In physiological terms, pain is one of our sensations. Its unpleasantness is reflected in its name, which is derived from ancient Greek and Latin words for punishment, penalty, retribution, and vengeance for the crimes of murder and manslaughter.
Through the process of evolution, we have been endowed with an apparatus in our nervous system designed to detect actual or impending tissue damage. This is called the ‘nociceptive apparatus’ (‘noci-’ means harm; nociception means harm detection).
Pain is always a response and never a stimulus. Just as there are no ‘pain receptors’, ‘pain messages’ or ‘pain pathways’, there is no such thing as a ‘pain system’. The more accurate terms are ‘nociceptors’, ‘nociceptive impulses’, and ‘nociceptive pathways’ and ‘nociceptive apparatus’.
Activation of the apparatus usually occurs in association with tissue damage.
It is when we become aware that our nociceptive apparatus has been activated that we experience pain. In certain circumstances such activation may not reach the level of consciousness. For example, a soldier wounded in the heat of battle may not feel pain at the time of wounding.
But activation can also occur indirectly when we perceive a traumatic situation as being a threat to our very existence.
Under these circumstances, the hypothalamo-pituitary axis (HPA axis) is activated and the immune components of the central nervous system produce an excessive amount of chemicals that can sensitise the nerve cells (nociceptors) of the apparatus. As a result, these cells can fire off, either spontaneously or in response to non-harmful stimuli such as light touch or cold temperature.
We can be confident about our sensations, whereas we can be quite wrong in our perceptions. For example, a clap of thunder is simply given to us as a loud sound. The brain does not have to make a ‘decision’ as to whether we should hear the sound.
But whether we interpret the loud sound as thunder, a car backfiring, a cannon firing or a bomb exploding is a matter of interpretation. We can always check whether our interpretation is correct.
Thus, we can be mistaken about the cause of the sound but, to reiterate, we cannot be mistaken about having heard the sound (ie the sensation).
The same can be said of pain. We cannot be mistaken when we experience pain. But we can come up with a limitless number of interpretations of the experience.
There is a popular but, in my opinion, misguided school of thought claiming that pain functions as a ‘protector’ of our body and is produced by the brain whenever it decides we are in danger and in need of protection. But the case of phantom limb pain utterly destroys this belief. How can a limb that is no longer present be a threat to us? Furthermore, the experience of pain is not dependent upon a decision made by our brain. People, and not their brains, are responsible for making decisions.
You might even be told that because we learn pain, we can unlearn it. This is nonsense. From an early age we learn when it is appropriate to use the word for the unpleasant experience. This learning stays with us throughout life.
Finally, there is no evidence whatsoever that we can experience pain without prior activation of our nociceptive apparatus. We cannot conjure up the experience of pain through our imagination!
It is obviously important that those experiencing pain, and their families, try to understand these complex matters.