CHRISTMAS LECTURES 2011: Bruce Hood - What's in your head?

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The first Christmas Lecture from 2011 with Professor Bruice Hood.

Your brain may look like a big walnut, but it has the ability to create an almost unlimited stream of images, thoughts, memories and dreams. Undoubtedly the most complex material in the universe, and yet it's just a collection of simple cells. Join us as we get under your skull and take a peek inside. What do brainwaves look like? How fast is a neuron? Why does your brain create its own version of reality?

Bruce uses technology to measure brain activity and follow eye movement, build a virtual brain out of audience volunteers and play some guessing games with your mind. In the process, he shows how everything you perceive is just an interpretation of the nerve impulses that your brain receives - which isn't really that much.

Ultimately, we are all experts at filling in the blanks.


Being Human


Christmas Lecture
Professor Bruce Hood
London, UK
Filmed in:
The Theatre


Collections with this video:
CHRISTMAS LECTURES 2011 - Meet your Brain

Licence: © 2011 The Royal Institution



Meet Charlie and Iona. And as you can plainly see, Charlie is much taller than Iona. But sometimes, reality is not what it seems.


Welcome to the 2011 Royal Institution Christmas Lectures, Meet Your Brain. Let me introduce myself. I'm Bruce Hood, and I'm a scientist interested in the human brain: what it is, and how it changes as we grew older.

Actually, when I said I am Bruce Hood, what I really should have said is this is Bruce Hood, because everything I am is really a product of my brain. It's not my heart. It's not my kidneys. These are important organs, but I could have them transplanted, and I'd still be the same person. And that's because it's our brain that makes us who we are.

In this series of lectures we're going to be looking at the human brain, what it is, how it works, and most importantly, how it interacts with other brains. But before I do so, I'd like to introduce you to someone else here, or rather, someone who is here no longer.

This is a real human brain from a person. Before they died, they made the decision to donate their brain to science so that we could discover the workings of this most astonishing, amazing organ. It is so mysterious and complicated we can't even begin to really know how it works.

I brought this brain along tonight to remind you exactly who we are and what we're trying to understand is truly awe-inspiring. Every one of you here tonight and watching at home has a brain inside your head. Every brain is important. Every brain is unique. But all brains have the same basic machinery working.

So how does a brain work? Well, to help me answer these questions, I've invited along another brain scientist, Professor Vince Walsh from University College, London. So give a big round of applause to Vince.


So Vince, you've brought along this special machine that influences the brain. So we're going to see it in action in a moment. But before we do so, let's start with a very simple demonstration. Do you know the nursery rhyme "Baa, Baa, Black Sheep"?

I think so.

Could you give us maybe the first line?

Baa, baa, black sheep, have you any wool?

That's very good. It's reassuring to know that professors still know their nursery rhymes. Or you can choose anyone. OK. I'm going to get you to repeat that, but this time I'm going to stimulate this part of your brain with your machine. Start, please.

Baa, baa, black - [CLICKING] [MUMBLING]


Don't be alarmed. You're perfectly OK, Vince, aren't you?

I'm fine. Yes, I do know it.

That's very good. Somehow this machine has disrupted Vince's brain. Well, this is a transmagnetic stimulator. It's delivering a very powerful magnetic pulse for a brief fraction of a second. But why is it disrupting Vince's ability to speak?

Well, I'm going to give you a clue with the next demonstration. Have a look at this old television over here. And I'm going to need a magnet. Now you can see the image on the television is perfectly normal. But look what happens when I bring a magnet close to it.

You can see that the image is being distorted by the magnet. Now why is this? Well, remarkably the answer comes from none other than the founder of the Royal Institution Christmas Lectures, Michael Faraday, because Faraday discovered over 150 years ago, and often demonstrated in this very theatre, that there's a relationship between magnets and electrical fields. Now the image on the television is produced by an electrified beam, so that when I bring a magnet close to it, it's distorting the path of that beam. And that's why the image is being distorted.

So let's put these pieces of information together. A magnet can disrupt an electrical field. And we know that the magnet is disrupting Vince's ability to speak, which is a product of his brain. So we can conclude that the brain must be using some form of electrical communication to make you speak. Is that roughly correct, Vince.

That's true, yes.

OK. Vince, but if I put a magnet next to my head, it doesn't seem to disrupt any of my ability to speak, so why is that?

That's because the field that you've got next to your head is static. Even though you're moving it about, it's moving very, very slowly. To create an electric field that disturbs brain cells, it's got to be moving very, very rapidly. Every one of those clicks you hear is 1/10,000 of a millisecond. So the field has to change very, very quickly to create any electricity in the brain.

Would you like me to do so more disruption of Vince's brain?


OK, Vince. I'm sorry, but we're going to put you through some more. OK. So what else should we try? How about some motor control?

We could do that. We could try left- and right-handed.

Can we try just affecting your right hand? Would that be OK?


All right. So I'm going to take the magnet, and now is it fully charged up again?

It is.


So I'll touch my nose a few times.

OK. Let's see how accurate you are when I place it up here. Is that the correct area?




Now, Vince tell the audience what that feels like.

It's actually quite painless, but I've lost control of my muscles. I've lost control of my ability to locate my hand in space. It's a very, very weird sensation.

Can we do one last example? Can you clap for us?


I'm just going to stick the magnet here. Here we go. You ready? Start clapping, please.




