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David Eagleman

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There is a simple thing we learn from studying our brain circuitry. Most of what we do think and feel is not under conscious control. The conscious you - the 'I' that flickers into life when you wake up in the morning - is the smallest bit of what is happening in your brain.

Although we are dependent on the functioning of the brain for our inner lives, it runs its own show. Most of its operations are not open to the conscious mind's security clearance.

Samuel Taylor Coleridge wrote a famous poem 'Kubla Khan' full of exotic and dreamy imagery. But he could only write it when he was high on opium. We credit him with authorship because the words came out of his brain and no-one else's. But if he couldn't access those words sober, who exactly wrote the poem?

If a drunk Mel Gibson is an anti-Semite, and a sober Mel Gibson is authentically apologetic, is there a real Mel Gibson?

We know that our brain does not register everything in our field of vision: the gorilla in the basketball game, the many drivers who hit a pedestrian or cycle right in plain view.

Our brain doesn't try to build a full 3D picture of the world - it just tries to figure out, on the fly, what it needs to pay attention to. If you're in a coffee shop you have a general idea that there are people walls and furniture around, but you don't bother constructing a detailed picture until someone asks "What color dress is she wearing?"

How do fielders catch a high ball in baseball or cricket? You'd think it involves the brain figuring out where the ball s going to land and then moving straight there. But what fielders actually do is run a curved path, with the curve continually changing so that the ball looks like it is travelling in a straight line.

About 15% of human females have a genetic mutation which gives them an extra (fourth) type of color receptor, allowing them to discriminate between colors that most of us see as identical. So it is possible to plug new data streams into the brain and it will figure out how to cope. As Paul Bach-y-Rita said "Just give the brain the information and it will figure it out."

10% of those with visual loss from eye disease will have visual hallucinations. Charles Bonnet syndrome, people losing their sight start seeing birds and people. Underdiagnosed because if tell doctor he assumes it's dementia, and reluctant to tell anyone because they'll assume that. But it isn't dementia or insanity, because person realizes that not there.

Anton's syndrome. Patient is blind (caused by stroke damage), but denies. When doctor asks "What color shirt am I wearing?" patient will confidently answer "blue" tho' shirt is white. Patient is not deliberately lying; genuinely believes the picture she has constructed internally. Only after bumping into enough furniture and walls does she seek help.

Frontotemporal dementia: frontal and temporal lobes degenerate, patients lose ability to control hidden impulses. Become paedophiles, shoplift, undress in public etc. Socialization depends on the control by this part of brain. When taken away, people become disinhibited. Does this mean that they are 'fundamentally' paedophiles, merely socialized to resist the temptation, or does it imply that we are all that way?

100 years ago, epilepsy, schizophrenia etc often treated as demonic possession, and treated with prayer, torture and deprivation. Philosophy that sufferer should just "toughen up". Scientific medicine brought change in attitudes. No amount of beatings or prayer help depression, but a little pill called fluoxertine often helps. Schizophrenia doesn't respond to exorcisms, but can be controlled by risperidone. Mania responds to lithium but not to public ostracism.

Illusion of truth effect: you are more likely to believe that something is true if you've heard it before. Works even when experimenter tells subject that sentences they are about to hear are false.

Consciousness tends to interfere with most of the things the brain is trying to do. If you try to pay too much attention to task system gets bogged down trying to solve problem in slow, inefficient think-it-through way. Professional athletes try not to think. They put in 10,000 hours of training so that in the heat of battle, the right techniques will automatically be applied.

When we think about people who've been blind since birth we imagine them walking round in blackness. But doesn't work like that. A bloodhound has much wider sense of smell than humans. But we don't perceive that as a gap - we perceive our range of smells as a full spectrum. We don't think of ourselves as (partially) color blind, but to that small group of women with 4 color photoreceptors, we are.

Our brains are good at solving social problems such as detecting cheaters, but we are nowhere near as good at figuring out logic problems.

We all have a selection of innate automatic behaviours, ideas so useful that those who genetically predisposed to them survived to pass them on, while those who didn't have them were gradually edited out of the population. These hardwired apps have advantage of speed and low energy consumption, but the disadvantage of being further away from conscious access. Conscious meddling would not improve them.

These behaviours are many and varied - sexual attraction, fear of the dark, arguing, getting jealous, seeking fairness, avoiding incest, recognizing facial expressions.

