Pain
Overview
 
Pain is an unpleasant sensation often caused by intense or damaging stimuli such as stubbing a toe, burning a finger, putting iodine on a cut, and bumping the "funny bone."

It motivates withdrawal from damaging or potentially damaging situations, protection of a damaged body part while it heals, and avoidance of similar experiences in the future. 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.

Pain is the most common reason for physician consultation in the United States.
Quotations

It never occurred to me to call 911 or my physician. […] As foolish as it may appear, you are, in a sense, a prisoner of the pain, which was intolerable. You're thinking, what could I do to relieve myself of it. If it becomes intense enough, you're perfectly willing to accept cardiac arrest as a possible way of getting rid of the pain.

Dr. Michael DeBakey|Michael DeBakey, heart surgery pioneer, on his own pain attack from a damaged aorta|aorta

But rejoice, inasmuch as you are partakers of Christ's sufferings; that, when his glory shall be revealed, you may be glad also with exceeding joy

The Bible,

Pain is temporary, glory is forever.

Anonymous, quoted as an anonymous proverb in Preaching Proverbs : Wisdom for the Pulpit‎ (1996) by Alyce M. McKenzie, p. 84

Encyclopedia
Pain is an unpleasant sensation often caused by intense or damaging stimuli such as stubbing a toe, burning a finger, putting iodine on a cut, and bumping the "funny bone."

It motivates withdrawal from damaging or potentially damaging situations, protection of a damaged body part while it heals, and avoidance of similar experiences in the future. 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.

Pain is the most common reason for physician consultation in the United States. It is a major symptom in many medical conditions, and can significantly interfere with a person's quality of life
Quality of life
The term quality of life is used to evaluate the general well-being of individuals and societies. The term is used in a wide range of contexts, including the fields of international development, healthcare, and politics. Quality of life should not be confused with the concept of standard of...

 and general functioning. Psychological factors such as social support
Social support
Social support can be defined and measured in many ways. It can loosely be defined as feeling that one is cared for by and has assistance available from other people and that one is part of a supportive social network...

, hypnotic suggestion, excitement in sport or war and distraction can significantly modulate pain's intensity or unpleasantness.

Classification

In 1994, responding to the need for a more useful system for describing chronic pain, the International Association for the Study of Pain
International Association for the Study of Pain
The International Association for the Study of Pain is an international professional organization promoting research, education and policies for the knowledge and management of pain. The IASP was founded in 1973, following the Seattle-Issaquah conference, under the leadership of John Bonica. Its...

 (IASP) classified pain according to specific characteristics: (1) region of the body involved (e.g., abdomen, lower limbs), (2) system whose dysfunction may be causing the pain (e.g., nervous, gastrointestinal), (3) duration and pattern of occurrence, (4) intensity and time since onset, and (5) etiology
Etiology
Etiology is the study of causation, or origination. The word is derived from the Greek , aitiologia, "giving a reason for" ....

. This system has been criticized by Woolf
Clifford J. Woolf
Clifford J. Woolf is professor of neurology and neurobiology at Harvard Medical School and director of the F.M. Kirby Neurobiology Center at Children’s Hospital Boston.-Career:...

 and others as inadequate for guiding research and treatment, and an additional category based on neurochemical mechanism has been proposed.

Duration

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
Rheumatoid arthritis is a chronic, systemic inflammatory disorder that may affect many tissues and organs, but principally attacks synovial joints. The process produces an inflammatory response of the synovium secondary to hyperplasia of synovial cells, excess synovial fluid, and the development...

, peripheral neuropathy
Peripheral neuropathy
Peripheral neuropathy is the term for damage to nerves of the peripheral nervous system, which may be caused either by diseases of or trauma to the nerve or the side-effects of systemic illness....

, cancer and idiopathic
Idiopathic
Idiopathic is an adjective used primarily in medicine meaning arising spontaneously or from an obscure or unknown cause. From Greek ἴδιος, idios + πάθος, pathos , it means approximately "a disease of its own kind". It is technically a term from nosology, the classification of disease...

 pain, may persist for years. Pain that lasts a long time is called chronic
Chronic pain
Chronic pain has several different meanings in medicine. 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 initiation of pain, though some theorists and...

, and pain that resolves quickly is called acute
Acute (medicine)
In medicine, an acute disease is a disease with either or both of:# a rapid onset, as in acute infection# a short course ....

. 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 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 durations is "pain that extends beyond the expected period of healing." Chronic pain may be classified as cancer pain
Cancer pain
Pain is a symptom frequently associated with cancer. Cancer can cause pain by irritating or damaging nerves, by stimulating nociceptors , or by releasing chemicals that make nociceptors respond to normally non-painful stimuli. Cancer pain may be caused by the tumor itself or by medical...

 or benign.

Nociceptive

Nociceptive pain is caused by stimulation of peripheral nerve fibers
Peripheral nervous system
The peripheral nervous system consists of the nerves and ganglia outside of the brain and spinal cord. The main function of the PNS is to connect the central nervous system to the limbs and organs. Unlike the CNS, the PNS is not protected by the bone of spine and skull, or by the blood–brain...

 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 structures
Viscus
In anatomy, a viscus is an internal organ, and viscera is the plural form. The viscera, when removed from a butchered animal, are known collectively as offal...

 are highly sensitive to stretch, ischemia
Ischemia
In medicine, ischemia is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. It may also be spelled ischaemia or ischæmia...

 and inflammation
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...

, but relatively insensitive to other stimuli that normally evoke pain in other structures, such as burning and cutting. Visceral pain is diffuse, difficult to locate and often referred
Referred pain
Referred pain is pain perceived at a location other than the site of the painful stimulus. An example is the case of ischemia brought on by a myocardial infarction , where pain is often felt in the neck, shoulders, and back rather than in the chest, the site of the injury...

