known as “emergence”, is what happens when simple units interact in the right ways and something larger arises.

get enough of these basic brain cells together, interacting in the right ways, and the mind emerges.

Ants and neurons spend their lives following local rules. The unwitting ants give rise to the sophisticated behavior of colonies; the neurons to us.

No single hunk of metal on an airplane has the property of flight, but when you arrange the pieces in the right way, flight emerges.

private, subjective experience: the show that only happens inside someone’s head.

We could exist digitally by running ourselves as a simulation, escaping the biological wetware from which we’ve arisen, becoming non-biological beings. That would be the single most significant leap in the history of our species, launching us into the era of transhumanism.

Imagine what it could look like to leave your body behind and enter a new existence in a simulated world. Your digital existence could look like any life you wanted. Programmers could make any virtual world for you – worlds in which you can fly, or live underwater, or feel the winds of a different planet.

Uploading would be equivalent to achieving the physics dream of finding a wormhole, allowing us to get from one part of the universe to another in a subjective instant.

Uploading may not be all that different from what happens to you each night when you go to sleep: you experience a little death of your consciousness, and the person who wakes up on your pillow the next morning inherits all your memories, and believes him or herself to be you.

Two thousand three hundred years ago, the Chinese philosopher Chuang Tzu dreamt he was a butterfly. Upon waking, he considered this question: how would I know if I was Chuang Tzu dreaming I’m a butterfly – or instead, if right now I’m a butterfly dreaming I’m a man named Chuang Tzu?

How do I know I’m not a brain in a vat? Maybe someone is stimulating that brain in just the right way to make me believe that I’m here and I’m touching the ground and seeing those people and hearing those sounds. Descartes concluded there might not be any way to know. But he also realized something else: there’s some me at the center trying to figure all this out. Whether or not I’m a brain in a vat, I’m pondering the problem. I’m thinking about this, and therefore I exist.

Only one thing is certain: our species is just at the beginning of something, and we don’t fully know what it is. We’re at an unprecedented moment in history, one in which brain science and technology are co-evolving. What happens at this intersection is poised to change who we are.

For thousands of generations, humans have lived the same sort of life cycle over and over: we’re born, we control a fragile body, we enjoy a small strip of sensory reality, and then we die.