Pain. No one likes it. So what if you could opt out of pain? Would you do it? There are actually reported cases of people not being able to feel pain – it's called congenital insensitivity to pain with anhidrosis (CIPA), and it's a rare genetic disorder. Though this might sound nice at first, it's actually a very debilitating condition. Ashlyn Blocker is a five year old with this condition, and because she can't feel pain she has fallen from dangerous heights, bitten through her tongue while eating and burned herself among other things. Scary. This can have even more serious consequences if there is a disease state. Like if a person develops an inflamed appendix, but has no idea because they can't feel any pain associated with it. Not having an alarm system that tells you when your body is at risk is very dangerous.
So pain is important. But considering how important pain is, we really don't understand it that well. In fact a quick scan with a Google search showed that most highly recognized sources still define it incorrectly. Most people think that pain is an input. That if you touch a hot stove with your finger, for example, a pain signal travels from your finger to your brain telling you that it hurts. Not only is this overly simplistic, but it is incorrect! Pain is actually an output… so let's spend some time talking about what that means.
Simply put pain is a danger alarm system. It's a response generated by the brain to an influx of information coming from bodily sensors, memories and your emotional state indicating that your tissues are in danger. So let's go back to our example of touching a hot stove. Your finger touches the stove and the temperature sensors in your finger tell your brain that what you have just touched is very hot. Your memory informs you that last time this happened you damaged your finger. On an emotional level you're very afraid of burning yourself like you did last time, you're also stressed that this incident could leave an ugly scar. Your brain evaluates this information and decides the threat level. Based on the amount of impending danger the brain sends out a corresponding pain sensation that gets you to stop what you're doing and get yourself out of that dangerous situation.
Not convinced? Think of jumping into a cold pool. You immediately feel the 'pain' of the cold water. But the longer you stay in the water, the more comfortable it feels. The temperature of the water didn't change, but your response to it did. If pain was an input, you'd feel that surge of 'pain' as long as you were in that cold water. You wouldn't be able to adapt the cold temperature. However, since pain is an output, your brain can evaluate the situation and decide that this isn't a dangerous situation and get you feeling comfortable pretty quickly. Another example is phantom limb pain. People with amputations have reported feeling sensations of pain in limbs that they no longer have! For them, it is physically impossible to have an input of pain. In this case the brain is actually creating pain based on an old map of the body when that limb used to exist.
The brain and the rest of the nervous system is an incredible ever-adapting network. Scientists call this plasticity. The brain achieves this by constantly rewiring its connections and replacing the sensors that feed it. For example, if you begin to learn the guitar, the area in the brain dedicated to sensing the inputs received by the fingertips grows larger. If you decide you actually hate playing the guitar – and throw it away forever, this area will shrink back to its previous size. In a similar way the brain is constantly adapting to how it responds to pain.
Let's get into the nitty gritty of how pain works for a minute and keep using the example of the fingertip. The fingertip has lots of little nerve endings, and those nerve endings have receptors that are sensitive to things like temperature, pressure and chemicals. If you have enough of that stimulus (temperature, pressure, chemical) it opens up that particular receptor and "ping!" - an alert gets sent along the length of the nerve. That nerve hits an intersection at the spinal cord. If there is enough of that stimulus to turn the light green, the alert get passed along to the next nerve sitting on the other side of that intersection, and it travels up to the brain. This second nerve is actually part of the spinal cord, and hence it's called a second order neuron. Now remember, this is NOT a pain signal. It is a danger alert saying 'brain, you might be interested in what's going on down here at the finger.' It's up to the brain to decide if this experience warrants a pain response or not.
If your finger is in fact touching a hot burner, and isn't just in a cozy mitten, the brain creates a pain signal and gets you to move your finger off that burner immediately. If it was too late and you already burned your finger, that intersection gets more interesting…. more on this next post.
That's the groundwork for understanding how pain works. Stay tuned for our next blog post where we'll talk about what happens with inflammation, swelling and chronic pain.