What is pain?
Scientists agree that pain is an unpleasant feeling in our body that makes us want to stop and change our behaviour.
Pain is a complex protective mechanism but is not a measure of tissue damage.
Pain can be a warning signal that something is damaged or something is wrong. But pain may also be a misinterpretation of a sensation.
People can suffer major trauma and have little pain while others can experience pain when there is no damage.
How does pain work?
Our body contains specialised nerves that detect changes in temperature, chemical balance or pressure.
These “danger detectors” (or “nociceptors”) send alerts to the brain. They cannot send pain to the brain because all pain is made by the brain.
Input comes from the wrist you broke, or the ankle you sprained.
When you’re injured, the brain guesses which part of the body is in danger and produces the pain there.
The pain you feel is the result of the brain evaluating information, including:
- data from the danger detection system,
- your expectations, previous exposure, cultural and social norms and beliefs,
- other sensory data such as what you see, hear and otherwise sense.
Usually the brain gets it right, but sometimes it doesn’t. An example is referred pain in your leg when it is your back that might need the protecting.
We now know that pain can be increased or decreased by anything that provides the brain with credible evidence that the body is in danger and needs protecting.
Is Pain all in your head?
No, these “danger detectors” run across almost all of our body tissues and act as the eyes of the brain.
When there is a sudden change in tissue environment (it is squashed, squeezed, pulled or pinched) – these danger detectors are our first line of defence.
They alert the brain and mobilise inflammatory mechanisms that increase blood flow and cause the release of healing molecules from nearby tissue. This triggers the repair process.
Local anaesthetic renders these danger detectors useless, so danger messages are not triggered. As such, we can be pain-free despite major tissue trauma, such as being cut into for an operation.
Inflammation renders these danger detectors more sensitive, so they respond to situations that are not actually dangerous.
When you move an inflamed joint it hurts a long way before the tissues of the joint are actually stressed.
Danger messages travel to the brain and are highly processed along the way, with the brain itself taking part in the processing.
The brain then amplifies or decreases the sensitivity of the neurons.
So, if the brain concludes the situation is dangerous, the danger transmission system becomes more sensitive (called descending facilitation). If the brain concludes things are not truly dangerous, then the danger transmission system becomes less sensitive (called descending inhibition).
Many brain regions are involved in evaluating pain, some more commonly that others.
Any credible evidence that the body is in danger increases the likelihood and intensity of pain.
Any credible evidence that the body is safe will decrease the intensity of pain.
To reduce pain, we need to reduce credible evidence of danger and increase credible evidence of safety.
Danger detectors can be turned off by local anaesthetic. We can also reduce the pain by accurately understanding how pain really works. Exercise, active coping strategies, safe people and places also help.
A very effective way to reduce pain is to make something else seem more important to the brain – this is called distraction. Only being unconscious or dead provide greater pain relief than distraction.
In chronic pain the sensitivity of the hardware (the biological structures) increases so the relationship between pain and the true need for protection becomes distorted: we become over-protected by pain.
Recovery requires patience, persistence, courage and good coaching. The best interventions focus on slowly training our body and brain to be less protective.