Why do we experience pain?

Acute pain is part of our evolutionary heritage. It is an essential part of our survival apparatus. It is the pain experienced in the short term following an injury. If you stub a toe or touch something hot, you feel an acute pain that is a direct consequence of a pain signal sent to the brain from the injured muscles, bones, ligaments, or skin. This pain is part of the body’s inbuilt alarm system, signaling that it is under attack and that there is a need to take care of the injured area to allow it to heal. Inflammation will probably be evident, such as a bruise, swelling, or blister, and pain will be felt at the site of the injury. Following an injury, chemical and physical responses in the affected cells and tissues begin healing the damage. Most healing is completed within six weeks and acute pain usually reduces over this period, while nearly all injured tissues are fully healed within six months. Acute pain also arises without obvious injury, as with a stomachache after overeating, or the headache that comes with a hangover. People who do not experience pain to warn them of damage—a condition called “congenital insensitivity to pain”—suffer repeated injuries and, very often, reduced life expectancy.

Chronic pain, also called persistent or long-term pain, is pain that has lasted for three months or more (Cole et al. 2005, p. 37)—sometimes it can continue for decades. Chronic pain can develop after an injury and persist, often inexplicably, after tissue healing has taken place. Or it may start for no obvious or specific reason. If the pain remains even when there is no continuing physical damage, the experience of pain becomes a medical problem in its own right and is often referred to as “chronic pain syndrome."

Chronic pain is complex and multi-faceted, involving physical, emotional, and mental reactions (see Wall 1999). Some pain is caused by obvious tissue damage that persists over time—for example, in the case of arthritis and cancer. This pain is caused by continuing physical processes at the area of disease or joint degeneration and there is a clear cause of the aversive sensations.

Neuropathic pain occurs in the nervous system rather than being prompted by tissue damage and can be confusing—often medical investigations reveal no obvious cause. Some neuropathic pain is caused by damage or injury to the nerves, the spinal cord, or the brain, but sometimes pain is felt even when there is no damage, or healing has finished at the site of the injury. The latest research suggests that the nervous system responds to the experience of pain by increasing its capacity to process pain signals, rather as a computer devotes extra circuits and memory to an important task. The central nervous system can then become over-sensitized so that a little pain feels far worse. The nervous system can act as an amplifier of pain sensations, such that when one develops chronic pain it is as if the amplifier has been turned up.

Neuropathic pain can also take the form of unusual sensations, such as electric shocks, the sensation of water or burning on the skin, or distorted perceptions of the body. Another example of neuropathic pain is phantom limb pain, when pain persists in a limb after it has been amputated. In each case, the sensation of pain is produced by nerves that have been damaged or whose signals have become confused in some way, so that neuropathic pain is an electrical rather than a mechanical fault.

Chronic and neuropathic pain offer no evolutionary advantage and arise through dysfunction of the nervous system. Such pain can be compared to useless “white noise” that is constantly present in the background; like being trapped in a room with a radio that is tuned off the station and produces constant hissing, crackling, and humming.

Recent studies show how the experience of pain is very complex and individual. We might assume, for example, that if a person has back pain then detailed MRI scans would allow us to see the cause of the problem. In fact, in a study where a number of people without back pain were scanned, 64% had disc abnormalities in the spine (Jensen 1994) while in another study of people with back pain, 85% had no obvious damage (Fordyce et al. 1984; Gamsa 1994). Research also shows huge individual variation in pain perception. Two individuals given the same pain stimulus while being monitored in the scanner can show vastly different brain activity (Wall 1999, p. 78).

One well-established view of pain is the “gate control theory” developed in the 1960s by Patrick Wall—a neuroscientist who specialized in studying pain— and his collaborator Ronald Melzack (Wall and Melzack 1982, p. 98). They suggested that there are “gates” in the nerve junctions, spinal cord, and the brain’s pain centers. For pain to be experienced, these gates need to be opened and this is what happens when a healthy person is injured. Pain messages are a signal to protect that part of the body that helps it to heal. The gates can also close, which means pain is reduced or stopped. Again, this is what happens in the case of a healthy person when healing is complete.

Opening and closing these gates is a complex process that is affected by emotional states, mental activity, and where attention is focused. Whether the brain expects pain or is primed to detect any damage or strain also has an impact. Then the pain pathways (or gates) open so the brain doesn’t miss anything— and the pain experience is amplified. People with chronic pain commonly report that they manage some pain effectively, but a sudden, unexpected increase in pain feels much worse because of the fear that it is caused by new damage. The anxiety causes the gates to open or to stay open longer.

Researchers are searching for ways to close the gates in people living with chronic pain so that their nervous systems can return to normal functioning. Mindfulness training and meditation may be one way to do this because it calms mental, physical, emotional, and nervous systems, allowing them to return to a state of balance. The view of pain emerging from this research includes the mind, the body, and the environment. As Wall (1999, p. 31) writes:

Pure pain is never detected as an isolated sensation. Pain is always accompanied by emotion and meaning so that each pain is unique to the individual. The word “pain” is used to group together a class of combined sensory-emotional events. The class contains many different types of pain, each of which is a personal, unique experience for the person who suffers.

This growing awareness ofthe complexity of pain shows that treating it involves the whole of a person’s experience. The bio-psychosocial model of pain, widely used in chronic pain management, suggests that the biological, psychological, and social aspects of an individual’s life all influence the way that person deals with pain. This has led to the development of multi-faceted pain management programs— intensive courses, often run in hospitals, which offer in-depth help in managing the many ways in which pain has affected a person’s life, drawing on psychology, occupational therapy, and physiotherapy, as well as advice from doctors.

Mindfulness-based pain management (MBPM), as developed at Breathworks (www.breathworks-mindfulness.org.uk) in the UK, is one such program. It combines a scientific view of pain with an understanding of the nature of experience that comes from the practice of meditation and mindfulness. These practices have ancient roots in the Buddhist tradition and they augment scientific understanding in practical ways by offering methods of learning to respond constructively to pain.

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