The perception of pain is not simple. Many people may be surprised to know that the sensation of pain does not come directly from an area of skin or body tissue which has been damaged in some way. There are many different cells and chemical reactions which lead to the sensation of pain and it is modulated by our brains. This means that it is highly complex and gives us the ability to feel pain as individuals based upon our memories, experiences and emotions, and that pain from the exact same stimulus may be perceived differently between from one person to the next and even differently to the same person on different days.
Lorimer Mosely uses a great story to demonstrate how the perception of pain is almost always an illusion: A man is walking through the woods when he hears a cracking sound and feels a sharp scratch on his leg. He thinks he stepped on a stick and rubs the area slightly before carrying on his walk not thinking any more of the pain. When he gets to the end of the woods he looks down and realises his leg has swollen and there are puncture wounds like fangs, he realises he’s actually been bitten by a snake. This caused great alarm and he rushed to the nearest hospital panicking. It was treated and healed nicely but the man was very shocked by the event and became quite fearful of the idea of snakes in the woods. The next time he takes a walk in the woods he is hyper-vigilant to sounds and anything touching his skin. Once again there was a cracking sound and a sharp scratch was felt which caused the man to panic, feel immense pain and imagine the snake bite all over again. Before he properly checked the wound he started limping as fast as he could to get out of the woods and call a hospital. He couldn’t catch his breath as he was panicking. He was too frightened to check the wound properly himself but once he got to the hospital the nurses assessed him and confirmed it was not a snake bite and the man just had a small scratch, likely from a stick, on his lower leg. He felt embarrassed and confused about this as he was certain he was in agony and that he had been bitten again. This story tells us how the memory of an emotional event can affect our perception of pain or even lead to phantom pain.
Some people who have had a limb amputation have described how they feel severe pain in the limb which no longer exists. This again is an example of how the perception of pain is driven by a central system from the brain rather than just a direct result of tissue injury.
Our mood also has a big effect on pain. Imagine waking up one morning, you’re on holiday, the sun is shining and you’re feeling happy and free, when you stub your toe. You bite your lip but quickly move on and carry on with your day not thinking much of it. But then imagine you’re at home, you’ve woken up late, you’re very stressed with deadlines for work and you are feeling your job is on the line, you are anxious and rushing around, it’s raining and cold outside and you bang your toe…this time you swear and stop what you’re doing and sit on the floor and cry in pain and frustration.
The perception of pain therefore is not a simple reflection of what has happened to the tissues in our bodies when damaged. In fact there is a great deal of evidence to show that if we scan our tissues for damage, for example an MRI of our lower back region, we may well find a lot of tissue changes and damage in someone who does not experience any pain at all. However another person may feel excruciating ongoing back pain preventing them from working, living their life to the full, and being able to feel happy, yet have a relatively clear MRI of their back. This is often found in cases of disc herniations in the spine, or osteoarthritis in knee joints.
This makes pain very difficult to assess the cause of, and very difficult to treat. Some approaches such as SIRPA treat ongoing pain using more psychology than physiology. Childhood trauma, relationships and life circumstances are all contributing factors to the perception of pain and the effect it has on our behaviour and interaction with the world.
To understand pain we need to understand the biology of it, the neurophysiology. Please read our next blog to find out the science behind pain!