{"schemaVersion":1,"id":"en-mechanism-pain","type":"mechanism","pillar":"body","locale":"en","translationGroupId":"mechanism-pain","slugPath":"body/systems/pain","title":"Pain","shortTitle":"Pain","summary":"Forty-six pages of this corpus use the word as a boundary, none made it a subject. The essential distinction is between the signal sent and the experience lived: they are not the same thing.","level":"intermediate","estimatedMinutes":9,"synonyms":["pain","nociception","pain signal","pain modulation","pain threshold"],"blocks":[{"id":"b1","type":"heading","level":2,"text":"A word used everywhere as a border","anchor":"a-word-used-everywhere-as-a-border"},{"id":"b2","type":"paragraph","content":[{"kind":"text","value":"Forty-six pages of Body Lab mention pain, and almost always for the same reason: to mark where an explanatory page stops and a health professional starts. That border does not move — it is even the subject of the end of this page."}]},{"id":"b3","type":"paragraph","content":[{"kind":"text","value":"But between the two there is a mechanism, and it is part of the basics of how the nervous system works. Not describing it leaves room for explanations that circulate and are wrong."}]},{"id":"b4","type":"heading","level":2,"text":"What the international definition says","anchor":"what-the-international-definition-says"},{"id":"b5","type":"paragraph","content":[{"kind":"text","value":"The body that holds authority on the subject revised its definition in 2020, for the first time in forty years."}]},{"id":"b6","type":"evidence","level":"established","statement":"Pain is defined as an unpleasant sensory and emotional experience associated with — or resembling that associated with — actual or potential tissue damage.","detail":"The revision came from an international, multidisciplinary task force, with consultation of the people concerned. It comes with explicit notes, two of which matter here: pain is always a personal experience, and a person's report of an experience as pain should be respected.","referenceIds":["raja2020"]},{"id":"b7","type":"paragraph","content":[{"kind":"text","value":"Two parts of that definition do all the work. "},{"kind":"strong","value":"Experience"},{"kind":"text","value":": pain is lived, it is not a physical quantity. "},{"kind":"strong","value":"Or potential"},{"kind":"text","value":": no lesion needs to exist for a pain to exist."}]},{"id":"b8","type":"heading","level":2,"text":"The signal and the experience are not the same thing","anchor":"the-signal-and-the-experience-are-not-the-same-thing"},{"id":"b9","type":"definition","term":"Nociception","definition":"The detection and transmission, by specialised receptors and fibres, of potentially damaging events — excessive heat, strong pressure, substances released by injured tissue. It is a signal, not a sensation.","alsoKnownAs":["damage signalling"]},{"id":"b10","type":"paragraph","content":[{"kind":"text","value":"The distinction underpins the whole field. Nociception is what fibres carry; pain is what a person undergoes. Passing from one to the other is neither automatic nor proportional."}]},{"id":"b11","type":"evidence","level":"established","statement":"The nociceptive signal is modulated all along its route: it can be amplified or damped before resulting in a painful experience.","detail":"The mechanisms are described at several levels — on entering the spinal cord, through descending pathways from the brainstem, and at the level of brain networks. This is what explains why the same stimulation does not produce the same pain depending on context, attention or the person's state.","referenceIds":["kandel2021","purves2018"]},{"id":"b12","type":"paragraph","content":[{"kind":"text","value":"Both dissociations exist and are documented. A serious injury may not hurt at the time — a wound discovered afterwards, with no memory of pain. And intense pain can exist with no lesion identifiable on examination."}]},{"id":"b13","type":"heading","level":2,"text":"What this above all does not mean","anchor":"what-this-above-all-does-not-mean"},{"id":"b14","type":"paragraph","content":[{"kind":"text","value":"This is the most important passage on the page, and the most often misread."}]},{"id":"b15","type":"callout","tone":"caution","title":"Three false, and dangerous, readings","content":[[{"kind":"strong","value":"\"So pain is in your head.