This article is about physical pain. For pain in the broader sense see Suffering. For other uses see Pain (disambiguation). Pain ICD-10 R52 ICD-9 338 DiseasesDB 9503 MedlinePlus 002164 MeSH D010146

Pain is "an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage."1 It is the feeling common to such experiences as stubbing a toe burning a finger putting iodine on a cut and bumping the "funny bone".2

Pain motivates us to withdraw from potentially damaging situations protect a damaged body part while it heals and avoid those situations in the future.3 Most pain resolves promptly once the painful stimulus is removed and the body has healed but sometimes pain persists despite removal of the stimulus and apparent healing of the body; and sometimes pain arises in the absence of any detectable stimulus damage or disease.4

Pain is the most common reason for physician consultation in the United States.5 It is a major symptom in many medical conditions and can significantly interfere with a person's quality of life and general functioning.6 Psychological factors such as social support hypnotic suggestion excitement in sport or war and distraction can significantly modulate pain's intensity or unpleasantness.78 Contents 1 Classification 1.1 Duration 1.2 Region and system 1.3 Cause 1.4 Nociceptive 1.5 Neuropathic 1.6 Phantom 1.7 Psychogenic 1.8 Pain asymbolia and insensitivity 2 Effect on functioning 3 Theory 3.1 Specificity 3.2 Pattern 3.3 Gate control 3.4 Dimensions 3.5 Theory today 3.6 Evolutionary and behavioral role 3.7 Thresholds 4 Assessment 4.1 Multidimensional pain inventory 4.2 In nonverbal patients 4.3 Other barriers to reporting 4.4 As an aid to diagnosis 5 Management 5.1 Medication 5.2 Psychological 5.3 Alternative medicine 6 Epidemiology 7 Society and culture 8 In other animals 9 Etymology 10 References 11 External links Classification

The International Association for the Study of Pain (IASP) classification system describes pain according to five categories: duration and severity anatomical location body system involved cause and temporal characteristics (intermittent constant etc.).4 This system has been criticized by Woolf and others as inadequate for guiding research and treatment9 and an additional category based on neurochemical mechanism has been proposed.10 Duration Main article: Chronic pain

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 peripheral neuropathy cancer and idiopathic pain may persist for years. Pain that lasts a long time is called chronic and pain that resolves quickly is called acute. Traditionally the distinction between acute and chronic pain has relied upon an arbitrary interval of time from onset; the two most commonly used markers being 3 months and 6 months since the onset of pain10 though some theorists and researchers have placed the transition from acute to chronic pain at 12 months.11 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.12 A popular alternative definition of chronic pain involving no arbitrarily fixed durations is "pain that extends beyond the expected period of healing."10 Chronic pain may be classified as "malignant" (caused by cancer) or "benign" (non-malignant).12 Region and system

Pain can be classed according to its location in the body as in headache low back pain and pelvic pain; or according to the body system involved such as myofascial pain (emanating from skeletal muscles or the fibrous sheath surrounding them) rheumatic pain (emanating from the joints and surrounding tissue) neuropathic pain (caused by damage or illness affecting the somatosensory system) or vascular (pain from blood vessels).10 Cause

The crudest example of classification by cause simply distinguishes "somatogenic" pain (arising from a perturbation of the body) from psychogenic pain (arising from a perturbation of the mind: when a thorough physical exam imaging and laboratory tests fail to detect the cause of pain it is assumed to be the product of psychic conflict or psychopathology).10 Somatogenic pain is divided into "nociceptive" and "neuropathic".13 Nociceptive

Nociceptive pain is caused by stimulation of peripheral nerve fibers that respond only to stimuli approaching or exceeding harmful intensity (nociceptors) and may be classified according to the mode of noxious stimulation; the most common categories being "thermal" (heat or cold) "mechanical" (crushing tearing etc.) and "chemical" (iodine in a cut chili powder in the eyes).

