Pain Is an Output, Not an Input — What That Actually Means

Nigel Peek, MSc Chiro (SA) | DIANM, Chiropractic Orthopaedist | PGDip HealSc Pain & Pain Management – Dist. (Otago) — Peek Practice, Grey Lynn, Auckland

Pain is not a signal that travels from damaged tissue to a passive brain. That model — intuitive, persistent, and wrong — has been substantially revised over the last three decades. Understanding what replaced it changes how pain is assessed, explained, and treated.

This is not a fringe position. It is the consensus view of contemporary pain neuroscience, and it underpins the clinical approach at Peek Practice — Auckland’s only Chiropractic Orthopaedist.

The Old Model and Why It Fails

For most of the twentieth century, pain was understood through a relatively simple input-output framework: tissue damage generates a signal, that signal travels up the spinal cord, and the brain registers pain proportional to the damage. More damage, more pain. Less damage, less pain.

The problem is that this model fails consistently in clinical practice. It does not explain why two people with structurally identical lumbar disc herniations on MRI can have entirely different pain experiences — one debilitating, one barely noticed. It does not explain why a soldier wounded in combat may feel nothing for hours. It does not explain why chronic pain frequently persists long after tissue healing is complete.

The data forced a rethink.

The Neuromatrix: Pain as a Brain-Generated Output

Ronald Melzack’s neuromatrix theory, developed across the 1990s and refined by Lorimer Moseley and others in the decades since, positions pain as an output — something the brain produces, not something it passively receives.

The brain continuously integrates information from multiple sources: damage signals from the periphery, yes, but also memory, expectation, context, emotional state, movement history, and social environment. It then generates pain — or not — based on a calculation of perceived threat. When the brain concludes that tissue is under genuine threat requiring protective action, it produces pain. When it does not, it may suppress damage input entirely. The brain is not a spectator. It is the author.

What This Means for Diagnosis

The clinical implication is significant. Pain intensity is not a reliable proxy for tissue damage severity. A patient in significant distress may have modest pathological change on imaging. A patient with substantial degenerative findings may be largely asymptomatic. Brinjikji et al. (2015), reviewing imaging findings in asymptomatic individuals, found that disc bulges were present in 30% of 20-year-olds and 84% of 80-year-olds — none of whom reported pain at the time of scanning.

This does not mean imaging is useless. It means imaging findings must be interpreted within a full clinical context: examination findings, symptom behaviour, psychological and social factors, and movement patterns. A finding on MRI is part of a process of determining how the tissue may be contributing to the problem but does not illustrate a persons individual pain experience.

It is thought that the degree of brain and spinal cord activation and amplification (sensitisation) of threat signals — contributes more to pain intensity in persistent pain states than the degree or magnitude of damage. The evidence triangulates around this consistently. Recognising it shifts the diagnostic question from “where is the damage?” to “why is the system calibrated this way?”

Why This Matters to Treatment

Once pain is understood as a protective output, treatment becomes something other than a search for the structural lesion to fix. Some lesions warrant treatment — a herniated disc compressing a nerve root, a facet joint generating referred pain, a ligamentous injury requiring load management. Specific structural diagnoses matter, and they require specific examination skills to establish.

But for a significant proportion of patients presenting with persistent or recurrent pain, the primary driver is not ongoing tissue damage. It is a nervous system that has re-calibrated toward threat — one that has learned, through repeated experience, injury history, and person specific cues (context) to produce pain at lower thresholds than the original tissue state warrants.

Contemporary thinking favours an approach that addresses both: precise structural diagnosis where that diagnosis exists, and active management of the central sensitisation component where it contributes. Neither in isolation is adequate for the majority of persistent pain presentations.

Pain neuroscience education — explaining this model to patients in accessible language — has a modest but consistent effect on pain outcomes across multiple systematic reviews (Louw et al., 2016). Not because explaining pain is curative, but because understanding the mechanism reduces fear, challenges unhelpful beliefs, and improves engagement with active rehabilitation.

A Note on What This Model Is Not

It does not mean pain is imaginary. It does not mean tissue is irrelevant. It does not mean psychological factors explain everything.

It means pain is produced by a brain operating with incomplete and contextually filtered information — and that context is as clinically significant as the structural findings. A patient told their spine is “crumbling” or “degenerating badly” may experience more pain after that consultation than before, despite no change in tissue state. Language, framing, and clinical communication are not soft skills. They have measurable neurophysiological consequences.

FAQ's

What is the neuromatrix theory of pain?

The neuromatrix theory, developed by Ronald Melzack and extended by Lorimer Moseley and others, proposes that pain is an output generated by the brain based on a threat assessment — integrating nociceptive signals, memory, emotional state, and context. It is not a direct read-out of tissue damage.

Does this mean my pain is not real?

No. Pain is always real — it is a genuine experience produced by the nervous system. The neuromatrix model does not question the reality of pain; it revises the explanation for why it occurs and why it varies so widely between individuals with similar tissue states.

Why do two people with the same MRI finding have different pain levels?

Because tissue damage is one input among many. The brain’s threat calculation also includes expectation, movement history, fear, context, and prior experience. Identical imaging findings can produce vastly different clinical presentations depending on these factors.

Can understanding pain neuroscience help reduce pain?

The evidence suggests it can contribute. Systematic reviews of pain neuroscience education consistently show improvements in fear of movement, pain catastrophising, and functional outcomes when education is integrated into a broader management plan — though it is not a standalone treatment.

What is central sensitisation?

Central sensitisation refers to an amplification of pain signalling within the central nervous system — where the pain system becomes hyper-responsive beyond what the peripheral tissue state warrants. It is associated with chronic pain, widespread pain, and allodynia (pain from stimuli that would not normally be painful).

REFERENCES

Melzack R. (1999). From the gate to the neuromatrix. Pain, Supplement 6, S121–S126.

Moseley GL, Butler DS. (2015). Fifteen years of explaining pain: the past, present, and future. Journal of Pain, 16(9), 807–813.

Brinjikji W et al. (2015). Systematic literature review of imaging features of spinal degeneration in asymptomatic populations. AJNR American Journal of Neuroradiology, 36(4), 811–816.

Louw A et al. (2016). The efficacy of pain neuroscience education on musculoskeletal pain: a systematic review of the literature. Physiotherapy Theory and Practice, 32(5), 332–355.

Woolf CJ. (2011). Central sensitization: implications for the diagnosis and treatment of pain. Pain, 152(3 Suppl), S2–S15.