What is meant by the term ‘pain’?
All forms of animal life on Earth have evolved into highly sophisticated survival machines which are able to escape and avoid harmful situations. At a very basic level of life, even simple multi-cellular organisms have the capacity to move away from harmful stimuli. For example work by Wittenburg & Baumeister (1999) demonstrated that the nematode worm Caenorhabditis elegans is able to detect and move away from a noxious heat source. Such detection of harmful stimuli is termed nociception, and triggers a reflex causing muscle contraction, moving the animal out of harm’s way. This type of avoidance behaviour has obvious benefits for survival, but does it bear any relation to what humans would describe as pain?
Humans recognise nociception as a component of the pain experience, but there is more to pain than just simple physical response to stimuli. The human feeling of pain only begins with the sensation of actual or potential tissue damage. The state of being ‘in pain’ is an abstract idea that we are able to communicate to ourselves and others. Pain is associated with behaviour changes such as guarding and resting the affected area to allow healing to take place, emotions such as fear and anxiety permit learning to avoid the harmful stimulus in the future, and we report to others the extent of the harm, using words to describe our pain experience.
In order to demonstrate that pain is more than just simple nociception, we need look no further than the many words with which we communicate about the richness and complexity of the human pain experience. One count, by Melzack & Torgerson (1971), put the number of words his patients commonly used to describe pain at 66, which could be sorted into three categories. The sensory words such as ‘pressing’ or ‘burning’ are used to describe the stimulus itself; the affective words describe what the pain is doing to a person, for example ‘sickening’, ‘fearful’; the evaluative words express the extent of the suffering, from ‘mild’ to ‘excruciating’.
We are also able to experience the pain of others in the absence of verbal communication. A number of neuroimaging studies reviewed by Jackson and colleagues (2006) have shown that not only do people report feeling pain when viewing an image of an injured person, but also there is activity in the same parts of the brain that are activated during nociception.
Being in pain therefore must be thought of as an experience that is simultaneously:
We will see in future posts that this bio-psycho-social model has emerged as the most useful approach to understanding and researching pain.
- Biological – as a mechanism to signal bodily harm
- Psychological – as an abstract concept that has meaning in and of itself
- Social – with a reliable set of observable behaviours and its own language by which it is described.
Melzack, R., & Torgerson, W. (1971). On the language of pain. Anesthesiology, 34(1), 50–59.
Wittenburg, N., & Baumeister, R. (1999). Thermal avoidance in Caenorhabditis elegans: an approach to the study of nociception. Proceedings of the National Academy of Sciences of the United States of America, 96(18), 10477–10482.
Jackson, P. L., Rainville, P., & Decety, J. (2006). To what extent do we share the pain of others? Insight from the neural bases of pain empathy. Pain, 125(1-2), 5–9. doi:10.1016/j.pain.2006.09.013.