Nociceptive pain may also be divided into "visceral" "deep somatic" and "superficial somatic" pain. Visceral pain originates in the viscera (organs) and often is extremely difficult to locate and nociception from some visceral regions produces "referred" pain where the sensation is located in an area distant from the site of the stimulus. Deep somatic pain is initiated by stimulation of nociceptors in ligaments tendons bones blood vessels fasciae and muscles and is dull aching poorly-localized pain. Examples include sprains and broken bones. Superficial pain is initiated by activation of nociceptors in the skin or superficial tissues and is sharp well-defined and clearly located. Examples of injuries that produce superficial somatic pain include minor wounds and minor (first degree) burns.11 Neuropathic Main article: Neuropathic pain Neuropathic pain is caused by damage or disease affecting the central or peripheral portions of the nervous system involved in bodily feelings (the somatosensory system).14 Peripheral neuropathic pain is often described as burning tingling electrical stabbing or pins and needles.15 Bumping the "funny bone" elicits peripheral neuropathic pain. Phantom Main article: Phantom pain Phantom pain is pain from a part of the body that has been lost or from which the brain no longer receives signals. It is a type of neuropathic pain. Phantom limb pain is a common experience of amputees. The prevalence of phantom pain in upper limb amputees is nearly 82% and in lower limb amputees is 54%.16 One study found that eight days after amputation 72 percent of patients had phantom limb pain and six months later 65 percent reported it.1718 Some amputees experience continuous pain that varies in intensity or quality; others experience several bouts a day or it may occur only once every week or two. 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 or phantom limb pain may accompany urination or defecation.19 Local anesthetic 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 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.19 Work by Vilayanur S. Ramachandran using mirror box therapy allows for illusions of movement and touch in a phantom limb which in turn cause a reduction in pain.20 Paraplegia 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 pain 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 fire running down the legs or 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.19 Psychogenic Main article: Psychogenic pain Psychogenic pain also called psychalgia or somatoform pain is pain caused increased or prolonged by mental emotional or behavioral factors.21 Headache back pain and stomach pain are sometimes diagnosed as psychogenic.22 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.23 People with 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 injuries to turn chronic but clinical evidence points the other way 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.24 The term 'psychogenic' assumes that medical diagnosis is so perfect that all organic causes of pain can be detected; regrettably we are far from such infallibility... All too often the diagnosis of neurosis as the cause of pain hides our ignorance of many aspects of pain medicine. Ronald Melzack 1996.24 Pain asymbolia and insensitivity Main articles: Pain asymbolia and Congenital insensitivity to pain The ability to experience pain is essential for protection from injury and recognition of the presence of injury. Episodic analgesia 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.25 Although unpleasantness is an essential part of the IASP definition of pain it is possible to induce a state described as intense pain devoid of unpleasantness in some patients with morphine injection or psychosurgery.23 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.26 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.27 Insensitivity to pain may also result from abnormalities in the nervous system. This is usually the result of acquired damage to the nerves such as spinal cord injury diabetes mellitus (diabetic neuropathy) or leprosy in countries where this is prevalent.28 These individuals are at risk of tissue damage due to undiscovered injury. People with diabetes-related nerve damage for instance sustain poorly healing foot ulcers as a result of decreased sensation.29 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".27 Children with this condition incur carelessly repeated damage to their tongue eyes joints skin and muscles. They may attain adulthood but 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 and congenital insensitivity to pain with anhidrosis).30These conditions feature decreased sensitivity to pain together with other neurological abnormalties particularly of the autonomic nervous system.2730 A very rare syndrome with isolated congenital insensitivity to pain has been linked with mutations in the SCN9A gene which codes for a sodium channel (Nav1.7) necessary in conducting pain nerve stimuli.3132 Effect on functioning