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Pain is a distressing feeling often caused by intense or damaging stimuli. The
International Association for the Study of Pain The International Association for the Study of Pain (IASP) is an international learned society A learned society (; also known as a learned academy, scholarly society, or academic association) is an organization that exists to promote an discip ...
defines pain as "an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage." In medical diagnosis, pain is regarded as a
symptom Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower temperature than normal, raised or lowered blood pressure or an abnormality show ...
of an underlying condition. Pain motivates the individual to withdraw from damaging situations, to protect a damaged body part while it heals, and to avoid similar experiences in the future. Most pain resolves once the
noxious stimulusA noxious stimulus is "an actually or potentially tissue damaging event." It is a prerequisite for nociceptionNociception (also nocioception, from Latin ''nocere'' 'to harm or hurt') is the Somatosensory system, sensory nervous system's process of en ...
is removed and the body has healed, but it may persist despite removal of the stimulus and apparent healing of the body. Sometimes pain arises in the absence of any detectable stimulus, damage or disease. Pain is the most common reason for physician consultation in most developed countries. It is a major symptom in many medical conditions, and can interfere with a person's
quality of life Quality of life (QOL) is defined by the World Health Organization The World Health Organization (WHO) is a specialized agency of the United Nations United Nations Specialized Agencies are autonomous organizations working with the United N ...

quality of life
and general functioning. Simple pain medications are useful in 20% to 70% of cases. Psychological factors such as
social support Social support is the perception and actuality that one is cared for, has assistance available from other people, and most popularly, that one is part of a supportive social network A social network is a social structure In the social scie ...
, hypnotic suggestion,
cognitive behavioral therapy Cognitive behavioral therapy (CBT) is a psycho-social intervention that aims to reduce symptoms of various mental health conditions, primarily depression and anxiety disorders. CBT focuses on challenging and changing cognitive distortions (e.g ...
, excitement, or distraction can affect pain's intensity or unpleasantness. In some debates regarding
physician-assisted suicide Assisted suicide, also known as assisted dying or medical aid in dying, is suicide undertaken with the aid of another person. The term usually refers to physician-assisted suicide (PAS), which is suicide that is assisted by a physician A p ...
or
euthanasia Euthanasia (from el, εὐθανασία 'good death': εὖ, ''eu'' 'well, good' + θάνατος, ''thanatos'' 'death') is the practice of intentionally ending life to relieve pain and suffering. Different countries have different Legality ...

euthanasia
, pain has been used as an argument to permit people who are terminally ill to end their lives.


Etymology

First attested in English in 1297, the word ''peyn'' comes from the
Old French Old French (, , ; Modern French French ( or ) is a Romance language The Romance languages, less commonly Latin or Neo-Latin languages, are the modern languages that evolved from Vulgar Latin Vulgar Latin, also known as Popular o ...
''peine'', in turn from
Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in relation with") is "an appa ...

Latin
''poena'' meaning "punishment, penalty" (also meaning "torment, hardship, suffering" in Late Latin) and that from
Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 million as of ...
ποινή (''poine''), generally meaning "price paid, penalty, punishment".


Classification

The
International Association for the Study of Pain The International Association for the Study of Pain (IASP) is an international learned society A learned society (; also known as a learned academy, scholarly society, or academic association) is an organization that exists to promote an discip ...
recommends using specific features to describe a patient's pain: # region of the body involved (e.g. abdomen, lower limbs), # system whose dysfunction may be causing the pain (e.g., nervous, gastrointestinal), # duration and pattern of occurrence, # intensity, and # cause


Chronic versus acute

Pain is usually transitory, lasting only until the noxious stimulus is removed or the underlying damage or pathology has healed, but some painful conditions, such as
rheumatoid arthritis Rheumatoid arthritis (RA) is a long-term autoimmune disorder that primarily affects synovial joint, joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and ...
,
peripheral neuropathy Peripheral neuropathy, often shortened to neuropathy, is a general term describing disease affecting the peripheral nerves, meaning nerves beyond the brain and spinal cord. Damage to peripheral nerves may impair sensation, movement, gland or org ...
,
cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumor A benign tumor is a mass of cells Cell most often refers to: * Cell (biolo ...
and
idiopathic An idiopathic disease is any disease with an unknown cause or mechanism of apparent wikt:spontaneous, spontaneous origin. From Ancient Greek, Greek ἴδιος ''idios'' "one's own" and πάθος ''pathos'' "suffering", ''idiopathy'' means approxim ...
pain, may persist for years. Pain that lasts a long time is called " chronic" or "persistent", and pain that resolves quickly is called "
acute Acute may refer to: Science and technology * Acute angle ** Acute triangle ** Acute, a leaf shape in the glossary of leaf morphology#acute, glossary of leaf morphology * Acute (medicine), a disease that it is of short duration and of recent onset. ...
". Traditionally, the distinction between acute and chronic pain has relied upon an arbitrary interval of time between onset and resolution; the two most commonly used markers being 3 months and 6 months since the onset of pain, though some theorists and researchers have placed the transition from acute to chronic pain at 12 months. Others apply "acute" to pain that lasts less than 30 days, "chronic" to pain of more than six months' duration, and "subacute" to pain that lasts from one to six months. A popular alternative definition of "chronic pain", involving no arbitrarily fixed duration, is "pain that extends beyond the expected period of healing". Chronic pain may be classified as " cancer-related" or "benign."


Allodynia

Allodynia Allodynia is a condition in which pain is caused by a stimulus that does not normally elicit pain. For example, bad sunburn can cause temporary allodynia, and touching sunburned skin, or running cold or warm water over it, can be very painful. It is ...
is pain experienced in response to a normally painless stimulus. It has no biological function and is classified by stimuli into dynamic mechanical, punctate and static.