\""},{"kind":"text","value":" No. Every experience is produced by the nervous system — that is true of sight, of taste and of the position of a limb. Saying that a pain is produced by the nervous system makes it neither imaginary, nor voluntary, nor less real."}],[{"kind":"strong","value":"\"So you can decide not to hurt.\""},{"kind":"text","value":" No. The modulation described here is not voluntary. It can no more be commanded than heart rate can."}],[{"kind":"strong","value":"\"So pain without a visible lesion is not to be taken seriously.\""},{"kind":"text","value":" The opposite. The international definition states explicitly that a person's report of an experience as pain should be respected, and the absence of a cause found on examination invalidates nothing."}]]},{"id":"b16","type":"heading","level":2,"text":"What this illuminates elsewhere in the corpus","anchor":"what-this-illuminates-elsewhere-in-the-corpus"},{"id":"b17","type":"paragraph","content":[{"kind":"text","value":"The "},{"kind":"link","value":"muscle soreness","href":"/en/recovery/muscle-soreness","external":false},{"kind":"text","value":" page describes a delayed pain whose causal chain is not established. The distinction set out here explains why an account in terms of damage alone does not suffice: between a tissue stress and a sensation, several stages of modulation come in between."}]},{"id":"b18","type":"paragraph","content":[{"kind":"text","value":"The "},{"kind":"link","value":"what limits range of motion","href":"/en/body/what-limits-range-of-motion","external":false},{"kind":"text","value":" page observes that a movement often stops on a sensation rather than a mechanical stop. "},{"kind":"link","value":"Proprioception","href":"/en/body/systems/proprioception","external":false},{"kind":"text","value":" supplies part of that sensation, nociception another."}]},{"id":"b19","type":"heading","level":2,"text":"Why no scene accompanies this page","anchor":"why-no-scene-accompanies-this-page"},{"id":"b20","type":"callout","tone":"limit","title":"Pathways absent from the models","content":[[{"kind":"text","value":"The receptors, fibres and pathways described here belong to the nervous system, which the anatomical sources Body Lab uses do not contain. Modulation, for its part, cannot be depicted: it is not a structure but a way of working."}]]},{"id":"b21","type":"heading","level":2,"text":"What this page does not do — and where Body Lab stops","anchor":"what-this-page-does-not-do-and-where-body-lab-stops"},{"id":"b22","type":"callout","tone":"caution","title":"No assessment, no treatment","content":[[{"kind":"text","value":"This page describes a general mechanism. It assesses no pain, identifies no cause, and proposes no treatment, no technique and no exercise. Persistent pain is an entire clinical field, with mechanisms, investigations and care of its own, none of which is addressed here."}],[{"kind":"text","value":"Pain that persists, that wakes you at night, that follows an impact, or that comes with loss of strength, swelling, a fever or a loss of sensation belongs to a health professional. Chest pain, pain radiating to the arm or jaw, or pain of sudden and severe onset warrants calling emergency services."}],[{"kind":"text","value":"No page — this one included — allows you to decide whether a pain can wait."}]]},{"id":"b23","type":"heading","level":2,"text":"Sources","anchor":"sources"},{"id":"b24","type":"sourceList","title":"Main sources","referenceIds":["raja2020","kandel2021","purves2018"]},{"id":"b25","type":"shapierAction","actionId":"recovery-nervous-system","label":"Sparing the nervous system day to day","description":"Building recovery habits that spare the nervous system is done in Shapier; Body Lab only explains how the pain signal is modulated.","webTarget":"https://shapier.app/en/conseils/recuperation-systeme-nerveux","appTarget":"shapier://conseils/recuperation-systeme-nerveux"},{"id":"b26","type":"quiz","title":"Check my understanding","questions":[{"id":"q1","prompt":"What does actual or potential tissue damage mean in the international definition of pain?","choices":[{"id":"q1c1","label":"A pain can exist without any lesion being present","correct":true,"explanation":"Or potential is one of the two parts that do all the work: no lesion needs to exist for a pain to exist."