PAIN

PAIN . Most religious traditions seek to minimize suffering and explain its causes. At the same time, many religions around the world promote painful behavior in specific ritual contexts and produce influential discourse that praises the value of pain or glorifies those who either endure pain or willfully hurt themselves. Although such positive evaluation of pain in religious contexts is diminishing, it is still widely normative. In 1984, Pope John Paul II stated that "Christianity is not a system into which we have to fit the awkward fact of pain.… In a sense, it creates, rather than solves the problem of pain."

Definitions of Pain

The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage." The vast majority of people know pain directly and vividly as a noxious feeling located somewhere in the body. Despite the fact that pain is notoriously difficult to express in a verbal way, most languages do provide tropes for speaking about the sensation. Over seventy words are used in the McGill Pain Questionnaire, which is administered to patients who complain of pain. These include physical, emotional, and evaluative terms, such as piercing, burning, drilling, punishing, nagging, and terrifying. Other languages are equally rich in pain terms. Biblical Hebrew (the books of Job and Jeremiah ) describes pain as tearing its victim, penetrating like arrows, and crushing like a storm. Similarly, Sanskrit and other Asian languages use terms that refer to tools or weapons, such as lances, darts, spears, or fire, in order to communicate the nature of the hurt.

The vocabulary of pain strongly suggests that pain and suffering are inseparable. In fact, the word pain is often used as a synonym for suffering : C. S. Lewis's famous book, The Problem of Pain (1940) is about emotional suffering. However, it is important to make a conceptual distinction between nociception (the perception of "physical" pain) and suffering. A back injury may be accompanied by suffering, for instance, due to isolation and loss of productivity leading to depression or anxiety. Other pains, however, may be experienced more ambiguously or even as desirable and joyful. A runner may report pleasant or desirable pain, and some cancer patients describe the severe discomfort of chemotherapy as healing. Similarly, most forms of suffering—the loss of a child to illness, for instance, or the fear of death—are not accompanied by pain.

Another distinction must be made: pain is distinct from either violence or death. Religious literature and rituals around the world describe violent executions, sacrifices, and the slaughter of nonbelievers and heretics as meaningful theological phenomena. A substantial body of scholarship is devoted to interpreting or analyzing violence and the sacred: Rene Girard's Violence and the Sacred (1977) stands out in this respect. The phenomenon of pain occupies a distinct domain of religious discourse and practice. The swift beheading of a heretic does not communicate the same information on the role of the body, power, self, and eschatology as the gradually increased and slow torment of a martyr who is given the option of ending the torture by conversion. Moreover, the self-willed pain of pilgrims and ascetics is different from both. Similarly, violent displays accompanied by heroic insensitivity to pain—the Malaysian piercers during the Thaipusam festival, for instance—are only indirectly linked to the subject of pain. Here pain is regarded as a meaningful existential category, but only to be transcended and ignored. Ritual analgesia is not pain behavior, but it is based on a profound religious evaluation of pain.

Distribution and Contexts

The use of pain, or the praise of it, in religious contexts has been extremely widespread and diverse. Virtually every known tradition describes pain in spiritual terms, praises its effects, or prescribes it to adherents. This can be seen anywhere from ancient Near East religions, the three Western monotheistic traditions, and Greek and mystery cults to the major South and East Asian traditions and the religions of the Americas, Africa, and Australia. Pain figures either as an important feature of ritual performances or as the subject of extremely diverse and elaborate discourse. The performative use of pain includes pilgrimages, initiations (including shamans, secret societies, rites of passage, and puberty rites), mourning and funerary rituals, judicial ordeals, rites of possession and exorcism, specialized mystical disciplines, monastic guidelines, and modern mind-altering practices such as body-piercing and tat-tooing.

The most commonly practiced rituals in which pain figures prominently are pilgrimages, initiations, and rites of mourning. Pilgrims are often encouraged to walk barefoot on rocky or hot terrain, crawl on hands and knees or prostrate on the hard ground, sleep under difficult conditions, expose themselves to the heat or cold of the elements, and avoid refreshment and nourishment. Such discomforts are practiced in such places as Sabarai Malai in South India, Mount Kailash in Nepal, Lourdes in France, Guadalupe in Mexico, Karbala in Iraq, Jerusalem in Israel, Mecca in Saudi Arabia, and numerous lesser known centers of pilgrimage. Pilgrimage discomforts and pain are not incidental to the goals of the pilgrims' journey, or merely contingent on being on the road. They are central to the goal of pilgrimage. In Sabarai Malai, for example, a pilgrim was recorded as saying: "At one moment everything is pain. But at the next moment everything is love (anpu )…for the Lord" (Daniel, 1984, p. 269).

Initiatory rituals, especially rites of passage for boys and girls at puberty, have been extremely common and are still widely practiced—often in a painful manner. Methods of hurting, applied to both sexes, commonly center on the genitals, with various forms of incision, insertion of objects such as twigs, and scraping or stabbing. Other types of initiatory pain include scarification, piercing of various body parts (e.g., nose, ears, cheeks), knocking out of teeth, the practice of kneeling on hot coals, suspension from hooks, and whippings and beatings. Similar and additional tortures are used in initiations to religious and military societies, as well as academic and athletic fraternities; such tortures are also associated with shamanic practices in Asia and the Americas. For instance, the Sun Dance rituals of the Arapahos, Cheyennes, Crows, and other Native Americans are lengthy and elaborate series of painful rites culminating with the piercing and tearing of tissue in the chest. Although ritual participants articulate numerous reasons for participating in the Sun Dance, the pain discourse focuses on self-sacrifice for the sake of the community, love, and compassion (Jorgensen, 1972).

Mourning rituals in which self-mutilation is practiced range from the merely symbolic tearing of the button in contemporary Judaism (a remnant of painful biblical practices) to self-beatings and head slashing by Muslim followers of the murdered Imam Ḥusayn. Mourning rituals involving self-mutilation also extend through numerous tribal religions in which such practices as tearing out one's hair, slashing the thighs with a knife, cutting the body with various objects, or banging one's head against the ground are ritually enacted (Durkheim, 1965/1912).

Pain Discourse

The discursive contexts in which pain is described, prescribed, or praised include scriptural teachings, myths, and folk narratives; biographies and hagiographies of mystics, saints, or martyrs; religious poetry; sermons; and ethnographic evidence. Unlike ritual performance, pain discourse explicitly addresses the nature and function of self-inflicted or involuntary pain. The literary and oral sources invariably couch their discussions of pain in tropes or elaborate models. These included juridical, medical, military, athletic, magical, communal, and psychotropic ways of conceptualizing pain. The tropes reveal both implicitly and explicitly a dual evaluation of the effects of pain on the agent. Pain is either a destructive force—a punishment—that causes aversion, or it is a necessary evil or even blessing, like medicine. In either case, pain in religious literature is a meaningful aspect of human experience, which either strengthens something of value (e.g., identity with God, community), or destroys something of perhaps lesser value (e.g., ego, self). Despite the varying cultural contexts in which religious discourse takes place, pain models always reveal this dualistic evaluation.

The juridical model

Narratives and discourses about pain that describe it in terms taken from the world of jurisprudence are included in this model. The clearest is pain as punishment, an obvious feature considering the etymology of the word from the Greek poena, meaning "payment" or "penalty." But pain may also be described as a debt or as damages owed, and it may be related to laws of evidence when it is linked to methods of eliciting truth. This model accounts for a large percentage of the cases found in religious literature, and many pain patients still use it today.

Pain is often described as a punishment by some personal agency (e.g., God, Satan, demons) or by some impersonal mechanism, such as karma. The punishment may be perceived as just, as the confessional writings of sinners and penitents indicate, or it may be entirely unwarranted and tragic. Such is the case of Job, or the cry of Prometheus, who rightly calls Zeus a tyrant.

Juridical pain straddles the boundary between lex tallionis (the law of retaliation) and the law of debts in a variety of cultures, from Judaism and ancient Greece to Hindu versions of karma. The difference between pain as punishment and an exchange of debts involves the legal distinction between owing something to a private party and being accountable to society as a whole. The strongest Jewish instance of this distinction may be found in the Yom Kippur (Day of Atonement) liturgy with its notion of redemption as exchange (pidyon ) or a debt. This mechanism, the restoration of a balance through the perhaps magical or sacrificial mediation of pain, is also seen in the South Asian vrata —the vow that utilizes self-sacrifice to bring about desired results.

Juridical pain evokes the laws of evidence: Pain serves as the instrument for obtaining the truth from reluctant witnesses or the accused. This principle operates not just in cases of ordeals or religious inquisitions, as one might expect, but also in cases of initiatory ordeal and asceticism. This pain is a test. In the New Testament the agony that Jesus suffered in Gethsemane is characterized as a test, a type of ordeal or trial that reveals a hidden truth: "Because he himself was tested by what he suffered, he is able to help those who are being tested" (Heb. 2:12). Buddhist and Hindu texts (e.g., Warrior Zen: The Diamond-hard Wisdom of Suzuki Shosan, the Bhagavadgītā, and Patañjali's Yoga Sūtra ) urge the practitioner to treat pain and pleasure alike in order to unmask the truth about the self.

Pain as medicine

Even though modern medical authorities characterize pain as an aversive sensation, religious sources often describe it as medical, and in so doing, evaluate it as a beneficial experience. A dramatic example comes from Prudentius, a fourth-century Christian poet who attributes to the martyr Saint Romanus the following words: "You will shudder at the handiwork of the executioners, but are doctors' hands gentler, when Hippocrates' cruel butchery is going on? The living flesh is cut and fresh-drawn blood stains lancers when festering matter is being scraped away." The claim, made forcefully by Saint Basil (d. 379) and others, is not that pain is pleasant, but that it benefits the soul. One need not seek it like a martyr, but if afflicted naturally, the pain ought to be taken as a spiritual sign—not just a reason for running to the doctor.

Medicine is both preventive and curative. It either cures diseases that have already been contracted (sin), or prevents ills to follow (punishment). In either case a familiar feature of classical medicine—and attendant aspects of this way of conceptualizing pain—is that the remedy is as bitter as the disease. In its Christian version this model may owe a great deal to the classic dictum that "medicine is the philosophy of the body, and philosophy is the medicine of the soul." This ideology can also be seen in Islamic metaphors for religious pain. The Ṣūfī poet Rūmī (1207–1273 ce) referred to "love" (of God) as pain without cure. The Sea of Precious Virtues (twelfth century) warns the man who seeks worldly gain that just as he is willing to suffer with a physician for physical health, so he must heed the health of the soul to avoid hell. And Shāh˓Abdul Laṭīf, an eighteenth-century Indian Ṣūfī, wrote that the true lover of God does not seek out the medicine of the physician. The South Asian Muslim mystic Mirzā Asaduʾllāh Ghālib exclaimed: "When pain transgresses the limits, it becomes medicine."

Additional models of pain

Pain can also be conceptualized as a weapon used to destroy self-love in a spiritual battle. This is evident in the writings of such Christian theologians as Augustine of Hippo (354–430), as well as John Calvin (1509–1564), who conceived of the spiritual life as a battle against "the old man." Simon the Stylite (d. 459) battled his own body, and Macarius (d. 390) wrestled against the "fiends" that occupied his body. Muslim ascetics such as Abū Bakr Wāsiṭī claimed to be practicing jihad or holy war against the individual soul that deluded itself into thinking that it was divine.

The athletic model of pain is evident in the word asceticism, which Plato and Aristotle took to mean "training." The attitude revealed in the athletic model toward the body is softer than the military. Hebrews 12 describes pain as God's training for his faithful, and both Tertullian (third century) and Prudentius (fourth century) identified martyrdom with an athletic contest against false religion. Still, the strong aversion toward the flesh or individual ego is relatively mute here.

Pain can also be conceived as an alchemical purifier that transforms ordinary humans into saved souls. It acts like the fire that melts impure gold, in the words of Gregory of Nyssa (fourth century), or in Rūmī's words: "I am the fire!" Magical metaphors extend beyond alchemy or the blacksmith's trade to agricultural tropes, or in the case of the tapas (heat) of Hindu mysticism, the metaphor extends to a tool that bestows supernatural powers. Similarly, the idea that pain can miraculously transform consciousness and identity in an implicit passage is indicated by the charter of the Midwives Alliance of North America: "Labor…is a rite of passage, a psychospiritual training ground for both mother and child."