 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, fasciae and muscles, and is dull, aching, poorly-localized pain. Examples include sprain
Sprain
A sprain is an injury in a joint, caused by the ligament being stretched beyond its capacity. A muscular tear caused in the same manner is referred to as a strain. In cases where either ligament or muscle tissue is torn, immobilization and surgical repair may be necessary...

s and broken bones. Superficial 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) burns.

Neuropathic

Neuropathic pain is caused by damage or disease affecting any part of the nervous system involved in bodily feelings (the somatosensory system
Somatosensory system
The somatosensory system is a diverse sensory system composed of the receptors and processing centres to produce the sensory modalities such as touch, temperature, proprioception , and nociception . The sensory receptors cover the skin and epithelia, skeletal muscles, bones and joints, internal...

). Peripheral neuropathic pain is often described as “burning,” “tingling,” “electrical,” “stabbing,” or “pins and needles.” Bumping the "funny bone" elicits acute peripheral neuropathic pain.

Phantom

Phantom pain
Phantom pain
Phantom pain sensations are described as perceptions 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 limb deficiency . However, phantom limb sensations can also occur following...

 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%. One study found that eight days after amputation, 72 percent of patients had phantom limb pain, and six months later, 65 percent reported it. 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.

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.

Work by Vilayanur S. Ramachandran
Vilayanur S. Ramachandran
Vilayanur Subramanian "Rama" Ramachandran, born 1951, is a neuroscientist known for his work in the fields of behavioral neurology and visual psychophysics...

 using mirror box
Mirror box
A mirror box is a box with two mirrors in the center , invented by Vilayanur S. Ramachandran to help alleviate phantom limb pain, in which patients feel they still have a limb after having it amputated....

 therapy allows for illusions of movement and touch in a phantom limb which in turn cause a reduction in pain.

Paraplegia
Paraplegia
Paraplegia is an impairment in motor or sensory function of the lower extremities. The word comes from Ionic Greek: παραπληγίη "half-striking". It is usually the result of spinal cord injury or a congenital condition such as spina bifida that affects the neural elements of the spinal canal...

, the loss of sensation and voluntary motor control after serious spinal cord damage, may be accompanied by girdle pain
Girdle pain
Girdle pain is pain that encircles the body like a belt. It accompanies some forms of spinal cord disease....

 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.

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.

People with long term pain frequently display psychological disturbance, with elevated scores on the Minnesota Multiphasic Personality Inventory
Minnesota Multiphasic Personality Inventory
The Minnesota Multiphasic Personality Inventory is one of the most frequently used personality tests in mental health. The test is used by trained professionals to assist in identifying personality structure and psychopathology....

 scales of hysteria
Hysteria
Hysteria, in its colloquial use, describes unmanageable emotional excesses. People who are "hysterical" often lose self-control due to an overwhelming fear that may be caused by multiple events in one's past that involved some sort of severe conflict; the fear can be centered on a body part, or,...

, depression
Depression (mood)
Depression is a state of low mood and aversion to activity that can affect a person's thoughts, behaviour, feelings and physical well-being. Depressed people may feel sad, anxious, empty, hopeless, helpless, worthless, guilty, irritable, or restless...

 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
Neuroticism
Neuroticism is a fundamental personality trait in the study of psychology. It is an enduring tendency to experience negative emotional states. Individuals who score high on neuroticism are more likely than the average to experience such feelings as anxiety, anger, guilt, and depressed mood...

. When long term pain is relieved by therapeutic intervention, scores on the neurotic triad and anxiety
Anxiety
Anxiety is a psychological and physiological state characterized by somatic, emotional, cognitive, and behavioral components. The root meaning of the word anxiety is 'to vex or trouble'; in either presence or absence of psychological stress, anxiety can create feelings of fear, worry, uneasiness,...

 fall, often to normal levels. Self-esteem, often low in chronic pain patients, also shows improvement once pain has resolved.

Breakthrough pain

Breakthrough pain is pain that comes on suddenly for short periods of time and is not alleviated by the patients' normal pain suppression management. It is common in cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...

 patients who commonly have a background level of pain controlled by medication
Medication
A pharmaceutical drug, also referred to as medicine, medication or medicament, can be loosely defined as any chemical substance intended for use in the medical diagnosis, cure, treatment, or prevention of disease.- Classification :...

s, but the pain periodically "breaks through" the medication. The characteristics of breakthrough cancer pain
Cancer pain
Pain is a symptom frequently associated with cancer. Cancer can cause pain by irritating or damaging nerves, by stimulating nociceptors , or by releasing chemicals that make nociceptors respond to normally non-painful stimuli. Cancer pain may be caused by the tumor itself or by medical...

 vary from person to person and according to the cause.

Incident pain

Incident pain is pain that arises as a result of activity, such as movement of an arthritic joint, stretching a wound, etc.

Pain asymbolia and insensitivity

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.

Although unpleasantness is an essential part of the IASP
International Association for the Study of Pain
The International Association for the Study of Pain is an international professional organization promoting research, education and policies for the knowledge and management of pain. The IASP was founded in 1973, following the Seattle-Issaquah conference, under the leadership of John Bonica. Its...

 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. 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. This is usually the result of acquired
Acquired disorder
An acquired disorder is a medical condition which develops post-fetally; in contrast with a congenital disorder, which is present at birth. A congenital disorder may be antecedent to an acquired disorder ....

 damage to the nerves, such as spinal cord injury
Spinal cord injury
A spinal cord injury refers to any injury to the spinal cord that is caused by trauma instead of disease. Depending on where the spinal cord and nerve roots are damaged, the symptoms can vary widely, from pain to paralysis to incontinence...

, diabetes mellitus
Diabetes mellitus
Diabetes mellitus, often simply referred to as diabetes, is a group of metabolic diseases in which a person has high blood sugar, either because the body does not produce enough insulin, or because cells do not respond to the insulin that is produced...

 (diabetic neuropathy
Diabetic neuropathy
Diabetic neuropathies are neuropathic disorders that are associated with diabetes mellitus. These conditions are thought to result from diabetic microvascular injury involving small blood vessels that supply nerves in addition to macrovascular conditions that can culminate in diabetic neuropathy...

