The Brain: The Story of You

by David Eagleman

On the face of it, that seems like a great advantage for other species – but in fact it signifies a limitation. Baby animals develop quickly because their brains are wiring up according to a largely preprogrammed routine. But that preparedness trades off with flexibility.

As many as two million new connections, or synapses, are formed every second in an infant’s brain. By age two, a child has over one hundred trillion synapses, double the number an adult has.

You become who you are not because of what grows in your brain, but because of what is removed.

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.

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.

The enemy of memory isn’t time; it’s other memories. Each new event needs to establish new relationships among a finite number of neurons. The surprise is that a faded memory doesn’t seem faded to you. You feel, or at least assume, that the full picture is there.

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.

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.

Today we’re living longer than at any point in human history – and this presents challenges for maintaining brain health. Diseases like Alzheimer’s and Parkinson’s attack our brain tissue, and with it, the essence of who we are.

His misfortune reveals something about the brain mechanisms that underlie memory: their purpose is not simply to record what has gone before but to allow us to project forward into the future. 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.

On the flip side, they found that negative psychological factors like loneliness, anxiety, depression, and proneness to psychological distress were related to more rapid cognitive decline. Positive traits like conscientiousness, purpose in life, and keeping busy were protective.

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.

Cognitive Reserve

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.

When you’re awake, your brain waves reveal that your billions of neurons are engaged in complex exchanges with one another: think of it like thousands of individual conversations in the ballgame crowd.

During sleep, neurons simply coordinate with one another differently, entering a more synchronized, rhythmic state.

It’s likely that a full understanding of consciousness will require new discoveries and theories; our field is still quite young.

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

The meaning problem is not yet solved. But here’s what I think we can say: the meaning of something to you is all about your webs of associations, based on the whole history of your life 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...

And because the physical stuff is constantly changing, we are too. We’re not fixed. From cradle to gr...

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.

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.

They detect a motley crew of information sources (including photons, air compression waves, molecular concentrations, pressure, texture, temperature) and translate them into the common currency of the brain: electrochemical signals.

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

In a city with visitors from all over the world, foreign money must be translated into a common currency before meaningful transactions can take place.

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?

The lesson that surfaces from Mike’s experience is that the visual system is not like a camera. It’s not as though seeing is simply about removing the lens cap. For vision, you need more than functioning eyes.

Today, fifteen years after his surgery, Mike still has a difficult time reading words on paper and the expressions on people’s faces. When he needs to make better sense of his imperfect visual perception, he uses his other senses to crosscheck the information: he touches, he lifts, he listens. This comparison across the senses is something we all did at a much younger age, when our brains were first making sense of the world.

Seeing requires more than the eyes

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.

Seeing feels so effortless that it’s hard to appreciate the effort the brain exerts to construct it.

The brain doesn’t really care about the details of the input; it simply cares about figuring out how to most efficiently move around in the world and get what it needs.

Visual data goes through more complex processing than auditory data.

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. How? 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.

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.

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.

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.

Locked in the Hole, his senses were providing his brain with no new input, so his internal model was able to run free, and he experienced vivid sights and sounds.

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.

When you’re confronted with the hollow side of a mask (right), it still looks like it’s coming towards you. What we see is strongly influenced by our expectations.

Neuroscientists weren’t the first to discover that fixing your gaze on something is no guarantee of seeing it. Magicians figured this out long ago. By directing your attention, magicians perform sleight of hand in full view. Their actions should give away the game, but they can rest assured that your brain processes only small bits of the visual scene.

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.

No one is having an experience of the objective reality that really exists; each creature perceives only what it has evolved to perceive.

Synesthesia is a condition in which senses (or in some cases concepts) are blended.

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.

In other words, when things are life-threateningly scary, it’s a good time to take notes.

This capacity to know the state of your muscles is called proprioception.