OK. I think we've put you through enough, Vince. Now before you go, tell us please, we've seen how a magnet can disrupt normal function, but does it have any application?

It does. What we've done has been very dramatic. We've been using very high magnetic fields to influence the brain, so we can see that it does affect the brain. But if we use lower fields and stimulate specific areas of the brain, we can work on treating things like depression or modeling brain disorders or modeling stroke in real research. So it's got lots and lots of applications.

Well, Vince, that's been absolutely fascinating. Would everyone give Vince a round of applause?


Do you realise we've just proved that the brain is an electrical system? And I think that's pretty cool. Not only do magnets disrupt brain function, but we can use magnets to look at the workings of the brain. But to do so, you have to have a very powerful magnet. And we happen to have access to one, not here in London, but up in Cheltenham, where we've set up a live link. We recorded this earlier.

Hello. I'm Dr. Thalia Gjersoe, and I'm here at the MRI scanner so that you can read my mind. I'm here with Iain Lyburn, who's going to take us through it.

Welcome. Welcome to the Cheltenham Imaging Centre. It's run by the Cobalt Appeal Fund that houses imaging for PET and MRI. And today we're going to have an MRI scan, looking at your brain, seeing how it works. And what I'd like to do is show you the scanner, first of all. Have you seen a scanner before?

No, I haven't.

Let's let you have a look inside.


It's got a big metal door because it's housed in a big metal cage. This is the scanner. You'll be going in with your head actually in the scanner. And it's got very strong magnetic fields, which is part of the way it works. Then Karen's going to show us how strong the magnet is with a bit of - she's actually got a -

I've got a spanner on the end of a bit of rope.

You see how powerful it is. So that's how strong it is.

Wow. Well, Iain, can you hear me?

Yes. Hi. Good evening.

We've just seen this magnet of yours. It's extraordinarily powerful. How powerful is it?

30,000 times as strong as the magnetic field of the earth.

Well, that sounds quite dangerous to me. Why doesn't it affect the human brain when you put someone in the scanner?

Well, the magnet's actually fixed. It doesn't move. There's no movement, so it's safe to go in. Very safe to go in and use for imaging.

So it's not like the TMS. It's a static method magnetic field. Is that correct?

It's a static magnetic field. So it's safe.

OK. Thalia, can you hear me?

Yes, I can, Bruce. Hello.

Hi. I wouldn't go into that machine with anything magnetic. Have you got something small that you can put in your hand?

I do. I've got a walnut.

You've got a walnut. All right. Look, Thalia, I want you to take the walnut into the scanner, OK? And don't tell us which hand you're going to put it in, because we're going to do a bit of mind-reading, I think.

But we'll be seeing a little bit more of you later on. Or should I say, we'll be seeing more of your brain? For the moment, though, could we give a warm round of applause to Thalia and Professor Iain Lyburn?


So all brains work by electrical signaling. And all brains are very similar, but they can also be quite different in some ways. Take a look at all these animal brains. Would you like to take a guess at which brain you think this animal belongs to? And I'm going to give you a pound coin so you can estimate the size. Now call out, what animal do you think that might be? Go ahead, just shout it out.


A spider. No. It's not a spider. Can we have another example?


Mouse. Who said mouse? Hands up. You're correct. It's a mouse. OK. What about this creature here?



Did someone say rat?

Chicken. Chicken!

It's a rat's brain. What about this brain here?




It's a chicken. Believe it or not, that's a chicken's brain. And what about this one here?



A tortoise? No.


It's a cat's brain. And here we have -


The dog. And finally this one. What's this one belong to?



A horse. Who said a horse? Hand up if you said horse. Now let's consider the horse for a moment. It's a very large animal, isn't it?

A horse on average is usually about three times bigger than a human. But look at the horse's brain in comparison to the human brain. Let me take it around to show you.

Even though a horse is much larger than a human, the brain is actually smaller. So this shows you that the size of the body size doesn't predict the size of the brain. In fact, if you think about the size of a human body on average, our brain is seven times larger than you would ever imagine.

So who would like to hold a human brain? That's an awful lot of you. Well, unfortunately, we can't let you hold the human brain, but I just happen to have one which is just as good, made out of synthetic plastic over here.

It's a very good copy. It's the same shape. It's the same size. And it's the same weight.

So would you like to hold the human brain? Who wants to hold the human brain? You do? OK. Put your hands up.

What's the first thing you notice about it?

It's quite heavy.

It's extraordinarily heavy, isn't it? It's about 1 and 1/2 pounds. You can pass it along. 1 and 1/2 kilos, I should say. OK.

It's really quite heavy. And what else is it? What else do you notice about it? Well, let me tell you. Can I have my brain back? Thank you.

The brain, as you can see, is made up of two halves. And each half is called a hemisphere. Now the interesting thing about the hemisphere is it controls the opposite side of the body. So if you remember when we were stimulating Vince's brain with the Trans Magnetic Stimulator, the TMS, when I was activating his left side of the brain, it was his right hand which was being affected.

Now, we don't really know why the brain is organised like that. It's a little bit of a mystery. And in fact, you probably wouldn't be aware unless you got some damage on the opposite side and noticed that the behavior was affected.

Now the other thing about the brain which I think is quite fascinating is all these folds and creases, because all brains have this to some extent. But if you look at, say, the example of the mouse brain or the rat brain, they're really quite smooth. In the human, these folds and creases are quite pronounced. So why is that?

