- Two out of the three fundamental mysteries

about our place in the universe have already been resolved.

The first is literally about our place in the universe.

Many years ago Copernicus told us that we were not at its

centre, that we were just a tiny dot suspended in the abyss.

This is an image of the earth taken from the probe Voyager 1

as it was leaving the solar system from about six

billion kilometres away.

All of human history, all of the history of life on Earth,

has taken place on that pale blue dot.

The second mystery, Darwin then revealed

that we humans are just one branch, or one twig,

of a beautifully rich and delicate evolutionary tree.

And that much of the machinery of life

is shared even with the lowliest of our fellow creatures.

The third mystery is that of consciousness,

our inner universe.

Now earlier this year, for the third time in my life,

I ceased to exist.

As the propofol anaesthetic flowed from the cannula

in my wrist into my bloodstream and then into my brain,

there was a falling apart.

A blackness.

An absence.

And then, I was back.

Drowsy and disoriented, but definitely there.

And when you wake from a deep sleep,

you might be confused what time it is, especially

in flying somewhere, but you'll know that some time has passed.

There seems to be some basic continuity

between your consciousness then, and your consciousness now.

But coming around from a general anaesthetic,

it could have been five minutes.

It could have been five hours.

It could have been five days, or five years.

I was simply not there.

A premonition of the oblivion of death.

And general anaesthesia doesn't just work on your brain.

It doesn't just work on your mind.

It works on your consciousness.

By altering the delicate electrochemical circuitry

inside your head, the basic ground state

of what it is to be is temporarily abolished.

And in this process lies one of the greatest remaining

mysteries in science and philosophy.

How does consciousness happen?

Why is life in the first person?

It is going away, and coming back.

The modern incarnation of this problem

is usually traced to Descartes, who in the 17th century

distinguished between matter stuff, res extensa, the stuff

that these desks are made of, that clothes are made of.

But also the brains and bodies and made of, material stuff.

And res cogitans, the stuff of thought, of feelings.

The stuff of consciousness.

And in making this distinction, he gave rise

to the now infamous mind/body problem,

and life has never been simple ever since.

But Descartes actually generated even more mischief

with his doctrine of the beast machine,

which I'm going to mention now, because it anticipates where

I'm going to end up as the bell rings when I finish in an hour.

Before Descartes, people commonly believed in something

called the great chain of being, with rocks and plants

at one end, and other non-human animals, a bit higher

up than humans, and then angels and gods at the very top.

And this great scale of being was also

a scale of moral virtue, so that humans had more moral virtues

than animals and plants, and then rocks and so on.

Now Descartes, in making this division between mind

and matter, argued that only humans had minds, and therefore

moral status, while other animals didn't have minds.

They were merely physiological machines, or beast machines,

morally equivalent to plants, and to rocks.

And in this view, the physiological mechanisms

that give rise to the property of being alive

were not relevant to the presence

of mind or consciousness.

Now I'm going to propose, at the end of this talk, the opposite.

That our conscious sense of self arises because of, and not

in spite of, the fact that we, too, are beast machines.

So to get there, let's return to the apparent mystery

of consciousness.

Now as recently as 1989, which is quite a while ago, but not

that long ago, Stuart Sutherland,

who was founding professor of experimental psychology

at my university of Sussex, had this to say.

"Consciousness is a fascinating but elusive phenomenon.

It is impossible to specify what it is, what it does,

or why it evolved.

Nothing worth reading has been written on it."

[LAUGHTER]

It's quite a pessimistic point of view.

And that may have been true then.

I don't think it was true then, but in any case

things have changed a lot since.

And more or less, about the time that Sutherland

made these remarks, we can see the birth, or the rebirth,

of the study of consciousness within the neurosciences.

And a good landmark is this paper

by Francis Crick and Christof Koch, published in 1990.

And they start their paper by saying that it is remarkable

that most of the work in cognitive sciences,

and the neurosciences, makes no reference to consciousness

or awareness at all.

And then they go on to propose their own theory

of what the neural correlates of consciousness are.

What it is in the brain that is responsible for being

conscious.

And since then, over the last 25 years,

there's been first a trickle, and now a deluge of research

on the brain basis of conscious experience.

Some of this work is being carried out

in my laboratory, the Sackler Centre, the consciousness

science, which was founded six years ago with Hugo

Critchley, my co-director.