Phantom

Phantom pain Phantom pain is a perception that an individual experiences relating to a limb or an organ that is not physically part of the body. Limb loss is a result of either removal by amputation or congenital A birth defect, also known as a congenital ...
is pain felt in a part of the body that has been
amputated Amputation is the removal of a Limb (anatomy), limb by Physical trauma, trauma, medical illness, or surgery. As a surgical measure, it is used to control pain or a disease process in the affected limb, such as cancer, malignancy or gangrene. In som ...
, or from which the brain no longer receives signals. It is a type of neuropathic pain. The
prevalence In epidemiology Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and risk factor, determinants of health and disease conditions in defined populations. It is a cornerstone of public health, and shapes p ...

prevalence
of phantom pain in upper limb amputees is nearly 82%, and in lower limb amputees is 54%. One study found that eight days after amputation, 72% of patients had phantom limb pain, and six months later, 67% reported it. Some amputees experience continuous pain that varies in intensity or quality; others experience several bouts of pain per day, or it may reoccur less often. It is often described as shooting, crushing, burning or cramping. If the pain is continuous for a long period, parts of the intact body may become sensitized, so that touching them evokes pain in the phantom limb. Phantom limb pain may accompany
urination Urination is the release of urine Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excretion, excreted ...
or
defecation frame, Human anatomy of the ''anorecturm'' (anus and rectum) Defecation (or defaecation) is the final act of digestion, by which organisms eliminate a solid, semisolid, or liquid waste material known as feces from the digestive tract via the a ...
.
Local anesthetic A local anesthetic (LA) is a medication A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to medical diagnosis, diagnose, cure, therapy, treat, or preventive medicine, prevent ...
injections into the nerves or sensitive areas of the stump may relieve pain for days, weeks, or sometimes permanently, despite the drug wearing off in a matter of hours; and small injections of
hypertonic Tonicity is a measure of the effective osmotic pressure gradient; the water potentialWater potential is the potential energy In physics, potential energy is the energy held by an object because of its position relative to other objects, st ...
saline into the soft tissue between vertebrae produces local pain that radiates into the phantom limb for ten minutes or so and may be followed by hours, weeks or even longer of partial or total relief from phantom pain. Vigorous vibration or electrical stimulation of the stump, or current from electrodes surgically implanted onto the spinal cord, all produce relief in some patients.
Mirror box Mirror therapy (MT) or mirror visual feedback (MVF) is a therapy for pain or disability that affects one side of the patient more than the other side. It was invented by Vilayanur S. Ramachandran to treat post-amputation patients who suffered fro ...
therapy produces the illusion of movement and touch in a phantom limb which in turn may cause a reduction in pain.
Paraplegia Paraplegia is an impairment in motor or sensory function of the lower extremities. The word comes from Ionic Greek () "half-stricken". It is usually caused by spinal cord injury or a congenital condition that affects the neural (brain) eleme ...
, the loss of sensation and voluntary motor control after serious spinal cord damage, may be accompanied by girdle pain at the level of the spinal cord damage,
visceral painVisceral pain is pain that results from the activation of nociceptors of the thoracic, pelvic, or abdominal viscera (organs). Visceral structures are highly sensitive to distension (stretch), ischemia and inflammation, but relatively insensitive to o ...
evoked by a filling bladder or bowel, or, in five to ten per cent of paraplegics, phantom body pain in areas of complete sensory loss. This phantom body pain is initially described as burning or tingling but may evolve into severe crushing or pinching pain, or the sensation of fire running down the legs or of a knife twisting in the flesh. Onset may be immediate or may not occur until years after the disabling injury. Surgical treatment rarely provides lasting relief.


Breakthrough

Breakthrough pain is transitory pain that comes on suddenly and is not alleviated by the patient's regular pain management. It is common in cancer patients who often have background pain that is generally well-controlled by medications, but who also sometimes experience bouts of severe pain that from time to time "breaks through" the medication. The characteristics of breakthrough
cancer pain Pain in cancer may arise from a tumor compressing or infiltrating nearby body parts; from treatments and diagnostic procedures; or from skin, nerve and other changes caused by a hormone imbalance or immune response. Most chronic (long-lasting) pain ...
vary from person to person and according to the cause. Management of breakthrough pain can entail intensive use of
opioid Opioids are substances that act on opioid receptor Opioid receptors are a group of inhibitory G protein-coupled receptors with opioids as ligands. The endogenous opioids are dynorphins, enkephalins, endorphins, endomorphins and nocicepti ...
s, including
fentanyl Fentanyl, also spelled fentanil, is a powerful opioid Opioids are substances that act on opioid receptor Opioid receptors are a group of inhibitory G protein-coupled receptors with opioids as ligands. The endogenous opioids are dynorp ...

fentanyl
.


Asymbolia and insensitivity

The ability to experience pain is essential for protection from injury, and recognition of the presence of injury. Episodic
analgesia An analgesic or painkiller is any member of the group of drugs used to achieve analgesia, relief from pain Pain is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain defines p ...
may occur under special circumstances, such as in the excitement of sport or war: a soldier on the battlefield may feel no pain for many hours from a traumatic amputation or other severe injury. Although unpleasantness is an essential part of the IASP definition of pain,Alt URL
Derived from
it is possible to induce a state described as intense pain devoid of unpleasantness in some patients, with
morphine Morphine is a of the family that is found naturally in a dark brown, resinous form, from the poppy plant ('). It can be taken orally or injected. It acts directly on the (CNS) to induce analgesia and alter perception and emotional respons ...

morphine
injection or
psychosurgery Psychosurgery, also called neurosurgery for mental disorder (NMD), is the neurosurgical treatment of mental disorder A mental disorder, also called a mental illness or psychiatric disorder, is a behavioral or mental pattern that causes si ...
. Such patients report that they have pain but are not bothered by it; they recognize the sensation of pain but suffer little, or not at all. Indifference to pain can also rarely be present from birth; these people have normal nerves on medical investigations, and find pain unpleasant, but do not avoid repetition of the pain stimulus. Insensitivity to pain may also result from abnormalities in the
nervous system In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mecha ...

nervous system
. This is usually the result of acquired damage to the nerves, such as
spinal cord injury A spinal cord injury (SCI) is damage to the spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. ...
,
diabetes mellitus Diabetes mellitus, commonly known as just diabetes, is a group of metabolic disorders characterized by a hyperglycemia, high blood sugar level over a prolonged period of time. Symptoms often include frequent urination, Polydipsia, increased th ...
(
diabetic neuropathy Diabetic neuropathy refers to various types of nerve damage associated with diabetes mellitus. Symptoms depend on the site of nerve damage and can include motor changes such as weakness; sensory symptoms such as numbness, tingling, or pain; or auton ...
), or
leprosy Leprosy, also known as Hansen's disease (HD), is a long-term Long-Term Capital Management L.P. (LTCM) was a hedge fund''A financial History of the United States Volume II: 1970–2001'', Jerry W. Markham, Chapter 5: "Bank Consolidation", M. E. ...