Well, to get an answer for that, you really have to zoom in to the building blocks of the brain, to a special kind of cell called a neuron. And here we have the image of a neuron. And as you can see, it looks like a kind of strange alien creature from outer space. And there's a lot of them. There are about 100 billion neurons in the average brain.

And all these tentacles, what we call our dendrites, and this is the way the neurons are communicating with each other, by sending electrical impulses. And each neuron typically has one very thick connecting fibre, called the axon. And it's the axon that sends out information to connect up with all the others.

Now, it turns out that the neurons and the connections which are related to those things that we consider intelligent and being clever, they're not throughout the brain. They're actually concentrated in just the outer layer of the brain, a layer that's only three to four millimeters thick. And we call this the cortex.

And the cortex comes from the Latin word for bark. So it's this outer layer, with all these connections, which make us very clever and flexible in our thinking. So it's not so much the size of the brain that's important. Rather, it's the surface area of the cortex and how big that is that allows for all these connections.

If you were to take the human brain and then just flatten it out, it would have this degree of surface area. So would you hold my brain for a moment? OK. So this is how big the human cortex is if you flatten it out.

Now, that's a very big area. So how do you get all of that inside a normal head? Well here's nature's solution. It's all folded up. So nature has come up with an answer for basically an engineering problem. Thank you very much.

Now, if it wasn't all folded up like that, your head would have to be half as big again, which is frankly not a very good look. And if there are any mothers watching, it's bad enough giving birth to a baby of a normal size head without it being any larger. OK.

So let's now consider some other animals. Look at these little guys. They're quite exotic, aren't they? Does anyone know what they are?


They're jellyfish. That's right. They're Australian Blubber jellyfish. And you can see them moving around in the pool.

So what's so special about the brain of a jellyfish? Would anyone like to answer? Sir?

Is it transparent?

That's a good answer. Anything else? Yes?

It doesn't have one?

It doesn't have one. Well done. It was a trick question. They do have a central nervous system, but they don't really have a brain as such.

So if jellyfish don't have brains, then why do all these other animals have brains? Why do you think we have a brain in the first place? Who would like to answer? Yes?

Because otherwise we wouldn't be alive?

Otherwise we wouldn't be alive. That's good. Any more answers? Yes?


Memory. These are all great answers. But the basic answer for all the animals which have brains is that we use brains to navigate around the world. The jellyfish can move, but it's not keeping track of where it's going. And jellyfish tend to just go with the ebb and the flow of the tides, whereas animals that have brains are using them to navigate their world, to find food, to seek mates, to avoid predators, and to keep track of where they're going in order to plan their movements in the world. So brains are really for figuring out and predicting what's going to go next.

Now if you think about it, an animal like us is really a kind of complex, mobile, moving factory, made up of many subdivisions, different processing plants and recycling centres and movement machinery. And that all has to be coordinated. If it wasn't, we kind of would fall apart. So brains are really for controlling all these different activities.

Now, some of these activities are fairly automated. For example, breathing and hearts are controlled by the brain stem, which is below the cortex, so it doesn't require a lot of consciousness. And other things, like your movements that you've learned well, well, you don't have to think about them. Even walking, you know where you're going and you can plan that, but coordinating the movements, you don't have to think about how you do that. And that's controlled by the cerebellum at the bottom here.

So whether they're automatic or controlled, the whole point is they still need to be coordinated by a system. And that's what the cortex does, sitting up here. So the information is flooding up into the brain through the central nervous system. And the information from the most extreme parts, for example, the arms or even the legs, they form part of the peripheral nervous system.

So how fast does a nerve impulse travel? Well, we're going to try a little experiment. We're going to measure the speed of a nerve impulse travelling the length of one arm. And I'm going to need some volunteers.

In fact, I'm going to need all of Row E. So stand up, Row E. Big round of applause.


What's your name, sir?

My name's Omar.



OK, Omar. And who do we have at the end there?


Hello, Tim. OK, Omar, what I'm going to do is I'm going to grip your left shoulder with my right hand, and with your right hand, you grip the left shoulder, and everyone copy everyone until we form a chain reaction there, OK? So are you all holding? Right.

Now what I'm going to do, Omar, is I'm going to squeeze your shoulder gently. And everyone do it gently. When you feel your shoulder being squeezed, and not before, you squeeze your neighbor's shoulder. So it's going to pass the entire length of Row E. OK?

And Tim, at the end, when you feel your shoulder being squeezed, you shout stop. Because we're going to measure the speed, the time it takes for that response to travel the full length of Row E. You got it? So let's go.


OK. That's pretty good. That's 3 seconds 10. Let's see if you can get it a little bit faster. All right. Ready again?


OK. That's just under three seconds. That's pretty good. So you are getting a bit better with practice. Now this time, I don't want you to grip the shoulder. I want you to hold hands.

Now you should be even faster now, shouldn't you? OK. So just squeeze your neighbor's hand when you feel your left hand being squeezed. And again, Tim, you shout stop when you feel that, OK? You ready?


That's 3 seconds 8. And now almost a full second longer. Now why does it take longer for the nerve impulses to travel the full distance? Well. If you think about it, the first time we did it, it's only travelling the length of one arm. But when we're holding hands, it has to travel length of one arm plus an extra arm to the person next to you.

So an arm is about almost a meter long, isn't it? And with 15 arms, that's an extra 15 meters that it has to travel in just under about a second. So it's somewhere between 10 and 15 meters per second, which is about right for that kind of nerve impulse. So a big round of applause for Row E.