And there are now even specialised academic journals,

The Neuroscience of Consciousness,

which I started last year with Oxford University Press.

And this is a real change of the tide.

When I started out more than 20 years ago,

it was thought to be a very-- it was thought

to be career suicide to want to study consciousness,

scientifically.

And it may still be, we don't know.

Let's see.

So while the brain basis of consciousness

is still a mystery, it is, in some sense,

an accessible mystery.

And the author, Mark Haddon, put this very nicely, I think.

He said the raw material of consciousness

is not on the other side of the universe.

It didn't happen 14 billion years ago.

And it's not squirrelled away deep inside an atom.

The raw material of consciousness

is right here, inside your head, and you can

hold the brain in your hands.

But the brain won't deliver its secrets very easily.

What's extraordinary about the brain

is not so much the number of neurons,

though there are about 90 billion.

It's not even the number of connections,

though there are so many that if you counted one every second,

it would take you about three million years

to finish counting.

What's truly extraordinary are the patterns

of connectivity, which to a large extent,

are still not known, but within which are inscribed everything

that makes you, you.

The challenge is then this, at least the the way I see it.

How can the structure and dynamics

of the brain, in connection with the body and the environment,

account for the subjective phenomenological properties

of consciousness?

And considering things this way, we

come up against what the philosopher David

Chalmers has often called the hard problem of consciousness.

And the idea is this.

There is an easy problem.

The easy problem is to understand how the combined

operations of the brain and the body give rise to perception,

to cognition, to thinking, to learning, to behaviour.

How the brain works, in other words.

The hard problem is to understand

why and how any of this should have anything

to do with consciousness at all.

Why aren't we just robots, or philosophical zombies,

without any in a universe?

Now there's a tempting intuition here,

which is that, even if we solve the hard problem, even if we

solve the easy problem, the hard problem would still remain

as mysterious as it seems now.

But this just seems wrong-headed to me.

It may not be necessary to explain why consciousness

exists at all, in order to make progress in understanding

its material basis.

And this for me, is the real problem of consciousness;

how to account for its various properties in terms

of biological mechanisms without pretending that it doesn't

exist at all, as you do if you solve the easy problem,

and without trying to account for why it's

parts of the universe in the first place, which

is the hard problem.

And in the history of science, we've

been somewhere similar before.

It's hard to say if it's exactly the same situation.

But in our understanding of life,

eminent biochemists of the time found it entirely mysterious

how biological mechanisms could give rise

to the property of being alive.

And there were proposed of things,

like elan vital and essence vital,

and all sorts of other stuff.

And although we don't yet understand everything

about life, this initial sense of mystery about life

has, to a large extent, dissolved

as biologists have just got on with the business

of understanding the properties of living systems in terms

of mechanisms.

An important part of this story was

the realisation that life is not just one thing,

but rather a constellation of partially dependent, partially

separable, processes, like metabolism, homeostasis,

and reproduction.

In the same way, to make progress

on the real problem of consciousness,

it can be useful to distinguish different aspects or dimensions

of what it is to be conscious.

The space of possible minds, if you like.

And one simple classification is into conscious level,

which is the property of being conscious at all.

For example, the difference between being

in a dreamless sleep, or under general anaesthesia,

and being awake and conscious as you are now.

And the conscious content, when you are conscious,

you're conscious of something.

The myriad of sights, sounds, smells, emotions, feelings,

and beliefs that populate your inner universe at any one time.

And one thing you are conscious of when you are conscious,

is the experience, the specific experience, of being you,

and this is conscious self.

And it's the third dimension of consciousness.

Now I don't claim these distinctions mark

completely independent aspects of what it is to be conscious,

but they're a pragmatically useful way of breaking down

the problem a bit.

So let's start with conscious level.

What are the fundamental brain mechanisms

that underlie our ability to be conscious at all?

And we can think of this, at least a first approximation,

as a scale from being completely unconscious,

as if you were in a coma, or under general anaesthesia,

to being awake, alert, and fully conscious as you are now.

And there's various states in between being drowsy,

being mildly sedated and so on.

What's important is that, while being conscious and being awake

often go together, this is not always the case.

For instance, when you are dreaming you are asleep,

but you are having conscious experiences.

The conscious experience of your dreams.

And on the other side of this diagram,

there are pathological states, like the vegetative state,

where physiologically you will go through sleep/wake cycles,