Experimental subjects challenged by acute pain and patients in chronic pain experience impairments in attention control working memory mental flexibility problem solving and information processing speed.33 Acute and chronic pain are also associated with increased depression anxiety fear and anger.34 "If I have matters right the consequences of pain will include direct physical distress unemployment financial difficulties marital disharmony and difficulties in concentration and attention" Harold Merskey 200035 Theory Specificity Descartes' pain pathway. In his 1664 Treatise of Man Ren Descartes traced a pain pathway. "Particles of heat" (A) activate a spot of skin (B) attached by a fine thread (cc) to a valve in the brain (de) where this activity opens the valve allowing the animal spirits to flow from a cavity (F) into the muscles that then flinch from the stimulus turn the head and eyes toward the affected body part and move the hand and turn the body protectively. The underlying premise of this model - that pain is the direct product of a noxious stimulus activating a dedicated pain pathway from a receptor in the skin along a thread or chain of nerve fibers to the pain center in the brain to a mechanical behavioral response - remained the dominant perspective on pain until the mid-nineteen sixties.36 Pattern This "specificity theory" (specific pain receptor and pathway) was challenged by the theory proposed initially in 1874 by Wilhelm Erb that a pain signal can be generated by stimulation of any sensory receptor provided the stimulation is intense enough: the pattern of stimulation (intensity over time and area) not the receptor type determines whether nociception occurs. Alfred Goldscheider (1894) proposed that over time activity from many sensory fibers might accumulate in the dorsal horns of the spinal cord and begin to signal pain once a certain threshold of accumulated stimulation has been crossed. In 1953 Willem Noordenbos observed that a signal carried from the area of injury along large diameter "touch pressure or vibration" fibers may inhibit the signal carried by the thinner "pain" fibers - the ratio of large fiber signal to thin fiber signal determining pain intensity; hence we rub a smack. This was taken as a demonstration that pattern of stimulation (of large and thin fibers in this instance) modulates pain intensity.37 Gate control Ronald Melzack and Patrick Wall introduced their "gate control" theory of pain in the 1965 Science article "Pain Mechanisms: A New Theory".38 The authors proposed that 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: the "inhibitory" cells and the "transmission" cells. Signals from both thin and large diameter fibers excite the transmission cells and when the output of the transmission cells exceeds a critical level pain begins. The job of the inhibitory cells is to inhibit activation of the transmission cells. The transmission cells are the gate on pain and inhibitory cells can shut the gate. When thin (pain) and large (touch etc.) fibers activated by a noxious event excite a spinal cord transmission cell they also act on its inhibitory cells. The thin fibers impede the inhibitory cells (tending to leave the gate open) while the large diameter fibers excite the inhibitory cells (tending to close the gate). So the more large fiber activity relative to thin fiber activity coming from the inhibitory cell's receptive field the less pain is felt. The authors had conceived a neural "circuit diagram" to explain why we rub a smack.36 They pictured not only a signal traveling from the site of injury to the inhibitory and transmission cells and up the spinal cord to the brain but also a signal traveling from the site of injury directly up the cord to the brain (bypassing the inhibitory and transmission cells) where depending on the state of the brain it may trigger a signal back down the spinal cord to modulate inhibitory cell activity (and so pain intensity). This was the first theory to offer a physiological explanation for the previously reported effect of psychology on pain perception.39 Dimensions In 1968 Ronald Melzack and Kenneth Casey described 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).40 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 (the cognitive-evaluative dimension) 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 dimensions of pain while suggestion and placebos may modulate 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) Theory today Regions of the cerebral cortex associated with pain. Wilhelm Erb's (1874) early pattern theory hypothesis that a pain signal can be generated by intense enough stimulation of any sensory receptor has been soundly disproved.41 The thin (A-delta and C) peripheral sensory fibers carry information regarding the state of the body to the spinal cord.42 Some of these thin fibers do not differentiate noxious from non-noxious stimuli while others nociceptors respond only to painfully intense stimuli.41 Because the A-delta fiber is thinly sheathed in an