How your brain hallucinates your conscious reality

Just over a year ago,

for the third time in my life,

I ceased to exist.

I was having a small operation,

and my brain was filling with anesthetic.

I remember a sense
of detachment and falling apart

and a coldness.

And then I was back,

drowsy and disoriented,

but definitely there.

When you wake from a deep sleep,

you might feel confused about the time
or anxious about oversleeping,

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

of a continuity between then and now.

Coming out from
anesthesia is very different.

I could have been under for five minutes,

five hours,

five years,

or even 50 years.

I simply wasn't there.

It was total obliviion.

Anesthesia --

it's a modern kind of magic.

It turns people into objects,

and then we hope,

back again into people.

In this process

is one of the greatest remaining
mysteries in science and philosophy.

How does consciousness happen?

Somehow, within each of our brains,

the combined activity
of many billions of neurons,

each one a tiny biological machine,

is generating a conscious experience.

And not just any conscious experience --

your conscious experience
right here and right now.

How does this happen?

Answering this question is so important

because consciousness
for each of us is all there is.

Without it there's no world,

there's no self,

there's nothing at all.

And when we suffer,

we suffer consciously

whether it's through
mental illness or pain.

And if we can experience
joy and suffering,

what about other animals?

Might they be conscious, too?

Do they also have a sense of self?

And as computers get faster and smarter,

maybe there will come a point,

maybe not too far away,

when my iPhone develops
a sense of its own existence.

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

And I think this because
my research is telling me

that consciousness has less to do
with pure intelligence

and more to do with our nature
as living and breathing organisms.

Consciousness and intelligence
are very different things.

You don't have to be smart to suffer,

but you probably do have to be alive.

In the story I'm going to tell you,

our conscious experiences
of the world around us,

and of ourselves within it,

are kinds of controlled hallucinations

that happen with, through
and because of our living bodies.

Now, you might have heard
that we know nothing

about how the brain and body
give rise to consciousness.

Some people even say it's beyond
the reach of science all together.

But in fact,

the last 25 years have seen an explosion
of scientific work in this area.

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

you'll find scientists
from all different disciplines,

and sometimes even philosophers.

All of us together trying to understand
how conscioussness happens

and what happens when it goes wrong.

The strategy is very simple.

I'd like you to think about consciousness

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

At one time,

people thought the property
of being alive could not be explained

by physics and chemistry --

that life had to be more
than just mechanism.

But people no longer think that.

As biologists got on with the job

of explaining the properties
of living systems

in terms of physics and chemistry --

things like metabolism,
reproduction, homeostasis --

the basic mystery of what life is
started to fade away,

and people didn't propose
any more magical solutions,

like a force of life or an élan vital.

So as with life,

so with consciousness.

Once we start explaining its properties

in terms of things happening
inside brains and bodies,

the apparently insoluble mystery
of what consciousness is

should start to fade away.

At least that's the plan.

So let's get started.

What are the properties of consciousness?

What should a science
of consciousness try to explain?

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

There are experiences
of the world around us,

full of sights, sounds and smells,

there's multisensory, panoramic,
3D, fully immersive inner movie.

And then there's conscious self.

The specific experience
of being you or being me.

The lead character in this inner movie,

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

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

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

Imagine being a brain.

You're locked inside a bony skull,

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

There are no lights inside the skull.

There's no sound either.

All you've got to go on is streams
of electrical impulses

which are only indirectly related
to things in the world,

whatever they may be.

So perception --

figuring out what's there --

has to be a process of informed guess work

in which the brain combines
these sensory signals

with its prior expectations or beliefs
about the way the world is

to form its best guess
of what caused those signals.

The brain doesn't hear sound or see light.

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

Let me give you a couple
of examples of all this.

You might have seen this illusion before,

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

If you look at those two patches, A and B,

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

But they are in fact
exactly the same shade.

And I can illustrate this.

If I put up a second version
of the image here,

and join the two patches
with a gray-colored bar,

you can see there's no difference.

It's exactly the same shade of gray.