Thanks. So we were estimating the speed of a nerve impulse in the arm, and it's usually roundabout that kind of speed. And that's usually a lot slower than people imagine, because when you think about nerve impulses, we often assume that they must be almost as fast as electricity, because it seems like it's an electrical impulse. But in fact, electricity travels about three million times faster than a nerve impulse.

So we've been using these sorts of experiments to try and estimate how the brain is working. But can you ever really measure directly nerve activity? Well, remarkably, you can, if you're an expert, you know what you're doing, and you happen to have a very thin wire. So would you give a warm welcome to two experts from Newcastle, Dr. Claire Rind and Dr. Peter Simmons.


So Claire, I believe you had some interesting traveling companions with you, is that right?

We have. We've come down on the train with a box full of locusts.

Oh, right. So these are live locusts?

Yes. They are all munching on the grass. There's about six of them in there, varying sizes.

So he's gently being placed on his back, is that right?

Yes, he's in a little bed of Plasticine. It's actually a she.

Oh, it's a she?

She's lying on her back in a bed of Plasticine. And we've restrained the animal with little loops of Plasticine and Peter is putting in a very fine wine into its chest. And the wire is rather like an acupuncture wire, very fine, just a small diameter wire.

So it doesn't hurt the locust at all.

No, not at all.

That's amazing. Well, whilst Peter is setting up, because this is a very delicate procedure, let me tell you a little bit about the locust. Now, the locust is really a giant kind of grasshopper. And it has this very simple nervous system for avoiding bumping into things.

The reason it needs to do this is because when they get large numbers, they can become these swarms, which are traveling and they're vast numbers. There's literally millions of them. And they can fly without bumping into each other. Now, swarms can be a real problem, because when they land on a crop, they'll just ravish a crop and eat it within sort of minutes.

So they are usually a pest to humans, but they've also been very helpful, because we can measure their brain activity without hurting them at all. And this is what you've been doing in your research, is that right?

Yes. We've been looking at particular nerve cells within its nervous system and using this recording equipment to record the electrical activity that the nerve cells make. And in fact, the noise that you will hear eventually is from a single nerve cell within the locust's nervous system. And it's a very important neuron. This neuron is one of the biggest in the body of the locust, and it communicates down to the wings and can actually shut off the flight cycle so the locust will make a dive and avoid a predator or adjust its flight to avoid another member of the swarm.

OK. So Peter, are we ready?

We are ready. And I think she's ready as well.

She's ready. I couldn't tell the difference, to be honest, but I presume they're larger, the females, is that right?

The female is larger, yes.

OK. So which part of the visual field are we going to be recording from? Which side is the locust looking -

We're recording from the right side of the locust, but it's the part of the eye, or the eye that is looking towards the left, She's on her back, so she's watching you.

She's watching me now?

She's watching you now.

Right. So we're going to listen in to her responding to me, is that correct?


OK. So let's have some silence. Listen very carefully. What you'll be hearing is the activity of the neurons.


Can you hear that? Do you realise you're listening to the brain of a locust? Now we know it's from that side because if I come from the other side, you don't get the effect. Whereas, actually I think she's paying quite a lot of attention to me now, isn't she?


That is absolutely fascinating. Should we try it with this? OK. This represents another large locust flying in the swarm towards it.

[ELECTRICAL NOISE] That's absolutely great. So tell me, Claire, with this research what have you been able to do with it? Does it have any application for humans at all?

Well, it's a fascinating circuit that the locust has. And we've built an artificial circuit that we've been able to put into a sensor that is used for collision avoidance in cars. So we're hoping in the future that the circuits based on the locust will be able to help drivers avoid collisions in traffic and things.

So the locust insect is helping humans to avoid pileups on the M1, is that about right?

Eventually, that's what we would think.

Well, I think that's very useful. Now can you release the locust, to just show that everything is fine with her? OK. Now can we get a close-up of the locust, just to assure you? We can't let go, because if she gets a chance, she'll run away. And you can see there that she's perfectly OK.

And she bit me.

And she bit you, so that's revenge. She's getting her own back on you Peter. So let's put her back with her friends and let them go. Can we have a big round of applause for the locust?


Thank you so much for coming down.

Thank you.

That was fascinating. But can we ever do the same thing for a human? Well, we chose a volunteer earlier. And this is Billy. And he can't talk to us at the moment, because we have him wired up.

We're not sticking an electrode into his brain, but rather we're recording from the outside. Because it turns out that if you have lots of neurons firing, they generate enough electrical activity that we can detect that with tiny electrodes. Now normally when scientists do this, they have lots of electrodes all over the head. But for tonight's purposes, we're just interested in the back of Billy's head, because this is where his visual area is, the visual cortex in the human.

So as before, we saw the locust was looking at a human, me, approaching the locust. This time we're presenting a locust to a human to see how they respond. And here we see this big pattern starting to build up. So this is the response of Billy's visual area. And there we can - thank you, Kate.

And as you can see, as the locust was coming on, it was responding. So the picture of the locust was generating activity in his eyes, then sending these impulses along the fiber, the optic fiber, to the back of the brain, where the visual processing area is, and then responding to that. And that's the onset of the pattern. That's when the locust first appears. And then this is the rest of the brainwave, showing how he processes it.

So Billy, it turns out that you do have a brain. So thank you very much. And a big round of applause to Kate and Billy.