Central to the Christian conception of pain is the model of vicarious or communal suffering. Colossians 1:24 states: "Now I rejoice in my suffering for your sake." Indeed the painful death of Christ is a vicarious force that extends in effect to the entire community. Such too is the ritual destruction of the scapegoat in numerous cultures; in the Zohar 's addition to the Yom Kippur liturgy, for example, the death of the righteous atones for the sins of others.

In contemporary Western discourse on self-hurting, describing for instance the performances of "modern primitives," brain processes are often invoked to explain the heightened states of consciousness achieved. Although excitement and euphoria are often reported as a result of the secretion of beta-endorphins, the language of transcendence—unity of spirit and body, for instance—prevails: "It's an ecstasy state where no matter what happens in the body, no matter how much more intense the physical sensations become, I feel no more. Sensations just 'are'" (Mufasar, 1995, p. 5).

Meaning and Function of Pain

The methods of causing oneself or others pain in religious contexts, and the manner of articulating the nature of pain have been extremely diverse. Pain, itself a biological and psychological phenomenon, has been so deeply embedded in cultural expression that it has proven elusive and difficult to theorize. Few theorists have even attempted to focus on pain perception apart from its theoretical and ritual contexts. Four distinct approaches for understanding religious pain may be identified: cultural-symbolic, psychoanalytical, sociobiological-ethological, and psychodynamic. To simplify this range, one may say that religious pain has been reduced either to cultural interpretation or to biological analysis.

Mircea Eliade is preeminent among those theorists who refuse to "reduce" ritual performance or religious discourse to universal transcultural principles other than the sacred itself. Consequently, he argues that the pain inflicted on novices, for instance among Native Americans, is symbolic of specific cultural interpretations of the sacred, and the ritual hurt aims at "the spiritual transformation of the victim." The torture may represent a symbolic death and rebirth; the genital incisions symbolically de-sexualize the youngster to create an androgynous being for the state that precedes the new birth. In either case, the important religious phenomenon is not the sensation of pain itself but the symbolic value of its ritualized application.

Biological reductions, or ethological theories based on biology, address the question of aggression and dominance, access to females, or in some sophisticated versions, imposing ritual constraints on biological drives. For example, in On Aggression (1963) Konrad Lorenz regards the violent torture of initiates as an expression of such biological principles as the natural aggression of adults toward young sexual competitors. The highly respected theories of René Girard and Walther Burkhert ultimately resolve into such universal—"human nature"—principles. Freudian psychoanalytical theory explains the self-hurting of religious individuals, or the tortures of initiates, in broadly reductive terms. The former may represent masochistic pathology, or the ego's response to the anxiety of a profound sense of guilt. Sigmund Freud's Civilization and Its Discontents (1930) discusses how the torture of youngsters may be due to aggressive and erotic drives as they manifest in competition over sexual resources, or it may serve to curtail such potentially destructive drives.

While none of these approaches focuses exclusively on the perception of pain as a distinct area of interest, Elaine Scarry in The Body in Pain (1985) isolates pain as a unique phenomenon—an overwhelming "objectless," and therefore mute, experience that destroys the victim's ability to communicate and ultimately shatters his or her entire world, including even the self. Scarry's theory, which is based on the observation of torture victims, has had a significant influence on religious scholarship. Historians of religions, especially scholars of mysticism, including Maureen Flynn and Maureen A. Tilley, now believe that mortification of the flesh is designed to "unmake the world" and eradicate language and identity through the mute power of pain.

The most recent and extended analysis of pain in religious contexts is Ariel Glucklich's Sacred Pain: Hurting the Body for the Sake of the Soul (2001). This book argues, based on neuropsychological and cybernetic theories, that self-inflicted pain makes the agent transparent and thereby strengthens values, which are held in high regard. The voluntary mortifications and discomforts of such mystical practitioners as Maria Maddalena de' Pazzi and Henry Suso dissolve personal identity while fortifying a new telos or valued goal, such as God or community. Unwanted or natural pain (e.g., illness, accidents) can be transformed into "sacred" pain through the psychological mechanisms of self-sacrifice, or by subsuming one's personal identity within a broader and more highly valued center. The neuropsychological work of Ronald Melzack and Patrick D. Wall on phantomlimb pain offers a specific and sophisticated explanation of what may be taking place when the organism is over-stimulated with pain or irritation. A shutting down or diminution of output from the central nervous system results in phenomenal experiences, which diminishes the sense of self and reinforces the religious psychology that values other sources of identity: God, Christ, community, and others. Pain here is understood in terms of its phenomenal effects, not as a pathology or a political weapon.

See Also

Healing and Medicine; Mortification; Ordeal; Suffering.

Bibliography

Bakan, David. Disease, Pain, and Sacrifice: Toward a Psychology of Suffering. Chicago, 1968. A psychoanalytical and phenomenological study of the two-fold effect of pain on the self: integrative and disintegrative (telic-centralizing and decentralizing).

Chittick, William C., trans. The Sufi Path of Love: The Spiritual Teachings of Rumi. Albany, N.Y., 1983.

Daniel, E. Valentine. Fluid Signs: Being a Person the Tamil Way. Berkeley, 1984. A sophisticated combination of ethnography, ethno-psychology, and traditional Indian philosophy as tools for understanding South Indian ritual.

Durkheim, Émile. The Elementary Forms of the Religious Life (1912). Translated by Joseph Ward Swain. New York, 1965. The foundational text for the sociology of religion, contains a large number of examples of ritualized pain, including in mourning and rites of expiation or penance.

Eliade, Mircea. Rites and Symbols of Initiation: The Mysteries of Birth and Rebirth. Translated by Willard R. Trask. New York, 1965. A comprehensive collection and symbolic interpretation of initiatory ordeals from around the world.

Flynn, Maureen. "The Spiritual Uses of Pain in Spanish Mysticism." Journal of the American Academy of Religion 64, no. 2 (1999): 257–278.

Freud, Sigmund. Civilization and Its Discontents (1930). Translated by James Strachey. New York, 1962. One of several cultural studies based on the psychology of biological drives. Useful primarily for the insight on the cultural curtailment of drives through ritual.

Girard, René. Violence and the Sacred. Translated by Patrick Gregory. Baltimore, Md., 1977. An extended and influential study of the religious and social psychology of the sacrifice.

Glucklich, Ariel. Sacred Pain: Hurting the Body for the Sake of the Soul. New York, 2001. A neuropsychological and psychodynamic study of the effect of self-hurting on states of consciousness sought by religious practitioners.

Jorgensen, Joseph G. The Sun Dance Religion: Power for the Powerless. Chicago, 1972. A comprehensive overview of several rituals and a number of ideologies and theories that explain them.

Lorenz, Konrad. On Aggression. New York, 1963. One of the early texts of ethology, the precursor to sociobiology.

Melzack, Ronald. "Pain: Past, Present, and Future." Canadian Journal of Experimental Psychology 47 (1993): 615–629. A relatively accessible explanation of the new theory of neuromatrix and neurosignature and its effect on the understanding and treatment of pain.

Melzack, Ronald, and Patrick D. Wall. The Challenge of Pain. New York, 1983.

Morris, David B. The Culture of Pain. Berkeley, 1991. A detailed literary and cultural study of pain, including one chapter on pain in religious contexts.

Mufasar, Fakir. "Editorial: Changes of Body-State." Body Play: And Modern Primitives 1, no. 3 (1995): 4–5.

Rey, Roselyne. The History of Pain. Translated by Louise Elliott Wallace, J. A. Cadden, and S. W. Cadden. Cambridge, Mass., 1993. A comprehensive study of pain in Western medical history and the interaction between medical theory and culture.

Scarry, Elaine. The Body in Pain: The Making and Unmaking of the World. New York, 1985. A literary and philosophical study of the destructive effect of extreme pain on consciousness and identity, and the creative potential embedded in this destruction.

Tilley, Maureen A. "The Ascetic Body and the Unmaking of the World of the Martyr." Journal of the American Academy of Religion 59, no. 3 (1990): 467–479.

Ariel Glucklich (2005)

Pain

Definition and classification

Pain is a universal human experience. The International Association for the Study of Pain (IASP) defines pain as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage." Pain may be a symptom of an underlying disease or disorder, or a disorder in its own right.

At the same time that pain is a universal experience, however, it is also a complex one. While the physical sensations involved in pain may be constant throughout history, the ways in which humans express and treat pain are shaped by their respective cultures and societies. Since the 1980s, research in the neurobiology of pain has been accompanied by studies of the psychological and sociocultural factors that influence people's experience of pain, their use of health care systems, and their compliance with various treatments for pain. As of 2003, the World Health Organization (WHO) emphasizes the importance of an interdisciplinary approach to pain treatment that takes this complexity into account.

Types of pain

Pain can be classified as either acute or chronic. Acute pain is a direct biological response to disease, inflammation, or tissue damage, and usually lasts less than one month. It may be either continuous or recurrent (e.g., sickle cell disease). Acute pain serves the long-term wellbeing of humans and the higher animals by alerting them to an injury or condition that needs treatment. In humans, acute pain is often accompanied by anxiety and emotional distress; however, its cause can usually be successfully diagnosed and treated. Some researchers use the term "eudynia" to refer to acute pain.

In contrast, chronic pain has no useful biological function. It can be defined broadly as pain that lasts longer than a month following the healing of a tissue injury; pain that recurs or persists over a period of three months or longer; or pain related to a tissue injury that is expected to continue or get worse. Chronic pain may be either continuous or intermittent; in either case, however, it frequently leads to weight loss, sleep disturbances, fatigue , and other symptoms of depression . According to an article in the New York Times, chronic pain is the most common under-lying cause of suicide. Unlike acute pain, chronic pain is resistant to most medical treatments. It is sometimes called "maldynia," and is considered a disorder in its own right.

Pain that is caused by organic diseases and disorders is known as somatogenic pain. Somatogenic pain in turn can be subdivided into nociceptive pain and neuropathic pain. Nociceptive pain occurs when pain-sensitive nerve endings called nociceptors are activated or stimulated. Most nociceptors in the human body are located in the skin, joints and muscles, and the walls of internal organs. There may be as many as 1,300 nociceptors in a square inch (6.4 square centimeter) of skin. However, there are fewer nociceptors in muscle tissue and the internal organs, as they are covered and protected by the skin. Nociceptors are specialized to detect different types of painful stimuli—some are sensitive to heat or cold, while others detect pressure, toxic substances, sharp blows, or inflammation caused by infection or overuse.

In contrast to nociceptive pain, neuropathic pain results from damage to or malfunctioning of the nervous system itself. It may involve the central nervous system (the brain and spinal cord); the peripheral nervous system (the nerve trunks leading away from the spine to the limbs, plus the 12 pairs of cranial nerves on the lower surface of the brain); or both. Neuropathic pain is usually associated with an identifiable disorder such as stroke , diabetes, or spinal cord injury , and is frequently described as having a "hot" or burning quality.

Psychogenic pain is distinguished from somatogenic pain by the influence of psychological factors on the intensity of the patient's pain or degree of disability. The patient is genuinely experiencing pain—that is, he or she is not malingering—but the pain has either no organic explanation or else a weak one. Common psychogenic pain syndromes include chronic headache or low back pain ; atypical facial pain; or pelvic pain of unknown origin.

Some cases of psychogenic pain belong to a group of mental disorders known as somatoform disorders. According to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV), somatoform disorders are defined by "the presence of physical symptoms that suggest a general medical condition," but cannot be fully explained by such a condition, by the direct effects of a drug or other substance, or by another mental disorder. The somatoform disorders include somatization disorder, characterized by chronic complaints of unexplained physical symptoms, often involving multiple sites in the body; hypochondriasis is a preoccupation with illness that persists in spite of the doctor's reassurance; and pain disorder, characterized by physical pain that is intensified by psychological factors, often becoming the focus of the patient's life and impairing his or her family relationships and ability to work.

It is important to recognize that some pain syndromes may involve more than one type of pain. For example, a cancer patient may suffer from neuropathic pain as a side effect of cancer treatment as well as nociceptive pain associated with pressure from the tumor itself on nociceptors in a blood vessel or hollow organ. In addition to the somatogenic pain, the patient may experience psychogenic pain related to the loss of physical functioning or attractiveness, coupled with anxiety about the progression or recurrence of the cancer. Other pain syndromes do not fit neatly into either somatogenic or psychogenic categories. A case in point would be certain types of chronic headache that involve the stimulation of nociceptors in the tissues of the head and neck as well as psychogenic factors related to the patient's handling of stress.

