Why things hurt | Lorimer Moseley | TEDxAdelaide

What is pain for? Where does it come from? How useful is it?

Lorimer Moseley, Professor of Clinical Neurosciences and Chair in Physiotherapy, University of South Australia, discusses these questions, and looks at what the answers might mean for us, and those who suffer from chronic pain.

This talk was given at a TEDx event using the TED conference format but independently organized by a local community. Learn more at http://ted.com/tedx

... just as everyone goes,
'Great, quick nap.'

Don't have a nap!

Raise your hand - just squeeze
your left ear as hard as you can.

Raise your hand if it hurt.

Fantastic. Thanks for having me.

(Laughter)

No, no - it's not true.

Let me tell you a story.

I just want to take that
off the screen for the moment.

I want to tell you a story
that will explain to you

the first three years
of the Neurobiology of Pain

that you would study
at university.

Eight years ago,
I was walking in the bush.

I had a sarong on.

(Laughter)

Very cool. This is what happened.

Did you see that?

Hang on, this is what happened.

Biologically, I'm going to tell you
what happened just then.

Something touched the outside
of my left leg in the skin.

That activates receptors

on the end of big fat, myelinated,
fast-conducting nerve fibres,

and they stream
straight up my leg - whizz -

straight into my spinal cord -
whizz - up to this part of my brain,

and they say,

'You've just been touched on the outside
of your left leg in the skin.'

(Panting) (Laughter)

Meanwhile, whatever it was

is sufficiently intense
to activate free nerve endings;

we call them 'nociceptors'.

They're thin, unmyelinated,
slow-conducting Lada Niva -

someone knows
what a Lada Niva is -

(Laughter)

nerve fibres.

And that message travels
up to my spinal cord,

and that's as far as it goes.

And it says to a fresh neuron
in my spinal cord,

'Something dangerous has happened on
the outside of your left leg in the skin,

mate.'

(Laughter)

And the spinal nociceptor
takes that message up to the thalamus,

which sits in there somewhere,

and says, 'There's danger on the outside
of your left leg in the skin, mate.'

Now the brain has to evaluate
how dangerous this really is.

So it looks at everything.

And the way that I make sense of this,
of what happened to me,

is the brain thought, 'Frontal lobe,
have we been anywhere like this before?'

Hang on, I'll just ask
the posterior parietal cortex.

Have we been in this environment before?

Yes, we have.

Has it happened at this stage
of the gait cycle?

Yes it has.

Is it coming from the same location?

Yes it is.
What is it?

Well your whole life growing up,
you used to scratch your legs on twigs.

This is not dangerous.

I'm going to give you,
the organism, something

so you can kick off the twig
and continue on your merry way.

And that's what happened for me.

I can't show you now,
but I took off my sarong,

got in the river, got out of the river,

and that's the last thing I remember,

having been bitten
by an eastern brown snake.

(Mumbling)

Survivor.

(Laughter)

Thank you very much.

(Applause)

Now, for some reason,

the eastern brown snake
works by poisoning you - clearly -

and one of the things it does is
activate nerve fibres.

So actually my brain
would have got these messages

saying, Danger! Danger! Danger! Danger!

and, in its wisdom, it said, No. No. No.

Six months later, I'm walking
in the bush with a boring talker.

You know what a boring talker is?

Those people, it doesn't matter
what they say, it's boring.

(Laughter)

It's irrelevant, but we'll call her Naomi

because that is her name.

(Laughter)

Anyway, this is what happened, right?

Ow! Wah!

And I'm in agony.

I have got a white-hot poke of pain
screaming up my leg.

I'll tell you, biologically,
what's happened.

Something touched the outside
of my left leg in the skin.

That activates big, fat,
myelinated nerve fibres

which send a message -
whizz - whizz - up to here.

Just been touched on the outside
of your left leg in the skin.

It's sufficiently intense to activate
these free nerve endings.

Danger receptors take
the message to my spinal cord:

something dangerous has happened on
the outside of your left leg in the skin.

(Audience) Mate.

Yes!

(Laughter)

Well done, you weren't planted.

