Your Brain Hallucinates Your Conscious Reality | Anil Seth | TED

0:12 Just over a year ago, for the third time in my life, I ceased to exist.

0:17 I was having a small operation, and my brain was filling with anesthetic.

0:22 I remember a sense of detachment and falling apart and a coldness.

0:27 And then I was back, drowsy and disoriented, but definitely there.

0:32 Now, when you wake from a deep sleep,

0:34 you might feel confused about the time or anxious about oversleeping,

0:37 but there's always a basic sense of time having passed,

0:40 of a continuity between then and now.

0:42 Coming round from anesthesia is very different.

0:44 I could have been under for five minutes,

0:46 five hours, five years or even 50 years.

0:48 I simply wasn't there.

0:50 It was total oblivion.

0:52 Anesthesia— it's a modern kind of magic.

0:54 It turns people into objects, and then, we hope, back again into people.

0:59 And in this process is one

1:01 of the greatest remaining mysteries in science and philosophy.

1:04 How does consciousness happen?

1:06 Somehow, within each of our brains,

1:08 the combined activity of many billions of neurons,

1:11 each one a tiny biological machine, is generating a conscious experience.

1:16 And not just any conscious experience—

1:18 your conscious experience right here and right now.

1:20 How does this happen?

1:22 Answering this question is so important because consciousness

1:25 for each of us is all there is.

1:27 Without it there's no world, there's no self, there's nothing at all.

1:33 And when we suffer, we suffer consciously

1:35 whether it's through mental illness or pain.

1:38 And if we can experience joy and suffering, what about other animals?

1:43 Might they be conscious, too?

1:44 Do they also have a sense of self?

1:46 And as computers get faster and smarter, maybe there will come a point,

1:51 maybe not too far away, when my iPhone develops a sense of its own existence.

1:54 I actually think the prospects for a conscious AI are pretty remote.

1:59 And I think this because my research is

2:01 telling me that consciousness has less to do

2:04 with pure intelligence and more to do

2:06 with our nature as living and breathing organisms.

2:09 Consciousness and intelligence are very different things.

2:12 You don't have to be smart to suffer, but you probably do have to be alive.

2:17 In the story I'm going to tell you,

2:18 our conscious experiences of the world around us, and of ourselves within it,

2:22 are kinds of controlled hallucinations that happen

2:25 with, through and because of our living bodies.

2:29 Now, you might have heard that we know nothing

2:33 about how the brain and body give rise to consciousness.

2:35 Some people even say it's beyond the reach of science altogether.

2:39 But in fact, the last 25 years have

2:41 seen an explosion of scientific work in this area.

2:44 If you come to my lab at the University of Sussex,

2:47 you'll find scientists from all

2:49 different disciplines and sometimes even philosophers.

2:53 All of us together trying to understand how

2:56 consciousness happens and what happens when it goes wrong.

2:59 And the strategy is very simple.

3:02 I'd like you to think about consciousness

3:04 in the way that we've come to think about life.

3:06 At one time, people thought the property of being alive could not be

3:09 explained by physics and chemistry— that life

3:12 had to be more than just mechanism.

3:14 But people no longer think that.

3:16 As biologists got on with the job of explaining the properties

3:19 of living systems in terms of physics

3:21 and chemistry— things like metabolism, reproduction,

3:24 homeostasis— the basic mystery of what life is started to fade away,

3:29 and people didn't propose any more magical solutions,

3:32 like a force of life or an élan vital.

3:35 So as with life, so with consciousness.

3:37 Once we start explaining its properties in terms

3:40 of things happening inside brains and bodies,

3:43 the apparently insoluble mystery of what

3:46 consciousness is should start to fade away.

3:49 At least that's the plan.

3:51 So let's get started.

3:52 What are the properties of consciousness?

3:54 What should a science of consciousness try to explain?

3:57 Well, for today I'd just like to think of consciousness in two different ways.

4:01 There are experiences of the world around us, full of sights,

4:05 sounds and smells, there's multisensory,

4:07 panoramic, 3D, fully immersive inner movie.