Description

How the body feels pain

A person begins to feel pain when nociceptors in the skin, muscles, or internal organs detect pressure, inflammation, a toxic substance, or another harmful stimulus. The pain message travels along peripheral nerve fibers in the form of electrical impulses until it reaches the spinal cord. At this point, the pain message is filtered by specialized nerve cells that act as gatekeepers. Depending on the cause and severity of the pain, the nerve cells in the spinal cord may either activate motor nerves, which govern the ability to move away from the painful stimulus; block out the painful message; or release chemicals that increase or lower the strength of the original pain message on its way to the brain. The part of the spinal cord that receives and "processes" the pain messages from the peripheral nerves is known as the dorsal horn.

After the pain message reaches the brain, it is relayed to an egg-shaped central structure called the thalamus, which transmits the information to three specialized areas within the brain: the somatosensory cortex, which interprets physical sensations; the limbic system, which forms a border around the brain stem and governs emotional responses to physical stimuli; and the frontal cortex, which handles thinking. The activation of these three regions explains why human perception of pain is a complex combination of sensation, emotional arousal, and conscious thought.

In addition to receiving and interpreting pain signals, the brain responds to pain by activating parts of the nervous system that send additional blood to the injured part of the body or that release natural pain-relieving chemicals, including serotonin, endorphins, and enkephalins.

Factors that affect pain perception

LOCATION AND SEVERITY OF PAIN Pain varies in intensity and quality. It may be mild, moderate, or severe. In terms of quality, it may vary from a dull ache to sharp, piercing, burning, pulsating, tingling, or throbbing sensations; for example, the pain from jabbing one's finger on a needle feels different from the pain of touching a hot iron, even though both injuries involve the same part of the body. If the pain is severe, the nerve cells in the dorsal horn transmit the pain message rapidly; if the pain is relatively mild, the pain signals are transmitted along a different set of nerve fibers at a slower rate.

The location of the pain often affects a person's emotional and cognitive response, in that pain related to the head or other vital organs is usually more disturbing than pain of equal severity in a toe or finger.

GENDER Recent research has shown that sex hormones in mammals affect the level of tolerance for pain. The male sex hormone, testosterone, appears to raise the pain threshold in experimental animals, while the female hormone, estrogen, appears to increase the animal's recognition of pain. Humans, however, are influenced by their personal histories and cultures as well as by body chemistry. Studies of adult volunteers indicate that women tend to recover from pain more quickly than men, cope more effectively with it, and are less likely to allow pain to control their lives. One explanation of this difference comes from research with a group of analgesics known as kappa-opioids, which work better in women than in men. Some researchers think that female sex hormones may increase the effectiveness of some analgesic medications, while male sex hormones may make them less effective. In addition, women appear to be less sensitive to pain when their estrogen and progesterone levels are high, as happens during pregnancy and certain phases of the menstrual cycle. It has been noted, for example, that women with irritable bowel syndrome (IBS) often experience greater pain from the disorder during their periods.

FAMILY Another factor that influences pain perception in humans is family upbringing. Some parents comfort children who are hurting, while others ignore or even punish them for crying or expressing pain. Some families allow female members to express pain but expect males to "keep a stiff upper lip." People who suffer from chronic pain as adults may be helped by recalling their family's spoken and unspoken "messages" about pain, and working to consciously change those messages.

CULTURE AND ETHNICITY In addition to the nuclear family, a person's cultural or ethnic background can shape his or her perception of pain. People who have been exposed through their education to Western explanations of and treatments for pain may seek mainstream medical treatment more readily than those who have been taught to regard hospitals as places to die. On the other hand, Western medicine has been slower than Eastern and Native American systems of healing to recognize the importance of emotions and spirituality in treating pain. The recent upsurge of interest in alternative medicine in the United States is one reflection of dissatisfaction with a one-dimensional "scientific" approach to pain.

There are also differences among various ethnic groups within Western societies regarding ways of coping with pain. One study of African American, Irish, Italian, Jewish, and Puerto Rican patients being treated for chronic facial pain found differences among the groups in the intensity of emotional reactions to the pain and the extent to which the pain was allowed to interfere with daily functioning. However, much more work on larger patient samples is needed to understand the many ways in which culture and society affect people's perception of and responses to pain.

Demographics

Acute pain, particularly in its milder forms, is a commonplace experience in the general population; most people can think of at least one occasion in the past week or month when they had a brief tension headache, felt a little muscle soreness, cut themselves while shaving, or had a similar minor injury. On the other hand, chronic pain is more widespread than is generally thought; the American Chronic Pain Association estimates that 86 million people in the United States suffer from and are partially disabled by chronic pain. Two Canadian researchers evaluating a set of 13 studies of chronic pain done in North America, Europe, and Australia reported that the prevalence of severe chronic pain in these parts of the world is about 8% in children and 11% in adults. In terms of the economic impact of chronic pain, various productivity audits of the American workforce have stated that such pain syndromes as arthritis, lower back pain, and headache cost the United States between $80 and $90 billion every year.

The demographics of chronic pain depend on the specific disorder, including:

• Chronic pelvic pain (CPP) is more common in women than in men; it is thought to affect about 14% of adult women worldwide. In the United States, CPP is most common among women of reproductive age, particularly those between the ages of 26 and 30. It appears to be more common among African Americans than among Caucasians or Asian Americans. In addition, a history of sexual abuse before age 15 is a risk factor for CPP in adult life.
• Lower back pain (LBP) is the most common chronic disability in persons younger than 45. One researcher estimates that 80% of people in the United States will experience an episode of LBP at some point in life. About 3–4% of adults are disabled temporarily each year by LBP, with another 1% of the working-age population disabled completely and permanently. While 95% of patients with LBP recover within six to 12 weeks, the back pain becomes a chronic syndrome in the remaining 5%.
• Headaches in general are very common in the adult population in North America; about 95% of women and 90% of men in the United States and Canada have had at least one headache in the past twelve months. Most of these are tension headaches. Migraine headaches are less common than tension headaches, affecting about 11% of the population in the United States and 15% in Canada. Migraines occur most frequently in adults between the ages of 25 and 55; the gender ratio is about 3 F:1 M. Cluster headaches are the least common type of chronic headaches, affecting about 0.4% of adult males in the United States and 0.08% of adult females. The gender ratio is 7.5–5 M:1 F.
• Atypical facial pain is a less-common chronic pain syndrome, affecting one or two persons per 100,000 population each year. It is almost entirely a disorder of adults. Atypical facial pain is thought to affect men and women equally, and to occur with equal frequency in all races and ethnic groups.

Evaluation of pain

Patient description and history

A doctor's first step in evaluating a patient's pain is obtaining a detailed description of the pain, including:

• severity
• timing (time of day; continuous or intermittent)
• location in the body
• quality (piercing, burning, aching, etc.)
• factors that relieve the pain or make it worse (temperature or humidity; body position or level of activity; foods or medications; emotional stress, etc.)
• its relationship to mood swings, anxiety, or depression

The doctor will then take the patient's medical history, including past illnesses, injuries, and operations as well as a family history. In some cases, the doctor may need to ask about experiences of emotional, physical, or sexual abuse. The doctor will also make a list of all the medications that the patient takes on a regular basis. Other information that may help the doctor evaluate the pain includes the patient's occupation and level of functioning at work; marriage and family relationships; social contacts and hobbies; and whether the patient is involved in a lawsuit for injury or seeking workers' compensation. This information may be helpful in understanding what the patient means by "pain" as well as what may have caused the pain, particularly because many people find it easier to discuss physical pain than anxiety, anger, depression, or sexual problems.

Some doctors may give the patient a brief written pain questionnaire to fill out in the office. There are a number of different instruments of this type, some of which are designed to measure pain associated with cancer, arthritis, HIV infection, or other specific diseases. Most of these rating questionnaires ask the patient to mark their pain level on a scale from zero to 10 or zero to 100 with zero representing "no pain" and the higher number representing "worst pain imaginable" or "unbearable pain." The patient then answers a few multiple-choice questions regarding the impact of the pain on his or her employment, relationships, and overall quality of life.

Physical examination

A thorough physical examination is essential in identifying the specific disorders or injuries that are causing the pain. The most important part of pain management is removing the underlying cause(s) whenever possible, even when there is a psychological component to the pain.

Special tests

Although there are no laboratory tests or imaging studies that can demonstrate the existence of pain as such or measure its intensity directly, the doctor may order special tests to help determine the cause(s) of the pain. These studies may include one or more of the following:

• Imaging studies, usually x rays or magnetic resonance imagings (MRIs ). These studies can detect abnormalities in the structure of bones or joints, and differentiate between healthy and diseased tissues.
• Neurological tests. These tests evaluate the patient's movement, gait, reflexes, coordination, balance, and sensory perception.
• Electrodiagnostic tests. These tests include electromyography (EMG), nerve conduction studies, and evoked potential (EP) tests. In EMG, the doctor inserts thin needles in specific muscles and observes the electrical signals that are displayed on a screen. This test helps to pinpoint which muscles and nerves are affected by pain. Nerve conduction studies are done to determine whether specific nerves have been damaged. The doctor positions two sets of electrodes on the patient's skin over the muscles in the affected area. One set of electrodes stimulates the nerves supplying that muscle by delivering a mild electrical shock; the other set records the nerve's electrical signals on a machine. EP tests measure the speed of transmission of nerve impulses to the brain by using two electrodes, one attached to the patient's arm or leg and the other to the scalp.
• Thermography. This is an imaging technique that uses infrared scanning devices to convert changes in skin temperature into electrical impulses that can be displayed as different colors on a computer monitor. Pain related to inflammation, nerve damage, or abnormalities in skin blood flow can be effectively evaluated by thermography.
• Psychological tests. Such instruments as the Minnesota Multiphasic Personality Inventory (MMPI) may be helpful in assessing hypochondriasis and other personality traits related to psychogenic pain.

Treatment

Treatment of either acute or chronic pain may involve several different approaches to therapy.

Medications

Medications to relieve pain are known as analgesics. Aspirin and other nonsteroidal anti-inflammatory drugs, or NSAIDs, are commonly used analgesics. NSAIDs include such medications as ibuprofen (Motrin, Advil), ketoprofen (Orudis), diclofenac (Voltaren, Cataflam), naproxen (Aleve, Naprosyn), and nabumetone (Relafen). These medications are effective in treating mild or moderate pain. A newer group of NSAIDs, which are sometimes called "superaspirins" because they can be given in higher doses than aspirin without causing stomach upset or bleeding, are known as COX-2 inhibitors. The COX-2 inhibitors include celecoxib (Celebrex), rofecoxib (Vioxx), and valdecoxib (Bextra).

For more severe pain, the doctor may prescribe an NSAID combined with an opioid, usually codeine or hydrocodone. Opioids, which are also called narcotics, are strong painkillers derived either from the opium poppy Papaver somniferum or from synthetic compounds that have similar effects. Opioids include such drugs as codeine, fentanyl (Duragesic), hydromorphone (Dilaudid), meperidine (Demerol), morphine, oxycodone (OxyContin), and propoxyphene (Darvon). They are defined as Schedule II controlled substances by the Controlled Substances Act of 1970, which means that they have a high potential for abuse in addition to legitimate medical uses. A doctor must have a special license in order to prescribe opioids. In addition to the risk of abuse, opioids cause potentially serious side effects in some patients, including cognitive impairment (more common in the elderly), disorientation, constipation, nausea, heavy sweating, and skin rashes.

If the patient's pain is severe and persistent, the doctor will give separate dosages of opioids and NSAIDs in order to minimize the risk of side effects from high doses of aspirin or acetaminophen. In addition, the doctor may prescribe opioids that are stronger than codeine—usually morphine, fentanyl, or levorphanol.

The "WHO Ladder" for the treatment of cancer pain is based on the three levels of analgesic medication. Patients with mild pain from cancer are given nonopioid medications with or without an adjuvant (helping) medication. For example, the doctor may prescribe a tranquilizer to relieve the patient's anxiety as well as the pain medication. Patients on the second "step" of the ladder are given a milder opioid and a nonopioid analgesic with or without an adjuvant drug. Patients with severe cancer pain are given stronger opioids at higher dosage levels with or without an adjuvant drug.