), or leprosy
Leprosy
Leprosy or Hansen's disease is a chronic disease caused by the bacteria Mycobacterium leprae and Mycobacterium lepromatosis. Named after physician Gerhard Armauer Hansen, leprosy is primarily a granulomatous disease of the peripheral nerves and mucosa of the upper respiratory tract; skin lesions...

 in countries where this is prevalent. 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.

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
Congenital insensitivity to pain , also known as congenital analgesia, is one or more rare conditions where a person cannot feel physical pain...

". 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
Hereditary sensory and autonomic neuropathy
Hereditary sensory and autonomic neuropathy or hereditary sensory neuropathy is a condition used to describe any of the types of this disease which inhibit sensation.They are less common than Charcot-Marie-Tooth disease....

 (which includes familial dysautonomia
Familial dysautonomia
Familial dysautonomia is a disorder of the autonomic nervous system which affects the development and survival of sensory, sympathetic and some parasympathetic neurons in the autonomic and sensory nervous system resulting in variable symptoms including: insensitivity to pain, inability to produce...

 and congenital insensitivity to pain with anhidrosis
Congenital insensitivity to pain with anhidrosis
Congenital insensitivity to pain with anhidrosis is an extremely rare inherited disorder of the nervous system which prevents the sensation of pain, heat, cold, or any real nerve-related sensations ; however, patients can still feel pressure. CIPA is the fourth type of hereditary sensory and...

). These conditions feature decreased sensitivity to pain together with other neurological abnormalties, particularly of the autonomic nervous system
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...

. 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.

Effect on functioning

Experimental subjects challenged by acute pain and patients in chronic pain experience impairments in attention control, working memory
Working memory
Working memory has been defined as the system which actively holds information in the mind to do verbal and nonverbal tasks such as reasoning and comprehension, and to make it available for further information processing...

, mental flexibility
Cognitive flexibility
Cognitive flexibility is the term used to describe one of the executive functions; a function which is an important component of human behavior; the ability to switch behavioral response according to the context of the situation...

, problem solving, and information processing speed. Acute and chronic pain are also associated with increased depression
Depression (mood)
Depression is a state of low mood and aversion to activity that can affect a person's thoughts, behaviour, feelings and physical well-being. Depressed people may feel sad, anxious, empty, hopeless, helpless, worthless, guilty, irritable, or restless...

, anxiety, fear, and anger.

Theory

Aristotle
Aristotle
Aristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...

 did not include a sense of pain when he enumerated the five senses; he, like Plato before him, saw pain and pleasure not as sensations but as emotions ("passions of the soul").

Specificity theory

The specificity theory, which states that pain is "a specific sensation, with its own sensory apparatus independent of touch and other senses," emerged in the nineteenth century, but had been prefigured in the 11th century by Avicenna
Avicenna
Abū ʿAlī al-Ḥusayn ibn ʿAbd Allāh ibn Sīnā , commonly known as Ibn Sīnā or by his Latinized name Avicenna, was a Persian polymath, who wrote almost 450 treatises on a wide range of subjects, of which around 240 have survived...

, who thought there are a number of feeling senses including touch, pain and titillation, and René Descartes
René Descartes
René Descartes ; was a French philosopher and writer who spent most of his adult life in the Dutch Republic. He has been dubbed the 'Father of Modern Philosophy', and much subsequent Western philosophy is a response to his writings, which are studied closely to this day...

 who traced a pain pathway in his 1664 Treatise of Man.

Scottish anatomist Charles Bell
Charles Bell
Sir Charles Bell was a Scottish surgeon, anatomist, neurologist and philosophical theologian.His three older brothers included John Bell , also a noted surgeon and writer; and the advocate George Joseph Bell .-Life:...

 proposed in 1811 that there exist different kinds of sensory receptor
Sensory receptor
In a sensory system, a sensory receptor is a sensory nerve ending that responds to a stimulus in the internal or external environment of an organism...

, each adapted to respond to only one stimulus type. In 1839 Johannes Müller
Johannes Peter Müller
Johannes Peter Müller , was a German physiologist, comparative anatomist, and ichthyologist not only known for his discoveries but also for his ability to synthesize knowledge.-Early years and education:...

, having established that a single stimulus type (e.g., a blow, electric current) can produce different sensations depending on the type of nerve stimulated, hypothesized that there is a specific energy
Law of specific nerve energies
The law of specific nerve energies, first proposed by Johannes Peter Müller in 1835, is that the nature of perception is defined by the pathway over which the sensory information is carried. Hence, the origin of the sensation is not important...

, peculiar to each of five nerve types that serve Aristotle's five senses, and that it is the type of energy that determines the type of sensation each nerve produces. He considered feelings such as itching, pleasure, pain, heat, cold and touch to be varieties of the single sense he called "feeling and touch." Müller's doctrine killed off the ancient idea that nerves carry actual properties or incorporeal copies of the perceived object, marking the beginning of the modern era of sensory psychology, and prompted others to ask, do the nerves that evoke the different qualities of touch and feeling have specific characteristics?