Artificial Intelligence started out promisingly dealing with lists of facts. But stumbled when tried to deal with the things which humans find 'easy' - walking down footpath, balancing a tall body on two small feet, recognizing a friend. Computer programmers assume that there is a 'best' way to solve any problem, so you should (a)identify that solution (b) program it in. But lesson from nature is that should maybe set up a team of routines which attack problem in different, overlapping ways. And perhaps best way to do that is in evo way - randomly generate little routines and let them reproduce with small mutations. This lets you continuously discover potential solutions instead of trying to think up a single perfect solution from scratch. A law of biology seems to be "Evolve solutions, and when you find a good one, don't stop looking.

We think of mother-child bonding as 'natural' but it is comically easy to interfere with. When mice pups are genetically engineered to lack a particular type of receptor in their opoid system (which is involved in pain suppression and reward) they stop caring about being separated from their mothers. They don't bond. No preference for their mum or a strange female. Suggest that sim mechanism involved in human attachment probs such as autism.

Prairie vole pair-bonding controlled by vasopressin hormone. Increasing levels can make polygamous mt voles monogamous. Swedish study looked at vasopressin receptor, and found that section of gene called RS3 334, men can have no copies, one copy or two copies. The more copies man had, less likely he was to get (or stay) married.

Not uncommon for elephants to go mad and gore people. In 1903 Topsy the elephant killed 3 of his handlers on Coney Island, and, in a display of new technology, was electrocuted by Thomas Edison. In 1916 Mary the elephant killed her keeper in front of a crowd in Tennessee. The circus owner had Mary hung on a massive noose from a railroad crane, the only known elephant-hanging in history.

Large eyes and round faces of babies are not naturally 'cute'. Because evo importance of caring for babies, those genetic lines which did not find their babies cute no longer exist, because their young were no longer properly cared for.

Our left and right brain hemispheres are essentially duplicates. To treat an intractable epilepsy called Rasmussen's encephalitis, half the brain is removed. As long as it is done before child 8 years old, kid is fine.

Nature seems to invent multiple ways of doing things. Normally, our memories are consolidated in the hippocampus. But frightening memories get stored as well by the amygdala on a secondary track. So you have a second memory of same event, but which 'flashes back' in a vivid and emotional way at unpredictable moments.

Alzheimers: autopsies often show people whose brains ravaged, but who showed little evidence while alive. Turns out that these people continually challenged their brains into old age - staying active, doing puzzles, learning new skills. Build up a cognitive reserve. Even while parts of their brain degrade, they have other ways of solving problems. Cognitive reserve achieved by blanketing a problem with overlapping solutions. The handyman with several tools in toolbox.

Keeping secrets: because care about our reputation. But there is a cost in maintaining neural conflict - we want to tell what we know. So popularity of confession, prayer, and websites such as

Impt argument about how should sentence criminals. Reason why they committed crime is irrelevant. We know that all serial killers were abused as children. What we care about is whether they can be changed. If they can't be changed we need to warehouse them - keep society safe by keeping them off the streets. If they an be modified, then put them into a program which does that.

Some argue that inhumane to use cold science to decide sentencing. But our present system fails - ugly people get longer sentences than attractive people, psychiatrists and parole officers can't predict who will reoffend, and our prisons are full of drug addicts who wd be more usefully dealt with by rehabilitation.

People want to believe that their actions are governed by themselves - their personality determines their choices - why I love my wife - "It's not chemistry, it's who I am". Yet narcotics demonstrate how our behaviour and our psychology can be commandeered at the molecular level. Cocaine happens to have a shape that fits the lock used by the dopamine cells for rewards. But it grossly exaggerates the response, making us feel invincible and euphoric.

Our genes may give us a vulnerability to disease or mental problems, but it's the environment that has casting vote. For example, the social stress of being an immigrant to a new country is one of the crucial factors in developing schizophrenia. And the bigger the difference between old culture and the new, the more likely stress. But not everyone. It's those who feel worst about their ethnic differences who are most likely to become psychotic. Those who are comfortable with their heritage are mentally safer.

Occam's Razor: the argument from parsimony but it has failed as often as succeeded. It is more parsiminous to assume that the sun goes round the Earth and that what we perceive is what is really there. These were long defended from viewpoint of parsimony, and they were wrong.


