We learn the meaning of pain from early childhood experiences with bumps and scrapes, and our understanding expands with ongoing experiences of danger and injury (“ IASP Terminology – IASP ,” 2017). Because our definition stems from our own experiences, part of a coherent narrative of our lives, pain seems relatively simple. We hurt, we heal, and pain diminishes as we get better.
Simple and appealing as this model is, we become aware of things that just don’t make sense if pain is simple nociception. We may know of cases where chronic pain persists even though doctors can find no evidence of remaining injury. We hear about American soldiers wounded at the Anzio beachhead during World War II, who “entirely denied pain from their extensive wounds or had so little that they did not want any medication to relieve it” (Beecher, 1959). We are forced to conclude that pain is a markedly more complex experience than we had first thought.
Of course, it’s difficult to really understand another person’s pain experiences. By 1980, Loeser was modelling a four-layer onion model that “emphasizes that nociception, pain, and suffering are personal, private, internal events that one cannot measure directly in another human being. Their existence can only be inferred by the assessment of pain behaviors.” (Loeser & Bonica, 2001) Still, we need to have some concept of others’ pain, however imperfect, in order to even express sympathy, let alone hope to alleviate it.
Melzack and Casey describe the history of thinking of pain as fluctuating between seeing it as purely a mental process and seeing it as a purely physical phenomenon, varying between thinkers and over time. Writing in the 1960s, they complained, “Characteristically, textbooks in psychology and physiology deal with “pain sensation” in one section and “aversive drives and punishment” in another, with no indication that both are facets of the same phenomenon.” (Melzack & Casey, 1968)
Instead of trying to decide whether pain is physiology or psychology, Melzack and Casey proposed a model that breaks pain into three components. They proposed a biopsychosocial model of pain that acknowledges the biological aspects, the nociceptive stimuli, as well as the psychological aspects of pain perception, and also the impact of the social environment. The position they took was that any one of these elements is insufficient to understand pain as it is actually experienced, but that they work together to create the experience. (Melzack & Casey, 1968)
More recent research on pain has often measured pain intensity and pain unpleasantness as separate axes, with study subjects reporting different values on each axis.
Writing in 2008, Michael Sullivan acknowledged the importance of the subjective experience of pain and the impact of social response, as well as the tissue damage. He further made a persuasive argument that behavioural aspects of pain have been under-investigated, specifically calling out avoidant, protective, and communicative behaviours. He notes, “From an evolutionary perspective, pain signals have been discussed as an internal mechanism that increases the probability of survival,” and goes on to point out, “central to the survival value of the pain system is the mobilization of behaviors that will act on the source of the pain, or tend to the consequences of pain. Indeed, it could be argued that without a pain behavior system, there would be no adaptive value to the pain signal itself.”
Sullivan critiques the classic Cartesian model of pain as devoid of context. The figure in the classic illustration experiences pain in a social void, shows no expression of distress, and takes no action to deal with the pain.” This is not only oversimplified, it strips pain of all meaning. (Sullivan, 2008) When we look at the figure in Descartes’ image, it seems almost bemused by the fire burning its foot; this “absent or inadequate emotional responses to painful stimuli” is symptomatic of a sensory-limbic disconnection disorder known as asymbolia for pain rather than a normal reaction to painful stimuli. (Berthier, Starkstein, & Leiguarda, 1988)
Sullivan provides an alternate image that accounts for more factors. His diagram acknowledges the nociceptive, tissue damaging component of pain, and the internal pain experience, but his explication of a biopsychomotor approach to pain spends more time on protective behaviour, pain communicative behaviour, and social response.
Protective behaviour includes actions “intended to reduce the probability of further injury, minimize the experience of pain, or promote recovery from injury.” In this diagram, grabbing the leg and pulling the foot away from the fire are obvious protective behaviours. Limping is another example, favouring one leg in an attempt to reduce stress so an injury to it can heal. Protective behaviours can backfire, as when limping to keep the leg off one joint overstresses the rest of the body; the intent to protect the injury is the salient feature, here.
Pain communicative behaviours include verbal expressions, body language and grimacing, and non-verbal vocalisations. Sullivan explains, “The overt display of distress during pain experience conveys information to observers about the internal state, pain-related limitations, and needs for assistance of the individual who is experiencing pain.” (Sullivan, 2008)
Social response helps contextualise the pain we feel. Small children will frequently check in with parents before appearing to decide how severe an injury is, but adults are also influenced by social responses. More solicitous responses from spouses of people with chronic pain have been associated with increased severity of and disability from chronic pain. (Kerns, Haythornthwaite, Southwick, & Giller, 1990) In another example, patients asked to lift weights while commenting on the severity of their pain during the exercise displayed more signs of distress than those asked to estimate the mass of the weights they were lifting. (Sullivan et al., 2006)
In reality, we respond to pain in many ways, but our experience of pain is also modulated by each of these aspects of experience. Nerve impulses are real, and do impact our experience of pain, but so are the ways in which our attitudes and beliefs change our experience, as are the effects of our escape and coping behaviours and what our culture tells us.