Acute pain following surgery is usually managed with opioid medications, most commonly morphine sulfate (Astromorph, Duramorph) or meperidine (Demerol). In some cases, NSAIDs that are available in injectable form (such as ketorolac) are also used. Patient-controlled analgesia, or PCA, allows patients to control the timing and amount of pain medication they receive. Although there are oral forms of PCA, the most common form of administration involves an infusion pump that delivers a small dose of medication through an intravenous line when the patient pushes a button. The PCA pump is pre-programmed to deliver no more than an hourly maximum amount of the drug.

Some types of chronic pain are treated by injections in specific areas of the body rather than by drugs administered by mouth or intravenously. There are three basic categories of injections for pain management:

• Joint injections. Joint injections are given to treat chronic pain associated with arthritis. The most common medications used are corticosteroids, which suppress inflammation in arthritic joints, and hyaluronic acid, which is a compound found in the joint fluid of healthy joints.
• Soft tissue injections. These are given to reduce pain in trigger points (areas of muscle that are hypersensitive to touch) and bursae, which are small pouches or sacs containing tissue fluid that cushions pressure points between tendons and bones. When a bursa becomes inflamed—a condition called bursitis—the person experiences pain in the nearby joint. Corticosteroids are the drugs most often used in soft tissue injections, although the doctor may also inject an anesthetic into a trigger point in order to relax the muscle.
• Nerve blocks. Nerve blocks are injections of anesthetic around the fibers of a nerve to prevent pain messages relayed along the nerve from reaching the brain. They may be used to relieve pain in specific parts of the body for a short period; a common example of this type of nerve block is the lidocaine injections given by dentists before drilling or extracting a tooth. Some nerve blocks are injected in or near the spinal column to control pain that affects a larger area of the body; an example is the epidural injection given to women in labor or to patients with sciatica . A third type of nerve block is administered to block the sympathetic nervous system as part of pain management in patients with complex chronic pain syndromes.

Medications used to treat neuropathic pain include tricyclic antidepressants, anticonvulsant medications, selective serotonin reuptake inhibitors, topical creams containing capsaicin or 5% lidocaine, and diphenhydramine (Benadryl).

Surgery

Because surgery is itself a cause of pain, few surgical treatments to relieve pain were available prior to the discovery of safe general anesthetics in the mid-nineteenth century. For most of human history, doctors were limited to procedures that could be completed within two to three minutes because the patients could not bear the pain of the operation. Ancient Egyptian doctors gave their patients wine mixed with opium, while early European doctors made their patients drunk with brandy, tied them to the benches that served as operating tables, or put pressure on a nerve or artery to numb a specific part of the body.

Modern surgeons, however, can perform a variety of procedures to relieve either acute or chronic pain, depending on its cause. These procedures include:

• removal of diseased or dead tissue to prevent infection
• removal of cancerous tissue to prevent the spread of the cancer and relieve pressure on nearby healthy organs and tissues
• correction or reconstruction of malformed or damaged bones
• insertion of artificial joints or other body parts to replace damaged structures
• organ transplantation
• insertion of pacemakers and other electrical devices that improve the functioning of damaged organs or help to control pain directly
• cutting or destroying damaged nerves to control neuropathic pain

PSYCHOTHERAPY Psychotherapy may be helpful to patients with chronic pain syndromes by exploring the connections between anger, depression, or anxiety and physical pain sensations. One type of psychotherapy that has been shown to be effective is cognitive restructuring, an approach that teaches people to "reframe" the problems in their lives—that is, to change their conscious attitudes and responses to these stressors. Some psychotherapists teach relaxation techniques, biofeedback, or other approaches to stress management as well as cognitive restructuring.

Another type of psychotherapy that is effective in treating some patients with chronic pain is hypnosis. Although there is some disagreement among researchers as to whether hypnosis works by distracting the patient's attention from painful sensations or whether it works by stimulating the release of endorphins (chemicals produced by the body that are released in response to stress or injury and act as natural analgesics), it has been approved by the American Medical Association since 1958 as a treatment for pain. Some therapists offer instruction in self-hypnosis to patients with chronic pain.

COMPLEMENTARY AND ALTERNATIVE (CAM) APPROACHES CAM therapies that are used in pain management include:

• Acupuncture . Studies funded by the National Center for Complementary and Alternative Medicine (NCCAM) since 1998 have found that acupuncture is an effective treatment for chronic pain in many patients. It is thought that acupuncture works by stimulating the release of endorphins, the body's natural painkillers.
• Exercise . Physical exercise stimulates the body to produce endorphins.
• Yoga. Practiced under a doctor's supervision, yoga helps to maintain flexibility and range of motion in joints and muscles. The breathing exercises that are part of a yoga practice also relax the body.
• Prayer and meditation. The act of prayer by itself helps many people to relax. In addition, prayer and meditation are ways to refocus one's attention and keep pain from becoming the center of one's life.
• Naturopathy. Naturopaths include dietary advice and nutritional therapy in their treatment, which is effective for some patients suffering from chronic pain syndromes.
• Hydrotherapy. Warm whirlpool baths ease muscular and joint pain.
• Music therapy. Music therapy may involve listening to music, making music, or both. Some researchers think that music works to relieve pain by temporarily blocking the "gates" of pain in the dorsal horn of the spinal cord, while others believe that music stimulates the release of endorphins.

Pain management

Pain management refers to a set of skills and techniques for coping with chronic pain. The goal of pain management is not complete elimination of pain; rather, the patient learns to keep the pain at a level that he or she can tolerate, and to make the most of life in spite of the pain. The American Chronic Pain Association (ACPA) lists seven coping skills that help in managing pain:

• not dwelling on physical pain symptoms
• emphasizing abilities rather than disabilities
• recognizing one's feelings about the pain and discussing them freely
• using relaxation exercises to ease the emotional tension that makes pain worse.
• doing mild stretching exercises every day (with medical approval)
• setting realistic goals for improvement and evaluating them on a weekly basis
• affirming one's basic rights: the right to make mistakes, the right to say no, and the right to ask questions

An important part of pain management is participation in a multidisciplinary pain program. Many hospitals and rehabilitation centers in the United States and Canada offer pain management programs. Ideally, the program will have its own unit apart from patient care areas. Good pain management programs offer comprehensive treatment that includes relaxation training and stress management techniques; group therapy, family therapy, personal counseling, and job retraining; physical therapy, including exercise and body mechanics; patient education regarding medications and other aspects of pain management; and aftercare or follow-up support.

The treatment team in a pain management program is usually headed by a neurologist , psychiatrist, or anesthesiologist with specialized training in pain management. Other members of the team include registered nurses, psychiatrists or psychologists, physical and occupational therapists, massage therapists, family therapists, and vocational counselors.

Clinical trials

As of December 2003, the National Institutes of Health (NIH) was sponsoring 35 studies related to various chronic pain conditions and the effectiveness of such treatments as acupuncture, hypnosis, yoga, COX-2 inhibitors, and several experimental drugs.

Special concerns

Pain management in special populations

Pain management in the elderly and in children poses additional challenges. Although 20% of adults over 65 take an analgesic on a regular basis, older people are more vulnerable to the drug's side effects, particularly the nausea and bleeding that sometimes results from long-term use of NSAIDs. Children require special attention because they do not have an adult's ability to describe their pain. New tools have been developed since the mid-1990s to measure pain in children and to help doctors understand their nonverbal cues.

Addiction and withdrawal

Doctors have debated the risk of opioid abuse for most of the past century. For many years, patients with severe chronic pain were not given enough of the drugs they needed to control their pain because of the fear that they would become addicted to the narcotics. In the mid-1980s, however, some experts in pain management argued that the risk of addiction was quite low, whether the patients suffered from cancer pain or from chronic pain unrelated to cancer. As a result, some synthetic narcotics—most notably oxycodone (OxyContin)—were widely prescribed and a growing number of patients became addicted to these drugs. As of 2003, researchers estimate that 3–14% of the population may have an underlying undiagnosed vulnerability to abuse these substances.

In addition to the risk of abuse, there is a risk of withdrawal symptoms and a temporary increase in pain (known as rebound pain) if opioid medications are dis-continued suddenly. Withdrawal symptoms include diarrhea, runny nose and watery eyes, restlessness, insomnia, anxiety, nausea, and abdominal cramps. These symptoms are usually treated with clonidine (Catapres), an antihypertensive drug, and NSAIDs or antihistamines. The various risks of long-term use of opioids in pain management are not yet fully understood.

Resources

BOOKS

Altman, Lawrence K., MD. Who Goes First? The Story of Self-Experimentation in Medicine. Berkeley, CA: University of California Press, 1998.

American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, 4th edition, text revision. Washington, DC: American Psychiatric Association, 2000.

Martin, John H. Neuroanatomy: Text and Atlas, 3rd ed. New York: McGraw-Hill, 2003.

"Pain." The Merck Manual of Diagnosis and Therapy, edited by Mark H. Beers, MD, and Robert Berkow, MD. Whitehouse Station, NJ: Merck Research Laboratories, 2002.

Pelletier, Kenneth R., MD. The Best Alternative Medicine, Part II, "CAM Therapies for Specific Conditions: Pain." New York: Simon & Schuster, 2002.

PERIODICALS

Daitz, Ben. "In Pain Clinic, Fruit, Candy and Relief." New York Times, December 3, 2002.

Duenwald, Mary. "Tales from a Burn Unit: Agony, Friendship, Healing." New York Times, March 18, 2003.

Halsey, James H., MD. "Atypical Facial Pain." eMedicine, February 9, 2001 (February 24, 2004). <http://www.emedicine.com/neuro/topic25.htm>.

Harstall, Christa, and Maria Ospina. "How Prevalent Is Chronic Pain?" Pain: Clinical Updates 11 (June 2003): 1–4.

Lasch, Kathryn E., PhD. "Culture and Pain." Pain: Clinical Updates 10 (December 2002): 1–11.

Meier, Barry. "The Delicate Balance of Pain and Addiction." New York Times, November 25, 2003.

Singh, Manish K., MD, Elizabeth Puscheck, MD, and Jashvant Patel, MD. "Chronic Pelvic Pain." eMedicine, November 7, 2003 (February 24, 2004). <http://emedicine.com/med/topic2939.htm>.

Wheeler, Anthony H., MD. "Therapeutic Injections for Pain Management." eMedicine, October 19, 2001 (February 24, 2004). <http://www.emedicine.com/neuro/topic514.htm>.

Wheeler, Anthony H., MD, James R. Stubbart, MD, and Brandi Hicks. "Pathophysiology of Chronic Back Pain." eMedicine, March 8, 2002 (February 24, 2004). <http://www.emedicine.com/neuro/topic516.htm>.

Yates, William R., MD. "Somatoform Disorders." eMedicine, November 20, 2003 (February 24, 2004). <http://www.emedicine.com/med/topic3527.htm>.

WEBSITES

<http://www.Pain.com>.

<http://www.PartnersAgainstPain.com>.

OTHER

National Institute of Neurological Disorders and Stroke (NINDS). "Pain—Hope Through Research." NIH Publication No. 01-2406. 2001. NINDS. "Chronic Pain Information Page." Bethesda, MD: NINDS, 2001. (February 24, 2004.) <http://www.ninds.nih.gov/health_and_medical/pubs/migraineupdate.htm>.

ORGANIZATIONS

American Academy of Neurology (AAN). 1080 Montreal Avenue, Saint Paul, MN 55116. (651) 695-2717 or (800) 879-1960; Fax: (651) 695-2791. memberservices@ aan.com. <http://www.aan.com>.

American Academy of Pain Medicine (AAPM). 4700 West Lake, Glenview, IL 60025. (847) 375-4731; Fax: (877) 734-8750. [email protected]. <http://www.painmed.org>.

American Chronic Pain Association. P. O. Box 850, Rocklin, CA 95677. (916) 632-3208 or (800) 533-3231. ACPA@ pacbell.net. <http://www.theacpa.org>.

American Pain Foundation. 201 North Charles Street, Suite 710, Baltimore, MD 21201-4111. (888) 615-PAIN. <http://www.painfoundation.org>.

International Association for the Study of Pain (IASP) Secretariat. 909 NE 43rd Street, Suite 306, Seattle, WA 98105-6020. (206) 547-6409; Fax: (206) 547-1703. [email protected]. <http://www.iasp-pain.org>.

NIH Neurological Institute. P. O. Box 5801, Bethesda, MD 20824. (301) 496-5751 or (800) 352-9424. <http://www.ninds.nih.gov>.