4:11 And then there's conscious self.

4:13 The specific experience of being you or being me.

4:15 The lead character in this inner movie,

4:17 and probably the aspect of consciousness we all cling to most tightly.

4:21 Let's start with experiences of the world around us,

4:24 and with the important idea of the brain as a prediction engine.

4:28 Imagine being a brain.

4:30 You're locked inside a bony skull,

4:32 trying to figure what's out there in the world.

4:34 There's no lights inside the skull.

4:36 There's no sound either.

4:37 All you've got to go on is streams of electrical

4:40 impulses which are only indirectly related to things in the world,

4:43 whatever they may be.

4:45 So perception— figuring out what's there— has to be a process

4:49 of informed guesswork in which the brain combines these sensory signals

4:53 with its prior expectations or beliefs about the way the world

4:57 is to form its best guess of what caused those signals.

5:00 The brain doesn't hear sound or see light.

5:03 What we perceive is its best guess of what's out there in the world.

5:09 Let me give you a couple of examples of all this.

5:12 You might have seen this illusion before,

5:14 but I'd like you to think about it in a new way.

5:16 If you look at those two patches, A and B,

5:18 they should look to you to be very different shades of gray, right?

5:23 But they are in fact exactly the same shade.

5:26 And I can illustrate this.

5:27 If I put up a second version of the image

5:29 here and join the two patches with a gray-colored bar,

5:32 you can see there's no difference.

5:34 It's exactly the same shade of gray.

5:36 And if you still don't believe me, I'll bring the bar across and join them up.

5:40 It's a single colored block of gray, there's no difference at all.

5:44 This isn't any kind of magic trick.

5:46 It's the same shade of gray, but take it away again, and it looks different.

5:51 So what's happening here is that the brain

5:53 is using its prior expectations built deeply

5:56 into the circuits of the visual cortex

5:58 that a cast shadow dims the appearance of a surface,

6:01 so that we see B as lighter than it really is.

6:05 Here's one more example, which shows just how quickly the brain can

6:09 use new predictions to change what we consciously experience.

6:12 Have a listen to this.

6:15 (Distorted voice) Sounded strange, right?

6:20 Have a listen again and see if you can get anything.

6:23 (Distorted voice) Still strange.

6:29 Now listen to this.

6:30 (Recording) Anil Seth: I think Brexit is a really terrible idea.

6:34 (Laughter) Which I do.

6:36 So you heard some words there, right?

6:38 Now listen to the first sound again.

6:40 I'm just going to replay it.

6:41 (Distorted voice) Yeah?

6:44 So you can now hear words there.

6:47 Once more for luck.

6:49 (Distorted voice) OK, so what's going on here?

6:55 The remarkable thing is the sensory information

6:57 coming into the brain hasn't changed at all.

7:00 All that's changed is your brain's best

7:02 guess of the causes of that sensory information.

7:05 And that changes what you consciously hear.

7:08 All this puts the brain basis of perception in a bit of a different light.

7:13 Instead of perception depending largely on signals

7:15 coming into the brain from the outside world, it depends as much, if not more,

7:21 on perceptual predictions flowing in the opposite direction.

7:26 We don't just passively perceive the world, we actively generate it.

7:29 The world we experience comes as much, if not more,

7:32 from the inside out as from the outside in.

7:35 Let me give you one more example of perception as this active,

7:39 constructive process.

7:41 Here we've combined immersive virtual reality with image processing

7:46 to simulate the effects of overly strong perceptual predictions on experience.

7:50 In this panoramic video, we've transformed the world— which is

7:54 in this case Sussex campus— into a psychedelic playground.

7:57 We've processed the footage using an algorithm based on Google's

8:00 Deep Dream to simulate the effects of overly strong perceptual predictions.

8:05 In this case, to see dogs.

8:07 And you can see this is a very strange thing.