And if you still don't believe me,

I'll bring the bar across
and join them up.

It's a single colored block of gray,

there's no difference at all.

This isn't any kind of magic trick.

It's the same shade of gray,

but take it away again,

and it looks different.

So what's happening here

is that the brain is using
its prior expectations

built deeply into the circuits
of the visual cortex

that a cast shadow dims
the appearance of a surface,

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

Here's one more example,

which shows just how quickly
the brain can use new predictions

to change what we consciously experience.

Have a listen to this.

[(Distorted voice)]

Sounded strange, right?

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

([Distorted voice])

Still strange.

Now listen to this.

Recording: I think breakfast
is a really terrible idea.

(Laughter)

Which I do.

So you heard some words there, right?

Now listen to the first sound again.

I'm just going to replay it.

([Distrorted voice])

Yeah?

So you can now hear words there.

Once more for luck.

([Distorted voice])

OK, so what's going on here?

The remarkable thing is the sensory
information coming into the brain

hasn't changed at all.

All that's changed is your
brain's best guess

of the causes of that sensory information.

And that changes
what you consciously hear.

All this puts the brain
basis of perception

in a bit of a different light.

Instead of perception depending largely
on signals coming into the brain

from the outside world,

it depends as much,

if not more,

on perceptual predictions
flowing in the opposite direction.

We don't just passively
perceive the world,

we actively generate it.

The world we experience
comes as much if not more

from the inside out

as from the outside in.

Let me give you one more
example of perception

as this active, constructive process.

Here we've combined immersive
virtual reality with image processing

to simulate the effects of overly
strong perceptual predictions

on our experience.

In this panoramic video,

we've tranformed the world --

which is in this case Sussex campus --

into a psychedilic playground.

We've processed the footage using
an alogrithm based on Google's Deep Dream

to simulate the effects
of overly strong perceptual predictions.

In this case, to see dogs.

You can see this is a very strange thing.

When perceptual
predictions are too strong,

as they are here,

the result looks very much like the kinds
of hallucinations people might report

in altered states,

or perhaps even in psychosis.

Think about this for a minute.

If hallucination is a kind
of uncontrolled perception,

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

but a controlled hallucination

in which the brain's predictions
are being reigned in

by sensory information from the world.

In fact, we're all
hallucinating all the time,

including right now.

It's just that when we agree
about our hallucinations,

we call that reality.

(Laughter)

Now I'm going to tell you that your
experience of being a self,

the specific experience of being you,

is also a controlled hallucination
generated by the brain.

This seems a very strange idea, right?

Yes, visual illusions
might deceive my eyes,

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

For most of us,

the experience of being a person
is so familiar, so unified

and so continuous

that it's difficult not
to take it for granted.

But we shouldn't take it for granted.

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

There's the experience of having a body

and of being a body.

There are experiences
of perceiving the world

from a first person point of view.

There are experiences
of intending to do things

and of being the cause of things
that happen in the world.

And there are experiences of being
a continuous and distinctive person

over time,

built from a rich set of memories
and social interactions.

Many experiments show,

and psychiatrists and
neurologists know very well

that these different ways in which
we experience being a self

can all come apart.

What this means is the basic
background experience

of being a unified self is a rather
fragile construction of the brain.

Another experience,

which just like all others,

requires explanation.

So let's return to the bodily self.

How does the brain generate
the experience of being a body

and of having a body?

Well, just the same principles apply.

The brain makes its best guess

about what is and what is not
part of its body.

There's a beautiful experiment
in neuroscience to illustrate this.

And unlike most neuroscience experiments,

this is one you can do at home.

All you need is one of these.

(Laughter)

And a couple of paint brushes.

In the rubber hand illusion,

a person's real hand is hidden from view,

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

Then both hands are simultaneously
stroked with a paintbrush

while the person stares at the fake hand.

Now for most people,

after a while,

this leads to the very uncanny sensation

that the fake hand is
in fact part of their body.

