Sean Mackey, M.D., Ph.D.
speaker
373 appearances
1 recordings
1 series
first heard Apr 2025
last heard Apr 2025
Sean Mackey, M.D., Ph.D.’s voice in public audio — every appearance, attributed to the second.
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There's the formal definition of pain, which is defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage. It's a mouthful. If you think of it as it's an unpleasant sensory and emotional experience, it's usually tied to something physically happening, but may not be.
I think sometimes what's missing in that definition, one of the things I wish they had put in but never did, is that pain is the great motivator. Pain is one of the most primitive experiences going back to, if you will, single-cell organisms. It's either pain or reward. You're either being driven towards oxygen, food, sex, or you're trying to get away from danger.
Pain is so wonderful because it's so terrible. It keeps us alive. Without pain, when we have these genetic issues of congenital insensitivity to pain, we would have never lived as a species. So pain is an unpleasant sensory and emotional experience. To understand pain, whether you're a Martian or you're a human now, I think you have to look back in history.
And so I'm going to evoke Rene Descartes, 17th century French philosopher, thought to be the father of modern philosophy. Incredible contributions brought Cartesian geometry to us, which led to calculus. And he had this dualistic model of pain. that he put forward.
To his credit, it was the first mechanistic foundation for pain because beforehand, pain was thought to be something mystical or religious. It was punishment of the gods. So he put this framework together that's often illustrated this famous picture of a little boy with his foot in the fire. And there's a little string from his foot going up into his brain.
And it ends up in the pineal gland, which was thought to be uniquely a human area. And the idea is the fire pulls on the little string, opens up pores in the pineal gland, rings a bell, and the boy withdraws his foot. The idea is in this dualistic model, there is a complete separation between body and mind. The body is where pain is generated. The mind is where it's perceived.
But the mind is simply a passive receptacle receiving these signals. That model put forward in the 17th century stuck with us for hundreds and hundreds of years and I would argue is with us today. And it has influenced medical care. It has influenced policy. It's influenced everything in our society about the way we think about pain. And it's utterly, completely wrong.
So, yes, he got Cartesian geometry right. But he really, complete bollocks, screwed it up when it came to pain. This biomedical model, this dualistic model, was with us for hundreds and hundreds and hundreds of years. And it's only been in the last number of decades that we've appreciated the nuance of what pain really is.
And instead of it being under this guise of this separate mind and body, we now appreciate it is this integrated biopsychosocial phenomenon. Meaning that, and I think this is one of the most important things that I'd like to drive across.
I'm going to introduce a term, we're going to get to a term called nociception, which are electrochemical injury signals that occur in the periphery, that what goes on in the body is And what goes on in the brain, the experience of pain, they may have nothing to do with each other or very little linkages. And we're going to hopefully unpack that.
So hundreds and hundreds of years, we're basing it on Rene Descartes' dualistic model. We still see this in medical care right now. You're a surgeon. For many, many, many, many years when I talked with the surgeons, They were firmly of the opinion that the amount of pain that a patient had after surgery was related to how much the scalpel cut and how much tissue damage was done.
And I think it's only more in the last 20 or so years I'm seeing surgeons really embracing this model that what people bring to the operating room table directly influences how much pain they have. Their early life experiences, all this stuff. And we'll talk about that.
Yeah. Had no influence on that model, which I think has had tragic consequences in the care of people, particularly with chronic pain. particularly women with chronic pain who have felt stigmatized, invalidated, because absent something that's obviously wrong out in the body of the periphery, they were just labeled as being histrionic housewives or being told it's all in their head.
Not just women, but also some men as well. And so it's only with that evolution of our perception or our model into a biopsychosocial model that that's gotten much better.
Let's talk about, is there a pain receptor? So let's break it down into the foundational stuff. So we have these things called nociceptors. Complicated name. It's basically a transducer, which is another technical name. Now, you're engineering background, so you all know that a transducer is simply a device that converts one form of energy into another form of energy.
This microphone is converting sound energy into electrical energy. The speakers convert electrical energy back into sound energy. We have these nociceptors that lie in our skin, our soft tissues, our deep tissues, our viscera, and they're specialized. And they convert different forms of energy into electrochemical impulses. They take pressure. They take heat, cold.
They take chemical changes in the form of pH that can occur during infection. They convert those into action potentials that are then transmitted up nerves. These are little electrical impulses transmitting up generally two different nerve fiber types. These two different nerve fiber types, one is called a C-fiber, which is thinned. thin and slow. It's really pokey.
And I don't know if I'm getting ahead if you wanted to go more into that, but you got this pokey, slow C-fiber that transmits at about one meter a second. And the frame of reference, if it helps, is think about your thumb is about a meter from your brain. So an impulse on a C-fiber from your thumb to a brain takes about a second to two seconds to get there. The other nerve fiber type
It's called an A-delta fiber. It's got some nice insulation around it. It transmits 10 times faster. So it takes a little under a tenth of a second to get your thumb to your brain. And to give a real-world sense of the difference in C-fibers and A-delta fibers...
Think back to the last time you stepped on a tack in the carpet, you hit your thumb with a hammer, you twisted your ankle coming off a curb. What happened? Think back to that experience. You get this sharp jolt of pain that goes right to your brain.
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