That goes to the thalamus
and says the same thing:

something dangerous has just happened

on the outside
of your left leg in the skin.

(Audience) Mate!

So the brain says, thanks very much,
Thalamus, kids alright? Good, anyway ...

(Laughter)

Frontal cortex,
anything to tell me about this?

Hang on, I'll ask the posterior
parietal cortex: where are we?

We're walking in the bush.

You're a bit 'mate' happy.

At this stage of the gait cycle?

Where's it coming from?
Have we been here before?

Oh yes, we have.

Last time we were here, you almost died.

I'm going to make this hurt so much
that you can do nothing else.

And I was in absolute agony
for what seemed like minutes.

Screaming pain -

until one of my mates looked at my leg,
and there's a little scratch from a twig.

(Laughter)

The pain in those situations
was totally different

because of meaning.

I want to convince you that pain
is an illusion 100% of the time.

Here's a visual illusion ...

So have a look at this picture,

you've got a square that's got A in it
and one that's got B in it.

Raise your hand if you think
that the square with A in it

looks darker than the square with B in it.

Thank goodness for that.

None of you have a really socially
embarrassing, neurological disorder.

Except you.

(Laughter)

That's not true.

Watch what happens
if we have another look at this.

These are those two squares
taken out of that picture.

Hopefully you can see they're identical,
and some of you may not believe me.

I'll just put A on top of that,
and I'll put B on top of that.

Some of you may still not believe me,

so why don't we
just move A over on top of B,

or B over on top of A.

No matter how long you look at this,
A will look darker than B

because your brain's doing
some really groovy stuff,

really quickly, outside of your awareness.

Have a look at this.

Turn your head on the side
and have a look at the same picture.

Nothing changes.

(Laughter)

Fantastic. 100% take!

So what really happens here,

exactly the same frequency
is hitting your retina,

and that sends a message
to the back of the brain,

and then all of this groovy stuff
happens very quickly

to ask the question,
What does this really mean?

What's biologically advantageous for me?

and then you get a visual image.

This is a visual illusion,
and vision's not about emotion,

vision's not necessarily about survival,

but pain is.

Now, some of you might not know,
if you're not medically trained,

but what's happening
at this guy's right leg,

that's not right, that's ...

(Laughter)

that's a dangerous situation,

and that danger message
arrives at the brain,

and the brain has to ask
exactly the same question.

What does this mean?
What should be done here?

And hopefully, the orchestra in this
person's brain will make your leg hurt.

In the work that
I've been doing for a long time,

we're trying our best to work out
how do we convince people in pain

that we understand they're in pain,

but it's not just about
the tissues of their body.

How do we convince them of that?

And a key conceptual shift
that we think is really important

is that you can understand
that pain is the end result.

Pain's an output of the brain
designed to protect you.

It's not something that comes
from the tissues of your body.

There's nothing there.

We show patients a really sharp knife,

and we say this knife is sharp, yeah?

Yeah.

And it might be a bit cold;
it's hard; it's got all those properties.

This knife - painful as it sits out there.

No, it's not. That knife does not
have the properties of pain.

And when you stick it into their belly -
we do this regularly, straight through -

the belly doesn't adopt
the property of pain.

The brain has to do some
very rapid and groovy things

to project this illusion
that pain exists there.

100% of the time,
pain is a construct of the brain.

We can mess with pain easily
without touching the tissues.

This is an experiment we did a while ago

where we got supposedly 'normal'
healthy volunteers.

They're not normal people,

because they're volunteering
for a pain experiment,

(Laughter)

but let's say they are
reasonably normal, right,

and we put a very cold piece of metal
on the back of their hand,

and we just show them one of two lights.

One light is red, and one light is blue.

We don't tell anything about the lights,
we just show them the light.

I see that hand.

We ask them, 'How much does it hurt?'

And if they see the red light, it hurts
more than if they see the blue light.

The stimulus is exactly the same,

what's different is
the meaning of the stimulus.

Now there's a cue that says,
'This is really hot.'

Because red means hot.