leprosy
in countries where that disease is prevalent. These individuals are at risk of tissue damage and infection due to undiscovered injuries. People with diabetes-related nerve damage, for instance, sustain poorly-healing foot ulcers as a result of decreased sensation. A much smaller number of people are insensitive to pain due to an inborn abnormality of the nervous system, known as "
congenital insensitivity to pain Congenital insensitivity to pain (CIP), also known as congenital analgesia, is one or more rare conditions in which a person cannot feel (and has never felt) physical pain Pain is a distressing feeling often caused by intense or damaging stimuli. ...
". Children with this condition incur carelessly-repeated damage to their tongues, eyes, joints, skin, and muscles. Some die before adulthood, and others have a reduced life expectancy. Most people with congenital insensitivity to pain have one of five hereditary sensory and autonomic neuropathies (which includes
familial dysautonomia Familial dysautonomia (FD) is a rare, progressive, recessive genetic disorder of the autonomic nervous system The autonomic nervous system (ANS), formerly the vegetative nervous system, is a division of the peripheral nervous system that supplie ...
and congenital insensitivity to pain with anhidrosis). These conditions feature decreased sensitivity to pain together with other neurological abnormalities, particularly of the
autonomic nervous system The autonomic nervous system (ANS), formerly the vegetative nervous system, is a division of the peripheral nervous system that supplies smooth muscle and glands, and thus influences the function of viscera, internal organs. The autonomic nervous ...

autonomic nervous system
. A very rare syndrome with isolated congenital insensitivity to pain has been linked with mutations in the ''
SCN9A Nav1.7 is a sodium ion channel that in humans is encoded by the ''SCN9A'' gene. It is usually expressed at high levels in two types of neuron A neuron or nerve cell is an electrically excitable cell Cell most often refers to: * Cell (biol ...
'' gene, which codes for a sodium channel ( Nav1.7) necessary in conducting pain nerve stimuli.


Functional effects

Experimental subjects challenged by acute pain and patients in chronic pain experience impairments in attention control,
working memory Working memory is a cognitive system with a limited capacity that can hold information temporarily. Working memory is important for reasoning and the guidance of decision-making and behavior. Working memory is often used synonymously with short-te ...
, mental flexibility, problem solving, and information processing speed. Acute and chronic pain are also associated with increased depression, anxiety, fear, and anger.


On subsequent negative emotion

Although pain is considered to be aversive and unpleasant and is therefore usually avoided, a
meta-analysis A meta-analysis is a statistical analysis that combines the results of multiple Randomized controlled trial, scientific studies. Meta-analyses can be performed when there are multiple scientific studies addressing the same question, with each i ...
which summarized and evaluated numerous studies from various psychological disciplines, found a reduction in
negative affect Negative affectivity (NA), or negative affect, is a personality variable that involves the experience of negative emotions and poor self-concept. Negative affectivity subsumes a variety of negative emotions, including anger, contempt, disgust, guil ...
. Across studies, participants that were subjected to acute physical pain in the laboratory subsequently reported feeling better than those in non-painful control conditions, a finding which was also reflected in physiological parameters. A potential mechanism to explain this effect is provided by the opponent-process theory.


Theory


Historical

Before the relatively recent discovery of
neuron A neuron or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapse In the nervous system In biology Biology is the natural science that studies life and living ...

neuron
s and their role in pain, various different body functions were proposed to account for pain. There were several competing early theories of pain among the ancient Greeks:
Hippocrates Hippocrates of Kos (; grc-gre, Ἱπποκράτης ὁ Κῷος, Hippokrátēs ho Kôios; ), also known as Hippocrates II, was a Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ε ...

Hippocrates
believed that it was due to an imbalance in vital fluids.Linton. Models of Pain Perception. Elsevier Health, 2005. Print. In the 11th century,
Avicenna Ibn Sina ( fa, ابن سینا), also known as Abu Ali Sina (), Pur Sina (), and often known in the West as Avicenna (;  – June 1037), was a Persian polymath who is regarded as one of the most significant physicians, astronomers, t ...

Avicenna
theorized that there were a number of feeling senses including touch, pain and titillation. In 1644,
René Descartes René Descartes ( or ; ; Latinized Latinisation or Latinization can refer to: * Latinisation of names, the practice of rendering a non-Latin name in a Latin style * Latinisation in the Soviet Union, the campaign in the USSR during the 1920s ...

René Descartes
theorized that pain was a disturbance that passed down along nerve fibers until the disturbance reached the brain. Descartes's work, along with Avicenna's, prefigured the 19th-century development of specificity theory. Specificity theory saw pain as "a specific sensation, with its own sensory apparatus independent of touch and other senses". Another theory that came to prominence in the 18th and 19th centuries was intensive theory, which conceived of pain not as a unique sensory modality, but an emotional state produced by stronger than normal stimuli such as intense light, pressure or temperature. By the mid-1890s, specificity was backed mostly by physiologists and physicians, and the intensive theory was mostly backed by psychologists. However, after a series of clinical observations by
Henry Head Sir Henry Head, FRS (4 August 1861 – 8 October 1940) was an English neurologist Neurology (from el, νεῦρον (neûron), "string, nerve" and the suffix -logia, "study of") is a branch of medicine Medicine is the Art (skill), a ...

Henry Head
and experiments by Max von Frey, the psychologists migrated to specificity almost en masse, and by century's end, most textbooks on physiology and psychology were presenting pain specificity as fact.


