David Eagleman

And we also looked at how plastic they are as a species. It turns out that the amount of dream sleep that a creature has exactly correlates with how plastic they are, which is to say, if your visual system is in danger of getting taken over because your brain is very flexible, then you have to have more dream sleep.

And by the way, when you look at human infants, they have tons of dream sleep at the beginning when their brains are very plastic. And as they age, the amount of dream sleep goes down.

At the moment, there are 19 papers that have cited this and discussed this. And I think it's right. I mean, look, everything can be wrong. Everything is provisional. But it's the single theory that is quantitative. It's the single theory about dreams that says not only here is a idea for why we dream, but we can compare across species and the predictions match exactly. No one would have...

suspected that you'd see a relationship between, you know, how long it takes you to walk or reach adolescence and how much dream sleep you have. But it turns out that is spot on.

Given that all the data running around in the brain is just data and the brain doesn't know where it came from, all it knows is, oh, here are electrical spikes, and it tries to figure out what to do with it. I got really interested in this idea of sensory substitution, which is, can you push information into the brain via an unusual channel?

Originally, we built a vest that was covered with vibratory motors. and we captured sound for people who are deaf. So the vest captures sound, breaks it up from high to low frequency, and you're feeling the sound on your torso. By the way, this is exactly what the inner ear does. It breaks up sound from high to low frequency and ships that off to the brain.

So we're just transferring the inner ear to the skin of the torso, and it worked. People who are deaf could come to hear the world that way. So I spun this out of my lab as a company, Neosensory, and we shrunk the vest down to a wristband, and we're on wrists of deaf people all over the world. The other alternative for somebody who's deaf is a cochlear implant, an invasive surgery.

This is much cheaper and does as good a job.

It's actually just vibratory motors. So it's just like the buzzer in your cell phone, but we have a string of these buzzers all along your wrist. And we're actually taking advantage of an illusion, which is if I have two motors next to each other and I stimulate them both, you will feel one virtual point right in between. Hmm.

And as I change the strength of those two motors relative to each other, I can move that point around. So we're actually stimulating 128 virtual points along the wrist.

Great question. It started off where we were doing a lot of training on people. And what we realized is it's all the same if we just let it be organic. The key is we just encourage people, be in the world. And that's it.

You see the dog's mouth moving and you feel the barking on your wrist, or you close the door and you feel that on your wrist, or you say something, you know, most deaf people can speak and they know what their motor output is and they're feeling the input.

And by the way, that's how you learned how to use your ears too. You know, when you're a baby, you're watching your mother's mouth move and you're hearing data coming in your ears and you clap your hands together and you hear something in your ears. It's the same idea. You're just training up correlations in the brain about, oh, this visual thing seems to always go with that auditory stimulus.

For the first few months, you're hearing it on your wrist. You can get pretty good at these correlations. But then after about six months, if I ask somebody, when the dog barks, do you feel something on your wrist? And you think, okay, what was that? That must have been a dog bark. And then you look for the dog. And they say, no, I just... hear the dog out there.

And that sounds so crazy, but remember, that's what your ears are doing. Your ears are capturing vibrations of the eardrum that moves through the middle ear to the inner ear, breaks up to different frequencies, goes off to your brain, goes to your auditory cord. It's this giant pathway of things. And yet, even though you're hearing my voice right now inside your head, you think I'm somewhere else.

And that's exactly what happens irrespective of how you feed the data in.

So tinnitus is a ringing in the ears. It's like beep. And about 15% of the population has this. And for some people, it's really, really bad. It turns out there is a mechanism for helping with tinnitus, which has to do with playing tones and then matching that with music. Stimulation on the skin. People wear the wristband. It's exactly the same wristband, but we have the phone play tones.

And you're feeling that all over your wrist. And you just do that for 10 minutes a day. And it drives down the tinnitus. Now, why does that work? There are various theories on this, but I think the simplest version is that...

your brain is figuring out, okay, real sounds always cause this correlating vibration on my wrist, but a fake sound, beep, you know, this thing in my head, that doesn't have any verification on the wrist. And so that must not be a real sound.

So because of issues of brain plasticity, the brain just reduces the strength of the tinnitus because it learns that it's not getting any confirmation that that's a real world sound. Now, how did you figure out that this bracelet could be used for this? This was discovered by a woman named Susan Shore, who's a researcher who discovered this about a decade ago.