Filippo Pacini
Filippo Pacini
Filippo Pacini was an Italian anatomist, posthumously famous for isolating the cholera bacillus Vibrio cholerae in 1854, well before Robert Koch's more widely accepted discoveries thirty years later....

 had isolated receptors in the nervous system which detect pressure and vibrations in 1831. Georg Meissner
Georg Meissner
Georg Meissner was a German anatomist and physiologist born in Hannover.He studied medicine at the University of Göttingen, where he worked closely with Rudolf Wagner . In 1851 he accompanied Wagner and Theodor Billroth on an expedition to Trieste, where he performed scientific studies of torpedo...

 and Rudolf Wagner
Rudolf Wagner
Rudolf Wagner was a German anatomist and physiologist and the co-discoverer of the germinal vesicle. He made important investigations on ganglia, nerve-endings, and the sympathetic nerves.-Life:...

 described receptors sensitive to light touch in 1852; and Wilhelm Krause
Wilhelm Krause
Wilhelm Krause was a German anatomist born in Hanover. In 1854 he earned his medical doctorate, and later became an associate professor at the University of Göttingen. In 1892 he was appointed head of the Anatomical Institute Laboratory in Berlin...

 found a receptor that responds to gentle vibration in 1860. Moritz Schiff
Moritz Schiff
Moritz Schiff was a German physiologist.While working in Bern, he showed that removing the thyroid gland from dogs was fatal, and later showed that animal thyroid extract could prevent the death...

 was first to definitively formulate the specificity theory of pain when, in 1858, he demonstrated that touch and pain sensations traveled to the brain along separate spinal cord pathways. In 1882 Magnus Blix
Magnus Blix
Magnus Gustaf Blix was a Swedish physiologist who was a professor at the universities of Uppsala and Lund....

 reported that specific spots on the skin elicit sensations of either cold or heat when stimulated, and proposed that "the different sensations of cool and warm are caused by stimulation of different, specific receptors in the skin." Max von Frey
Maximilian von Frey
Maximilian Ruppert Franz von Frey was an Austrian-German physiologist who was born in Salzburg. He received his doctorate from the University of Leipzig in 1877, and subsequently worked at Carl Ludwig's Physiological Institute in Leipzig...

 found and described these heat and cold receptors and, in 1896, reported finding "pain spots" on the skin of human subjects. Von Frey proposed there are low threshold cutaneous spots that elicit the feeling of touch, and high threshold spots that elicit pain, and that pain is a distinct cutaneous sensation, independent of touch, heat and cold, and associated with free nerve ending
Free nerve ending
A free nerve ending is an unspecialized, afferent nerve ending, meaning it brings information from the body's periphery toward the brain. They function as cutaneous receptors and are essentially used by vertebrates to detect pain.-Structure:...

s.

Intensive theory

In the first volume of his 1794 Zoonomia; or the Laws of Organic Life
Zoönomia
Zoonomia; or the Laws of Organic Life is a two-volume medical work by Erasmus Darwin dealing with pathology, anatomy, psychology, and the functioning of the body...

, Erasmus Darwin
Erasmus Darwin
Erasmus Darwin was an English physician who turned down George III's invitation to be a physician to the King. One of the key thinkers of the Midlands Enlightenment, he was also a natural philosopher, physiologist, slave trade abolitionist,inventor and poet...

 supported the idea advanced in Plato's
Plato
Plato , was a Classical Greek philosopher, mathematician, student of Socrates, writer of philosophical dialogues, and founder of the Academy in Athens, the first institution of higher learning in the Western world. Along with his mentor, Socrates, and his student, Aristotle, Plato helped to lay the...

 Timaeus
Timaeus
Timaeus is a Greek name, meaning "Honour". It may refer to:*Timaeus , a Socratic dialogue by Plato*Timaeus of Locri, the 5th-century Pythagorean philosopher, appearing in Plato's dialogue...

, that pain is not a unique sensory modality, but an emotional state produced by stronger than normal stimuli such as intense light, pressure or temperature. Wilhelm Erb
Wilhelm Heinrich Erb
Wilhelm Heinrich Erb was a German neurologist who was a native of Winnweiler, Rhineland-Palatinate.- Academic career :...

, in 1874, also argued that pain can be generated by any sensory stimulus, provided it is intense enough, and his formulation of the hypothesis became known as the intensive theory.

Alfred Goldscheider
Alfred Goldscheider
Johannes Karl Eugen Alfred Goldscheider was a German neurologist who was born in Sommerfeld ....

 (1884) confirmed the existence of distinct heat and cold sensors, by evoking heat and cold sensations using a fine needle to penetrate to and electrically stimulate different nerve trunks, bypassing their receptors. Though he failed to find specific pain sensitive spots on the skin, Goldscheider concluded in 1895 that the available evidence supported pain specificity, and held the view until a series of experiments were conducted in 1889 by Bernhard Naunyn
Bernhard Naunyn
Bernhard Naunyn was German pathologist who was born in Berlin. After receiving his degree at the University of Berlin in 1863, he became an assistant to pathologist Friedrich Theodor von Frerichs...

. Naunyn had rapidly (60–600 times/second) prodded the skin of tabes dorsalis
Tabes dorsalis
Tabes dorsalis is a slow degeneration of the sensory neurons that carry afferent information. The degenerating nerves are in the dorsal columns of the spinal cord and carry information that help maintain a person's sense of position , vibration, and discriminative touch.-Cause:Tabes dorsalis is...

 patients, below their touch threshold (e.g., with a hair), and in 6–20 seconds produced unbearable pain. He obtained similar results using other stimuli including electricity to produce rapid, sub-threshold stimulation, and concluded pain is the product of summation. In 1894 Goldscheider extended the intensive theory, proposing that each tactile nerve fiber can evoke three distinct qualities of sensation – tickle, touch and pain – the quality depending on the intensity of stimulation; and extended Naunyn's summation idea, proposing that, over time, activity from peripheral fibers may accumulate in the dorsal horn of the spinal cord, and "spill over" from the peripheral fiber to a pain-signalling spinal cord fiber once a threshold of activity has been crossed. The British psychologist, Edward Titchener
Edward B. Titchener
Edward Bradford Titchener, D.Sc., Ph.D., LL.D., Litt.D. was a British psychologist who studied under Wilhelm Wundt for several years. Titchener is best known for creating his version of psychology that described the structure of the mind; structuralism...

, pronounced in his 1896 textbook, "excessive stimulation of any sense organ or direct injury to any sensory nerve occasions the common sensation of pain."