Modern

Some sensory fibers do not differentiate between noxious and non-noxious stimuli, while others,
nociceptor A nociceptor ("pain receptor") is a sensory neuron Sensory neurons, also known as afferent neurons, are neuron A neuron or nerve cell is an membrane potential#Cell excitability, electrically excitable cell (biology), cell that communicates w ...
s, respond only to noxious, high intensity stimuli. At the peripheral end of the nociceptor, noxious stimuli generate currents that, above a given threshold, send along the nerve fiber to the spinal cord. The "specificity" (whether it responds to thermal, chemical or mechanical features of its environment) of a nociceptor is determined by which
ion channel Ion channels are pore-forming membrane protein Membrane proteins are common proteins that are part of, or interact with, biological membranes. Membrane proteins fall into several broad categories depending on their location. Integral membrane ...

ion channel
s it expresses at its peripheral end. Dozens of different types of nociceptor ion channels have so far been identified, and their exact functions are still being determined. The pain signal travels from the periphery to the spinal cord along an A-delta or C fiber. Because the A-delta fiber is thicker than the C fiber, and is thinly sheathed in an electrically insulating material (
myelin Myelin is a lipid-rich (fatty) substance that surrounds nerve cell axons (the nervous system's "wires") to Insulator (electricity), insulate them and increase the rate at which electrical impulses (called action potentials) are passed along the a ...
), it carries its signal faster (5–30  m/s) than the unmyelinated C fiber (0.5–2 m/s). Pain evoked by the A-delta fibers is described as sharp and is felt first. This is followed by a duller pain, often described as burning, carried by the C fibers. These A-delta and C fibers enter the spinal cord via Lissauer's tract and spinal cord nerve fibers in the central gelatinous substance of the spinal cord. These spinal cord fibers then cross the cord via the anterior white commissure and ascend in the
spinothalamic tract The spinothalamic tract (part of the anterolateral system or the ventrolateral system) is a sensory pathway to the thalamus The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter located in the wikt:dorsal, dorsal ...
. Before reaching the brain, the spinothalamic tract splits into the
lateral Lateral is a geometric term of location {{unreferenced, date=March 2014 Geometric terms of location describe directions or positions relative to the shape of an object. These terms are used in descriptions of engineering, physics, and other scienc ...
, neospinothalamic tract and the
medial Medial may refer to: Mathematics * Medial magma, a mathematical identity in algebra Geometry * Medial axis, in geometry the set of all points having more than one closest point on an object's boundary * Medial graph, another graph that repres ...
, paleospinothalamic tract. The neospinothalamic tract carries the fast, sharp A-delta signal to the ventral posterolateral nucleus of the
thalamus The thalamus (from Greek language, Greek Wikt:θάλαμος, θάλαμος, "chamber") is a large mass of gray matter located in the wikt:dorsal, dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the tha ...

thalamus
. The paleospinothalamic tract carries the slow, dull, C-fiber pain signal. Some of these fibers peel off in the brain stem, connecting with the reticular formation or midbrain periaqueductal gray, and the remainder terminate in the intralaminar nuclei of the thalamus. Pain-related activity in the thalamus spreads to the
insular cortex The insular cortex (also insula and insular lobe) is a portion of the cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cer ...

insular cortex
(thought to embody, among other things, the feeling that distinguishes pain from other
homeostatic emotion A homeostatic emotion (or primordial emotion, or primordial feeling) is an attention-demanding feeling (e.g., thirst, pain, fatigue) evoked by an internal body state that drives behavior (drinking, withdrawing and resting in these examples) aimed a ...
s such as itch and nausea) and
anterior cingulate cortex In the human brain The human brain is the central organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-ex ...
(thought to embody, among other things, the affective/motivational element, the unpleasantness of pain), and pain that is distinctly located also activates
primary Primary or primaries may refer to: Arts, entertainment, and media Music Groups and labels * Primary (band), from Australia * Primary (musician), hip hop musician and record producer from South Korea * Primary Music, Israeli record label Works * ...
and
secondary Secondary is an adjective meaning "second" or "second hand". It may refer to: * Secondary (chemistry), term used in organic chemistry to classify various types of compounds * The group of (usually at least four) defensive backs in gridiron football ...
somatosensory cortex. Spinal cord fibers dedicated to carrying A-delta fiber pain signals, and others that carry both A-delta and C fiber pain signals to the
thalamus The thalamus (from Greek language, Greek Wikt:θάλαμος, θάλαμος, "chamber") is a large mass of gray matter located in the wikt:dorsal, dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the tha ...

thalamus
have been identified. Other spinal cord fibers, known as wide dynamic range neurons, respond to A-delta and C fibers, but also to the large A-beta fibers that carry touch, pressure and vibration signals.In 1955, DC Sinclair and G Weddell developed peripheral pattern theory, based on a 1934 suggestion by John Paul Nafe. They proposed that all skin fiber endings (with the exception of those innervating hair cells) are identical, and that pain is produced by intense stimulation of these fibers. Another 20th-century theory was
gate control theory The gate control theory of pain asserts that non-painful input closes the nerve "gates" to painful input, which prevents pain sensation from traveling to the central nervous system. The gate control theory of pain describes how non-painful sensatio ...
, introduced by
Ronald Melzack Ronald Melzack (July 19, 1929 – December 22, 2019) was a Canadian psychologist A psychologist is a professional who practices psychology and studies normal and abnormal mental states, perceptual, cognitive, emotional, and social proce ...
and
Patrick Wall Sir Patrick Henry Bligh Wall, (14 October 1916 – 15 May 1998) was a British commando Royal Marines from 40 Commando on patrol in the Sangin">40_Commando.html" ;"title="Royal Marines from 40 Commando">Royal Marines from 40 Commando on patr ...
in the 1965 ''Science'' article "Pain Mechanisms: A New Theory". The authors proposed that both thin (pain) and large diameter (touch, pressure, vibration) nerve fibers carry information from the site of injury to two destinations in the dorsal horn of the spinal cord, and that the more large fiber activity relative to thin fiber activity at the inhibitory cell, the less pain is felt.