electrically insulating material (myelin) it carries its signal faster (1030 m/s) than the unmyelinated C fiber (2.5 m/s).43 Pain evoked by the (faster) 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.44 Spinal cord fibers dedicated to carrying A-delta fiber pain signals and others dedicated to carrying C fiber pain signals up the spinal cord to the thalamus in the brain have been identified.45 Pain-related activity in the thalamus spreads to the insular cortex (thought to embody among other things the feeling that distinguishes pain from other homeostatic emotions such as itch and nausea) and anterior cingulate cortex (thought to embody among other things the motivational element of pain);42and pain that is distinctly located also activates the primary and secondary somatosensory cortices.46 Melzack and Casey's 1968 picture of the dimensions of pain is as influential today as ever firmly framing theory and guiding research in the functional neuroanatomy and psychology of pain. A. D. (Bud) Craig and Derek Denton include pain in a class of feelings they name respectively "homeostatic" or "primordial" emotions. These are feelings such as hunger thirst and fatigue evoked by internal body states communicated to the central nervous system by interoceptors which motivate behavior aimed at maintaining the internal milieu at its ideal state. Craig and Denton distinguish these feelings from the "classical emotions" such as love fear and anger which are elicited by environmental stimuli sensed through the nose eyes and ears.4748 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.349 It is an important part of animal life vital to healthy survival. People with congenital insensitivity to pain have reduced life expectancy.50 In his book The Greatest Show on Earth biologist Richard Dawkins grapples with the question of why pain has to be so very painful. He describes the alternative as a simple mental raising of a "red flag". To argue why that red flag might be insufficient Dawkins explains that drives must compete with each 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 (lack of food too much cold or serious injuries are felt as agony whereas minor damage is felt as mere discomfort). This resemblance will not be perfect however because natural selection can be a poor designer. The result is often glitches in animals including supernormal stimuli. Such glitches help explain pains which are not or at least no longer directly adaptive (e.g. perhaps some forms of toothache or injury to fingernails).51 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 psychologists argue that such pain is psychogenic enlisted as a protective distraction to keep dangerous emotions unconscious.52 Thresholds In pain science thresholds are measured by gradually increasing the intensity of a stimulus such as electric current or heat applied to the body. The pain perception threshold is the point at which the stimulus begins to hurt and the pain tolerance threshold is reached when the subject acts to stop the pain. Differences in pain perception and tolerance thresholds are associated with among other factors ethnicity genetics and sex. People of Mediterranean origin report as painful some radiant heat intensities that northern Europeans describe as nonpainful and Italian women tolerate less intense electric shock than Jewish or Native American women. Some individuals in all cultures have significantly higher than normal pain perception and tolerance thresholds. For instance patients who experience painless heart attacks have higher pain thresholds for electric shock muscle cramp and heat.53 Women have lower pain perception and tolerance thresholds than men and this sex difference appears to apply to all ages including newborn infants.54 Assessment See also: Pain scales and Pain ladder A person's self report is the most reliable measure of pain with health care professionals tending to underestimate severity.55 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".56 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 indicating which words best describe their pain.6 Multidimensional pain inventory The Multidimensional Pain Inventory (MPI) is a questionnaire designed to assess the psychosocial state of a person with chronic pain. Analysis of MPI results by Turk and Rudy (1988) found three classes of chronic pain patient: "(a) dysfunctional people who perceived the severity of their pain to be high reported that pain interfered with much of their lives reported a higher degree of psychological distress caused by pain and reported low levels of activity; (b) interpersonally distressed people with a common perception that significant others were not very supportive of their pain problems; and (c) adaptive copers patients who reported high levels of social support relatively low levels of pain and perceived interference and relatively high levels of activity."57 Combining the MPI characterization of the person with their IASP five-category pain profile is recommended for