Why Do We Feel Pain?
If you’re reading this post, I’m guessing that you have experienced some pain over the past year. Pain is a very normal experience. Almost every single person on earth experiences pain. However, there are a handful of people with a genetic mutation that causes them not to experience pain. Unfortunately, these people often live quite short lives because they lack the warning signals to protect themselves from potentially dangerous scenarios. These dangerous scenarios may be something as extreme as not feeling a stab from a sharp knife, to something more trivial such as not feeling when they need to roll over in bed because they are starting to develop a pressure sore. Although it is generally an unpleasant experience, pain is not always a bad thing. In fact, it is a vey important protective mechanism.
Although everyone’s pain experience is different, there is one thing that can be said definitively about pain, “It hurts because your brain is convinced that your body needs protecting.” However, your brain’s perceived danger and the true danger may not match up. The picture on the right-hand side is often used to describe how we feel pain. However, this is not the process of pain perception. This is a process known as nociception. Nociception is our body’s ability to transmit a noxious stimulus (i.e. thermal, chemical or mechanical) to our brain. Our body has specialized receptors known as nociceptors that can perceive these signals. These signals are then relayed to the spinal cord where they synapse (connect) with nerves that send the signal to the brain. This is the process of nociception. Nociception has a small but important difference from pain perception. Pain perception is dependent upon nociception, but also involves the simultaneous interpretation of millions of other neural signals to make an overall judgement of whether our body is in danger. Ultimately, it is the combination of all those signals which help the brain determine if there is a threat to our body.
To highlight this point, I want you to imagine stubbing your toe in a couple different scenarios. The first is during a soccer match. You stub your toe as you pass the ball to your teammate and your team tries to score the winning goal. In this scenario it is likely that you will experience very little pain, or maybe none at all. This is because you have adrenaline rushing through your body and you have an external focus of trying to score a goal. These additional factors create a perception of safety within the brain so it is less likely you will feel pain. So, even though there is a nociceptive signal from your toe being sent to the brain, no pain was perceived.
In the second scenario you stub your toe on the corner of your bed. But in this scenario, you have a cold and last week your friend was telling you about how they broke their toe from stubbing it on a table. The additional factors of having a cold and the fear from your friend’s story have the potential to increase your brain’s perception of danger. Therefore, it is likely you will experience more pain in the second scenario even though the nociceptive signal was the same. Ultimately, it is the combination of millions of other neural signals that our brain is simultaneously interpreting that will influence whether we feel pain.
Most people can understand how nociception can lead to pain. However, from the toe stubbing example, you can also see how nociception does not equal pain. In fact there are scenarios when nociception occurs but it does not result in pain, as in the soccer example. The most difficult concept to understand is that we can experience pain without any nociception occurring. Furthermore, we can experience pain without injury or tissue damage. Some people have conditions such as chronic pain and fibromyalgia that increase our pain sensitivity.
I’m going to use a metaphor to help highlight how sensitivity can play a role in the output of a system. Imagine you are laying in bed and you see that the motion sensor light on the side of your house is continually being turned on. You might start freaking out thinking that someone is on your property, perhaps they are trying to break into your house. You can’t see anyone out there but all night you are stressed and have a poor sleep. The next day you realize that the motion sensor sensitivity is set to the maximum and it is sensing every car that drives by, every person that walks by on the sidewalk and every time the wind causes the bushes to move. In this scenario you realize that there was no threat of danger, the sensitivity was just set extremely high. This is what happens in some patients with chronic pain and/or fibromyalgia. The sensitivity is set extremely high and the brain is perceiving a danger to the body, even though there is no real threat.
As you can see, pain is a very complex phenomenon. It isn't as simple as the amount of pain we experience matching the tissue damage in our body. So the next time you experience pain, take a step back and think about the factors that may be contributing to your pain experience. Keep an eye out for future posts where I will discuss the biopsychosocial model of health and how it relates to our pain experience.