Three dimensions of pain

In 1968 Ronald Melzack and
Kenneth Casey Kenneth Casey (January 10, 1899 – August 10, 1965) was an American composer, publisher, author, and child movie star in early silents. Biography Born in New York City, Casey worked as a child actor in over thirty films for Vitagraph Studios betw ...
described chronic pain in terms of its three dimensions: * "sensory-discriminative" (sense of the intensity, location, quality and duration of the pain), * "affective-motivational" (unpleasantness and urge to escape the unpleasantness), and * "cognitive-evaluative" (cognitions such as appraisal, cultural values, distraction and hypnotic suggestion). They theorized that pain intensity (the sensory discriminative dimension) and unpleasantness (the affective-motivational dimension) are not simply determined by the magnitude of the painful stimulus, but "higher" cognitive activities can influence perceived intensity and unpleasantness. Cognitive activities may affect both sensory and affective experience or they may modify primarily the affective-motivational dimension. Thus, excitement in games or war appears to block both the sensory-discriminative and affective-motivational dimensions of pain, while suggestion and placebos may modulate only the affective-motivational dimension and leave the sensory-discriminative dimension relatively undisturbed. (p. 432) The paper ends with a call to action: "Pain can be treated not only by trying to cut down the sensory input by anesthetic block, surgical intervention and the like, but also by influencing the motivational-affective and cognitive factors as well." (p. 435)


Evolutionary and behavioral role

Pain is part of the body's defense system, producing a reflexive retraction from the painful stimulus, and tendencies to protect the affected body part while it heals, and avoid that harmful situation in the future. It is an important part of animal life, vital to healthy survival. People with
congenital insensitivity to pain Congenital insensitivity to pain (CIP), also known as congenital analgesia, is one or more rare conditions in which a person cannot feel (and has never felt) physical pain Pain is a distressing feeling often caused by intense or damaging stimuli. ...
have reduced
life expectancy Life expectancy is a statistical measure of the average time an organism is expected to live, based on the year of its birth, its current age, and other demographic Demography (from prefix ''demo-'' from Ancient Greek Ancien ...

life expectancy
. In '' The Greatest Show on Earth: The Evidence for Evolution'', biologist
Richard Dawkins Richard Dawkins (born 26 March 1941) is a British evolutionary biology, evolutionary biologist and author. He is an Oxford fellow, emeritus fellow of New College, Oxford and was Simonyi Professor for the Public Understanding of Science, Prof ...

Richard Dawkins
addresses the question of why pain should have the quality of being painful. He describes the alternative as a mental raising of a "red flag". To argue why that red flag might be insufficient, Dawkins argues that drives must compete with one other within living beings. The most "fit" creature would be the one whose pains are well balanced. Those pains which mean certain death when ignored will become the most powerfully felt. The relative intensities of pain, then, may resemble the relative importance of that risk to our ancestors. This resemblance will not be perfect, however, because natural selection can be a poor designer. This may have maladaptive results such as supernormal stimuli. Pain, however, does not only wave a "red flag" within living beings but may also act as a warning sign and a call for help to other living beings. Especially in humans who readily helped each other in case of sickness or injury throughout their evolutionary history, pain might be shaped by natural selection to be a credible and convincing signal of need for relief, help, and care. Idiopathic pain (pain that persists after the trauma or pathology has healed, or that arises without any apparent cause) may be an exception to the idea that pain is helpful to survival, although some
psychodynamic Psychodynamics, also known as psychodynamic psychology, in its broadest sense, is an approach to psychology that emphasizes systematic study of the psychological forces that underlie human behavior, feelings, and emotions and how they might relate ...
psychologists argue that such pain is psychogenic, enlisted as a protective distraction to keep dangerous emotions unconscious.


Thresholds

In pain science, thresholds are measured by gradually increasing the intensity of a stimulus in a procedure called quantitative sensory testing which involves such stimuli as
electric current An electric current is a stream of charged particle In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, ...
, thermal (heat or cold), mechanical (pressure, touch, vibration),
ischemic Ischemia or ischaemia is a restriction in blood Blood is a body fluid Body fluids, bodily fluids, or biofluids are liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressi ...
, or chemical stimuli applied to the subject to evoke a response. The " pain perception threshold" is the point at which the subject begins to feel pain, and the "pain threshold intensity" is the stimulus intensity at which the stimulus begins to hurt. The "
pain tolerance Pain tolerance is the maximum level of pain that a person is able to tolerate. Pain tolerance is distinct from pain threshold (the point at which pain begins to be felt).


Assessment

A person's self-report is the most reliable measure of pain. Some health care professionals may underestimate pain severity. A definition of pain widely employed in nursing, emphasizing its subjective nature and the importance of believing patient reports, was introduced by
Margo McCaffery in 1968: "Pain is whatever the experiencing person says it is, existing whenever he says it does". To assess intensity, the patient may be asked to locate their pain on a scale of 0 to 10, with 0 being no pain at all, and 10 the worst pain they have ever felt. Quality can be established by having the patient complete the
McGill Pain Questionnaire The McGill Pain Questionnaire, also known as McGill Pain Index, is a scale of rating pain Pain is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain defines pain as "an unpleasa ...
indicating which words best describe their pain.


Visual analogue scale

The visual analogue scale is a common, reproducible tool in the assessment of pain and pain relief. The scale is a continuous line anchored by verbal descriptors, one for each extreme of pain where a higher score indicates greater pain intensity. It is usually 10 cm in length with no intermediate descriptors as to avoid marking of scores around a preferred numeric value. When applied as a pain descriptor, these anchors are often 'no pain' and 'worst imaginable pain". Cut-offs for pain classification have been recommended as no pain (0-4mm), mild pain (5-44mm), moderate pain (45-74mm) and severe pain (75-100mm).


Multidimensional pain inventory

The Multidimensional Pain Inventory (MPI) is a questionnaire designed to assess the
psychosocial The psychosocial approach looks at individuals in the context of the combined influence that psychological Psychology is the scientific Science () is a systematic enterprise that Scientific method, builds and organizes knowledge i ...
state of a person with chronic pain. Combining the MPI characterization of the person with their IASP five-category pain profile is recommended for deriving the most useful case description.


Assessment in non-verbal people

Non-verbal Nonverbal communication (NVC) is the transmission of messages or signals through a nonverbal platform such as eye contact Eye contact occurs when two people look at each other's eyes at the same time. In human beings Humans (''Homo sapi ...
people cannot use words to tell others that they are experiencing pain. However, they may be able to communicate through other means, such as blinking, pointing, or nodding. With a non-communicative person, observation becomes critical, and specific behaviors can be monitored as pain indicators. Behaviors such as facial grimacing and guarding (trying to protect part of the body from being bumped or touched) indicate pain, as well as an increase or decrease in vocalizations, changes in routine behavior patterns and mental status changes. Patients experiencing pain may exhibit withdrawn
social behavior Social behavior is behavior Behavior (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United St ...
and possibly experience a decreased appetite and decreased nutritional intake. A change in condition that deviates from baseline, such as moaning with movement or when manipulating a body part, and limited
range of motion Range of motion (or ROM), is the linear or angular distance that a moving object may normally travel while properly attached to another. It is also called range of travel (or ROT), particularly when talking about mechanical devices and in mechanic ...
are also potential pain indicators. In patients who possess language but are incapable of expressing themselves effectively, such as those with dementia, an increase in confusion or display of aggressive behaviors or agitation may signal that discomfort exists, and further assessment is necessary. Changes in behavior may be noticed by caregivers who are familiar with the person's normal behavior. Infants do feel pain, but lack the language needed to report it, and so communicate distress by crying. A non-verbal pain assessment should be conducted involving the parents, who will notice changes in the infant which may not be obvious to the health care provider. Pre-term babies are more sensitive to painful stimuli than those carried to full term. Another approach, when pain is suspected, is to give the person treatment for pain, and then watch to see whether the suspected indicators of pain subside.