Rebecca J. Frey, PhD

Pain

Psychological aspects of pain perception

Medical aspects of pain

Psychophysiology of pain

Affect and motivation

Toward a definition of pain

bibliography

The relief of pain and suffering has been a continuing human endeavor since the dawn of recorded history (see Keele 1957). Yet despite centuries of observation and study, we are only beginning to achieve an understanding of the subtleties and complexities of pain. Even though pharmacologists have provided effective “painkillers,” we know little about where and how these drugs act. Surgical procedures that are usually effective in relieving pain can sometimes produce dismal failures, often enough to convince us that we are far from understanding the neurological mechanisms that subserve pain perception.

Part of the difficulty of understanding pain mechanisms lies in the divergent empirical approaches to the problem. Sensory physiologists, anatomists, and psychologists (see Ruch & Fulton 1960, pp. 300-368) have studied pain as a sensory phenomenon and have tended to neglect its motivating aspects. Learning theorists (Miller 1951; Bindra 1959) have dealt with pain primarily as a drive producer and negative reinforcing agent but have generally ignored the other facets of the problem. Finally, medical clinicians, such as anesthetists (Beecher 1959) and surgeons (White & Sweet 1955), have regarded pain as indicative of tissue pathology that has to be treated and abolished and have often had to postulate hypothetical neural mechanisms to account for the complex phenomena they observe. These three approaches are so different that it is not surprising that “pain” has never been satisfactorily defined (Beecher 1959).

The major obstacle to understanding pain, however, has been the perpetuation of a number of theories that have had a powerful influence on the field. The persistence of these theories has resulted in heated controversies that have endured since the beginning of this century. Consequently, one of the most difficult tasks in this field is to separate fact from theory. For this reason the psychological and clinical phenomena of pain, which must be accounted for by any satisfactory theory, will be described before physiological theories and experiments are discussed.

Psychological aspects of pain perception

The obvious biological significance of pain has led to the general belief that it must always occur after injury and that the intensity of pain perceived is proportional to the amount and extent of the damage. The positive aspect of pain is universally recognized: it warns us that something biologically harmful is happening. Reports (Sternbach 1963) of people who are born without the ability to feel pain provide convincing testimony to its value. Such a person sustains extensive burns and bruises during childhood and learns only with difficulty to avoid inflicting severe wounds on himself. Nevertheless, there is convincing evidence that pain, in higher species at least, is not simply a function of the amount of bodily damage alone. Rather, the amount and quality of pain perceived are also determined by past experience and attention, by the ability to understand the cause of the pain and to grasp its consequences. This fact, supported by a large body of evidence, presents a challenge to pain theorists.

Cultural factors

Cultural values are known to play an essential role in the way a person perceives and responds to pain. In Western culture, for example, childbirth is considered by many to be one of the worst pains a human being can experience. Yet the practice of couvade (Kroeber [1923] 1948, pp. 542-543) in cultures throughout the world indicates the extent to which culture contributes to the intensity of pain. In some of these cultures a woman who is going to have a baby continues to work until the child is about to be born. Her husband then gets into bed and groans as though he were in great pain while she bears the child. In more extreme cases, the husband stays in bed with the baby to recover from the terrible ordeal and the mother returns almost immediately to her household work. Dick-Read (1944) has stressed the great extent to which culturally determined fear enhances the amount of pain felt during labor and birth and points out how difficult it is to dispel such fear.

Role of anxiety

The effect of anxiety on the intensity of perceived pain is further demonstrated by studies on the effectiveness of placebos. Beecher found that severe pains (such as postsurgical pain) can be relieved in about 35 per cent of patients by giving them a placebo, such as sugar or saline solution, in place of morphine or other analgesic drugs. As Beecher has pointed out, only about 75 per cent of patients experiencing severe pain are satisfactorily relieved even when given large doses of morphine; the placebo effect thus accounts for about 50 per cent of the drug effectiveness (1959, p. 169). This in no way implies that people who are helped by a placebo do not have real pain; no one will deny the reality of postsurgical pain. Rather it illustrates the powerful contribution of anxiety to pain perception, since the physician may often relieve pain significantly by prescribing placebos to lower the patient’s anxiety as well as by treating the wounded areas of the body. Similarly, experiments by Hall and Stride (1954) have shown that the anticipation of pain raises the level of anxiety and, consequently, the intensity of perceived pain. Experiments by Hill and his associates (1952a; 1952b) have shown that a given level of electric shock or burning heat is perceived as significantly more painful when anxiety is experimentally induced than it is after anxiety has been dispelled. These studies also show that morphine diminishes pain if the anxiety level is high but has no demonstrable effect under conditions of low anxiety.

Role of attention

Attention to stimulation also contributes to pain intensity. It is frequently noted that contestants in a fight or in the heat of a game can receive severe wounds without being aware that they have been hurt. Indeed, almost any situation that attracts a sufficient degree of excited, prolonged attention may provide the conditions for other stimulation to go by unnoticed, including wounds that would cause considerable suffering under normal circumstances. Hypnosis, a trance state in which attention is focused intensely on a person or an object, is perhaps the best-known condition in which people can be cut or burned without their reporting any perception of the event (Barber 1959). Failure in attention may also account for the fact that dogs raised in sensory isolation in specially constructed cages from infancy to maturity (Melzack & Scott 1957) show a frequent failure to respond to normally painful stimulation, such as a flaming match or pinprick, after they are released from their cages. Since these dogs exhibit a remarkably high level of excitement, it is reasonable to suppose (Melzack & Burns 1963) that they fail to attend selectively to these noxious stimuli when they are presented in an unfamiliar environment in which all stimuli are equally attention-demanding. [SeeAttentionandHypnosis.]

Role of meaning

Finally, there is striking evidence to show that the meaning associated with a pain-producing situation is extremely important in determining the degree and quality of pain that are perceived. Beecher observed soldiers who were severely wounded in battle and found that only one out of three claimed that he had enough pain to require morphine. Most of the soldiers denied having pain from their wounds or had so little that they did not want medication to relieve it. In contrast, four out of five hospitalized civilians who had surgical incisions matching the wounds received by the soldiers claimed that they were in severe pain and demanded a morphine injection. Beecher concluded that in the wounded soldier, the response to injury was relief, thankfulness for his escape alive from the battlefield, even euphoria (his wound was a good thing); to the civilian, his major surgery, even though essential, was a depressing, calamitous event; there is no simple direct relationship between the wound per se and the pain experienced (1959, p. 165).

The importance of the meaning associated with a pain-producing situation is made especially clear in conditioning experiments by Pavlov (1923). He found that if electric shocks administered to a dog’s paw are followed consistently by the presentation of food, they eventually fail to elicit signs of pain and produce an entirely different response: the dog salivates, wags its tail, and turns toward the food dish. Masserman (1950) has carried these experiments still further. After cats had been taught to respond to electric shock as a signal for feeding, they were trained to administer the shock to themselves by walking up to a switch and closing it.

Medical aspects of pain

Theories of pain are satisfactory only to the extent that they are able to account for all of the relevant phenomena. There are many forms of pathological or clinical pain that present bizarre features that are difficult to explain; yet they must fit into the framework of pain theory. Two pain syndromes, phantom-limb pain and causalgia, have been studied in detail and represent the most terrible of human pain experiences.

Phantom-limb pain

The presence of a painless phantom limb is reported by the majority of amputees almost immediately after amputation. About 30 per cent, however, have the misfortune to develop pains in the phantom limb, and in about 5 per cent the pain is severe. These pains may be occasional or continuous, but they are felt in definite parts of the phantom limb (Livingston 1943; Feinstein et al. 1954). The pain tends to decrease and eventually disappear in most amputees. There are a few, however, in whom the pain increases in severity over the years and may even spread to other regions of the body, so that merely touching these new “trigger zones” will provoke spasms of severe pain in the phantom limb (Cronholm 1951). Unfortunately, the conventional surgical procedures for controlling pain usually fail to bring permanent relief; thus, these patients may undergo a series of such operations without any decrease in the severity of the pain (Livingston 1943). Phenomena such as these defy explanation in terms of our present physiological knowledge. Attempts have been made to label these unfortunate people as “neurotic” (see Kolb 1954), but there is convincing evidence that argues against such an explanation for all cases (Livingston 1943).

There are a number of features of phantomlimb pain that provide clues toward understanding the mechanisms underlying it.

Peripheral factors. It is known (Livingston 1943) that the neuromas (small nodules of regenerating nerve tissue) in the stumps of amputated patients contribute to phantom-limb pain, since pressure on them can trigger bouts of unbearable pain. Yet excision of neuromas or reamputation at a higher level usually fails to relieve pain for more than a few weeks or months (Livingston 1943; Cronholm 1951). Indeed there is almost unanimity of opinion that peripheral operations are likely to fail and that other procedures should be sought.

Role of sympathetic nervous system. The sympathetic nervous system also plays an important role, because cutting or temporarily anesthetizing the sympathetic ganglia entering the spinal cord (Livingston 1943) is capable of dramatically removing the pain for variable periods of time. Yet it is clearly not the sole cause of phantom-limb pain because pain often returns after the sympathetic ganglia are surgically removed. The contribution that the autonomic nervous system as a whole makes to phantom-limb pain is clear, moreover, from observations (Henderson & Smyth 1948) that pain is triggered in many patients at the start of urination or defecation. Similar sudden increases of pain may be triggered by sexual excitement and orgasm (Kolb 1954).

Emotional factors. Phantom-limb pain is greatly enhanced by emotional factors. Seeing a disturbing movie (Kolb 1954), having an argument with wife or husband (Livingston 1943), and other emotionally disturbing situations are capable of initiating or increasing the intensity of phantom-limb pain.

Role of sensory input. Either increasing or decreasing the sensory input from the stump or related areas is capable of providing relief from phantom-limb pain. Feinstein, Luce, and Langton (1954) have demonstrated that injection of the vertebral tissues of amputees with 6 per cent salt solution produces severe pain at the site of injection, which then radiates into the phantom limb. After this initial onset of pain, there is usually a decrease of the phantom-limb pain. Occasionally the pain vanishes completely following a single injection. Similarly dramatic results may occur after an injection of anesthetic procaine into the vertebral tissues in the attempt to decrease sensory input from these regions. Comparable findings are reported when stimulation is increased or decreased at the peripheral level. Injection of the tender neuromas of the stump with procaine solution often brings about sudden and dramatic relief for variable periods of time. On the other hand, stimulation of the stump, by massage or by hitting it with a small rubber mallet, often produces the only possible relief from phantom-limb pain in a large number of patients (Russell & Spalding 1950).

Spread of pain and trigger sites. Finally, there is the spread of pain and of trigger sites beyond the segments directly involved in the limb. Thus Cronholm (1951) found that touching the small of the back or the forehead may induce spasms of pain in a phantom leg. These trigger zones spread in unusual, seemingly random patterns and are not related in any apparent way to the segmental distribution of the somatic afferent nerves.

Causalgia

Causalgia is a severe, unremitting, burning pain that occurs in about 2 per cent of people who have sustained a peripheral-nerve injury. The pain is felt in the affected limb but may spread to other parts of the body. It exhibits many of the features of phantom-limb pain as well as other even more bizarre characteristics. Surgical procedures have only limited success in the treatment of causalgic pain. Section of the peripheral nerve at a higher level, amputation of the limb, and cutting the dorsal sensory roots that enter the spinal cord have all produced as many failures as successes. Indeed, operations have been performed for causalgic pain at nearly every possible site in the pathway from the peripheral receptors to the sensory cortex, and at every level the story is the same: some encouraging results but a disheartening tendency for the pain to return (see Livingston 1943).

Nonspecific triggering stimuli. A further remarkable feature of causalgia is that a variety of stimuli that can hardly be called “adequate pain stimuli” can produce increases in pain. Sudden noises, the sound of airplanes, the scraping of a shoe on the floor, emotional disturbances, almost any stimulus that elicits a startle response, touching the damaged leg or arm or even blowing lightly on it are all capable of making the pain worse (Livingston 1943).

Sympathetic nervous system in causalgia. The involvement of the sympathetic nervous system in causalgia, as in phantom-limb pain, is obvious. The skin becomes dry and cool, and sweat may drip from a single finger (Livingston 1943). Moreover, injection of anesthetic procaine into the sympathetic ganglia may dramatically abolish the pain for variable periods of time. But the fact that pain may return after surgical removal of sympathetic ganglia (Livingston 1943) indicates that sympathetic-nervous-system activity is not the primary cause of the pain.

