Pain is not a signal: a clearer account for clinicians
A useful explanation needs to distinguish pain, nociception and tissue state without reducing the experience to any one part of the person.
A familiar model treats tissue damage as producing pain signals that travel to the brain, where pain is then experienced. This model is simple, but it does not describe the relationship between nociception and pain well.
Nociception is neural activity related to actual or threatened tissue damage. It can contribute to pain, but it is not pain and it is not a pain signal.
Pain is an experience of the person, shaped by many sources of information and by the context in which it occurs.
What the evidence shows
The brain is always involved in pain, but the brain itself does not feel pain. The person does.
This helps explain why pain and tissue state can diverge. Significant injury may occur with little pain, and severe pain may occur without clear evidence of ongoing tissue damage.
Research supports this distinction, although no single example explains an individual's pain.
Why the peripheral story is insufficient
Changes in nociceptive processing can matter, including peripheral and central sensitisation. These processes still need to be understood in relation to the person's broader experience and context.
Persistent pain may involve many interacting contributors. Their relative importance can change over time and cannot be read directly from symptoms alone.
The relationship between tissue state and pain is not one-to-one. It may be close in some situations and less clear in others, particularly when pain persists. Understanding the person requires more than anatomy alone.
The allostatic load angle
Allostatic accounts ask how repeated demands and adaptation across bodily systems may contribute to a person's experience over time (McEwen, 2017).
Predictive processing offers another account. Perception depends on information from the body, prior experience, expectations and context. These processes can influence physiology across bodily systems, but pain remains an experience of the whole person.
Palpitations, gut symptoms, fatigue, anxiety and sleep problems have been reported more often in people with persistent pain (Tschudi-Madsen et al., 2011). This association does not establish a single cause.
The predictive brain
Predictive processing describes perception as active inference rather than passive reception. Expectations and incoming information are continually compared and updated (Friston, 2010).
Clinical interactions may contribute new information. What that information means depends on the person and the wider situation.
Our role is to listen carefully, offer accurate information and develop a plan with the person. We should be cautious about claiming to know the cause of an experience we cannot directly observe.
What this requires of clinical practice
Pain is not carried from the tissues as a signal. Nociception and pain are distinct, although they often relate.
Keeping that distinction clear can improve assessment, explanation and clinical reasoning without promising a simple answer.
The biopsychosocial course examines these ideas in more detail and considers how they may inform clinical practice.