TEDxAdelaide - Lorimer Moseley - Why Things Hurt

Summary

In this engaging talk, the speaker explores the neurobiology of pain, illustrating how pain is not a direct response from the body's tissues but an illusion created by the brain. Through personal anecdotes and visual illusions, they demonstrate the brain's role in interpreting and responding to stimuli, emphasizing the importance of understanding pain as a protective mechanism rather than a mere physical sensation. The discussion also touches on the complexities of chronic pain and its significant impact on society.

Takeaways

• 🧠 Pain is processed in the brain: The speaker explains that the perception of pain is a result of how the brain interprets sensory input, not just a direct response from the body's tissues.
• 🐍 A snakebite story: The speaker recounts a personal experience with an eastern brown snake, illustrating how the brain's interpretation of danger can influence the experience of pain.
• 👂 Nociceptors at work: The activation of 'nociceptors', or pain receptors, sends a message to the spinal cord and then to the brain, where the potential danger is evaluated.
• 🔍 The brain's role in pain: The brain assesses the situation and uses past experiences to determine the level of danger and the appropriate pain response.
• 🤔 The meaning of pain: Pain is presented as an illusion, entirely constructed by the brain based on the meaning and context of the sensory input.
• 🎨 Visual illusion example: A visual illusion is used to demonstrate how the brain processes information differently based on context, similar to how it processes pain.
• 🗡️ Pain is not inherent: The speaker argues that an object, like a knife, does not inherently possess pain-causing properties; it's the brain's interpretation that matters.
• 🔴 Color influences pain perception: An experiment showed that the color of a light (red or blue) could influence the perceived intensity of pain from the same physical stimulus.
• 🧠 Pain is a brain output: Pain is described as an output from the brain designed to protect the individual, not a direct result of tissue damage.
• 🤲 Phantom pain and body perception: The speaker discusses experiments with artificial limbs, showing that the brain can be tricked into feeling pain in a non-existent limb.
• 🕊️ Pain and the power of suggestion: The speaker highlights how the brain's interpretation of stimuli can be influenced by suggestion, as in the case of a 'painful' stimulus applied to a person's arm during a virtual reality experience.

Q & A

What is the main point the speaker is trying to convey about pain?

The speaker is trying to convey that pain is an illusion created by the brain and is not solely a result of physical tissue damage.

What happened when the speaker was bitten by an eastern brown snake?

The speaker experienced an intense activation of nerve fibers due to the snake's venom, which led to a significant pain sensation.

How does the brain evaluate the danger of a stimulus?

The brain evaluates the danger by comparing the stimulus with past experiences and assessing the environment and the body's current state.

What is the significance of the visual illusion presented in the script?

The visual illusion demonstrates how the brain can quickly interpret and alter perceptions without the person's awareness, which is similar to how it processes pain.

What role does the thalamus play in the pain experience?

The thalamus relays the danger signal from the spinal cord to the brain, where it is evaluated for potential threats.

How does the speaker illustrate the concept that pain is not just about physical tissues?

The speaker uses the example of a sharp knife and a patient's belly, explaining that neither has inherent pain properties and that pain is a brain construct.

What was the purpose of the cold metal experiment with the red and blue lights?

The experiment aimed to show how the perception of pain can be influenced by the meaning associated with a stimulus, such as the color of a light.

What is the effect of persistent pain on the brain's pain-producing neurons?

Persistent pain can cause the neurons to become more sensitive, requiring less stimulus to produce pain, which can be unhelpful and lead to increased sensitivity and pain spreading.

What is the economic impact of pain in Australia as mentioned in the script?

Pain costs Australia more than 40 billion dollars a year, which is more than the combined cost of cancer, cardiovascular disease, and diabetes.

How can the brain's perception of pain location be manipulated, as demonstrated in the script?

The brain's perception of pain location can be manipulated through visual illusions and virtual reality, as shown in the rubber hand experiment and the Microsoft clipart people experiment.

What is the broader implication of the speaker's research on pain?

The research implies that understanding pain as a brain construct could lead to new approaches in pain management and treatment, potentially reducing the economic and personal impact of chronic pain.

Outlines

00:00

🐍 The Neurobiology of Pain: A Snakebite Story

In this paragraph, the speaker, a neuroscientist, shares a personal story of being bitten by an eastern brown snake to illustrate the neurobiology of pain. The narrative begins with the activation of nerve receptors when the skin is touched, leading to a rapid transmission of signals to the brain. The brain evaluates the danger by referencing past experiences and environmental context. In the case of the snakebite, the brain interprets the situation as non-threatening, allowing the speaker to remove the twig and continue walking. The story highlights the brain's role in interpreting pain signals and the body's response to perceived danger.

05:04

🎨 Pain as an Illusion: The Power of Perception

This paragraph delves into the concept of pain as an illusion, influenced by the brain's interpretation of sensory input. The speaker uses a visual illusion to demonstrate how the brain can be tricked into perceiving differences that do not exist. This concept is then applied to pain, explaining that the brain evaluates sensory input to determine the level of threat and the appropriate response. The speaker argues that pain is not a direct result of tissue damage but is an output of the brain designed to protect the individual. The paragraph also discusses experiments that manipulate pain perception, showing that the brain can be influenced by visual cues and expectations to alter the experience of pain.