Competing theories

By the mid-1890s, specificity was mainly backed by physiologists (prominently by von Frey) and clinicians; and the intensive theory received most support from psychologists. But after Henry Head
Henry Head
Sir Henry Head, FRS was an English neurologist who conducted pioneering work into the somatosensory system and sensory nerves. Much of this work was conducted on himself, in collaboration with the psychiatrist W. H. R. Rivers, by severing and reconnecting sensory nerves and mapping how sensation...

 in England published a series of clinical observations between 1893 and 1896, and von Frey's experiments between 1894 and 1897, 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, with Titchener in 1898 now placing "the sensation of pain" alongside that of pressure, heat and cold. Though the intensive theory no longer featured prominently in textbooks, Goldscheider's elaboration of it nevertheless stood its ground in opposition to von Frey's specificity at the frontiers of research, and was supported by some influential theorists well into the mid-twentieth century.

William Kenneth Livingston advanced a summation theory in 1943, proposing that high intensity signals, arriving at the spinal cord from damage to nerve or tissue, set up a reverberating, self-exciting loop of activity in a pool of interneurons, and once a threshold of activity is crossed, these interneurons then activate "transmission" cells which carry the signal to the brain's pain mechanism; that the reverberating interneuron activity also spreads to other spinal cord cells that trigger a sympathetic nervous system and somatic motor system response; and these responses, as well as fear and other emotions elicited by pain, feed into and perpetuate the reverberating interneuron activity. A similar proposal was made by RW Gerard in 1951, who proposed also that intense peripheral nerve signalling may cause temporary failure of inhibition in spinal cord neurons, allowing them to fire as synchronized pools, with signal volleys strong enough to activate the pain mechanism.

Pattern theory

Building on John Paul Nafe's 1934 suggestion that different cutaneous qualities are the product of different temporal and spatial patterns of stimulation, and ignoring a large body of strong evidence for receptor fiber specificity, DC Sinclair and G Weddell's 1955 "peripheral pattern theory" 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. In 1953, Willem Noordenbos had 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.

Gate control theory

Ronald Melzack
Ronald Melzack
Ronald Melzack, is a Canadian psychologist.After studying for his Ph.D. in 1954 with D. O. Hebb at McGill University in Montreal, he began to work with patients who suffered from "phantom limb" pain — people who feel pain in an arm or leg that has been removed...

 and Patrick Wall
Patrick David Wall
Patrick David "Pat" Wall was a leading British neuroscientist described as 'the world's leading expert on pain' and best known for the Gate control theory of pain.-Early life and academia:...

 introduced their "gate control" theory of pain in the 1965 Science
Science (journal)
Science is the academic journal of the American Association for the Advancement of Science and is one of the world's top scientific journals....

 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: transmission cells that carry the pain signal up to the brain, and inhibitory interneurons that impede transmission cell activity. Activity in both thin and large diameter fibers excites transmission cells. Thin fiber activity impedes the inhibitory cells (tending to allow the transmission cell to fire) and large diameter fiber activity excites the inhibitory cells (tending to inhibit transmission cell activity). So, the more large fiber (touch, pressure, vibration) activity relative to thin fiber activity at the inhibitory cell, the less pain is felt. The authors had drawn a neural "circuit diagram"
Neural network
The term neural network was traditionally used to refer to a network or circuit of biological neurons. The modern usage of the term often refers to artificial neural networks, which are composed of artificial neurons or nodes...

 to explain why we rub a smack. 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). The theory offered a physiological explanation for the previously observed effect of psychology on pain perception.

Three dimensions of pain

In 1968 Ronald Melzack and Kenneth Casey
Kenneth L. Casey
Kenneth Lyman Casey is professor emeritus of neurology and professor emeritus of molecular and integrative physiology at the University of Michigan, and consultant in neurology at the Ann Arbor Veteran’s Affairs Medical Center.-Career:...

 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). 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 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

Wilhelm Erb's (1874) "intensive" theory, that a pain signal can be generated by intense enough stimulation of any sensory receptor, has been soundly disproved. The thin (A-delta
A delta fiber
A delta fibers, or Aδ fibers, are a type of sensory fiber.They are associated with cold and pressure, and as nociceptors stimulation of them is interpreted as fast/first pain information....

 and C) peripheral sensory fibers carry information regarding the state of the body to the spinal cord. Some of these thin fibers do not differentiate noxious from non-noxious stimuli, while others, nociceptor
Nociceptor
A nociceptor is a sensory receptor that responds to potentially damaging stimuli by sending nerve signals to the spinal cord and brain. This process, called nociception, usually causes the perception of pain.-History:...

s, respond only to painfully intense stimuli.

Because the A-delta fiber is thicker than the C fiber and is thinly sheathed in an electrically insulating material (myelin
Myelin
Myelin is a dielectric material that forms a layer, the myelin sheath, usually around only the axon of a neuron. It is essential for the proper functioning of the nervous system. Myelin is an outgrowth of a type of glial cell. The production of the myelin sheath is called myelination...

), it carries its signal faster (5–30 m/s) than the unmyelinated C fiber (0.5–2 m/s). 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.

Spinal cord fibers dedicated to carrying A-delta fiber pain signals, and others that carry both A-delta and C fiber pain signals up the spinal cord to the thalamus
Thalamus
The thalamus is a midline paired symmetrical structure within the brains of vertebrates, including humans. It is situated between the cerebral cortex and midbrain, both in terms of location and neurological connections...

 in the brain have been identified. Other spinal cord fibers, known as wide dynamic range neuron
Wide dynamic range neuron
The wide dynamic range or "convergent" neuron is the most populous type of those neurons whose cell bodies are located in the dorsal horn of the spinal cord. WDR neurons are responsive to all sensory modalities and a broad range of intensity of stimulation from peripheral nerves...

s, respond to A-delta and C fibers, but also to the large A-beta fibers that carry touch, pressure and vibration signals. Pain-related activity in the thalamus spreads to the insular cortex
Insular cortex
In each hemisphere of the mammalian brain the insular cortex is a portion of the cerebral cortex folded deep within the lateral sulcus between the temporal lobe and the frontal lobe. The cortical area overlying it towards the lateral surface of the brain is the operculum...