Now, animals might be all moving and interacting in the same environment, like the locusts and the humans, but their brains are very different. And what they're experiencing must be different. And even our own experience is often not what it seems.

So consider vision again. Most of us think that vision is just rich and full of detail. In fact, a lot of us think it's almost like a camera. But is it really? Let's test that idea out.

So Joe, would you come in here? Let's see. Joe's got a camera on his shoulder. And now he's taking the image, and you can see above me that the image is projected up there. And it's nice and rich and full of detail. And this is what we think vision is really like.

But actually, human vision isn't like that at all, because we know from the studies using these techniques that you're only ever processing the centre part of your vision. And in fact, it's about the size of your thumb held at arm's length.

So can we make the camera appear like human vision? So now you can see that it's all blurred at the edge, and it's only the central part of the field which is clear and detailed. So that's a bit strange, because that's not the way you experience vision, do you? You see it as full and complex.

So why is that? Well, let me show you. If I move a bit closer, the way that it seems more detailed is of course I simply move my eyes around. And I'm moving them quite rapidly, about four or five times per second. These are called saccades. And this is how the brain builds up a picture of complexity, because you're sampling the world and then storing that information. And the brain is remembering it, and this is what makes the world seem much more complex.

Now there's a problem, though. Because if a camera was to move like human vision, then there would be a real distortion. So let's take that away. Now, Joe, can you move your camera like an eye movement? Let's see what that looks like.

Now what's wrong with that? Any suggestions? Yes?

It's kind of moving quite fast.

It's very jerky, isn't it? It's very blurred. If that was your normal vision, it'd make you very seasick very quickly, OK? So your brain does a very clever trick. Every time you move your eyes, it cuts off the visual information. So you don't see all those jerky, smeared, blurred images. So Joe, can you simulate that? Can you turn off the visual signal every time you're moving the camera?

OK. Your brain is literally cutting off all the visual information. In fact, you can't see anything. And we know that's true and I'm going to prove it.

And I'll need a volunteer for that. So let's see who we can choose. Do we have anyone - young lady. What's your name?


Amy. OK. Amy, would you hold the mirror like this, OK? Now Josh, can you pick up Amy? Good. We've got you good. Now Amy, have a look at your left eye. Now look at your right eye. Left eye. Swap backwards and forwards. Now can you see your eyes moving?




Can you see your eyes moving at all? Can anyone else see her eyes moving?


Amy, your eyes are moving. Would you like for me to prove it to you? Have a look up there. Ready?


It would seem like you're a bit surprised. But don't worry. You're perfectly normal. You can't see your own eyes moving at all. Applause for Amy, please.


You can try that all at home, actually. If you're brushing your teeth, just look in the mirror and then focus on your left eye and then shift and look at your right eye and see if you can see your eyes moving. And you won't be able to do so, because no matter how you try, your brain is making you blind. Effectively, if you add up all the gaps and you're moving your eyes all the time when you're awake, you're blind for about two hours of the waking day, and you never even know that. Isn't that remarkable?

Clearly, the mind has amazing tricks that keep the world looking rich and full of detail and full of information. So what happens to all that information once you've detected it?

Ice creams! Get your ice creams here. Ice creams!

Ah. Well, here's some rich information. An ice cream. Thank you very much.

So consider an ice cream. It's full of lots of information. It looks delicious. It smells delicious. I'm going to do this. Now you can hear the crunch. It's cold. And it tastes very yummy.

But somehow, my brain combines all these differences sensations into one experience, a delicious ice cream. Now how does it do that? Well, I'm going to show you by building a very simple brain in this auditorium, OK?

So we had some helmets given out earlier, so pop your helmets on. And those with the helmets, would you mind standing up? OK. These are our volunteers.

Now, you're going to represent different groups of neurons. Now, let's say this part of the brain is coding for shape. So sir, at the back, you code for anything which is round. And you, in the front, code for anything which is long, like a pencil.

Now this part of the audience, you're going to represent the part of the brain which codes for colour. So you're going to be green. And you're going to respond to anything that's yellow.

And over here, we've got a part of the brain which codes for taste. So you're getting information from the mouth. And you, at the back, you're going to be sweet. And you're going to be salty. OK?

So now hold up these connections, because these are going to stand for all the connections between the different regions of the brain. So now press your buttons, and let's see all the activity. The brain is sending out signals. And actually, you can flash them. Let's see a lot of random connections.

So here's our simple brain. Now, how does a simple brain learn about objects? Well, we're going to teach it to learn about fruit. OK, so pop your lights off for a moment.

Now imagine that you've never eaten a banana before. So let's have you responding. If your feature's present, hold down your button.

So let's see what that looks like. So it's long. It's yellow and you pop it in your mouth and what does it taste like? Sweet. So that's the pattern for a banana, OK? All right.

Now everyone switch your lights on again, communicating again. There it's talking to itself. OK, and put them off and let's come across another fruit.

Now this time it's round. Hold it down. It's green. And you pop it into your mouth, and it's sweet.

And every time you eat a banana or you eat a grape, that pattern becomes stronger. This is because the neurons that fire together are wiring together. Now, you might notice how the banana and the grape are activating the same part, which is the sweet centers. And that shows you the brain can reuse the same regions to code for different objects.

So what happens when you go to a new part of the world and you encounter a new food you've never had before? Turn your lights off for a moment. Let's say you go to the Mediterranean and you see this small, round, green thing. So it's round. It's green.