Role of sensory input in causalgia. Similarly, an abnormal sensory input from the site of the nerve lesion is clearly implicated as an important cause of causalgic pain. Procaine blocks proximal or distal to the lesion may abolish pain for hours or days, and on rare occasions it never returns. Livingston (1943) reports, moreover, that the pain can be abolished if the patient is trained to tolerate sensory stimulation of the affected limb and is encouraged to use it normally. But the frequent failure of peripheral-nerve surgery to abolish pain indicates that more is involved than simply an irritating peripheral lesion.

Psychophysiology of pain

The psychological and clinical phenomena of pain that have been described above must be taken into account in any satisfactory theory of pain. Since physiological evidence on the sensory mechanisms of pain is intimately bound up with the theories in vogue at the time, it is necessary to consider the physiology in terms of theoretical orientation.

Orthodox specificity theory

The orthodox theory of pain, still the most widely held, was first proposed by Max von Frey in 1895 (see Melzack & Wall 1962) and was subsequently extended in a vast literature on pain mechanisms (see Bishop 1946; White & Sweet 1955). Von Frey’s theory, also known as specificity theory, proposed that there are specific pain receptors (the free nerve endings) which, when stimulated, give rise to pain and only to pain. Following this idea, physiologists proposed that pain is carried by peripheral-nerve fibers of particular diameter (the A delta and C fibers), a distinct spinal-cord system (the spinothalamic tract), and a particular projection area in the thalamus, which is presumed to be the seat of pain sensation. Specificity theory has been the subject of heated debate and controversy since it was first proposed, and an attempt has recently been made (Melzack & Wall 1962) to analyze the features of this theory that make it both attractive and repugnant.

Von Frey’s specificity theory has three underlying assumptions. The first is physiological: the theory assumes that each receptor in the skin has a specific irritability, that is, a lowest threshold for some particular stimulus energy. There is convincing evidence to indicate that this assumption is valid, and it has been restated by Sherrington (1906) as the law of the adequate stimulus. The second assumption concerns the morphological receptor that is associated with pain experience. It is now certain (Weddell 1955) that the free nerve endings transmit information not only about pain but also about warmth, cold, touch, itch, tickle, and the myriad other experiences that derive from cutaneous stimulation. The third assumption of specificity theory is psychological: it assumes a one-to-one relation between skin receptor and psychological experience.

Inadequacy of specificity theory. It is the assumption of a one-to-one relation between skin receptor and psychological experience that has led to attempts at outright rejection of von Frey’s theory. The theory implies a direct transmission system in which there is an invariant, one-to-one relationship between stimulus intensity, peripheral receptor, central-nervous-system pathway, and intensity of pain perceived. Almost all of the psychological and clinical phenomena described above argue against this simple one-to-one relationship. The fact that a light puff of air on the skin, emotional disturbance, or arousal of the autonomic nervous system can elicit bouts of excruciating causalgic and phantom-limb pain indicates that there is more to pain mechanisms than a straight-through system from specific peripheral receptors to a pain center in the brain.

Pattern theory

Alternative theories have been proposed to replace specificity theory. Their history dates back to the time of von Frey’s theory, and each is characterized by complex physiological mechanisms that are postulated to account for the complex psychological and clinical phenomena of pain. Collectively, these alternative theories may be brought together under a single conceptual name: pattern theory. It proposes essentially that information at the skin is coded in the form of nerve-impulse patterns, which provide the basis of our sensory perceptions. These patterns, moreover, can undergo modification during their transmission centrally, that is, the quality and intensity of pain can be modulated by events in the central nervous system, such as memories, emotions, and attention. The most recent formulation of a pattern theory for cutaneous perceptions (Melzack & Wall 1962) proposes that skin receptors have specialized physiological properties for the transmission of particular kinds and ranges of stimuli into patterns of nerve impulses, rather than modality-specific information, and that every discriminably different somesthetic perception is produced by a unique pattern of nerve impulses.

The concept of patterning of nerve impulses, together with three recently discovered features of the skin sensory system, provides the basis for a new theory of pain (Melzack & Wall 1965). First, there is now abundant physiological and anatomical evidence of efferent fiber systems that run from the brain down to the afferent pathways and are capable of modifying or inhibiting the afferent pattern in the course of its transmission centrally (see Livingstone 1959). Second, the dorsal-column and dorsolateral systems of the spinal cord have properties (see Melzack & Wall 1965) indicating that their function may well be that of arousing the central processes subserving memories of prior experience, attention, and so forth, which are then able to act downward on the afferent impulse patterns.

The third line of evidence derives from the recent work of Wall (1962), which shows that a sensory input arriving at the spinal cord has two effects. First, it transmits information from the peripheral nerve to spinal-cord cells whose fibers go to the brain, and, second, it influences the properties of the substantia gelatinosa, a diffusely interconnected band of tissue lying throughout the length of the spinal cord in the dorsal horn. Mendell and Wall (1964) have shown that the substantia gelatinosa can both inhibit and facilitate the transmission of the coded sensory information from peripheral fiber to central cell. They point out that there is a continuous tonic input from the periphery to the substantia gelatinosa, so that continual inhibitory control is exerted over the transmission of nerve impulses across the synapses from peripheral fibers to central cells.

This tonic inhibition can be increased or decreased by the size of the fiber stimulated. Thus the largest A fibers increase the tonic inhibitory effect of the substantia gelatinosa, while the smalldiameter C fibers decrease the inhibitory influence, that is, actually facilitate the transmission of information in such a way that there is a greater likelihood of all inputs, from the peripheral and autonomic nervous systems, as well as from the brain, summating and thereby producing the characteristic pattern of high-frequency bursts of impulses that signals pain. The substantia gelatinosa,moreover, is a functionally continuous unit, so that different parts of the body are connected in a way that permits the spread of trigger zones observed in phantom-limb and causalgic pain.

Gate control theory

These three features of the skin sensory system provide the basis for a gate control theory of pain (Melzack & Wall 1965). The theory proposes that (1) the substantia gelatinosa functions as a gate control system that modulates the amount of input transmitted from the peripheral fibers to the dorsal horn transmission (T) cells; (2) the dorsal column and dorsolateral systems of the spinal cord act as a central control trigger, which activates selective brain processes that influence the modulating properties of the gate control system; and (3) the T cells activate neural mechanisms that constitute the action system responsible for both response and perception.

Figure 1 provides a schematic diagram of the gate control theory, showing the large-diameter and small-diameter peripheral fibers and their projections to the substantia gelatinosa (SG) and T cells in the dorsal horn. The inhibitory effect exerted by the substantia gelatinosa on the afferent fiber terminals is shown to be increased by activity in the large fibers and decreased by activity in the small fibers. The central control trigger is represented by the heavy line running from the largefiber system to the central control mechanisms; these mechanisms, in turn, project back to the gate control system. The T cells project to the entry cells

of the action system. Excitation is represented by +; inhibition by –.

The theory proposes that pain phenomena are determined by interactions among these three systems. For example, a marked loss of the large peripheral-nerve fibers, which may occur after traumatic peripheral-nerve lesions or in some of the neuropathies (Greenfield 1958), such as postherpetic neuralgia (Noordenbos 1959), would decrease the normal presynaptic inhibition of the input by the gate control system. Thus, the input arriving over the remaining large and small fibers is transmitted through the unchecked, open gate produced by the small-fiber input. This, together with the opportunity for summation of inputs into thesubstantia gelatinosa from other parts of the body and from the brain, provides the basis for the triggering of pain by a variety of stimuli that are normally not noxious.

Affect and motivation

Pain has generally been considered primarily a sensory experience somewhat similar to sight or hearing. In one important respect, however, pain differs from vision and hearing: it has a unique, distinctly unpleasant quality that wells up in consciousness and obliterates anything we may have been thinking or doing at the time. It becomes overwhelming and demands immediate attention. Besides its sensory component, then, pain also has a strong emotional quale that drives (or motivates) the organism into doing something about it. Ensuing responses are such as to stop the pain quickly by whatever course of action is possible.

Introspectionist psychologists at the turn of the century made a sharp distinction between the sensory and the affective dimensions of the pain experience. Titchener (1909) was convinced that there is a continuum of feeling in conscious experience, distinctly different from sensation, that ranges through all degrees of pleasantness and unpleasantness. These two dimensions, the sensory quality and the affective quale, are brought clearly into focus by clinical studies on prefrontal lobotomy (Freeman & Watts 1942), a neurosurgical operation for intense pain in which the connections between the prefrontal lobes and the rest of the brain are severed. Typically, these patients report after the operation that they still have pain but that it no longer bothers them; they simply no longer care about the pain and often forget it is there. It is certain that the operation does not stop pain perception entirely, since the sensory component is still present. The predominant effect of the operation seems to be on the affective coloring of the total pain experience; the terribly unpleasant quality of the pain has been abolished.

Brain areas involved. Recent experiments suggest that there are portions of the brain that are particularly concerned with the motivating aspects of behavior. Miller (1957) has recently found subcortical areas in the brain that produce vigorous escape reactions, cries, and other emotional behavior characteristic of pain perception when they are stimulated electrically. It seems possible that the activities in these areas provide the neural substrate for the affective, “driving” component of pain perception. [SeeNervous System, article onBrain Stimulation.]

Toward a definition of pain

In recent years the evidence on pain has moved in the direction of recognizing the plasticity and modifiability of events occurring in the central nervous system. In the lower part of the brain at least, the patterns of nerve impulses evoked by noxious stimulation travel over multiple pathways going to widespread regions of the brain and not along a single path going into a “pain center.” The psychological evidence lends strong support to the consideration of pain as a perception determined by the unique past history of the individual, by the meaning the stimulus has to him, by his “state of mind” at the moment, as well as by the sensory nerve patterns evoked by a physical cause. In this way, pain becomes a function of the whole individual, including even his thoughts and hopes for the future.

Pain, then, refers to a category of complex experiences, not to a kind of stimulation. Clearly, there are many varieties and qualities of experience that are simply categorized under the broad heading of pain because they defy more subtle verbal description. There are the pains of a scalded hand, a stomach ulcer, a sprained ankle; there are headaches and toothaches. But there is also the heartache of the scorned lover, the pain of losing a dear friend. It may be argued that the pain of bereavement is very different from the pain that follows surgery. But the pain of a coronary occlusion is just as uniquely different from the pain of a scalded hand.

Why is it so difficult to achieve a satisfactory definition of pain? The answer appears to be that pain is not a single, specific experience that can be analyzed and manipulated. It may be agreed that pain, like vision and hearing, is a complex perceptual experience. But the numerous, diverse causes of pain prevent the specification of a particular kind of environmental energy as the specific stimulus for pain, in the way that light can be specified as the adequate stimulus for vision, and air pressure waves for hearing. Pain is a category of experiences, signifying a multitude of different unique events having different causes and characterized by different qualities varying along a number of sensory and affective dimensions.

Ronald Melzack

[Directly related are the entriesNervous System; Senses; Skin Sensesand Kinesthesis. Other relevant material may be found inDrugs; Hysteria; Psychology, article onPhysiological Psychology; Psychosomatic Illness.]

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PAIN

There is no consistent philosophical view concerning the nature of pain, how to understand it, or what an understanding of pain might mean for philosophy of mind. Just about every conceivable position concerning the nature of pain is held by some leading thinker. Each of these positions has become grist for someone's mill in arguing either that pain is a paradigm instance of a conscious state or that pain is a special case and should not be included in any general theory of consciousness.

Philosophical Views of Pain

Some philosophers and psychologists hold that pain is completely subjective: Either it is essentially private and completely mysterious, or it does not correlate with any biological markers but is completely nonmysterious. The International Association for the Study of Pain (IASP), the formal organization charged with defining pain, has articulated a paradigm subjective view. They write: "Pain is always subjective…. Many people report pain in the absence of tissue damage or any pathophysiological cause; usually this happens for psychological reasons. There is usually no way to distinguish their experience from that due to tissue damage if we take the subjective report…. [Pain] … is always a psychological state" (1986).

However, if one holds that pain does not correlate in some way with some sort of bodily state or event, one becomes a dualist. If pain just is a private experience, and that experience has no consistent underlying physical cause or correlate, then any interesting connection between the mind and the body over pain is lost.

Philosophers can eschew dualism by retreating to so-called token-token identity theory. Every experience in some creature is correlated with—identical to—some event or other in that creature's brain. And every experience in some other creature is correlated with—identical to—some event or other in that creature's brain. If the subjectivists are right, then there is no identifiable neural activity that is the same across all experiences of a type of pain. There is no brain correlate for the type "having a migraine headache," for example. Generic headache experiences occur only at a level of abstraction above brain activity—namely, in the mind and its cognitive states.