There is a chasm between what your brain knows and what your mind is capable of accessing. Consider the simple act of changing lanes while driving a car. Try this: Close your eyes, grip an imaginary steering wheel, and go through the motions of a lane change. Imagine that you are driving in the left lane and you would like to move over to the right lane. Before reading on, actually try it. I'll give you 100 points if you can do it correctly.

It's a fairly easy task, right? I'm guessing that you held the steering wheel straight, then banked it over to the right for a moment, and then straightened it out again. No problem. Except that, like almost everyone else, you got it completely wrong. The motion of turning the wheel rightward for a bit, then straightening it out again would steer you off the road: you just piloted a course from the left lane onto the sidewalk. The correct motion for changing lanes is banking the wheel to the right, then back through the center, and continuing to turn the wheel just as far to the left side, and only then straightening out. Don't believe it? Verify it for yourself when you're next in the car. It’s such a simple motor task that you have no problem accomplishing it in your daily driving. But when forced to access it consciously, you're flummoxed.

The lane-changing example is one of a thousand. You are not consciously aware of the vast majority of your brain's ongoing activities, nor would you want to be - it would interfere with the brain's well-oiled processes. The best way to mess up your piano piece is to concentrate on your fingers; the best way to get out of breath is to think about your breathing; the best way to miss the golf ball is to analyze your swing.

The ability to remember motor acts like changing lanes is called procedural memory, and it is a type of implicit memory - meaning that your brain holds knowledge of something that your mind cannot explicitly access. Riding a bike, tying your shoes, typing on a keyboard, and steering your car into a parking space while speaking on your cell phone are examples of this. You execute these actions easily but without knowing the details of how you do it. You would be totally unable to describe the perfectly timed choreography with which your muscles contract and relax as you navigate around other people in a cafeteria while holding a tray, yet you have no trouble doing it. This is the gap between what your brain can do and what you can tap into consciously.

The concept of implicit memory has a rich, if little-known, tradition. By the early 1600s, Rene Descartes had already begun to suspect that although experience with the world is stored in memory, not all memory is accessible. The concept was rekindled in the late 1800s by the psychologist Hermann Ebbinghaus, who wrote that "most of these experiences remain concealed from consciousness and yet produce an effect which is significant and which authenticates their previous existence."

To the extent that consciousness is useful, it is useful in small quantities, and for very particular kinds of tasks. It's easy to understand why you would not want to be consciously aware of the intricacies of your muscle movement, but this can be less intuitive when applied to your perceptions, thoughts, and beliefs, which are also final products of the activity of billions of nerve cells. We turn to these now.

Chicken Sexers and Plane Spotters

When chicken hatchlings are born, large commercial hatcheries usually set about dividing them into males and females, and the practice of distinguishing gender is known as chick sexing. Sexing is necessary because the two genders receive different feeding programs: one for the females, which will eventually produce eggs, and another for the males, which are typically destined to be disposed of because of their uselessness in the commerce of producing eggs; only a few males are kept and fattened for meat. So the job of the chick sexer is to pick up each hatchling and quickly determine its sex in order to choose the correct bin to put it in. The problem is that the task is famously difficult: male and female chicks look exactly alike.

Well, almost exactly. The Japanese invented a method of sexing chicks known as vent sexing, by which experts could rapidly ascertain the sex of one-day-old hatchlings. Beginning in the 1930s, poultry breeders from around the world traveled to the Zen-Nippon Chick Sexing School in Japan to learn the technique.

The mystery was that no one could explain exactly how it was done. It was somehow based on very subtle visual cues, but the professional sexers could not say what those cues were. They would look at the chick's rear (where the vent is) and simply seem to know the correct bin to throw it in.

And this is how the professionals taught the student sexers. The master would stand over the apprentice and watch. The student would pick up a chick, examine its rear, and toss it into one bin or the other. The master would give feedback: yes or no. After weeks on end of this activity, the student's brain was trained to a masterful - albeit unconscious—level.

Meanwhile, a similar story was unfolding oceans away. During World War II, under constant threat of bombings, the British had a great need to distinguish incoming aircraft quickly and accurately. Which aircraft were British planes coming home and which were German planes coming to bomb? Several airplane enthusiasts had proved to be excellent spotters, so the military eagerly employed their services. These spotters were so valuable that the government quickly tried to enlist more spotters - but they turned out to be rare and difficult to find. The government therefore tasked the spotters with training others.It was a grim attempt. The spotters tried to explain their strategies but failed. No one got it, not even the spotters themselves. Like the chicken sexers, the spotters had little idea how they did what they did - they simply saw the right answer.