And your brain thinks, well, it looks like a grape, so it's going to be sweet. So sweet, pop your light on. But then when you pop it into mouth, mmm. Yuck! It's salty. So this is why you can be very surprised when you encounter something new which seems so familiar. And that's why new foods can surprise you.

So let's consider our simple brain again. If I show you this pattern, tell us, audience, what do you think that stands for, that pattern?


It stands for banana. But it's not really a banana, is it? It's just how the brain stands for, recreates, the sensation of eating bananas. It's what we call a representation, because the brain is re-presenting the original experience. And representations are really the language of the brain.

Now I've given you a very simple demonstration, with only a few groups of neurons, just to give you an idea of the different patterns. But the brain is much more complex. If this were a real brain, there would be 100 billion neurons and you wouldn't just be holding a couple of connections, because all the neurons have up to 10,000 connections between them. And if you add up all the connections end to end, that stretches to 180,000 kilometers. And that's long enough to stretch around the world four times.

So that's rather mind-blowing, isn't it? Because it means that your brain has the capacity to encode an almost infinite number of patterns. Which is why we say the human brain is the most complex structure be found in nature. So let's have a big round of applause for our small brain.


So our world is full of rich experiences that are combined together into these meaningful patterns. And these representations reflect all the structure and order that we encounter on a regular basis in our existence and our lives. So for example, if I have this garbage lid, you're processing this in different parts of your brain. So you have areas which are processing the vision, and if I drop it, you have areas of your brain processing the sound.

So your visual areas are active, and so are your sound areas. In fact, you've got a set of neurons which are combining that experience of sight and sound. This representation of sight and sound is usually quite reliable, because sights usually go with sounds. But sometimes they can lead you to some false and surprising conclusions.


Let's try that one more time.


So what you're doing there is you think that the skull is burping, but of course he isn't really burping. What's happening there is you're seeing the skull move, and you're hearing the sound, and your brain is readily putting those things together. And this is called the ventriloquist effect.

And so when people see ventriloquists, they think that they're throwing their voice. But they're not really throwing their voice at all. What they're doing is they're minimizing the movement of their own mouths, making a sound, and exaggerating the mouth of the puppet.

So I can do that for a little bit. Let's see if I can try and convince you that this skull is talking. So if I go she sells sea shells on the sea shore. OK. Now not only does the ventriloquist effect shape where you think a sound is coming from, because sights and sounds usually come from the same points in space, but of course the ventriloquist effect can also influence what you're hearing.

So in this next example, I want you to watch very carefully this little bit of video. And see if you can hear what I'm saying. So watch this.


Ba ba ba ba ba ba.


What did you hear?

Ba ba ba ba ba ba ba ba.

Who heard da da? Put your hand up if you heard that. OK. If you're sitting in the middle. Let's try it again.


Ba ba ba ba ba ba.


What do you hear?

Da da.

Da da. Especially in the middle section only, what did you hear?


Da. Da.


Ba. OK. All right. All right. All right. Let's make this easier. This time I want you to listen again, but close your eyes. OK? Listen again.


Ba ba ba ba ba ba.


What did you hear this time?


Definitely it was ba. If you've heard da, then you were being fooled by an illusion called the McGurk effect. Because I'm not actually mouthing ba ba or da, da, what I'm actually mouthing is ga ga.

And so the brain gets the signal of ga and it's hearing ba. But these are patterns it's never encountered before and it comes up with a solution, which is da. So your brain is always trying to interpret experiences to come up with the best solution.

Now this way when you're watching people speak, you watch their mouths moving. And the shape of their mouths can actually influence what you think you're hearing. So here's a very simple party trick you can try. I want you to turn to the person next to you. And I want you to mouth the words elephant juice. Don't say it. Just say 'elephant juice' and just mouth it. Turn to the person next to you.


What does it sound like? What do you think the person might be saying? Why are you laughing? OK. OK. Does it look like the person could be saying, I love you? Do I hear I love you? I love you all. Wouldn't the world be a greater place if everyone said elephant juice a little bit more often to each other?

OK. So your brain - OK, let's settle down. Your brain is not just forming representations of the outside world. It's also storing these representations of your own bodies. And so for this next demonstration, I'm going to require someone who doesn't mind losing their hand. Lady on the end here, why don't you come on down?


That's all right. Just there. What's your name, first of all?


It's Josie. That's right. So you're quite prepared to lose your hand for medical science, is that correct? You don't mind losing a hand?


Well, don't worry. I'm not actually going to remove your hand. I'm going to create the illusion that you might be losing your hand, OK? So for this, I need you to put on this very strange jacket, OK? It's actually got three arms.

So put your arm through that one. And then put your arm through the other one. So that's the regular part of the jacket. Whoops. Is that going to be a bit small for you? Perfect. Now we're going to torture you. OK. So now - is it Josie, did you say?


OK, Josie, take a seat. Now Josie, I want you to put your other hand up here, so your left hand. Both hands are there. OK. Now that looks a little bit strange.

But I want you just to focus on this. This is a rubber hand. It's about the same size as Josie's hand. And I want you not to look at the audience, but just concentrate on the hand, OK?

Now this illusion takes about a minute or two to form, but what should happen is that Josie is looking at this hand of hers, and it's in the same place that her normal hand is. So her brain is a little bit confused, because that hand should belong to her. And at the same time, to make the illusion even more strong, Kate is simultaneously stroking the hands so the brain is now receiving all this touch information.

