The Brain: The Story of You

by David Eagleman

we’re so trapped inside our reality that it is inordinately difficult to realize we’re trapped inside anything.

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

nucleus accumbens).

orbitofrontal cortex

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.

Rather than memory being an accurate video recording of a moment in your life, it is a fragile brain state from a bygone time that must be resurrected for you to remember.

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.

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.

That word was “meaning”.

You don’t perceive objects as they are. You perceive them as you are.

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.

All of your sensory experiences are taking place in storms of activity within the computational material of your brain.

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

It does so by comparing the signals it receives from the different sensory inputs, detecting patterns that allow it to make its best guesses about what’s “out there”.

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.

To synchronize the incoming information from the senses, the cost is that our conscious awareness lags behind the physical world.

Detailed expectations about the world – in other words, what the brain “guesses” will be out there – are being transmitted by the visual cortex to the thalamus. The thalamus then compares what’s coming in from the eyes. If that matches the expectations (“when I turn my head I should see a chair there”), then very little activity goes back to the visual system. 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.

Even when brains are unanchored from external data, they continue to generate their own imagery. Remove the world and the show still goes on.

Your brain makes assumptions about what you’re seeing based on your internal model, built up from years of experience of walking other city streets.

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.

Color is an interpretation of wavelengths, one that only exists internally.

Each creature picks up on its own slice of reality.

each creature perceives only what it has evolved to perceive.

Molecules floating through the air bind to receptors in our nose and are interpreted as different smells by our brain.

inroad

Timewarp

ripcord

careened

MEASURING THE SPEED OF SIGHT: THE PERCEPTUAL CHRONOMETER

The answer appears to lie in the way our memories are stored.

When we practice new skills, they become physically hardwired, sinking below the level of consciousness.

This ability to burn programs into the structure of the brain is one of its most powerful tricks.

There is a consequence to this automization: new skills sink below the reach of conscious access. You lose access to the sophisticated programs running under the hood, so you don’t know precisely how you do what you do.

Take an effect called “priming”, in which one thing influences the perception of something else.

NUDGING THE UNCONSCIOUS

Unbeknownst

Consciousness gets involved when the unexpected happens, when we need to work out what to do next. Although the brain tries to tick along as long as possible on autopilot, it’s not always possible in a world that throws curveballs.

Even when decisions seem spontaneous, they don’t exist in isolation.

We feel like we have autonomy – that is, we make our choices freely.

Whatever the activity in their brain was up to, they took credit for it as though it were freely chosen. The conscious mind excels at telling itself the narrative of being in control.

The brain is a machine built from conflict

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.

Fundamentally, the brain is tuned to detect unexpected outcomes – and this sensitivity is at the heart of animals’ ability to adapt and learn.

Overcoming the power of now: the Ulysses contract

rapt

This sort of deal between your present and future self is known as a Ulysses contract.

cajoling

burgeoning