David Eagleman

was to drop us into the world half-baked. If you look at the way an alligator drops into the world, it essentially is pre-programmed. It eats, mates, sleeps, does whatever it's doing. But we spend our first several years absorbing the world around us based on our neighborhood and our moment in time and our culture and our friends and our universities.

We absorb all of that such that we can then springboard off of that and create our own things. There are many things that are essentially pre-programmed in us. But we are incredibly flexible. And that is the key about live wiring. When I ask you to think of the name of your fifth grade teacher, you might be able to pull that up, even though it's been years since you saw that fifth grade teacher.

But somehow there was a change made in your brain and that stayed in place. You've got 86 books. billion neurons. Each neuron is as complicated as a city. This entire forest of neurons, every moment of your life is changing. It's reconfiguring, it's strengthening connections here and there. It's actually unplugging over here and replugging over there.

And so that's why I've started to feel that the term plasticity is maybe underreporting what's going on. And so that's why I may have the term live wiring.

It is organized around the senses, but the interesting thing is that the cortex, this wrinkly outer bit, is actually a one-trick pony. It doesn't matter what you plug in. It'll say, okay, got it. I'll just wrap myself around that data and figure out what to do with that data.

It turns out that in almost everybody, you have functioning eyeballs that plug into the back of the head, and so we end up calling the back part of the brain the visual cortex. We call this part the auditory cortex, and this the somatosensory cortex that takes in information from the body and so on.

So what you learned back in high school or college is correct most of the time, but what it overlooks is the fact that the brain is so flexible. If a person goes blind or is born blind, That part of the brain that we're calling the visual cortex, that gets taken over by hearing, by touch, by other things. And so it's no longer a visual cortex.

The same neurons that are there are now doing a totally different job.

Turns out the kid will be just fine. You can be born without half the brain or you can do what's called a hemispherectomy, which happens to children who have something called Rasmussen's encephalitis, which is a form of epilepsy that spreads from one hemisphere to the other. The surgical intervention for that is to remove half the brain.

You can just imagine as a parent the horror you would feel if your child had to go in for something like that. But you know what? Kid's just fine. I can't take my laptop and rip out half the motherboard and expect it to still function. But with a brain, with a live wired system, it'll work.

So it turns out that blind people can make all kinds of sounds, either with their mouth, like clicking... or the tip of their cane, or snapping their fingers, anything like this, and they can get really good at determining what is coming back as echoes and figure out, oh, okay, this is an open space in front of me. Here, there's something in front of me.

It's probably a parked car, and oh, there's a little gap between two parked cars here, so I can go in here. The key is the visual part of the brain is no longer being used because for whatever reason, there's no information coming down those pipelines anymore. So that part of the brain is taken over by audition, by hearing and by touch and other things.

What happens is that the blind person becomes really good at these other things because they've just devoted more real estate to it. And as a result, they can pick up on all kinds of cues that would be very difficult for me and you because our hearing just isn't that good.

That is exactly right. This was my colleagues at Harvard. They did this over the course of five days. They demonstrated that people could get really good at, there are actually a number of studies like this. They can get really good at reading Braille. They can do things like echolocation. And the speed of it was sort of the surprise.

But the real surprise for me came along when they blindfolded people tightly and put them in the brain scanner and they were making sounds or touching the hand. And they were starting to see activity in the visual cortex after 60 minutes of being blind.

REM sleep is rapid eye movement sleep. We have this every night, about every 90 minutes, and that's when you dream. So if you wake someone up when their eyes are moving rapidly and you say, hey, what are you thinking about? They'll say, well, I was just riding a camel across a meadow. But if you wake them up at other parts of their sleep, they typically won't have anything going on.

So that's how we know we dream during REM sleep. But here's the key. My student and I realized that at nighttime, when the planet rotates, We spend half our time in darkness and obviously we're very used to this electricity blessed world, but think about this in historical time over the course of hundreds of millions of years, it's really dark. I mean, half the time you are in blackness.

Now you can still hear and touch and taste and smell in the dark, But the visual system is at a disadvantage whenever the planet rotates into darkness. And so given the rapidity with which other systems can encroach on that, what we realized is it needs a way of defending itself against takeover every single night. And that's what dreams are about.

So what happens is you have these midbrain mechanisms that simply blast random activity into the visual cortex instantly. every 90 minutes during the night. And when you get activity in the visual cortex, you say, oh, I'm seeing things. And because the brain is a storyteller, you can't activate all the stuff without feeling like there's a whole story going on there.

But the fascinating thing is when you look at the circuitry carefully, it's super specific, much more specific than almost anything else in the brain. It's only hitting the primary visual cortex and nothing else. And so that led us to a completely new theory about dreams. We studied 25 different species of primates, and we looked at the amount of REM sleep they have every night.