And the idea is that the congruence
between seeing touch and feeling touch

on an object that looks like hand,

and is roughly where a hand should be,

is enough evidence for the brain
to make its best guess

that the fake hand is in fact
part of the body.

(Laughter)

So you can measure
all kinds of clever things.

Like you can measure skin conductants

and [startle] responses,

but there's no need.

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

This means that even experiences
of what our body is

is kind of best guessing --

a kind of controlled
hallucination by the brain.

There's one more thing.

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

we also experience them from within.

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

And sensory signals coming from
the inside of the body

are continually telling the brain
about the state of the internal organs,

how the heart is doing,

what the blood pressure is like,

lots of things.

This kind of perception,

which we call interoception,

is rather overlooked.

But it's critically important

because perception and regulation
of the internal state of the body --

well, that's what keeps us alive.

Here's another version
of the rubber hand illusion.

This is from our lab at Sussex.

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

which flashes [red and back]

either in time or out of time
with their heartbeat.

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

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

So experiences of having a body
are deeply grounded

in perceiving our bodies from within.

There's one last thing I want
to draw your attention to,

which is that experiences of the body
from the inside are very different

from experiences of the world around us.

When I look around me,

the world seems full of objects --

tables, chairs, rubber hands,

people,

[you lot] --

even my own body in the world,

I can perceive it as an object
from the outside,

but my experiences
of the body from within,

they're not like that at all.

I don't perceive my kidneys here,

my liver here,

my spleen ...

I don't know where my spleen is,

but it's somewhere.

I don't perceive my insides as objects.

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

And this is important I think.

Perception of the internal
state of the body

isn't about figuring out what's there,

it's about control and regulation --

keeping the physiological variables
within the tight bounds

that are compatible with survival.

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

we can see objects
as the causes of sensations.

When the brain uses predictions
to control and regulate things,

we experience how well
or how badly that control is going.

So our most basic experiences
of being a self,

of being an embodied organism,

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

When we follow this idea
all the way through,

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

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

all stem from this basic
drive to stay alive.

We experience the world and ourselves

with, through and because of
our living bodies.

Let me bring things together step-by-step.

What we consciously see depends
on the brain's best guess

of what's out there.

Our experienced world
comes from the inside out,

not just the outside in.

The rubber hand illusion shows
that this applies to our experienes

of what is and what is not our body.

And these self-related predictions
depend critically on sensory signals

coming from deep inside the body.

And finally,

experiences of being an embodied self
are more about control and regulation

than figuring out what's there.

So our experiences of the world
around us and ourselves within it --

well, they're kinds
of controlled hallucinations

that have been shaped
over millions of years of evolution

to keep us alive in worlds
full of danger and opportunity.

We predict ourselves into existence.

Now I leave you with three
implications of all this.

First, just as we can
misperceive the world,

we can misperceive ourselves

when the mechanisms
of prediction go wrong.

Understanding this opens many new
opportunities in psychiatry and neurology,

because we can finally
get at the mechanisms

rather than just treating the symptoms

in conditions like
depression and schizophrenia.

Second:

what it means to be me cannot be
reduced to or uploaded to

a software program running on a robot,

however smart or sophisticated.

We are biological, flesh-and-blood animals

whose conscious experiences
are shaped at all levels

by the biological mechanisms
that keep us alive.

Just making computers smarter
is not going to make the sentient.

Finally,

our own individual inner universe,

our way of being conscious,

is just one possible
way of being conscious.

And even human consciousness generally --

it's just a tiny region in a vast space
of possible consciousnesses.

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

but they're all grounded

in biological mechanisms shared
with many other living creatures.

Now, these are fundamental changes
in how we understand ourselves,

but I think they should be celebrated,

because as so often in science,

when Copernicus --

we're not at the center
of the universe --

to Darwin --

we're related to all other creatures --

to the present day.

With a greater sense of understanding

comes a greater sense of wonder,

and a greater realization that we
are part of and not apart from

the rest of nature.

And ...

when the end of consciousness comes,

there's nothing to be afraid of.

Nothing at all.

Thank you.

(Applause)