However, if philosophers deny type-type identity for larger brain structures across organisms, then they are also denying any hope of discovering mind-brain connections. For mental event-physical state correlations taken one at a time are all a robust token-token identity theory allows.

At the same time, scientists do believe that there are areas in the brain dedicated to pain processing, just as there are other areas dedicated to vision, audition, touch, and so forth. They believe that these areas are basically the same across humans, despite individual variation. Thus, even though a strict type-type identity might fail for particular sensory experiences, it still underlies views of our sensory systems taken as a whole. Types in science are allowed some play in them. They have to, or else there would be no mechanism by which to pick out any sort of cognitive processing in the brain at all.

All these lessons are missed by proponents of the subjective view, for they identify pain with the experience of pain and then explicitly deny that that experience has any correlation with any particular bodily reaction. But insofar as they want to be materialists interested in a scientific understanding of pain, they will have to permit generalizations connecting something in the body with the sensation of pain (see Hardcastle 1999).

Other philosophers and neurophysiologists argue that pain is completely objective; it is either intrinsic to the injured body part, a functional state, a set of behavioral reactions, or a type of perception. Pain is something that can be measured in bodies or behavior. As such, its connection to mentality, to sensations of pain, is secondary at best. Humans might recognize pain in terms of how it feels—the skin burns, for example. But, according to objective views that take pain as intrinsic to the injured body part, the pain itself is in the tissue. Hence, beliefs or judgments about the condition of the tissue are derivative—that is, pain is inferred from peripheral nociceptive or pain information (Annad and Craig 1996, Derbyshire 1996).

Similarly, if pain is understood as a type of perceptual process, then it works no differently than vision or olfaction. Animals receive some sort of perceptual input on their transducers, manipulate that information in their brains, and then use that manipulated information to alter motor reactions and other mental states. Part of the manipulated information might come into conscious awareness, but that sensation would constitute only a subset of what is meant by pain processing. According to this view, conscious experiences of pain, the damaged tissue itself, and the bodily and emotional reactions are all fundamental to pain processing. Each is one component in a larger process. Working together, these components take pressure, temperature, and chemical readings of tissues and use this information to track what is happening in bodies (Wall and Melzack 1989).

In these cases and most other instances of the objective view, pain is something entirely physical. Prima facie, it appears that the states or processes identified with pain could occur without any awareness of them at all. Most objective views of pain have the unintuitive consequence of divorcing pain from sensations of pain or making the mental events associated with pain processing secondary to and dependent upon the pain processing itself.

There are a few objectivist philosophers who hold that pain is not a purely physical event. Instead, it is something like an attitudinal relation. Pain requires both a bodily state and then cognition over that state. Pain itself is the attitude, the belief, regarding one's bodily condition. This approach gets around the intuitive difficulties of the objective views by identifying pain with the consequent mental state. "Pain" then just refers to the mental event associated with pain processing. According to this view, there is pain processing and then pain proper.

Central Philosophical Issues

There are three large philosophical difficulties in defending any of the theories about pain processing outlined above: the problem of mental causation, the problem of naturalizing content, and the threat of eliminativism.

The difficulty with mental causation is roughly as follows. If one drops a hammer on one's foot and subsequently experiences pain, that experience is the proximal cause of one's writhing, cursing, and gnashing of teeth. Dropping a hammer on one's foot leads to pain behavior only if it causes in one the sensation of pain and the belief that one is in pain. If one were unconscious or otherwise oblivious to one's surroundings, then one could not sense any pain, nor could one believe that one were in pain. One could manifest no pain-related behavior either.

On the other hand, a neurophysiological view of the hammer-dropping incident seems be able to explain exactly the same events without appealing to mentality or any sort of psychological entities at all. Neurophysiologists might talk about how the intense pressure of the hammer head on a foot stimulates various nerve endings and thus causes action potentials to travel up a leg to a spinal column, where other nerves are then stimulated to fire. These nerves transmit the firing pattern to other nerves, and so it goes until nerves that cause muscles to contract are likewise stimulated and one gets the writhing, wincing, and teeth-gnashing behavior. Why doesn't the possibility of this sort of more precise, purely physical explanation rule out the higher-level, more general mental account? Or why doesn't it make the mental account nothing more than a placeholder until the details of our central nervous system get figured out? As long as one is persuaded by reductionism, then pain provides an exemplar case for why psychological explanations appear so tricky.

There is some evidence that depression is related to pain processing. One view is that untreatable chronic pain causes depression, which in turn increases the sensations of pain. This is a (grossly oversimplified) mentalistic explanation of how a mood causally interacts with other psychological states. At the same time, we know that depression is correlated with a decrease in the neurotransmitter serotonin. Persons suffering from just an imbalance of a neurotransmitter and sensations of pain are some neural state or other, then it seems that the relation between depression and pain should be explained in terms of neurotransmitters affecting neural activity. In this case, the mentalistic explanation is just a stand-in until all the more basic neurphysiological details are revealed.

Mental events causing other mental events seems to be a natural part of the explanatory world. At the same time, accounts of mental causation appear to be nothing over and above a sloppy characterization of more fine-grained and little understood physical details. The difficulty for those who would like to keep the mind intact as an explanatory unit is explicating how it is that mental causation has a legitimate place in an understanding of the universe above and beyond being a surrogate for the real causal story.

Though most philosophers of mind treat mental causation separately from issues concerning reference, explaining the causal powers of the mind really piggybacks on the problem of naturalizing content. What makes the question of mental causality peculiar is that the content of the mental states is relevant to their efficacy. One winces and nurses one's foot because one's corresponding mental states are about one's foot. If they were about something else, then one would most likely be doing something else. To explain exactly how it is that mental events cause other things, philosophers are first going to have to explain how it is they refer. That is, to justify privileging a mentalistic explanation of sensations and beliefs over a lower-level physicalistic one of neuronal firing patterns or ionic flow, first philosophers have to have a clear grasp on what it means to have mental events with content, since their content is what is causally relevant to subsequent behavior.

The question about the power of the content of beliefs and other mental states is quite important to understanding pain processing (Gamsa 1994). What one is thinking and believing about the world strongly influences how much pain one feels. Athletes intently focusing on their game can break large bones and not even notice it. But the same athletes, alone in their living rooms, will writhe on the floor if they stub their toes. Chronic pain patients can be trained to diminish their sensation of pain by changing their focus of attention and their beliefs about death and disease. Those suffering congenital indifference to pain often lead short and unpleasant lives both because they can't sense painful stimuli but also because they cannot form appropriate beliefs about the meaning of the vague tinglings they do feel. How pain feels depends to a large extent on the current doxastic milieu. Hence, understanding pain is going to require understanding what beliefs and desires (and other mental states) are and how they refer.

One implication of current scientific theories of pain is that folk ways of describing pains are inadequate and people would be better off eliminating the descriptors from everyday practices (Dennett 1978). The claim is that folkways of talking about pain comprise a rough and ready theory of pain. This theory assumes that pains are identical to the sensations of pain and that the word pain can capture the essence of that sensation. From the perspective of some objective views of pain, both assumptions are dubious. Pain processing is enormously complicated, and sensations of pain form only a tiny subset of what these processors do. But even if one focuses exclusively on sensations, the most important to folkways of being, the folk theory is still inadequate. Words to express all the dimensions of pain experiences simply do not exist. The descriptors used are either metaphorical or nonexistent. The folk theory of pain needs to be replaced by something commensurate with the phenomenology.

Consider that not only can the sensory, affective, and cognitive dimensions of pain be distinguished phenomenologically, but they can also be manipulated independently of one another. Mammals can feel a shooting pain in their legs but not suffer in the least from it; they can be in agony from pain without feeling any particular sensation localized to any part of their bodies. Philosophers could just decide by fiat that pain is going to refer to the localized sensations, or they could just decide that pain is going to refer to the suffering. But either way they do violence to folk notions of pain, which require that a single simple sense datum both seem to occur in some place and be unpleasant.

In response to these sorts of claims, some have argued that folk views of pain do not constitute a theory in any meaningful sense. Some believe that certain introspective facts are known indubitably. Pain is touted as one of those things. Perhaps there are some sensory states, like pain, about which people have special first-person apprehension; no inference of judgment is required.

However, it is quite easy to demonstrate that introspective knowledge of pain can be mistaken. If one burns one's hand by touching something hot, one jerks one's hand away from the heat source. This is a reflex action; the nociceptive information travels up the arm to the spinal column and then back down again. It takes about 20 to 40 msec from stimulus to behavior. The information also travels up the spinal column to the brain. One feels the burn as well. Unlike the reflex movement, this processing is more complicated and takes about 200 to 500 msec from stimulus to percept, a full order of magnitude longer.

Nevertheless, if one introspectively reports on what the incident feels like, one says that one moved one's hand away after one felt the pain; feeling pain initiated the motor sequence. For whatever reason, brains backdate pain sensations so that they seem causally relevant to reflex behavior. But clearly the effect is not caused after it occurs, so the introspective report has to be wrong. There is not any special, first-person knowledge of pains. Whatever knowledge is had is embedded and informed by a conceptual framework of the brains' devising. Despite protests to the contrary, pain experiences have all the earmarks of being at least prototheoretical in nature.

Other detractors point out that even if a completed science of pain does not use folk terms for pain, that would not imply that those sorts of mental states do not exist; they just would not be referred to in scientific discourse. The notion of pain would be analogous to ideas about tables and chairs, germs and gems, and birthday presents and birthday cake. These are perfectly legitimate terms. Science just does not use them. Being cultural artifacts of one stripe or another, they do not refer to things about which there are laws. There might not be a mental science or laws about pains, but folk psychology could still be used as it is now, in everyday explanations of behavior.

There is something undoubtedly right about this charge. In many ways, pain experiences are environmentally determined. Puppies raised without ever experiencing pain and without ever seeing any other dog in pain will exhibit no pain behavior. They will repeatedly sniff a lighted match without fear and then show no reaction when burned. Children learn both pain behaviors and the emotional concomitants to pain from the reactions of others around them. Expressions of pain and reports of sensation and experience are significantly different across cultures. Most of pain experiences and expressions are socially relative, a cultural artifact of sorts.

However, social relativity is not enough to show that folkways of understanding pain are adequate. Different cultures have different experiences; they also have different ways of understanding these experiences. Nevertheless, the burden falls on the folk psychologist to demonstrate how folk theories of pain are actually successful. This work has not just begun.

The Ethics of Pain Treatment

One of the most hotly debated subjects in pediatric care concerns whether infants are insensitive to pain (cf. Lawson 1988). The presumption historically has been that because young infants are not conscious, they cannot sense pain. As a result, analgesics and anesthesias are rarely used, even in the most invasive of procedures.

At first, this presumption of insensitivity is curious because infants' reactions to painful stimuli are well documented. Even premature neonates exhibit stress responses, hormonal fluctuations, and slowed recovery to painful interventions. In fact, the afferent nociceptive system is up and running by twenty-nine weeks of gestation, even though the pain inhibitory systems do not come on line until later. If anything, infants should be more sensitive to pain than adults. At least, by all indications, infants are sensitive to pain in some sense or other.

However, the question for many doctors is whether infants are aware of their pain. Some argue that unless neonates can consciously apprehend pain, then any sort of response they give to noxious stimuli are merely reflexes. Hence, there is no reason to treat infants' pain because the infants cannot feel anything.

Suppose they are right, even though there is much that goes on in brains that is neither conscious nor mere reflex. It is still the case that infants react to pain, both behaviorally and physiologically, that these reactions can be modified with relatively simple treatments, and that treating pain has an impact on recovery. Early exposure to pain, whether remembered or not, affects later experiences of and reactions to pain by altering the developmental course of the nervous system. Infants, like other newborn animals, learn to attach particular meanings or emotions or importance to particular experiences in virtue of what is associated with those experiences. This sort of behavioral malleability is very important if an organism is going to survive in a complex environment. Consequently, manipulating early experiences can have drastic effects later on, as animal studies show. Merely by changing the smells associated with suckling, scientists can alter adult sexual behavior in male rats, for example. Similar changes occur with pain processing in young infants. Nociceptive stimuli increase the size of the somatic receptive fields for neurons sensitive to pain and help maintain dendritic connections that would otherwise be eliminated over time. Perhaps, as some believe, chronic pain and hypersensitivity can result from early acute pain episodes, given how the neural receptors change. Early pain experiences have been shown to influence later personality and temperament. Something as common as circumcision can have lasting effects on pain sensitivity if done without anesthesia.