deriving the most useful case description.10 In nonverbal patients See also: Pain and dementia and Pain in babies When a person is non-verbal and cannot self report pain observation becomes critical and specific behaviors can be monitored as pain indicators. Behaviors such as facial grimacing and guarding 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 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 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. Infants feel pain but they lack the language needed to report it so communicate distress by crying. A non-verbal pain assessment should be conducted involving the parents who will notice changes in the infant not obvious to the health care provider. Pre-term babies are more sensitive to painful stimuli than full term babies.58 Other barriers to reporting An aging adult may not respond to pain in the way that a younger person would. Their ability to recognize pain may be blunted by illness or the use of multiple prescription drugs. Depression may also keep the older adult from reporting they are in pain. The older adult may also quit doing activities they love because it hurts too much. Decline in self-care activities (dressing grooming walking etc.) may also be indicators that the older adult is experiencing pain. The older adult may refrain from reporting pain because they are afraid they will have to have surgery or will be put on a drug they become addicted to. They may not want others to see them as weak or may feel there is something impolite or shameful in complaining about pain or they may feel the pain is deserved punishment for past transgressions.59 Cultural barriers can also keep a person from telling someone they are in pain. Religious beliefs may prevent the individual from seeking help. They may feel certain pain treatment is against their religion. 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 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 right away and get immediate relief.58 Gender can also be a factor in reporting pain. Gender differences are usually the result of social and cultural expectations with women expected to be emotional and show pain and men stoic keeping pain to themselves.58 As an aid to diagnosis 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 while chest pain described as tearing may indicate aortic dissection.6061 Management Main article: Pain management Inadequate treatment of pain is widespread throughout surgical wards intensive care units accident and emergency departments in general practice in the management of all forms of chronic pain including cancer pain and in end of life care.62 This neglect is extended to all ages from neonates to the frail elderly.63 African and Hispanic Americans are more likely than others to suffer needlessly in the hands of a physician;64 and women's pain is more likely to be undertreated than men's.65 The International Association for the Study of Pain 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.66 It is a specialty only in China and Australia at this time.67 Elsewhere pain medicine is a subspecialty under disciplines such as anesthesiology physiatry neurology palliative medicine and psychiatry.68 Medication Acute pain is usually managed with medications such as analgesics and anesthetics. Management of chronic pain however is much more difficult and may require the coordinated efforts of a pain management team which typically includes medical practitioners clinical psychologists physiotherapists occupational therapists and nurse practitioners.69 Sugar taken orally reduces the total crying time but not the duration of the first cry in newborns undergoing a painful procedure (a single lancing of the heel). It does not moderate the effect of pain on heart rate70 and a recent single study found that sugar did not significantly affect pain-related electrical activity in the brains of newborns one second after the heel lance procedure.7172 Sweet oral liquid moderately reduces the incidence and duration of crying caused by immunization injection in children between one and twelve months of age.73 Psychological Individuals with more social support experience less cancer pain take less pain medication report less labor pain and are less likely to use epidural anesthesia during childbirth or suffer from chest pain after coronary artery bypass surgery.74 Suggestion can significantly affect pain intensity. About 35% of people report marked relief after receiving a saline injection they believe to have been morphine. This "placebo" effect is more pronounced in people who are prone to anxiety so anxiety reduction may account for some of the effect but it does not account for all of the effect. Placebos are more effective in intense pain than mild pain; and they produce progressively weaker effects with repeated administration.75 It is possible for many chronic pain sufferers to become so absorbed in an activity or entertainment that the pain is no longer felt or is greatly diminished.76 Cognitive behavioral