},{"id":"q1c2","label":"A pain is only real if an examination finds a lesion","correct":false,"explanation":"The opposite: the definition states that the absence of a cause found on examination invalidates nothing, and a person's report should be respected."},{"id":"q1c3","label":"A potential lesion will inevitably appear later","correct":false,"explanation":"The term describes what is lived, not a prognosis: passing from nociception to pain is neither automatic nor proportional."}]},{"id":"q2","prompt":"Why does the same stimulation not always produce the same pain?","choices":[{"id":"q2c1","label":"Because the nociceptive signal is amplified or damped all along its route","correct":true,"explanation":"Modulation happens at several levels — spinal cord, descending pathways, brain networks — and depends on context, attention and the person's state."},{"id":"q2c2","label":"Because everyone decides their own pain","correct":false,"explanation":"The modulation described here is not voluntary: it can no more be commanded than heart rate can."},{"id":"q2c3","label":"Because the receptors of some tissues malfunction","correct":false,"explanation":"The page describes no failure: modulation is a normal way of working of the nervous system."}]},{"id":"q3","prompt":"Saying a pain is produced by the nervous system — what does that mean?","choices":[{"id":"q3c1","label":"The same as for sight or taste: it makes the pain neither imaginary nor less real","correct":true,"explanation":"Every experience is produced by the nervous system, which says nothing about the reality of what is lived."},{"id":"q3c2","label":"That it is in your head and therefore imaginary","correct":false,"explanation":"This is one of the three false and dangerous readings the page corrects: produced by the nervous system does not mean made up."},{"id":"q3c3","label":"That you can decide not to hurt","correct":false,"explanation":"No: since modulation is not voluntary, that conclusion does not follow, and the pain remains an experience to be respected."}]}]},{"id":"b27","type":"relatedContent","title":"Read next","targetIds":["en-mechanism-nervous-system","en-mechanism-proprioception","en-mechanism-muscle-soreness"]}],"relations":[{"type":"prerequisite","targetId":"en-mechanism-nervous-system"},{"type":"explains","targetId":"en-mechanism-proprioception"},{"type":"explains","targetId":"en-mechanism-muscle-soreness"},{"type":"next-step","targetId":"en-mechanism-brain"}],"authors":["equipe-editoriale-shapier"],"reviewers":["Thanh Chau"],"references":[{"id":"raja2020","authors":"Raja SN, Carr DB, Cohen M, Finnerup NB, Flor H, Gibson S, Keefe FJ, Mogil JS, Ringkamp M, Sluka KA, Song XJ, Stevens B, Sullivan MD, Tutelman PR, Ushida T, Vader K","year":2020,"title":"The revised International Association for the Study of Pain definition of pain: concepts, challenges, and compromises","source":"Pain","kind":"position-stand","doi":"10.1097/j.pain.0000000000001939"},{"id":"kandel2021","authors":"Kandel ER, Koester JD, Mack SH, Siegelbaum SA","year":2021,"title":"Principles of Neural Science, 6th edition","source":"McGraw Hill","kind":"book","url":"https://www.mheducation.com/highered/mhp/product/principles-neural-science-sixth-edition.html?viewOption=student"},{"id":"purves2018","authors":"Purves D, Augustine GJ, Fitzpatrick D, Hall WC, LaMantia AS, Mooney RD, Platt ML, White LE","year":2018,"title":"Neuroscience, 6th edition","source":"Oxford University Press","kind":"book","url":"https://lccn.loc.gov/2017028094"}],"review":{"publishedAt":"2026-08-02","reviewedAt":"2026-08-02","reviewDueAt":"2027-08-02","evidenceLevel":"established"},"limitations":["No scene accompanies this page: the pathways described belong to the nervous system, absent from every anatomical source Body Lab uses.","This page describes a general mechanism. It assesses no pain, identifies no cause and proposes no treatment.","Persistent pain is an entire clinical field, with mechanisms, investigations and care of its own. None of that is addressed here.","Any pain that persists, that wakes you at night, that follows an impact, or that comes with loss of strength or a fever belongs to a health professional."],"seo":{"title":"Pain — the difference between the signal and the experience","description":"Nociception, modulation and the international definition: what physiology establishes about pain, and above all what it does not let you conclude.","canonicalPath":"/en/body/systems/pain","image":"/og/en/mechanism-pain.png"},"app":{"offlineEligible":true},"version":1}