So again, it's combining the information, trying to make sense of it. How does that feel? Is it starting -

Yes. It feels really weird.

Does it feel very weird?


OK. So just keep doing that for a moment. Now just keep focusing on the hand. OK. Ready? Did you get a strange - did that feel a bit odd? OK. Don't worry. I wasn't going to hurt your hand.


Round of applause.

[APPLAUSE] Thank you, Josie. Thank you very much. Well done. Now the reason that happened is because the brain wasn't exactly sure whether it was the rubber hand anymore. And that's why most people, when you do that experiment, get this surprise.

Now I can't bring you all down to try out the rubber hand illusion, but I can show you how you can get a similar experience. So I'll need another volunteer. Someone from this side. Young lady in the blue. Why don't you come down?


What's your name?


Charlotte. OK, Charlotte, here's a very simple way to induce the rubber hand illusion. So I'm just going to turn you this way for a bit now. Very good, Charlotte. Now put up your right hand like that. OK.

Now, with your other hand, just grip like this. Now just looking at the index finger and just move your fingers up and down whilst you're doing it. Does that feel a little strange?


You can all try this. Just turn to the person next to you, OK? OK. And with your thumb and forefinger, see if you can do this.

That's strange, isn't it? It is very, very weird. You can try it at home as well if you'd like. OK. All right, guys. Let's settle down. Let's give a round of applause for Charlotte.


Thank you, Charlotte. So you see, your brain is always trying to interpret the world and make sense of it. And sometimes when it gets these strange signals, it comes up with these strange experiences and illusions.

In fact, we see things all the time. It might be faces in the clouds or it might be animals in ink stains. Just a simple - if you take some coffee beans and I just scatter them onto the pavement, onto the ground here, you can see all sorts of patterns in that. Can anyone see a pattern forming there at all?


Shout out if you see anything.


There's a mouse.


Yes. What else have you got there?


OK. So you're all seeing lots of patterns. That's very good. OK. So clearly, you're all seeing lots of different things. That's very reassuring. Your brain is always trying to impose structure and order. And this is most obvious with certain types of illusions where you have patterns which could be seen in more than one way.

Probably one of most famous examples is called the Necker Cube. So here is a Necker Cube. Now just look at this for a moment. It's just an outline of a cube.

Now, if you look at it long enough, you think it's pointing in one direction. But then if you stare at it long enough, your brain suddenly switches and it appears to be in the opposite direction. Is anyone having that experience? Hands up if you can get that. Wow. That's great.

You know what? We can make this even stronger if we put a little bit of movement into it. So just watch this as it turns. Now it seems to be going in one direction and then suddenly - is anyone getting it flipping, turning in the opposite direction?


Yes. Just watch it. You know what makes it really good? If you blink whilst you're looking at it. If you blink whilst you're watching, you'll see it switching. Now we're not using any computer trickery here. It's simply your brain switching between one version versus the other. Isn't that remarkable?

Now here's another interesting point. Your brain doesn't allow you to see all the patterns at once. It forces you into one perception versus the other.

And this might explain why some of you sometimes see things like ghosts, for example. So I'm going to conjure up a ghost right in front of your very eyes, OK? But don't worry. It's not going to be a headless horseman. It's going to be a little bit more simple, a little bit more friendly than that.

So all you need for this, and you can try this at home if you want, are just four circles of paper. It's such a simple illusion, but it's very compelling. And all I have to do is just simply cut out a quarter of the circle.

Because if you then line up these circles, you will see something that isn't really there. What does anyone see? Hands up. Shout out.


That's right. There's a square. But of course there isn't a square there, is there? Because when I take this away, it disappears. And back it comes again.

Now this is a very simple illusion, but it's also a very powerful one, because I think it explains one of the most important points about the brain. If I went into the back of your brain with a wire, I could actually measure activity of neurons which are firing as if there really was a square there. So this is remarkable. The brain is creating its own experience, isn't it?

In fact, we can even show that you can think this is a real solid object. And they've done this recently in an experiment where they put people inside a brain scanner and they showed them this square. It's called the Kanizsa illusion.

Here we have the square here. And then they made the square move. You see, it's traveling across. Here it is again. Watch as it moves across the screen.

Oh. Wow.

There it goes again, undulating like a real object. Isn't that very bizarre? Have you all got it?

It's moving across the screen. Let's see if we can make it go a bit faster. There it goes, moving across the screen.

And what's remarkable is that the movement areas of the brain are being activated, movement areas which are going in the same direction as the illusory ghostly square. So your brain doesn't allow you to have contact with reality. It's generating your reality the whole time. It's quite remarkable.

So let's come back to Charlie and Iona. Do you remember Charlie and Iona at the beginning? Let's get them back in for the rest of the show. Where are you Charlie and Iona? Come on down. Big round of applause, please.


So guys, how are you enjoying the show so far?

It's great.

It's great, yes? I see reality hasn't changed for you. You're still very tall, aren't you, Charlie? And Iona, you're still a bit shorter, aren't you?


Would you like to be taller than Charlie?


Well, you know, with the Ri Christmas show, we can actually make that happen. So please follow Kate and follow her out of room for a moment. OK. We'll be seeing them very shortly.

