TEDxUCLA 2019: Time
Space, time & imagination: how virtual reality changes the brain
Mayank R. Mehta, M.Sc., Ph.D. is Associate Professor of Neurology, Physics, and Astronomy at the Brain Research Institute, UCLA.
Mayank earned his Bachelors in physics and mathematics and Masters in nuclear physics from Bombay University and later earned his Ph.D. in quantum field theory from the Indian Institute of Science, Bangalore. He was a postdoctoral fellow at the University of Arizona, and then because a research scientist at the Massachusetts Institute of Technology.
Hello everyone. I’m going to share with you some recent insights about this exciting new field called neurophysics.
So what is neurophysics? Here we ask questions which human beings have pondered for the longest time but then do experiments to find answers. And what you will see are a series of surprising answers that are relevant for you today.
So let’s get started. Let’s start asking these deep questions. Space. What is space? I can’t feel it, but I know it’s there. I can see the walls, but I can’t see the space in between. But it’s there. In fact you can close your eyes and the space is still there. What’s that? Even more complex, time. To catch that, it’s gone. Where did it go? Anybody? What is it? What are these things? Are these just figments of our imagination, or are these real things?
So I asked my set these questions and the answer was you had to study a lot of physics. So that’s what I did. I did a Ph.D. in physics, wrote lots of interesting equations. And I, at the end of my Ph.D., had my own theory of how the universe began, and I was very happy. And at that moment, the question occurred to me: How come, sitting in a remote corner in India with nothing but paper and pencil, I’m able to figure out how the universe began, something I have never experienced nor will experience?
Black holes, which heaven forbid any one of us ever experiences, we can understand them. How come this weird imagination that we have make sense of things that don’t seem to exist? Do they exist? It’s that ability to create perception of things that don’t seem to exist are uniquely human.
Do animals have that? Yes. This little bird can fly from North Pole to South Pole with that so-called little bird brain, without GPS. it can navigate perfectly well, it can even catch a fish from the ocean on the way. The bird and the fish live in totally different environments. Still, they share a perfect idea of space and time with amazing precision. If their precision was off by even the smallest amount, the bird will never catch a fish and so on, and life on this planet will come to an end.
So something fundamental is going on. When you perceive simply this space and time, it’s not just to the imagination, it is universal imagination. How does the brain do that?
Brain is a lump of tissue. Pretty small. Still, more than a third of diseases are neurological in nature so these questions are really important. The brain has billions of neurons, and the special thing about the brain is there are trillions of synapses or connections, unlike the rest of the body.
These generate amazingly complex circuits, and scientists have developed these circuits over many, many years. That’s a circuit diagram of just the visual part of your brain. All the way at the bottom is the eye and all the way at the top is the tiny little region called HC, or hippocampus. That hippocampus is far removed from all the sensory cortices. Hippocampus is also very fragile region, unfortunately gets inflicted with a whole range of neurological disorders, for many of which, despite huge amounts of efforts, there are no cures. So it’s really important how that wiring diagram works.
Hippocampus, as I mentioned, creates perception of space so it’s universal across species. The way it does that is by creating its own rhythms, and you’re going to listen to those rhythms in a few seconds. Those rhythms are generated by the brain, from those rhythms it creates motifs, and those rhythms and motifs not only go on when you’re acting in space and time but even when you are sleeping. And this combination of rhythms across many parts of the brain generates lasting memories.
So how does that work? If you wanted to ask that question, you ought to have the ability to measure the activity of just one neuron out of a hundred billion without harming not only the animal but the neuron itself. That’s a challenge. But when you have amazingly bright graduate students in the lab and lots of time and patience, you can do that.
So we’re going to listen to the activity of just one neuron while the rats are running around in a maze that’s about size, half the size of this space. We want to keep happy memories, so the experiment is called Chocolate Rain. (laughter) Right? Want to wish?
There’s little bits of chocolate that appears from nowhere. All that the rat has to do is to eat a bit of chocolate. The idea is that the space information should still be there.
So we’re going to show the actual data rendered here. The rat will be shown by two circles, and the path followed by the rat in a blue line, and the activity of one neuron will be a crackle. Pay attention to the music of the neuron. So there he goes. We’re going to speed it up now.
So across this half an hour of experiment, the rat did every single thing that the rat would do. He ran, he ate chocolate, he scratched himself, he looked around, and this one neuron created its music and activity in just one corner of space. This is how every one of the hundred billion neurons in your brain sounds, but you don’t hear it. Fascinating.