With a little ingenuity, the British finally figured out how to successfully train new spotters: by trial-and-error feedback. A novice would hazard a guess and an expert would say yes or no. Eventually the novices became, like their mentors, vessels of the mysterious, ineffable expertise.

The Knowledge Gap

There can be a large gap between knowledge and awareness. When we examine skills that are not amenable to introspection, the first surprise is that implicit memory is completely separable from explicit memory: You can damage one without hurting the other.

Consider patients with anterograde amnesia, who cannot consciously recall new experiences in their lives. If you spend an afternoon trying to teach them the video game Tetris, they will tell you the next day that they have no recollection of the experience, that they have never seen this game before - and, most likely, that they have no idea who you are, either. But if you look at their performance on the game the next day, you'll find that they have improved exactly as much as nonamnesiacs. Implicitly their brains have learned the game: The knowledge is simply not accessible to their consciousness. (Interestingly, if you wake up an amnesic patient during the night after he has played Tetris, he'll report that he was dreaming of colorful falling blocks but will have no idea why.)

Of course, it's not just sexers and spotters and amnesiacs who enjoy unconscious learning. Essentially everything about your interaction with the world rests on this process. You may have a difficult time putting into words the characteristics of your father's walk, or the shape of his nose, or the way he laughs - but when you see someone who walks, looks, or laughs the way he does, you know it immediately.

Flexible Intelligence

One of the most impressive features of brains - and especially human brains - is the flexibility to learn almost any kind of task that comes their way. Give an apprentice the desire to impress his master in a chicken-sexing task and his brain devotes its massive resources to distinguishing males from females. Give an unemployed aviation enthusiast a chance to be a national hero and his brain learns to distinguish enemy aircraft from local flyboys. This flexibility of learning accounts for a large part of what we consider human intelligence. While many animals are properly called intelligent, humans distinguish themselves in that they are so flexibly intelligent, fashioning their neural circuits to match the task at hand. It is for this reason that we can colonize every region on the planet, learn the local language we're born into, and master skills as diverse as playing the violin, high-jumping, and operating space shuttle cockpits.

The Liar in Your Head

On December 31, 1974, Supreme Court Justice William O. Douglas was debilitated by a stroke that paralyzed his left side and confined him to a wheelchair. But Justice Douglas demanded to be checked out of the hospital on the grounds that he was fine. He declared that reports of his paralysis were a myth. When reporters expressed skepticism, he invited them to join him for a hike, a move interpreted as absurd. He even claimed to be kicking football field goals with his paralyzed leg. As a result of this apparently delusional behavior, Douglas was dismissed from his seat on the Supreme Court.

What Douglas experienced is called anosognosia. This term describes a total lack of awareness about an impairment. It's not that Justice Douglas was lying - his brain actually believed that he could move just fine. But shouldn't the contradicting evidence alert those with anosognosia to a problem? It turns out that alerting the system to contradictions relies on particular brain regions, especially one called the anterior cingulate cortex. Because of these conflict-monitoring regions, incompatible ideas will result in one side or another's winning: The brain either constructs a story that makes them compatible or ignores one side of the debate. In special circumstances of brain damage, this arbitration system can be damaged, and then conflict can cause no trouble to the conscious mind.

Now Batting: Your Subconscious

On August 20, 1974, in a game between the California Angels and the Detroit Tigers, The Guinness Book of Records clocked Nolan Ryan's fastball at 100.9 miles per hour. If you work the numbers, you'll see that Ryan's pitch departs the mound and crosses home plate - 60 feet, 6 inches away - in four-tenths of a second. This gives just enough time for light signals from the baseball to hit the batter's eye, work through the circuitry of the retina, activate successions of cells along the loopy superhighways of the visual system at the back of the head, cross vast territories to the motor areas, and modify the contraction of the muscles swinging the bat. Amazingly, this entire sequence is possible in less than four-tenths of a second; otherwise no one would ever hit a fastball. But even more surprising is that conscious awareness takes longer than that: about half a second. So the ball travels too rapidly for batters to be consciously aware of it.

One does not need to be consciously aware to perform sophisticated motor acts. You can notice this when you begin to duck from a snapping tree branch before you are aware that it's coming toward you, or when you're already jumping up when you first become aware of a phone's ring.

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