therapy (CBT) is effective in reducing the suffering associated with chronic pain in some patients but the reduction in suffering is quite modest and the CBT method employed seems to have no effect on outcome.77 Alternative medicine Pain is the most common reason for people to use complementary and alternative medicine.78 An analysis of the 13 highest quality studies of pain treatment with acupuncture published in January 2009 in the British Medical Journal concluded there is little difference in the effect of real sham and no acupuncture.79 There is interest in the relationship between vitamin D and pain but the evidence so far from controlled trials for such a relationship other than in osteomalacia is unconvincing.80 A 2007 review of 13 studies found evidence for the efficacy of hypnosis in the reduction of pain in some conditions though the number of patients enrolled in the studies was low bringing up issues of power to detect group differences and most lacked credible controls for placebo and/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."81 A 2003 meta-analysis of randomized clinical trials found that spinal manipulation was "more effective than sham therapy but was no more or less effective than general practitioner care analgesics physical therapy exercise or back school" in the treatment of low back pain.82 Epidemiology Pain is the main reason for visiting the emergency department in more than 50% of cases83 and is present in 30% of family practice visits.84 Several epidemiological studies from different countries have reported widely varying prevalence rates for chronic pain ranging from 12-80% of the population.85 It becomes more common as people approach death. A study of 4703 patients found that 26% had pain in the last two years of life increasing to 46% in the last month.86 A survey of 6636 children (0-18 years of age) found that of the 5424 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 ages12 and 14.87 Society and culture The okipa ceremony as witnessed by George Catlin circa 1835. The nature or meaning of physical pain has been diversely understood by religious or secular traditions from antiquity to modern times.8889 Physical pain is an important political topic in relation to various issues including pain management policy drug control animal rights or animal welfare torture pain compliance. In various contexts the deliberate infliction of pain in the form of corporal punishment is used as retribution for an offence or for the purpose of disciplining or reforming a wrongdoer or to deter attitudes or behaviour deemed unacceptable. In some cultures extreme practices such as mortification of the flesh or painful rites of passage are highly regarded. Philosophy of pain is a branch of philosophy of mind that deals essentially with physical pain. Identity theorists assert that the mental state of pain is completely identical with some physiological state. Functionalists consider that pain as a mental state is constituted solely by its functional role by its causal relations to other mental states sensory inputs and behavioral outputs. More generally it is often as a part of pain in the broad sense i.e. suffering that physical pain is dealt with in culture religion philosophy or society. In other animals Main article: Pain in animals Portrait of Ren Descartes by Jan Baptist Weenix 1647-1649 The most reliable method for assessing pain in most humans is by asking a question: a person may report pain that cannot be detected by any known physiological measure. However like infants (Latin infans meaning "unable to speak") non-human animals cannot answer questions about whether they feel pain; thus the defining criterion for pain in humans cannot be applied to them. Philosophers and scientists have responded to this difficulty in a variety of ways. Ren Descartes for example argued that animals lack consciousness and therefore do not experience pain and suffering in the way that humans do.90 Bernard Rollin of Colorado State University the principal author of two U.S. federal laws regulating pain relief for animals91 writes 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.92 In his interactions with scientists and other veterinarians he was regularly asked to "prove" that animals are conscious and to provide "scientifically acceptable" grounds for claiming that they feel pain.92 Carbone writes that the view that animals feel pain differently is now a minority view. Academic reviews of the topic are more equivocal noting that although the argument that animals have at least simple conscious thoughts and feelings has strong support93 some critics continue to question how reliably animal mental states can be determined.9094 The ability of invertebrate species of animals such as insects to feel pain and suffering is also unclear.9596 The presence of pain in an animal cannot be known for certain but it can be inferred through physical and behavioral reactions.97 Specialists currently believe that all vertebrates can feel pain and that