Other reporting barriers

The way in which one experiences and responds to pain is related to sociocultural characteristics, such as gender, ethnicity, and age. An aging adult may not respond to pain in the same way that a younger person might. Their ability to recognize pain may be blunted by illness or the use of
medication A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to medical diagnosis, diagnose, cure, therapy, treat, or preventive medicine, prevent disease. Drug therapy (pharmacotherapy) ...
. Depression may also keep older adult from reporting they are in pain. Decline in
self-care Self-care has been defined as the process of taking care of oneself with behaviors that promote health and active management of illness when it occurs. Individuals engage in some form of self-care daily with food choices, exercise, sleep, and d ...
may also indicate the older adult is experiencing pain. They may be reluctant to report pain because they do not want to be perceived as weak, or may feel it is impolite or shameful to complain, or they may feel the pain is a form of deserved punishment. Cultural barriers may also affect the likelihood of reporting pain. Sufferers may feel that certain treatments go against their religious beliefs. They may not report pain because they feel it is a sign that death is near. Many people fear the stigma of addiction, and avoid pain treatment so as not to be prescribed potentially addicting drugs. Many Asians do not want to lose respect in society by admitting they are in pain and need help, believing the pain should be borne in silence, while other cultures feel they should report pain immediately to receive immediate relief. Gender can also be a perceived factor in reporting pain.
Gender differences Sex differences in humans have been studied in a variety of fields. Sex chromosome#Sex determination, Sex determination occurs by the presence or absence of a Y in the 23rd pair of chromosomes in the human genome. Phenotypic sex refers to an indiv ...
can be the result of social and cultural expectations, with women expected to be more emotional and show pain, and men more stoic. As a result, female pain is often stigmatized, leading to less urgent treatment of women based on social expectations of their ability to accurately report it. This leads to extended emergency room wait times for women and frequent dismissal of their ability to accurately report pain.


Diagnostic aid

Pain is a symptom of many medical conditions. Knowing the time of onset, location, intensity, pattern of occurrence (continuous, intermittent, etc.), exacerbating and relieving factors, and quality (burning, sharp, etc.) of the pain will help the examining physician to accurately diagnose the problem. For example, chest pain described as extreme heaviness may indicate
myocardial infarction A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow Hemodynamics American and British English spelling differences#ae and oe, or haemodynamics are the Fluid dynamics, dynamics of blood flow. The circulatory sy ...

myocardial infarction
, while chest pain described as tearing may indicate
aortic dissection Aortic dissection (AD) occurs when an injury to the innermost layer of the aorta The aorta ( ) is the main and largest artery An artery (plural arteries) () is a blood vessel The blood vessels are the components of the circula ...
.


Physiological measurement

Functional magnetic resonance imaging Functional magnetic resonance imaging or functional MRI (fMRI) measures brain activity by detecting changes associated with blood flow Hemodynamics American and British English spelling differences#ae and oe, or haemodynamics are the Fluid dynami ...

Functional magnetic resonance imaging
brain scanning has been used to measure pain, and correlates well with self-reported pain.


Mechanisms


Nociceptive

Nociceptive pain is caused by stimulation of
sensory nerve fibers An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences Despite the various English dialects Dialect The term dialect (from Latin , , from the Ancient Greek word , , "discourse", from ...
that respond to stimuli approaching or exceeding harmful intensity (
nociceptor A nociceptor ("pain receptor") is a sensory neuron Sensory neurons, also known as afferent neurons, are neuron A neuron or nerve cell is an membrane potential#Cell excitability, electrically excitable cell (biology), cell that communicates w ...
s), and may be classified according to the mode of noxious stimulation. The most common categories are "thermal" (e.g. heat or cold), "mechanical" (e.g. crushing, tearing, shearing, etc.) and "chemical" (e.g.
iodine Iodine is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical ele ...

iodine
in a cut or chemicals released during
inflammation Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogen In biology Biology is the natural science that studies life and living organisms, including their anato ...
). Some nociceptors respond to more than one of these modalities and are consequently designated polymodal. Nociceptive pain may also be classed according to the site of origin and divided into "visceral", "deep somatic" and "superficial somatic" pain. Visceral structures (e.g., the heart, liver and intestines) are highly sensitive to stretch,
ischemia Ischemia or ischaemia is a restriction in blood Blood is a body fluid in humans and other animals that delivers necessary substances such as nutrients and oxygen to the Cell (biology), cells and transports metabolic waste products away fr ...
and
inflammation Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogen In biology Biology is the natural science that studies life and living organisms, including their anato ...
, but relatively insensitive to other stimuli that normally evoke pain in other structures, such as burning and cutting.
Visceral painVisceral pain is pain that results from the activation of nociceptors of the thoracic, pelvic, or abdominal viscera (organs). Visceral structures are highly sensitive to distension (stretch), ischemia and inflammation, but relatively insensitive to o ...
is diffuse, difficult to locate and often referred to a distant, usually superficial, structure. It may be accompanied by nausea and vomiting and may be described as sickening, deep, squeezing, and dull. ''Deep somatic'' pain is initiated by stimulation of nociceptors in ligaments, tendons, bones, blood vessels,
fascia A fascia (; plural fasciae ; adjective fascial; from Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Thro ...
e and muscles, and is dull, aching, poorly-localized pain. Examples include
sprain A sprain, also known as a torn ligament, is an injury resulting in the stretching or tearing of ligaments A ligament is the fibrous connective tissue Connective tissue is one of the four basic types of animal Animals (also called Meta ...
s and broken bones. ''Superficial somatic'' pain is initiated by activation of nociceptors in the skin or other superficial tissue, and is sharp, well-defined and clearly located. Examples of injuries that produce superficial somatic pain include minor wounds and minor (first degree)
burn A burn is a type of injury Injury, also known as physical trauma, is damage Damage is any change in a thing, often a physical object, that degrades it away from its initial state. It can broadly be defined as "changes introduced into a ...

burn
s.