 (thought to embody, among other things, the feeling that distinguishes pain from other homeostatic emotions such as itch and nausea) and anterior cingulate cortex
Anterior cingulate cortex
The anterior cingulate cortex is the frontal part of the cingulate cortex, that resembles a "collar" form around the corpus callosum, the fibrous bundle that relays neural signals between the right and left cerebral hemispheres of the brain...

 (thought to embody, among other things, the motivational element of pain); and pain that is distinctly located also activates the primary and secondary
Secondary somatosensory cortex
The human secondary somatosensory cortex is a region of cerebral cortex lying mostly on the parietal operculum.Region S2 was first described by Adrian in 1940, who found that feeling in cats' feet was not only represented in the previously described primary somatosensory cortex but also in a...

 somatosensory cortices. 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
Derek Denton
Emeritus Professor Derek Ashworth Denton AC is an Australian scientist renowned for his research exploring the nature of consciousness in animals....

 include pain in a class of feelings they name, respectively, "homeostatic
Human homeostasis
Human homeostasis is derived from the Greek, homeo or "same", and stasis or "stable" and means remaining stable or remaining the same.The human body manages a multitude of highly complex interactions to maintain balance or return systems to functioning within a normal range...

" 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.

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
Congenital insensitivity to pain , also known as congenital analgesia, is one or more rare conditions where a person cannot feel physical pain...

 have reduced life expectancy
Life expectancy
Life expectancy is the expected number of years of life remaining at a given age. It is denoted by ex, which means the average number of subsequent years of life for someone now aged x, according to a particular mortality experience...

.

In his book, The Greatest Show on Earth
The Greatest Show on Earth
The Greatest Show on Earth is a 1952 drama film set in the Ringling Bros. and Barnum & Bailey Circus. The film was produced, directed, and narrated by Cecil B. DeMille, and won the Academy Award for Best Picture...

, biologist Richard Dawkins
Richard Dawkins
Clinton Richard Dawkins, FRS, FRSL , known as Richard Dawkins, is a British ethologist, evolutionary biologist and author...

 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
Argument from poor design
The dysteleological argument or argument from poor design is an argument against the existence of God, specifically against the existence of a creator God...

. 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
Toothache
A toothache, also known as odontalgia or, less frequently, as odontalgy, is an aching pain in or around a tooth.-Causes:* Dental etiology, In most cases toothaches are caused by problems in the tooth or jaw, such as** Dental caries...

, or injury to fingernails).

Idiopathic
Idiopathic
Idiopathic is an adjective used primarily in medicine meaning arising spontaneously or from an obscure or unknown cause. From Greek ἴδιος, idios + πάθος, pathos , it means approximately "a disease of its own kind". It is technically a term from nosology, the classification of disease...

 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.

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
Threshold of pain
The threshold of pain is the point at which pain begins to be felt. It is an entirely subjective phenomenon. The intensity at which a stimulus begins to evoke pain is the threshold intensity. So, if a hotplate on a person's skin begins to hurt at 42°C , then that is the pain threshold temperature...

 is the point at which the stimulus begins to hurt, and the pain tolerance threshold
Pain tolerance
Pain tolerance is the maximum level of pain that a person is able to tolerate. Pain tolerance is distinct from pain threshold .-Factors affecting pain tolerance:...

 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. Women have lower pain perception and tolerance thresholds than men, and this sex difference appears to apply to all ages, including newborn infants.

Assessment



A person's self report is the most reliable measure of pain, with health care professionals tending to underestimate 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
Margo McCaffery
Margo McCaffery is a registered nurse and pioneer of the field of pain management nursing. McCaffery's oft-quoted definition of pain as "whatever the experiencing person says it is, existing whenever and wherever the person say it does" has become the prevailing conceptualisation of pain for...

 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
McGill Pain Questionnaire
The McGill Pain Questionnaire, also known as McGill pain index, is a scale of rating pain developed at McGill University by Melzack and Torgerson in 1971....

 indicating which words best describe their pain.

Multidimensional pain inventory

The Multidimensional Pain Inventory (MPI) is a questionnaire designed to assess the psychosocial
Psychosocial
For a concept to be psychosocial means it relates to one's psychological development in, and interaction with, a social environment. The individual needs not be fully aware of this relationship with his or her environment. It was first commonly used by psychologist Erik Erikson in his stages of...

 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." Combining the MPI characterization of the person with their IASP five-category pain profile is recommended for deriving the most useful case description.

In nonverbal patients

When a person is non-verbal
Nonverbal communication
Nonverbal communication is usually understood as the process of communication through sending and receiving wordless messages. Messages can be communicated through gestures and touch , by body language or posture, by facial expression and eye contact...

 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
Social behavior
In physics, physiology and sociology, social behavior is behavior directed towards society, or taking place between, members of the same species. Behavior such as predation which involves members of different species is not social...

 and possibly experience a decreased appetite
Anorexia (symptom)
Anorexia is the decreased sensation of 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
Range of motion , is the distance that a movable object may normally travel while properly attached to another object. It is also called range of travel, particularly when talking about mechanical devices and in mechanical engineering fields...

 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
Pain in babies
Pain in babies, and whether babies feel pain, has been the subject of debate within the medical profession for centuries. Prior to the late nineteenth century it was generally considered that babies hurt more easily than adults...

 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.

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 drug
Prescription drug
A prescription medication is a licensed medicine that is regulated by legislation to require a medical prescription before it can be obtained. The term is used to distinguish it from over-the-counter drugs which can be obtained without a prescription...

s. 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.

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. Gender can also be a factor in reporting pain. Gender differences
Gender differences
A sex difference is a distinction of biological and/or physiological characteristics associated with either males or females of a species. These can be of several types, including direct and indirect. Direct being the direct result of differences prescribed by the Y-chromosome, and indirect being...

