Why Things Hurt: Lorimer Moseley (Full Transcript)

Here is the full transcript of Lorimer Moseley’s talk titled “Why Things Hurt” at TEDxAdelaide conference.

Listen to the audio version here:

TRANSCRIPT:

The Brain

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. 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. 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.”

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 – 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.” 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. Survivor. Thank you very much.

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.

Walking in the Bush

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. It’s irrelevant, but we’ll call her Naomi because that is her name. 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. Yes! Well done, you weren’t planted.

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

Visual Illusion

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. 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. Fantastic. 100% take!

Pain

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… 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.

Understanding Pain

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.

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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, but let’s say they are reasonably normal, right.

Experiment

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 them 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 are 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.

Head Stimulator

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?

Clinical Perspective

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? 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. 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.

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Groovy Experiment

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.” 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, cardiovascular 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.

SUMMAR OF THIS TALK:

Lorimer Moseley’s talk, “Why Things Hurt,” explores the complex nature of pain and its origins in the brain rather than the body’s tissues. He argues that pain is a protective output of the brain, designed to alert us to potential danger, rather than a direct sensation from injured parts.

Through engaging anecdotes and experiments, Moseley illustrates how the brain interprets signals and can be influenced by various factors to perceive pain, even in the absence of physical harm. He demonstrates this with experiments involving visual cues, like the color of a light, which can alter the intensity of pain felt from the same stimulus. Moseley also discusses the concept of referred pain and the brain’s ability to project pain onto artificial limbs, highlighting the brain’s role in the pain experience.

He emphasizes the importance of understanding pain’s psychological and neurological dimensions for clinical treatment. The talk concludes with a discussion on the challenges of chronic pain and the need for research focused on managing pain beyond the physical symptoms. Moseley’s engaging presentation sheds light on the intricate relationship between the brain, perception, and pain, offering new perspectives on pain management and treatment.