Given the impact early pain processing can have on later development, doctors have every reason to prevent infant pain, even if it feels dissimilar to an adult's, even if it feels like nothing at all to the infant. Whether infants consciously experience pain—and whether they are aware of some noxious stimulus or their own suffering—is a red herring. Available evidence converges around the idea that infants process pain, though perhaps not in the same way adults do. This processing has an impact on current behavior and later development. Because this influence is generally negative, insofar as we are able to prevent or alleviate some of their pain, we should.

See also Qualia.

Bibliography

Anand, K. J. S., and K. S. Craig. "New Perspectives on the Definition of Pain." Pain 67 (1996): 3–6.

Deberyshire, S. W. G. "Comment on Editorial by Anand and Craig." Pain 67 (1996): 210–211.

Dennett, D. C. "Why You Can't Make a Computer That Feels Pain." Synthese 38 (1978): 449.

Gamsa, A. "The Role of Psychological Factors in Chronic Pain, I and II." Pain 57 (1994): 5–29.

Hardcastle, V. G. The Myth of Pain. Cambridge, MA: The MIT Press, 1999.

International Association for the Study of Pain (IASP). Subcommittee on Classification. "Pain Terms: A Current List with Definitions and Notes on Usage." Pain (supplement) 3 (1986): 217.

Lawson, J. "Pain in the Neonate and Fetus." New England Journal of Medicine 318 (1988): 1, 398.

Wall, P. D., and R. Melzack, eds. Textbook of Pain. 2nd ed. New York: Churchill Livingstone, 1989.

Valerie Gray Hardcastle (2005)

Pain

The physical origins of pain

Types of pain

Psychological factors in the individual experience of pain

Pain control

Resources

Pain is an unpleasant feeling that is carried to the brain by the nervous system. Injury is a major cause, but pain may also arise from an illness. It may accompany a psychological condition, such as depression, or may even occur for no obvious reason. Pain, in its most basic form, results from a variety of outside stimuli such as a pinprick or a serious burn. However, pain is a complex experience that eludes simple definitions. Not only does the central nervous system play a crucial role in the experience of pain, but psychological factors can also affect how an individual perceives pain. Most pain results from the intense stimulation of nerve endings beneath the skin that serve as the body’s alarm system for detecting injury.

Pain can be classified as acute (brief) or chronic (long-lasting). Acute pain often results from tissue damage, such as a skin burn or broken bone. Acute pain can also be associated with headaches or muscle cramps. This type of pain usually goes away as the injury heals or the cause of the pain is removed.

Chronic pain is pain that lingers after an injury heals, or is related to a disease, or has no known cause but will not go away. It is estimated that one in three people in the United States will experience chronic pain at some time in their lives.

For the majority of people, pain is immediate and intense. However, in certain situations, the feeling of pain may be delayed or may fail to occur altogether (as sometimes happens with soldiers in the midst of battle). Another baffling aspect of pain is its persistence after the source of pain is gone, such as phantom limb pain that continues even after the injured limb has been amputated. Although people usually seek to avoid pain, some people, called sadomasochists, can derive pleasure from pain.

Everyone experiences and describes pain in their own way, so it can be difficult to communicate precisely about its quality and intensity. There are no tests that can show what type of pain a person is having or how severe it is. This is the reason why doctors ask patients many questions about their pain, including where it is located and what type of pain it is—burning, shooting, stinging, stabbing, throbbing, or aching, for example. Doctors also ask what kinds of things increase or relieve the pain, how long it has lasted, and whether there are any variations in it. Sometimes patients are asked to rate their pain on a scale of zero (no pain) to ten (the worst pain ever experienced).

The physical origins of pain

Despite the advances made in the study of pain over the past 50 years and the evolution of several pain theories—such as the specificity, pattern, and gate-control theories—many questions remain about the physiological and psychological components of this enigmatic but common experience. Most scientists agree, however, that the physiology of pain is a complex biochemical process that begins with pain receptors on nerve fibers that lie beneath the skin. An outside stimulus, such as intense heat, a cut, or even an exceptionally strong handshake, causes biochemicals on the nerve endings to produce a series of electrical nerve impulses. These impulses pass a pain message through the spinal cord to the brain’s thalamus, which is located on top of the brain stem and processes the signals to the cerebral cortex. It is the cerebral cortex that interprets the feeling of pain and produces the appropriate reaction, such as pulling the hand away from a hot surface.

A number of biochemicals are involved in the experience of pain. Prostaglandins are biochemicals that are released where the injury occurs. These prostaglandins increase blood circulation in the injured area in order to battle infection and promote healing by increasing the supply of white blood cells, antibodies, and oxygen. Prostaglandins also work in concert with other biochemicals, like bradykinin, to increase nerve-ending sensitivity and transmit electrical impulses to the brain. The speed at which these electrical impulses travel will vary according to the type of pain. For example, a pinprick may cause only a slight pain, but the impulse it triggers travels at the astonishing rate of 98 ft/sec (30 m/sec). In contrast, the pain impulse of a slight burn or ache travels at approximately 6.5 ft/sec (2 m/sec). As a result, some types of pain may cause immediate flinching whereas other kinds of pain produce a delayed response.

As scientists continue to study pain, they are uncovering more detailed information concerning its physiological intricacies. For example, they have identified certain receptors in the brain’s neurons, called the NMDA (N-methyl-D-aspartic acid) receptors, that may amplify pain messages in the spinal cord, causing an individual to feel pain after touching an area that has been burned. Scientists are also locating with increased precision the areas of the brain that process pain information. One study has indicated that three specific structures in the cerebral cortex interpret pain messages, including where the pain is located. One structure, the anterior cingulate gyrus (which is thought to control emotions), may also play a crucial role in an individual’s response to pain. Another group of researchers have found that a complex network of nerves in the brain may control the various responses that different people will have to the identical amount of pain.

Types of pain

Pain occurs in various degrees, from dull and aching to piercing and intense. Acute pain is usually associated with tissue injury and, for the most part, occurs for only a short amount of time. Chronic pain, however, persists for long periods of time, even years after the injury that originally caused the pain has gone away. For example, severe burns can create scar tissue that can continue to cause excruciating discomfort. Certain disorders, such as arthritis or cancer, may also cause persistent pain. In the case of phantom limb pain, an individual may continue to perceive pain in an arm or leg that has been amputated as though the appendage was still there. The precise cause of phantom limb pain is unknown. One theory is that the nerve endings remaining after the amputation continue to process the electrical pain impulses. Other theories focus on the firing of spinal cord neurons and the intricate neuronal circuitry of the brain.

Specific types of pain include causalgia (caused by severe burning that injures the nerve fibers under the skin) and neuralgia (caused by factors like viral infections and nerve degeneration that damages peripheral nerves). Headaches are the most common of all pain and may be chronic or acute in nature. Vascular headaches, like migraines, are caused by the constriction and dilation of the blood vessels in the area around the brain. Tension headaches have their origin in muscular contractions and are usually associated with psychological factors such as stress and depression. Traction or inflammatory headaches, which account for approximately 2% of all headaches, are caused by diseases.

KEY TERMS

Anterior cingulate gyrus —A part of the brain that may play a critical role in controlling emotions and response to pain.

Biochemical —The biological or physiological chemicals of living organisms.

Bradykinin —A biochemical present in the blood that acts as a vasodilator (which causes the dilation of blood vessels).

Causalgia —A type of pain caused by severe burning of the skin.

Central nervous system —The brain and spinal cord components of the nervous system that control the activities of internal organs, movements, perceptions, thoughts, and emotions.

Cerebral cortex —The external gray matter surrounding the brain and made up of layers of nerve cells and fibers; it is thought to process sensory information and impulses.

Endorphins —Biochemicals produced by the brain that act as opiates and reduce pain.

Neuralgia —Severe throbbing or stabbing pain that originates in the nerve fibers. Neurons—Nervous system unit that includes the nerve cell, dendrites, and axons.

NMDA receptors —Specific neuron receptors that strengthen neural connections and may play a role in pain perception.

Prostaglandins —A biochemical substance, present in many tissues, that plays an important role in healing injured areas and relaying pain messages to the brain.

Thalamus —A structure at the top of the brain stem that acts as the primary relay station for biochemical messages from the spinal cord to the brain.

Psychological factors in the individual experience of pain

The psychology of pain is a complex area of study. Although pain is universal, in that every human being experiences it in one form or another, individual feelings of and responses to pain vary greatly. Each individual has a unique pain threshold (the point at which they first begin to experience pain) and tolerance to pain. Cultural heritage, tension, emotions, fears, and expectations all play a role in the experience of pain.

For example, in certain cultures specific rites and rituals may involve a pain that is readily accepted by the people within that particular society. Scientists believe that people in these cultures experience that pain to a far lesser degree than others from different cultures would if they underwent the same experience. In such cases, the ability to focus on other aspects of the ritual, such as its social or religious ramifications, may act as a psychological sedative that helps the individual better tolerate the pain or, perhaps, feel no pain at all. The expectation of pain also determines how much pain is felt. Two people, for example, may go to the dentist; the person who has greater anxiety about the experience is likely to feel a greater amount of pain. Tension and emotional states may also cause biochemical changes that lower the amount of endorphins (naturally occurring opiates) produced by the brain.

Pain control

Many drugs are available for preventing or treating pain. Drugs from different classes may be combined to handle certain types of pain.

Nonopioid analgesics, such as aspirin, acetaminophen (Tylenol^®), and ibuprofen (Advil^®) are most often used for minor pain. These drugs are available without a doctor’s prescription, but there are also some prescription-strength medications in this class.

Narcotic analgesics are available only with a doctor’s prescription and are used for more severe pain, such as cancer pain. These drugs include codeine, morphine, and methadone. Contrary to earlier beliefs, physiological addiction to these painkillers when used therapeutically is not common.

Anticonvulsants as well as antidepressant drugs, initially developed to treat seizures and depression, respectively, also can be used as pain-killers. Furthermore, it is not unusual for people with chronic or extreme pain to experience some depression, so treatment with anti-depressants may serve a dual role. Commonly prescribed anticonvulsants for pain include phenytoin, carbamazepine, and clonazepam. Antidepressants used for this purpose include doxepin, amitriptyline, and imipramine.

Pain that cannot be relieved with the drugs discussed above may be treated by injections of local anesthetics directly into or near the nerve that is transmitting the pain signal. These root blocks may also be useful in determining the source of pain.

Drugs are not always effective in controlling pain. Surgical methods are used as a last resort if drugs and local anesthetics fail.

Alternative treatments are sometimes used to help patients deal with both the physical and psychological aspects of pain. Some of the most popular treatment options include acupressure and acupuncture, massage, chiropractic, and relaxation techniques, such as yoga, hypnosis, and meditation. Herbal therapies are gaining increased recognition as viable options. For example, capsaicin, the component that makes cayenne peppers spicy, is used in ointments to relieve the joint pain associated with arthritis. Contrast hydro-therapy can also be very beneficial for pain relief.

Psychological approaches to reduce pain by increasing an individual’s pain threshold and tolerance were largely developed for chronic pain sufferers, but may also work in cases of acute pain. One such method involves focusing the attention on something other than the pain, such as a past pleasant experience, music, or even a complex mathematical problem. Relaxation and meditation techniques are used to reduce stress and muscle tension that may increase feelings of pain. Exercise can also help reduce pain because it causes the brain to produce more endorphins, the body’s natural painkillers.

See also Analgesia; Anesthesia.

Resources

BOOKS

Butler, David S. Explain Pain. Adelaide, Australia: Noigroup Publictions, 2003.

Mailis-Gagnon, Angela. Beyond Pain: Making the Mind-Body Connection. Ann Arbor, MI: University of Michigan Press, 2003.

McMahon, Stephen B., and Martin Koltzenburg, eds. Wall and Melzack’s Textbook of Pain. Philadelphia, PA: Elsevier/Churchill Livingstone, 2006.

Moller, Aage R. Sensory Systems: Anatomy and Physiology. New York: Academic Press, 2002.

Usunoff, K.G., et al., eds. Functional Neuroanatomy of Pain. Berlin, Germany: Springer, 2006.

PERIODICALS

Kiefer, D. M. “Chemistry Chronicles: Miracle Medicines.” Today’s Chemist 10, no. 6 (June 2001): 59-60.

David Petechuk