 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.

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
Myocardial infarction
Myocardial infarction or acute myocardial infarction , commonly known as a heart attack, results from the interruption of blood supply to a part of the heart, causing heart cells to die...

, while chest pain described as tearing may indicate aortic dissection
Aortic dissection
Aortic dissection occurs when a tear in the inner wall of the aorta causes blood to flow between the layers of the wall of the aorta and force the layers apart. The dissection typically extends anterograde, but can extend retrograde from the site of the intimal tear. Aortic dissection is a medical...

.

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. This neglect is extended to all ages, from neonates to the frail elderly. African and Hispanic Americans are more likely than others to suffer needlessly in the hands of a physician; and women's pain is more likely to be undertreated than men's.

The International Association for the Study of Pain
International Association for the Study of Pain
The International Association for the Study of Pain is an international professional organization promoting research, education and policies for the knowledge and management of pain. The IASP was founded in 1973, following the Seattle-Issaquah conference, under the leadership of John Bonica. Its...

 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. 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
Neurology
Neurology is a medical specialty dealing with disorders of the nervous system. Specifically, it deals with the diagnosis and treatment of all categories of disease involving the central, peripheral, and autonomic nervous systems, including their coverings, blood vessels, and all effector tissue,...

, palliative medicine and psychiatry
Psychiatry
Psychiatry is the medical specialty devoted to the study and treatment of mental disorders. These mental disorders include various affective, behavioural, cognitive and perceptual abnormalities...

.

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
Pain management
Pain management is a branch of medicine employing an interdisciplinary approach for easing the suffering and improving the quality of life of those living with pain. The typical pain management team includes medical practitioners, clinical psychologists, physiotherapists, occupational therapists,...

 team, which typically includes medical practitioners, clinical psychologists, physiotherapists, occupational therapist
Occupational therapist
An occupational therapist is trained in the practice of occupational therapy. The role of an occupational therapist is to work with a client to help them achieve a fulfilled and satisfied state in life through the use of "purposeful activity or interventions designed to achieve functional...

s, and nurse practitioner
Nurse practitioner
A Nurse Practitioner is an Advanced practice registered nurse who has completed graduate-level education . Additional APRN roles include the Certified Registered Nurse Anesthetist s, CNMs, and CNSs...

s.
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 rate and a recent single study found that sugar did not significantly affect pain-related electrical activity
EEG
EEG commonly refers to electroencephalography, a measurement of the electrical activity of the brain.EEG may also refer to:* Emperor Entertainment Group, a Hong Kong-based entertainment company...

 in the brains of newborns one second after the heel lance procedure. Sweet oral liquid moderately reduces the incidence 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
Social support can be defined and measured in many ways. It can loosely be defined as feeling that one is cared for by and has assistance available from other people and that one is part of a supportive social network...

 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.

Suggestion can significantly affect pain intensity. About 35% of people report marked relief after receiving a saline
Saline (medicine)
In medicine, saline is a general term referring to a sterile solution of sodium chloride in water but is only sterile when it is to be placed intravenously, otherwise, a saline solution is a salt water solution...

 injection they believe to have been morphine
Morphine
Morphine is a potent opiate analgesic medication and is considered to be the prototypical opioid. It was first isolated in 1804 by Friedrich Sertürner, first distributed by same in 1817, and first commercially sold by Merck in 1827, which at the time was a single small chemists' shop. It was more...

. This "placebo
Placebo
A placebo is a simulated or otherwise medically ineffectual treatment for a disease or other medical condition intended to deceive the recipient...

" 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.

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.

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.

Alternative medicine

Pain is the most common reason for people to use complementary and alternative medicine. An analysis of the 13 highest quality studies of pain treatment with acupuncture
Acupuncture
Acupuncture is a type of alternative medicine that treats patients by insertion and manipulation of solid, generally thin needles in the body....

, published in January 2009 in the British Medical Journal, concluded there is little difference in the effect of real, sham and no acupuncture. There is interest in the relationship between vitamin D
Vitamin D
Vitamin D is a group of fat-soluble secosteroids. In humans, vitamin D is unique both because it functions as a prohormone and because the body can synthesize it when sun exposure is adequate ....

 and pain, but the evidence so far from controlled trials
Clinical trial
Clinical trials are a set of procedures in medical research and drug development that are conducted to allow safety and efficacy data to be collected for health interventions...

 for such a relationship, other than in osteomalacia
Osteomalacia
Osteomalacia is the softening of the bones caused by defective bone mineralization secondary to inadequate amounts of available phosphorus and calcium, or because of overactive resorption of calcium from the bone as a result of hyperparathyroidism...

, is unconvincing.

A 2007 review of 13 studies found evidence for the efficacy of hypnosis
Hypnosis
Hypnosis is "a trance state characterized by extreme suggestibility, relaxation and heightened imagination."It is a mental state or imaginative role-enactment . It is usually induced by a procedure known as a hypnotic induction, which is commonly composed of a long series of preliminary...

 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."

A 2003 meta-analysis of randomized clinical trials found that spinal manipulation
Spinal manipulation
Spinal manipulation is a therapeutic intervention performed on spinal articulations which are synovial joints . These articulations in the spine that are amenable to spinal manipulative therapy include the z-joints, the atlanto-occipital, atlanto-axial, lumbosacral, sacroiliac, costotransverse...

 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
Low back pain
Low back pain or lumbago is a common musculoskeletal disorder affecting 80% of people at some point in their lives. In the United States it is the most common cause of job-related disability, a leading contributor to missed work, and the second most common neurological ailment — only headache is...

.

Epidemiology

Pain is the main reason for visiting the emergency department in more than 50% of cases and is present in 30% of family practice visits. Several epidemiological studies from different countries have reported widely varying prevalence rates for chronic pain, ranging from 12-80% 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 ages12 and 14.

Society and culture

The nature or meaning of physical pain has been diversely understood by religious or secular traditions from antiquity to modern times.