10:04

🤕 Chronic Pain and the Brain's Adaptations

The final paragraph addresses the complexities of chronic pain, emphasizing the economic and personal impact it has on society. The speaker, a clinical neuroscientist, explains how persistent pain can lead to changes in the brain, making it more sensitive and less specific in its response to stimuli. This can result in pain that is both unhelpful and uninformative. The speaker also discusses the importance of understanding that pain is a construct of the brain, which can be influenced by psychological factors and beliefs. The paragraph concludes by highlighting the need for further research into managing and treating chronic pain, hinting at the potential for future solutions.

Keywords

💡Neurobiology of Pain

The study of how pain is processed in the nervous system, including the brain and spinal cord. This concept is central to the video as it explains the biological mechanisms behind pain perception and how the brain interprets pain signals. The speaker's story about being bitten by a snake and later experiencing intense pain from a mere scratch illustrates this topic.

💡Nociceptors

Specialized nerve fibers that detect harmful stimuli and send pain signals to the brain. These are activated during both minor and severe injuries, as described in the video when the speaker's leg is touched and when he is bitten by a snake. Nociceptors play a crucial role in the body's response to danger.

💡Thalamus

A brain structure that acts as a relay station for sensory information, including pain. In the video, the thalamus receives danger messages from the spinal cord and helps the brain evaluate the significance of the pain signal. The speaker references the thalamus multiple times when describing how pain messages are processed.

💡Frontal Cortex

Part of the brain involved in higher cognitive functions and decision-making. The video explains how the frontal cortex helps assess the context of pain, such as recalling past experiences and determining the danger level. This is illustrated when the speaker's brain evaluates whether the sensation on his leg is dangerous based on previous experiences.

💡Pain as an Illusion

The idea that pain is a construct created by the brain, rather than a direct response to tissue damage. The video emphasizes that pain is an output of the brain designed to protect the body, highlighting how the brain can modulate pain perception based on context and past experiences. This is demonstrated through the speaker's contrasting reactions to the snake bite and the twig scratch.

💡Visual Illusions

Optical phenomena where the brain interprets visual information in a way that differs from reality. The video uses visual illusions, such as the A and B squares appearing different in color, to illustrate how the brain processes sensory information and creates perceptions. This analogy helps explain the concept of pain as a mental construct.

💡Referred Pain

Pain perceived in a location different from the site of the actual stimulus. The video discusses experiments showing how pain can be felt in a non-injured area, such as a phantom limb, demonstrating the brain's role in projecting pain. This concept underscores the complexity of pain perception and the influence of the brain on where pain is experienced.

💡Sensitization

The process by which neurons become more responsive to stimuli over time, leading to increased pain sensitivity. The video explains how persistent pain can cause the brain's pain-producing neurons to become hypersensitive, resulting in chronic pain conditions. This is an important aspect of understanding why pain can persist and become debilitating.

💡Pain Modulation

The brain's ability to alter the perception of pain based on various factors, such as context and previous experiences. The video describes experiments where the perception of pain is changed by altering visual cues, demonstrating the brain's role in modulating pain intensity. This highlights the potential for psychological and contextual interventions in pain management.

💡Clinical Implications

The practical applications of pain research in medical practice. The video discusses how understanding the brain's role in pain can lead to better treatment strategies for chronic pain sufferers. It emphasizes the importance of educating patients about the nature of pain to help them manage their symptoms more effectively. This concept is vital for improving pain management and reducing the burden of chronic pain.

Highlights

The speaker introduces a unique method to wake up by squeezing the left ear instead of taking a nap.

A personal story is shared to illustrate the neurobiology of pain, experienced during a bushwalk encounter with an eastern brown snake.

The biological response to touch and pain is explained through the activation of specific nerve fibers and their transmission to the brain.

The brain's evaluation process of pain signals is described, involving the frontal lobe and posterior parietal cortex.

The concept of pain as an illusion is introduced, with the brain constructing the experience of pain based on past experiences and environmental context.

A visual illusion is used to demonstrate how the brain processes information and can create perceptions that differ from reality.

The speaker argues that pain is 100% a construct of the brain, not originating from the body's tissues.

An experiment is described where the color of a light influences the perceived intensity of pain from a cold stimulus.

The placebo effect is discussed in the context of pain, with an example of a fake stimulator increasing perceived pain based on a visible intensity knob.

The impact of medical imagery, such as a slipped disc, on the brain's perception of pain is highlighted, showing how language can influence pain experience.

Referred pain is explained, where pain is felt in a different location from the source, demonstrating the brain's role in pain localization.

An experiment with a rubber hand and virtual reality shows how the brain can be tricked into feeling pain in a non-existent limb.

The speaker discusses the economic cost of chronic pain, emphasizing its significant burden on society.

The neural changes that occur with persistent pain are explained, including increased sensitivity and less specificity in pain signals.

The importance of understanding the brain's role in pain for clinical treatment and management is emphasized.

The speaker concludes by highlighting ongoing research into pain and its implications for future treatment strategies.

Transcripts

Translator: Dinah Challen Reviewer: Peter van de Ven

... 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 -

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)