Neuropathic

Neuropathic pain is caused by damage or disease affecting any part of the
nervous system In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mecha ...

nervous system
involved in bodily feelings (the
somatosensory system The somatosensory system is a part of the sensory nervous system The sensory nervous system is a part of the nervous system In biology, the classical doctrine of the nervous system determines that it is a Complex system, highly comple ...
). Neuropathic pain may be divided into peripheral,
central Central is an adjective In linguistics Linguistics is the scientific study of language A language is a structured system of communication used by humans, including speech (spoken language), gestures (Signed language, sign languag ...
, or mixed (peripheral and central) neuropathic pain.
Peripheral A peripheral or peripheral device is an auxiliary device used to put information into and get information out of the computer. The term peripheral device refers to all hardware components that are attached to a computer and are controlled by the co ...
neuropathic pain is often described as "burning", "tingling", "electrical", "stabbing", or "pins and needles". Bumping the " funny bone" elicits acute peripheral neuropathic pain. Some manifestations of neuropathic pain include: traumatic neuropathy, tic douloureux, painful
diabetic neuropathy Diabetic neuropathy refers to various types of nerve damage associated with diabetes mellitus. Symptoms depend on the site of nerve damage and can include motor changes such as weakness; sensory symptoms such as numbness, tingling, or pain; or auton ...
, and postherpetic neuralgia.


Nociplastic

Nociplastic pain is pain characterized by a changed nociception (but without evidence of real or threatened tissue damage, or without disease or damage in the
somatosensory system The somatosensory system is a part of the sensory nervous system The sensory nervous system is a part of the nervous system In biology, the classical doctrine of the nervous system determines that it is a Complex system, highly comple ...
). In some debates regarding
physician-assisted suicide Assisted suicide, also known as assisted dying or medical aid in dying, is suicide undertaken with the aid of another person. The term usually refers to physician-assisted suicide (PAS), which is suicide that is assisted by a physician A p ...
or
euthanasia Euthanasia (from el, εὐθανασία 'good death': εὖ, ''eu'' 'well, good' + θάνατος, ''thanatos'' 'death') is the practice of intentionally ending life to relieve pain and suffering. Different countries have different Legality ...

euthanasia
, pain has been used as an argument to permit people who are terminally ill to end their lives. This applies, for example, to fibromyalgia patients.


Psychogenic

Psychogenic pain, also called ''psychalgia'' or ''somatoform pain'', is pain caused, increased or prolonged by mental, emotional or behavioral factors. Headache, back pain and stomach pain are sometimes diagnosed as psychogenic. Sufferers are often stigmatized, because both medical professionals and the general public tend to think that pain from a psychological source is not "real". However, specialists consider that it is no less actual or hurtful than pain from any other source."International Association for the Study of Pain , Pain Definitions".
Retrieved 12 October 2010.
People with chronic pain, long-term pain frequently display psychological disturbance, with elevated scores on the Minnesota Multiphasic Personality Inventory scales of hysteria, depression and hypochondriasis (the "neurotic triad"). Some investigators have argued that it is this neuroticism that causes acute pain to turn chronic, but clinical evidence points the other direction, to chronic pain causing neuroticism. When long-term pain is relieved by therapeutic intervention, scores on the neurotic triad and anxiety fall, often to normal levels. Self-esteem, often low in chronic pain patients, also shows improvement once pain has resolved.


Management

Pain can be treated through a variety of methods. The most appropriate method depends upon the situation. Management of chronic pain can be difficult and may require the coordinated efforts of a pain management team, which typically includes medical practitioners, clinical pharmacists, clinical psychologists, physiotherapists, occupational therapists, physician assistants, and nurse practitioners. Inadequate treatment of pain is widespread throughout surgical wards, intensive care units, and accident and emergency departments, in General practitioner, general practice, in the management of all forms of chronic pain including cancer pain, and in End-of-life care, end of life care. This neglect extends to all ages, from newborns to medically frail elderly. In the US, African Americans, African and Hispanic and Latino Americans, Hispanic Americans are more likely than others to suffer unnecessarily while in the care of a physician; and women's pain is more likely to be undertreated than men's. The
International Association for the Study of Pain The International Association for the Study of Pain (IASP) is an international learned society A learned society (; also known as a learned academy, scholarly society, or academic association) is an organization that exists to promote an discip ...
advocates that the relief of pain should be recognized as a human right, that chronic pain should be considered a disease in its own right, and that pain medicine should have the full status of a Specialty (medicine), medical specialty. It is a specialty only in China and Australia at this time. Elsewhere, pain medicine is a subspecialty under disciplines such as anesthesiology, physiatry, neurology, palliative medicine and psychiatry. In 2011, Human Rights Watch alerted that tens of millions of people worldwide are still denied access to inexpensive medications for severe pain.


Medication

Acute pain is usually managed with medications such as analgesics and anesthetics. Caffeine when added to pain medications such as ibuprofen, may provide some additional benefit. Ketamine can be used instead of opioids for short-term pain. Pain medications can cause paradoxical side effects, such as opioid-induced hyperalgesia (severe pain caused by long-term opioid use). Sugar (sucrose) when taken by mouth reduces Pain in babies, pain in newborn babies undergoing some medical procedures (a Incision and drainage, lancing of the heel, venipuncture, and intramuscular injections). Sugar does not remove pain from circumcision, and it is unknown if sugar reduces pain for other procedures. Sugar did not affect pain-related EEG, electrical activity in the brains of newborns one second after the heel lance procedure. Sweet liquid by mouth moderately reduces the rate and duration of crying caused by immunization injection in children between one and twelve months of age.