8:09 When perceptual predictions are too strong, as they are here,

8:13 the result looks very much like the kinds

8:15 of hallucinations people might report in altered states,

8:18 or perhaps even in psychosis.

8:21 Now, think about this for a minute.

8:23 If hallucination is a kind of uncontrolled perception,

8:28 then perception right here and right now is also a kind of hallucination,

8:32 but a controlled hallucination in which the brain's predictions

8:36 are being reined in by sensory information from the world.

8:40 In fact, we're all hallucinating all the time, including right now.

8:44 It's just that when we agree about our hallucinations, we call that reality.

8:49 (Laughter) Now I'm going to tell you that your experience of being a self,

8:56 the specific experience of being you,

8:58 is also a controlled hallucination generated by the brain.

9:01 This seems a very strange idea, right?

9:04 Yes, visual illusions might deceive my eyes,

9:06 but how could I be deceived about what it means to be me?

9:10 For most of us, the experience of being a person is so familiar,

9:13 so unified and so continuous that it's difficult not to take it for granted.

9:17 But we shouldn't take it for granted.

9:19 There are in fact many different ways we experience being a self.

9:22 There's the experience of having a body and of being a body.

9:26 There are experiences of perceiving the world from a first person point of view.

9:30 There are experiences of intending to do things and of being

9:33 the cause of things that happen in the world.

9:35 And there are experiences of being

9:37 a continuous and distinctive person over time,

9:40 built from a rich set of memories and social interactions.

9:44 Many experiments show, and psychiatrists and neurologists know very well,

9:47 that these different ways in which we

9:49 experience being a self can all come apart.

9:52 What this means is the basic background experience of being

9:56 a unified self is a rather fragile construction of the brain.

10:00 Another experience, which just like all others, requires explanation.

10:04 So let's return to the bodily self.

10:06 How does the brain generate the experience of being a body and of having a body?

10:10 Well, just the same principles apply.

10:12 The brain makes its best guess about what is and what is not part of its body.

10:16 And there's a beautiful experiment in neuroscience to illustrate this.

10:20 And unlike most neuroscience experiments, this is one you can do at home.

10:24 All you need is one of these.

10:26 (Laughter) And a couple of paintbrushes.

10:30 In the rubber hand illusion, a person's real hand is hidden from view,

10:34 and that fake rubber hand is placed in front of them.

10:36 Then both hands are simultaneously stroked with a paintbrush

10:40 while the person stares at the fake hand.

10:43 Now, for most people, after a while,

10:45 this leads to the very uncanny sensation that the fake

10:48 hand is in fact part of their body.

10:51 And the idea is that the congruence between seeing touch and feeling touch

10:55 on an object that looks like hand and is roughly where a hand should be,

11:00 is enough evidence for the brain to make its best guess

11:03 that the fake hand is in fact part of the body.

11:06 (Laughter) So you can measure all kinds of clever things.

11:17 You can measure skin conductance and startle responses, but there's no need.

11:22 It's clear the guy in blue has assimilated the fake hand.

11:25 This means that even experiences of what our body is is

11:28 a kind of best guessing— a kind of controlled hallucination by the brain.

11:33 There's one more thing.

11:36 We don't just experience our bodies as objects in the world from the outside,

11:39 we also experience them from within.

11:41 We all experience the sense of being a body from the inside.

11:47 And sensory signals coming from the inside of the body are

11:49 continually telling the brain about the state of the internal organs,

11:53 how the heart is doing, what the blood pressure is like, lots of things.

11:57 This kind of perception, which we call interoception, is rather overlooked.

12:02 But it's critically important because perception and regulation

12:04 of the internal state of the body— well, that's what keeps us alive.

12:09 Here's another version of the rubber hand illusion.

12:11 This is from our lab at Sussex.

12:13 And here, people see a virtual reality version of their hand,

12:16 which flashes red and back either in time or out of time with their heartbeat.

12:21 And when it's flashing in time with their heartbeat,

12:23 people have a stronger sense that it's in fact part of their body.

