Why do we feel pain?

First though, Alan talked about two “types” of pain: acute - or short term - and chronic, or long-term pain. In a moment we’ll hear why we think some people develop long term pain syndromes, but first we need to understand why things hurt at all. Stephanie Koch is a lecturer in neuroscience at UCL where she studies how we react to pain and touch. She told me why feeling pain is not necessarily a bad thing…

Stephanie - It's something that really grabbed my attention when I first started studying pain - we all think of it as such a bad thing, but it is the cue that our body is giving us to say, stay away from that. That's not good for you. That's going to harm you or potentially harm you. And a really clear example of this is a group of patients who are studied actually by another group at UCL and they don't feel pain. They have a genetic mutation within their pain fibers within the skin. And this means they don't respond to pain. And this group of patients rarely live beyond the ages of 20/30 because they'll burn themselves and not treat the burn because they don't realise they have it. It becomes infected. They'll break a limb and not realise and get septicemia. All these little events, if you think about any time that you felt pain throughout the day, you then take more care to take care of your body to make sure what's happening around you. And these patients don't have that. And as a result they suffer, hugely, actually.

James - Pain is good, right? It's an evolutionary advantage. It's something our body needs to do to stop us causing ourselves more injury. Acute pain in particular is what I want to chat about for now. When does a non-painful stimulus become something painful? Is there a kind of trigger where me just touching my wrist doesn't do anything, but if I was to prick it with a pin, I would feel pain?

Stephanie - Within the skin itself, you have different types of nerve fibers. There's nerve fibers that respond to heat. So those are the ones that are also sensitive to chili peppers, which is why chili pepper feels like a burn. And then we have ones for itch, we have ones for touch. So the first point is you'll have a nerve and whatever the stimulus is, be it pressure, be it pain, you'll kind of activate the nerve. With a pin prick, for example, the nerve suddenly becomes excitable and this nerve will start firing the method by which the central nervous system can communicate with small electrical impulses. So you'll start to get action potentials that begin to fire these, then reach the central nervous system through the spinal cord. They'll activate, which leads to eventually not only a reflex recruitment, it goes directly to the motor neuron. So you move your hand away and the pin prick. So that's one pathway and the other is it goes up to the brain.

James - Yeah, it's fascinating. The actual mechanism by which the nerve fibers sensitive to damage sort of get turned on in a way. How these connect to the central nervous system and the messages going back and forth there.

Stephanie - So you have skin, spinal cord, brain that tells you this pain is in your left finger exactly at the tip. So you know what to move within the spinal cord itself. It's just telling you that's bad, move away.

James - Interesting.

Stephanie - You have many layers of discrimination, of understanding what the stimulus is because essentially our whole body, the outside of our body, we have a lot of surface area of the skin right within the spinal cord as well as within the brain. The biology sort of evolves that we have a 3D representation of our whole surface of the body kind of smushed together into a much smaller plain.

James - Like a map almost.

Stephanie - Yeah, exactly. Exactly. There's many different ways we have so that your body knows how to respond to the information that's coming in.

James - And what is the natural response? When the messages do get to the brain, what does it do about it?

Stephanie - This is why we have this, what I called convergence. So why we have all the information that starts off separate, first touch, pain, itch in the skin, it suddenly gets brought together within the spinal cord because the response in the brain depends on what you're doing. So everything has to come together. You'll have a quick response, which is what we were talking about before, when it synapses onto the motor neurons, and you'll move away your hand, you move away your foot. But when it comes to what happens within the brain, it really depends on what you're doing. So the classic thing to think of is battlefield analgesia. If someone's on a battlefield, they're shot whilst they're running, they won't realise that they've been shot. Why? Because there's an area within the brain, within the brainstem, that kind of stops all pain from coming through whilst you have a more pressing need to survive. So stress, a fight or flight response essentially. In contrast, if you're exhausted, if you're really tired, you've not had coffee in the morning, you stub your toe, it's suddenly the most painful thing you've ever experienced in your life because the body's like, okay, you need to stop, you need to calm down, you need to lie down, you need to take care of your toe. So the contrast of how you respond to something when you're stressed, when you're running, when you're rushed, versus when you are even very poorly, when you have a really bad cold. The body isn't just like, this is pain, this is bad. It also says this is pain, but what else is happening in your life right now? How are you going to respond to that to make sure that you're getting the best out of this? And we're able to protect what's needed to be able to survive. It's all about survival.