Psychological

Individuals with more
social support Social support is the perception and actuality that one is cared for, has assistance available from other people, and most popularly, that one is part of a supportive social network A social network is a social structure In the social scie ...
experience less cancer pain, take less pain medication, report less labor pain and are less likely to use Epidural administration, epidural anesthesia during childbirth, or suffer from chest pain after coronary artery bypass surgery. Suggestion can significantly affect pain intensity. About 35% of people report marked relief after receiving a Saline (medicine), saline injection they believed to be
morphine Morphine is a of the family that is found naturally in a dark brown, resinous form, from the poppy plant ('). It can be taken orally or injected. It acts directly on the (CNS) to induce analgesia and alter perception and emotional respons ...

morphine
. This placebo effect is more pronounced in people who are prone to anxiety, and so anxiety reduction may account for some of the effect, but it does not account for all of it. Placebos are more effective for intense pain than mild pain; and they produce progressively weaker effects with repeated administration. It is possible for many with chronic pain to become so absorbed in an activity or entertainment that the pain is no longer felt, or is greatly diminished. Acute pain is usually managed with medications such as analgesics and anesthetics. Caffeine when added to pain medications such as ibuprofen, may provide some additional benefit. Ketamine can be used instead of opioids for short-term pain. Pain medications can cause paradoxical side effects, such as opioid-induced hyperalgesia (severe pain caused by long-term opioid use). A number of meta-analyses have found clinical hypnosis to be effective in controlling pain associated with diagnostic and surgical procedures in both adults and children, as well as pain associated with cancer and childbirth. A 2007 review of 13 studies found evidence for the efficacy of hypnosis in the reduction of chronic pain under some conditions, though the number of patients enrolled in the studies was low, raising issues related to the statistical power to detect group differences, and most lacked credible controls for placebo or expectation. The authors concluded that "although the findings provide support for the general applicability of hypnosis in the treatment of chronic pain, considerably more research will be needed to fully determine the effects of hypnosis for different chronic-pain conditions."


Alternative medicine

An analysis of the 13 highest quality studies of pain treatment with acupuncture, published in January 2009, concluded there was little difference in the effect of real, faked and no acupuncture. However, more recent reviews have found some benefit. Additionally, there is tentative evidence for a few herbal medicines. There has been some interest in the relationship between vitamin D and pain, but the evidence so far from Clinical trial, controlled trials for such a relationship, other than in osteomalacia, is inconclusive. For chronic (long-term) Low back pain, lower back pain, spinal manipulation produces tiny, Clinical significance, clinically insignificant, short-term improvements in pain and function, compared with sham therapy and other interventions. Spinal manipulation produces the same outcome as other treatments, such as general practitioner care, pain-relief drugs, physical therapy, and exercise, for acute (short-term) lower back pain.


Epidemiology

Pain is the main reason for visiting an emergency department in more than 50% of cases, and is present in 30% of family practice visits. Several epidemiological studies have reported widely varying prevalence rates for chronic pain, ranging from 12 to 80% of the population. It becomes more common as people approach death. A study of 4,703 patients found that 26% had pain in the last two years of life, increasing to 46% in the last month. A survey of 6,636 children (0–18 years of age) found that, of the 5,424 respondents, 54% had experienced pain in the preceding three months. A quarter reported having experienced recurrent or continuous pain for three months or more, and a third of these reported frequent and intense pain. The intensity of chronic pain was higher for girls, and girls' reports of chronic pain increased markedly between ages 12 and 14.


Society and culture

Physical pain is a universal experience, and a strong motivator of human and animal behavior. As such, physical pain is used politically in relation to various issues such as pain management policy, drug control, animal rights or animal welfare, torture, and pain compliance. The deliberate infliction of pain and the medical management of pain are both important aspects of biopower, a concept that encompasses the "set of mechanisms through which the basic biological features of the human species became the object of a political strategy". In various contexts, the deliberate infliction of pain in the form of corporal punishment is used as retribution for an offence, for the purpose of disciplining or reforming a wrongdoer, or to deter attitudes or behaviour deemed unacceptable. In Western societies, the intentional infliction of severe pain (torture) was principally used to extract confession prior to its abolition in the latter part of the 19th century. Torture as a means to punish the Citizenship, citizen has been reserved for offences posing severe threat to the social fabric (for example, treason). The administration of torture on bodies othered by the cultural narrative, those observed as not ‘full members of society’ met a resurgence in the 20th century, possibly due to the heightened warfare. Many cultures use painful ritual practices as a catalyst for psychological transformation. The use of pain to transition to a 'cleansed and purified' state is seen in Catholic self-flagellation practices, or personal catharsis in Suspension_(body_modification) , neo-primitive body suspension experiences. Beliefs about pain play an important role in sporting cultures. Pain may be viewed positively, exemplified by the 'no pain, no gain' attitude, with pain seen as an essential part of training. Sporting culture tends to normalise experiences of pain and injury and celebrate athletes who 'play hurt'. Pain has psychological, social, and physical dimensions, and is greatly influenced by cultural factors.


Non-humans

René Descartes René Descartes ( or ; ; Latinized Latinisation or Latinization can refer to: * Latinisation of names, the practice of rendering a non-Latin name in a Latin style * Latinisation in the Soviet Union, the campaign in the USSR during the 1920s ...

René Descartes
argued that animals lack consciousness and therefore do not experience pain and suffering in the way that humans do.Working party of the Nuffield Council on Bioethics (2005)
"The ethics of research involving animals. London: Nuffield Council on Bioethics."
. Archived from the original on 25 June 2008. Retrieved 12 January 2010.
Bernard Rollin of Colorado State University, the principal author of two U.S. federal laws regulating pain relief for animals, wrote that researchers remained unsure into the 1980s as to whether animals experience pain, and that veterinarians trained in the U.S. before 1989 were simply taught to ignore animal pain. cited in The ability of invertebrate species of animals, such as insects, to feel pain and suffering is unclear. Specialists believe that all vertebrates can feel pain, and that certain invertebrates, like the octopus, may also. The presence of pain in animals is unknown, but can be inferred through physical and behavioral reactions, such as paw withdrawal from various noxious mechanical stimuli in rodents.


See also

* Hedonic adaptation, the tendency to quickly return to a relatively stable level of happiness despite major positive or negative events * Pain (philosophy), the branch of philosophy concerned with suffering and physical pain * Pain and suffering, the legal term for the physical and emotional stress caused from an injury


Explanatory notes


References

*


External links

*
"Pain"
''Stanford Encyclopedia of Philosophy'' {{Authority control Pain, Acute pain Nociception Sensory systems Suffering Symptoms and signs