certain invertebrates like the octopus might too.9899 As for other animals plants or other entities their ability to feel physical pain is at present a question beyond scientific reach since no mechanism is known by which they could have such a feeling. In particular there are no known nociceptors in groups such as plants fungi and most insects100 except for instance in fruit flies.101 In vertebrates endogenous opioids are neurochemicals that moderate pain by interacting with opiate receptors. Opioids and opiate receptors occur naturally in crustaceans and although at present no certain conclusion can be drawn102 their presence indicates that lobsters may be able to experience pain.102103 Opioids may mediate their pain in the same way as in vertebrates.103 Veterinary medicine uses for actual or potential animal pain the same analgesics and anesthetics as used in humans.104 Etymology First attested in English in 1297 the word pain comes from the Old French peine in turn from Latin poena "punishment penalty"105 (in L.L. also "torment hardship suffering") and that from Greek "" (poine) generally "price paid" "penalty" "punishment".106107 References "International Association for the Study of Pain Pain Definitions". 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Pain Stanford Encyclopedia of Philosophy Pain at the Open Directory Project v d eNeuroscience Affective neuroscience  Behavioral neurology  Behavioral genetics  Behavioral neuroscience  Braincomputer interface  Chronobiology  Clinical neurophysiology  Clinical neuroscience  Cognitive neuroscience  Computational neuroscience  Connectomics  Imaging genetics  Molecular cellular cognition  Movement disorder  Neural development  Neural engineering  Neural network (both artificial and biological)  Neural signal processing  Neural tissue regeneration  Neuroanatomy  Neuroanthropology  Neuroaesthetics  Neurobioengineering  Neurobiology  Neurobiotics  Neurocardiology  Neurochemistry  Neurochip  Neuroculture  Neurodegeneration  Neurodevelopmental disorders  Neurodiversity  Neuroeconomics  Neuroeducation  Neuroembryology  Neuroendocrinology  Neuroepidemiology  Neuroergonomics  Neuroethics  Neuroethology  Neuroevolution  Neurogastroenterology  Neurogenetics  Neuroimaging  Neuroimmunology  Neuroinformatics  Neurointensive care  Neurolaw  Neurolinguistics  Neurology  Neuromarketing  Neurometrics  Neuromodulation  Neuromonitoring  Neurooncology  Neuro-ophthalmology  Neuropathology  Neuropharmacology  Neurophilosophy  Neurophysics  Neurophysiology  Neuroplasticity  Neuropolitics  Neuroprosthetics  Neuropsychiatry  Neuro-psychoanalysis  Neuropsychology  Neuroradiology  Neurorehabilitation  Neurorobotics  Neurosociology  Neurosurgery  Neurotechnology  Neurotheology  Neurotransmitter  Neurovirology  Pain  Psychiatric genetics  Psychiatry  Psychology  Sensory neuroscience  Sleep  Social neuroscience  Systems neuroscience v d ePain and nociception Head and neck Headache  Neck  Odynophagia (swallowing)  Otalgia (ear)  Toothache Torso Abdomen  Back (Upper Lower)  Chest  Mastodynia (Breast)  Pelvic pain Musculoskeletal Arthralgia (joint)  Bone pain  Myalgia (muscle) Other conditions Delayed onset muscle soreness  Congenital insensitivity to pain  HSAN (Type I II congenital sensory neuropathy III familial dysautonomia IV congenital insensitivity to pain with anhidrosis V congenital insensitivity to pain with partial anhidrosis)  Neuralgia  Pain asymbolia  Pain disorder  Paroxysmal extreme pain disorder  Allodynia  Breakthrough pain  Chronic pain  Hyperalgesia  Hypoalgesia  Hyperpathia  Phantom pain  Referred pain Tests Cold pressor test  Dolorimeter Related concepts Anterolateral system  Pain management (Anesthesia Cordotomy)  Pain scale  Pain threshold  Pain tolerance  Posteromarginal nucleus  Substance P  Suffering  OPQRST   Philosophy of pain M: CNS anat(n/s/m/p/4/e/b/d/c/a/f/l/g)/phys/devp noco(m/d/e/h/v/s)/cong/tumr sysi/epon injr proc drug(N1A/2AB/C/3/4/7A/B/C/D) M: PNS anat(h r t c b l s)/phys/devp/prot/nttr/nttm/ntrp noco/auto/cong/tumr sysi/epon injr proc drug(N1B) v d eNervous system receptors: somatosensory system (GA 10.1059) Medial lemniscus Touch/mechanoreceptors: Lamellar/Pacinian corpuscles  vibration  Tactile/Meissner's corpuscles  light touch  Merkel's discs  pressure  Bulbous/Ruffini endings - stretch  Free nerve endings  pain  Hair cells  Baroreceptor Proprioception: Golgi organ  tension/length  Muscle spindle  velocity of change (Intrafusal muscle fiber  Nuclear chain fiber  Nuclear bag fiber) Spinothalamic tract Pain: Nociception and Nociceptors Temperature: Thermoreceptors M: PNS anat(h r t c b l s)/phys/devp/prot/nttr/nttm/ntrp noco/auto/cong/tumr sysi/epon injr proc drug(N1B) v d eNervous system: Sensory systems / senses (TA A15) Special senses Visual system/sight Auditory system/hearing Chemoreception (Olfactory system/smell  Gustatory system/taste) Touch Pain (Nociception)  Heat (Thermoception)  Balance (Equilibrioception)  Mechanoreception (Pressure vibration proprioception) Other Sensory receptor