So what was special about that place? Nothing. So actually, if you listen to another neuron it will be active in another part of the maze, and so on. Different neurons are active in many different parts of the maze such that if you simply listen to only a hundred neurons out of millions of them in this part of the brain, you can tell where the rat is with that much accuracy. You can read off his brain and tell where he is. In fact you can do that when he’s sleeping. And you can tell what is he dreaming of going, where is he going in his dreams. Fascinating possibilities.
But the question remains: what is that space? How did the brain create that perception of amazingly precise space? To do that, we need an ability to measure the activity of rat’s brain in the same condition as humans, because a rat’s nose is an inch from the ground, and I never ran that way in the world, so I don’t think you did too. Maybe it is some piece of chocolate. Maybe it is something else. So how do we convince the rat to behave like us, and how do we manipulate that space, because in science we need to manipulate space?
So enter many bright students and an interesting idea: a non-invasive virtual reality for rat. We built it right here at UCLA. The rat wears a little tuxedo, which is like a harness, and nothing else, and is held in that place gently. They like to be swaddled and like to wear tuxedo, so they walk around happily, they eat up little bits of chocolate, and as the rat moves, this movement causes the world around him to move. And the world is created entirely by us.
Does the rat buy into that world? If I told you for my research I’m going to ask the rats to watch television, you will be skeptical. Does he buy into this world where he is now behaving like human, making sense of the world which is entirely made up, and the space is created entirely by vision and nothing else? Is that possible?
So that’s how the virtual world looks, and I’m going to show you the webcam view where the view looks, the world looks kind of distorted. That’s the way human beings might use virtual reality, perhaps for entertainment or in a clinic. The rat virtual reality is even more comfortable, he can see his own shadow.
So there he goes, and all that the rat has to do is to go underneath some chandeliers to get a little bit of soda. And he does that happily. So there we go. He gets going now and when he goes under that little pillar, two beeps of sound appear and say that “Yes you did it!” And he gets a little bit of soda. He likes that.
Then the chandelier magically appears at some other place. He has to go there. You can see he’s looking at it like a human being would. He’s creating a three-dimensional space out of the chandelier. Can he detect the edge of the table, just based on vision? He can. Turns away from the edge just using vision.
So we have hours of these videos where the rats behave as if this virtual reality is real. So it’s the cleanest possible maze you can make where the rat has to make a map of space using only vision, and all of us expected that we’ll get the most, the cleanest, and the most beautiful maps of space.
So months and years of efforts later, that’s the answer. It’s gone. There is no spatial selectivity left.
So we got worried something is wrong with the equipment. Maybe the brain is corrupted. We measured, in fact, the activity of the same neuron on the same day in the real world with the same set of visual cues and the same behavior. Beautiful map exists. In fact, when we looked even more closely, more than half of the hippocampus shut down in virtual reality.
If somebody had told me there is a drug that can shut down the brain by 50 percent, I would be skeptical. Without a drug, we can shut down the brain. We didn’t expect that, but now we have that ability to use. Why did that happen?
Let’s listen to the activity of that neuron. And what I’m going to tell you is that the answer lies in time. So there we go. He’s now running in the same visual cues in virtual reality. There he starts going. Notice the same motif and the rhythm. The music is still the same. We’re going to speed it up.
And what you notice is that the brain itself is generating this rhythm, and it’s generating this little motif which is several seconds long, which is thousands of times longer than the neurons on speed of one thousandth of a second. And our brain is stitching together these brief segments of time to create abstract ideas such as space and time. And when those brief segments are all in register with each other, things work beautifully in the real world and you get wonderful maps, and in virtual reality they get busted.
We are now developing the next generation of virtual reality where we can activate the brain by more than the real world. We’ll now soon have the ability to turn on and to turn on the brain’s activity without any drugs. Fascinating possibilities to treat many neurological disorders.
Not only that, we have discovered something else that we never thought we could ask scientifically. Just what is the reality? How do we know what is real? That little rat’s brain figured out there is space, he’s going into it, but it is not real space.
There are several diseases where people that are not able to tell what is real or not. Happens to all of us. Sometimes when we forget what we said or saw, or think and we don’t know where that was.
Now we can scientifically ask these questions about how space, time, memory, reality, and music are related to create lasting memories. Thank you.