Physical pain is an important political topic in relation to various issues, including pain management
Pain management
Pain management is a branch of medicine employing an interdisciplinary approach for easing the suffering and improving the quality of life of those living with pain. The typical pain management team includes medical practitioners, clinical psychologists, physiotherapists, occupational therapists,...

 policy, drug control, animal rights
Animal rights
Animal rights, also known as animal liberation, is the idea that the most basic interests of non-human animals should be afforded the same consideration as the similar interests of human beings...

 or animal welfare
Animal welfare
Animal welfare is the physical and psychological well-being of animals.The term animal welfare can also mean human concern for animal welfare or a position in a debate on animal ethics and animal rights...

, torture
Torture
Torture is the act of inflicting severe pain as a means of punishment, revenge, forcing information or a confession, or simply as an act of cruelty. Throughout history, torture has often been used as a method of political re-education, interrogation, punishment, and coercion...

, and pain compliance
Pain compliance
Pain compliance is the use of painful stimulus to control or direct a person or animal. The stimulus can be manual , use tools such as a whip or electroshock weapon, or use of chemical such as tear gas or pepper spray.The purpose of pain compliance is to direct the actions of...

. In various contexts, the deliberate infliction of pain in the form of corporal punishment
Corporal punishment
Corporal punishment is a form of physical punishment that involves the deliberate infliction of pain as retribution for an offence, or for the purpose of disciplining or reforming a wrongdoer, or to deter attitudes or behaviour deemed unacceptable...

 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
Mortification of the flesh
Mortification of the flesh literally means "putting the flesh to death". The term is primarily used in religious and spiritual contexts. The institutional and traditional terminology of this practice in Catholicism is corporal mortification....

 or painful rites of passage
Rites of Passage
Rites of Passage is an African American History program sponsored by the Stamford, Connecticut US public schools. The program consists of an extra day of schooling on Saturday for 12 weeks, service projects, and a culminating educational trip to Gambia and Senegal. Gambia and Senegal are the...

 are highly regarded.

Philosophy of pain
Pain (philosophy)
Philosophy of pain may be about suffering in general or more specifically about physical pain. The experience of pain is, due to its seeming universality, a very good portal through which to view various aspects of human life...

 is a branch of philosophy of mind
Philosophy of mind
Philosophy of mind is a branch of philosophy that studies the nature of the mind, mental events, mental functions, mental properties, consciousness and their relationship to the physical body, particularly the brain. The mind-body problem, i.e...

 that deals essentially with physical pain, especially in connection with such views as dualism
Dualism (philosophy of mind)
In philosophy of mind, dualism is a set of views about the relationship between mind and matter, which begins with the claim that mental phenomena are, in some respects, non-physical....

, identity theory
Type physicalism
Type physicalism is a physicalist theory, in philosophy of mind. It asserts that mental events can be grouped into types, and can then be correlated with types of physical events in the brain...

, and functionalism
Functionalism (philosophy of mind)
Functionalism is a theory of the mind in contemporary philosophy, developed largely as an alternative to both the identity theory of mind and behaviourism. Its core idea is that mental states are constituted solely by their functional role — that is, they are causal relations to other mental...

.

More generally, it is often as a part of pain in the broad sense, i.e. suffering
Suffering
Suffering, or pain in a broad sense, is an individual's basic affective experience of unpleasantness and aversion associated with harm or threat of harm. Suffering may be qualified as physical or mental. It may come in all degrees of intensity, from mild to intolerable. Factors of duration and...

, that physical pain is dealt with in culture, religion, philosophy, or society.

In other animals

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. René Descartes
René Descartes
René Descartes ; was a French philosopher and writer who spent most of his adult life in the Dutch Republic. He has been dubbed the 'Father of Modern Philosophy', and much subsequent Western philosophy is a response to his writings, which are studied closely to this day...

 for example argued that animals lack consciousness and therefore do not experience pain and suffering in the way that humans do. Bernard Rollin
Bernard Rollin
Bernard E. Rollin is an American philosopher who specializes in animal rights and animal consciousness. He is a professor of philosophy, animal sciences, and biomedical sciences at Colorado State University....

 of Colorado State University
Colorado State University
Colorado State University is a public research university located in Fort Collins, Colorado. The university is the state's land grant university, and the flagship university of the Colorado State University System.The enrollment is approximately 29,932 students, including resident and...

, the principal author of two U.S. federal laws regulating pain relief for animals, 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. 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. 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 support, some critics continue to question how reliably animal mental states can be determined. The ability of invertebrate species of animals, such as insects, to feel pain and suffering is also unclear.

The presence of pain in an animal cannot be known for certain, but it can be inferred through physical and behavioral reactions. Specialists currently believe that all vertebrates can feel pain, and that certain invertebrates, like the octopus, might too. 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 insects, except for instance in fruit flies
Drosophila melanogaster
Drosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting from Charles W...

.

In vertebrates, endogenous opioid
Opioid
An opioid is a psychoactive chemical that works by binding to opioid receptors, which are found principally in the central and peripheral nervous system and the gastrointestinal tract...

s 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 drawn, their presence indicates that lobsters may be able to experience pain. Opioids may mediate their pain in the same way as in vertebrates. Veterinary medicine
Veterinary medicine
Veterinary Medicine is the branch of science that deals with the prevention, diagnosis and treatment of disease, disorder and injury in non-human animals...

 uses, for actual or potential animal pain, the same analgesics and anesthetics as used in humans.

Etymology

First attested in English in 1297, the word pain comes from the Old French
Old French
Old French was the Romance dialect continuum spoken in territories that span roughly the northern half of modern France and parts of modern Belgium and Switzerland from the 9th century to the 14th century...

 peine, in turn from Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 poena, "punishment, penalty" (in L.L. also "torment, hardship, suffering") and that from Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

"ποινή" (poine), generally "price paid", "penalty", "punishment".

External links

  • Pain Stanford Encyclopedia of Philosophy
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