So throughout the lecture tonight we've been watching how reality is created by the brain. And it uses past experiences to make sense of the world. But things are not always as they seem. So sometimes we can fool the -

Oh, hello guys. There we go. Can you give a wave, Charlie? So Charlie, that room seems a bit small for you, doesn't it?


Oh, OK. Well, maybe you should try going to the opposite corner. And Iona, why don't you switch places?



Oh my gosh. How did that - OK. Switch places again. Can you hold hands? Can you reach each other? Can you reach out and hold hands? There we go. Look, it's a giant and a smaller person.

Now OK, you have a bit of fun in there, because I'm going to explain what's going on in here. And to do that, I need a model. Because what you can't see is that's not obviously a normal room.

In fact, the room has this sort of shape. OK? It's just the way that we set up the camera angle. And what we're doing is we're fooling and tricking your brain into thinking that is in fact a square room.

And I can illustrate this with this next example over here. Do these lines look equally long to you?



The green lines? Who says the look the same? Well, that's a very strange brain you have. For the rest of you, I hope, who thinks they look longer? That's great, because of course it's an illusion.

This is the Ponzi illusion, because, in fact, the lines are exactly the same length. And I'll go and make that big again. So what's going on here is your brain is being fooled by what are called perspective cues. It's almost like it's on a railway track, and because railway tracks, as they recede off into the distance, they converge, the lines start to become slanted like that. And because this seems to be further away and it's stretching over the edge here, you assume that this must be much larger than this block, which is sitting inside the tracks.

So once again, even though your brain tells you that they look different, in fact they're exactly the same length. So this is what's going on in the Ames Room. The Ames Room uses these perspective cues of slanted lines to fool your brain into thinking that the room is actually the same distance where in fact, it's actually longer. I suppose the best way to show you how that's going to work is if I go out there and you can see what I'm like and what the room's really like. OK?

So here we are at the Ames Room. Hi, guys. How are you doing?

Hello. I'm fine.

Now if you have a look around, you can see that the room isn't in fact straight or normal. It's all these slanted lines and the way that the team have built it, because when you shoot it from one angle, it looks as if the perspective is correct, but in fact, it's entirely wrong. So why don't you swap over again?

In fact, I think I'll join you, so you can watch me going into the room. And look how I transform in size. Here I come. So I'm big. And now, Iona, you're bigger than both of us. So that's part of the magic of the Royal Institution. Why don't you come back in and give a big round of applause for everyone.


So all these illusions demonstrate our brains are constantly trying to make sense of the world and understanding based on these stored representations. I think the remarkable thing about illusions is that even when you know how they work - and I've just demonstrated with the models, and I've shown that these are illusions - you can't help but see them one way or the other. It's because your brain is creating your mind's experience and you can't avoid that.

So you remember I promised you that we were going to look at Thalia's brain and read her mind? Yes? Well, let's go back to Cheltenham and see if we've made that link. Hello, Cheltenham, can you hear me at all?

Yes, it's Cheltenham here. Hi, London.

Is that Iain, is it?

Yes. Hi, Bruce. Hi.

Hi. Hi. How's it been going? Have you managed to scan Thalia's brain?

Yes. We got some great pictures, thank you. It looks very good.

Good. Good. So can you send through the first image so we can get an idea of what you've got? OK. So that's the structural image, is that correct?


OK. So I'm going to tell the audience, to give them an idea of what they're looking at. So imagine that I'm Thalia and I'm lying inside the scanner. So here I am. And so the scan is going from the bottom of my brain up to the top of my head. So this side of the screen is the right side of my brain. OK? And this side of the image on this side of the screen is the left side of my brain.

So Iain, am I correct? Did you try showing Thalia a visual image earlier? Is that right?

Yes, we did. We showed her a visual object, yes.

OK. So can you show us what the brain activation was like when she was looking at a visual object? OK. So tell us, what part of the brain is that, everybody, that's being activated?

The back.

The back. So if it's the back part of the brain, what's going on? Which area is that?


Vision. That's right. So we showed Thalia a picture, and when she was looking at the picture the back of her brain was more active. So this was showing the functions of her brain working.

Now Thalia, we had a walnut, and we asked her to put in one of her hands. Have you been processing the image, Iain?

Yes. We have been processing the image. You say she had a walnut in one hand. We took some pictures while she was squeezing the walnut with her hand.

Great. And have you got those images ready for us? OK. So if that's the image, which side of the brain is more active? Which side of the image is it?


So it's on the right side. So this is the right side of my brain, and what you've learned tonight about how things cross over, which hand is Thalia holding the walnut in?


Thalia, could you confirm to me which hand you were squeezing the walnut with?

My left hand.

Thank you.


You have just mind read Thalia, because you've predicted which hand she was holding it in. Do you realise that's over 100 miles away? A big round of applause, everyone.


Before we go, can we say thank you and good night to Thalia and Iain? Good night, Cheltenham.

Good night.

So that's what's inside your head. Your brain is interpreting the world around you into meaningful patterns and storing those patterns and representations. And with these technologies, we can read the activity of the brain. But does that mean to know what's on someone's mind we simply have to look at their brain activity?

Well, the technologies are useful if you know what you're looking for and the tasks are very simple, like squeezing a walnut in one hand. But the thing about humans is that we're very complicated and the tasks that we can do are very difficult. And that's what makes us human in many ways.

So that raises the question, who is coordinating all these difficult tasks and activities? Who is in charge anyway? And we'll be addressing that in the next lecture. So good night, and look after your brains. Good night.


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