12:27 So experiences of having a body are

12:30 deeply grounded in perceiving our bodies from within.

12:35 There's one last thing I want to draw

12:37 your attention to, which is that experiences

12:39 of the body from the inside are very

12:41 different from experiences of the world around us.

12:44 When I look around me,

12:45 the world seems full of objects— tables, chairs, rubber hands, people,

12:49 you lot— even my own body in the world,

12:52 I can perceive it as an object from the outside.

12:55 But my experiences of the body from within, they're not like that at all.

12:58 I don't perceive my kidneys here, my liver here, my spleen...

13:03 I don't know where my spleen is, but it's somewhere.

13:06 I don't perceive my insides as objects.

13:08 In fact, I don't experience them much at all unless they go wrong.

13:13 And this is important, I think.

13:15 Perception of the internal state of the body

13:17 isn't about figuring out what's there,

13:19 it's about control and regulation— keeping the physiological variables

13:23 within the tight bounds that are compatible with survival.

13:28 When the brain uses predictions to figure out what's there,

13:31 we perceive objects as the causes of sensations.

13:34 When the brain uses predictions to control and regulate things,

13:38 we experience how well or how badly that control is going.

13:41 So our most basic experiences of being a self, of being an embodied organism,

13:46 are deeply grounded in the biological mechanisms that keep us alive.

13:52 And when we follow this idea all the way through,

13:55 we can start to see that all of our conscious experiences,

13:58 since they all depend on the same mechanisms of predictive perception,

14:03 all stem from this basic drive to stay alive.

14:07 We experience the world and ourselves

14:09 with, through and because of our living bodies.

14:13 Let me bring things together step-by-step.

14:16 What we consciously see depends on the brain's best guess of what's out there.

14:20 Our experienced world comes from the inside out, not just the outside in.

14:24 The rubber hand illusion shows that this applies to our experiences

14:27 of what is and what is not our body.

14:30 And these self-related predictions depend critically on sensory

14:33 signals coming from deep inside the body.

14:36 And finally, experiences of being an embodied self are

14:40 more about control and regulation than figuring out what's there.

14:44 So our experiences of the world around us and ourselves within it— well,

14:48 they're kinds of controlled hallucinations that have

14:50 been shaped over millions of years

14:52 of evolution to keep us alive in worlds full of danger and opportunity.

14:56 We predict ourselves into existence.

15:00 Now, I leave you with three implications of all this.

15:03 First, just as we can misperceive the world,

15:05 we can misperceive ourselves when the mechanisms of prediction go wrong.

15:09 Understanding this opens many new opportunities in psychiatry and neurology,

15:14 because we can finally get at the mechanisms rather than

15:17 just treating the symptoms in conditions like depression and schizophrenia.

15:21 Second: what it means to be me cannot be reduced

15:25 to or uploaded to a software program running on a robot,

15:29 however smart or sophisticated.

15:31 We are biological, flesh-and-blood animals

15:34 whose conscious experiences are shaped

15:36 at all levels by the biological mechanisms that keep us alive.

15:40 Just making computers smarter is not going to make them sentient.

15:45 Finally, our own individual inner universe, our way of being conscious,

15:50 is just one possible way of being conscious.

15:53 And even human consciousness generally— it's just a tiny

15:57 region in a vast space of possible consciousnesses.

15:59 Our individual self and worlds are unique to each of us,

16:03 but they're all grounded in biological

16:06 mechanisms shared with many other living creatures.

16:09 Now, these are fundamental changes in how we understand ourselves,

16:16 but I think they should be celebrated, because as so often in science,

16:19 from Copernicus— we're not at the center of the universe—

16:22 to Darwin— we're related to all other creatures— to the present day.

16:28 With a greater sense of understanding comes a greater sense of wonder,

16:33 and a greater realization that we are part

16:36 of and not apart from the rest of nature.

16:40 And...

16:42 when the end of consciousness comes, there's nothing to be afraid of.

16:48 Nothing at all.

16:50 Thank you.

16:51 (Applause)