So the sensible brain,
the clever brain should say,

'Well, I really don't want you to do it,
so I'm going to make it really hurt.'

There's people in the States that are
allowed to get their psychology students

to participate in experiments
in exchange for credit points -

or sex, or something -

anyway, they put their head inside what
they think is a stimulator for their head,

and they make sure that
the subject can see the intensity knob.

And as they turn up the intensity knob,

this little figure there showing
the lines going up at a steady rate,

that's their reported head pain,

and it matches the intensity knob.

But the stimulator's doing nothing.

It's just one of those
old-fashioned plastic hair dryers

that doesn't do anything.

You know those things?

You probably use one - yeah?

The trick is that they
have to see the intensity knob.

I always think it'd be fun
to do an experiment

based on that Spinal Tap film
where the intensity knob goes up to 11.

Remember that film?

What's really important
from a clinical perspective,

and I'm a clinical neuroscientist,
and I see patients in pain,

any piece of credible evidence
that they're in danger

should change their pain,

and they're all walking
into hospital departments

with models like this on the desk.

What does your brain say
when it sees a disc

that's slipped so far out
it's sitting on its own?

(Laughter)

If you've ever seen a disc in a cadaver,
you can't slip the suckers.

They're immobile, you can't slip a disc.

But that's our language,
and it messes with your brain.

It cannot not mess with your brain.

We can even modulate the location of pain.
We can do some groovy things.

It's quite well established
that referred pain

gives you pain in an area of your body
that might be physiologically normal.

Most of you would have heard
of referred pain.

(Sneezing)

Bless you.

We do experiments where we give you
pain in an artificial limb -

it's not even yours.

This is Meng, who was a postdoc
in my lab in Oxford in the UK,

and we stole a prosthetic limb,

which is a whole other story
which is really funny -

but I won't tell it to you -

and we can do this manipulation

so that you start to feel like
the plastic limb in front of you is yours.

And we can make the rubber hand hurt.

And we can bring in a knife,
and run the knife across the rubber hand,

and you have your brain responses
to protect that rubber hand.

You're feeling pain
in a lump of plastic, effectively.

Here's a groovy experiment where
we take two Microsoft clipart people,

and we put a webcam
on the forehead of one of them

and a set of virtual reality glasses
on the other one.

And then we get them to shake hands.

And as they're shaking hands,

the person on your right,
who's wearing the goggles,

their visual field is coming
from the other person's forehead.

Have you got it?

So they are effectively looking
at the other person, thinking it's them

because they're shaking hands,
the motor command fits, everything's good.

And then we come in and put
a painful stimulus on that person's arm,

and they see it hit that arm
of the person over there,

with whom they're shaking hands,
and they say, 'Ouch! It really hurts.'

And we say, 'Where does it hurt?'

'On that man's arm.'

(Laughter)

They get it right every time,
pointing exactly where it is,

but if you were on the outside,
taking a photo, they're literally -

we've got the painful stimulus here,
and they're saying, 'It hurts there.'

So the brain is not only producing pain,

it's projecting it
to this location in mid-air.

We can mess with that.

This all becomes really important
when pain persists

because two things happen
when pain persists

that make the life
of someone in pain really difficult,

that costs our country
40 billion dollars a year.

It costs Australia more than cancer,

cardio-vascular disease
and diabetes combined.

Thanks for that facial expression,
I wanted someone to go ...

This is the problem,
that if we keep running the neurons,

the brain cells that produce pain,
they get better at producing pain.

They become more and more sensitive,

so we need a smaller
and smaller influence.

The illusion, if you like,
in increasing sensitivity

becomes very unhelpful.

It's trying to protect you from something
that's not needing protection.

It's very real.

The other thing that happens
is that all of these networks

lose their capacity to be specific
and precise, so the pain spreads.

The pain changes its quality.
Ultimately, it's not even informative.

It's both unhelpful and uninformative.

Maybe the next TED Talk ever
is the really important question,

'What do we do about it?'

Who knows?

No, we do know,

that's what we're really researching,
but that's the end of my 18 minutes.

Thank you very much for having me.

(Applause)