As long as humans have experienced pain, they have given explanations for its existence and sought soothing agents to dull or cease painful sensations. Archaeologists have uncovered clay tablets dating back as far as 5,000 BC which reference the cultivation and use of the opium poppy to bring joy and cease pain. The Greek writer Homer's The Odyssey, written in 800 BC, features the character of Telemachus using opium to soothe his pain and forget his worries. While some cultures researched analgesics and allowed or encouraged their use, others perceived pain to be a necessary, integral sensation. Physicians of the 19th century used pain as a diagnostic tool, theorizing that a greater amount of personally perceived pain was correlated to a greater internal vitality, and as a treatment in and of itself, inflicting pain on their patients to rid the patient of evil and unbalanced humors.
This article focuses both on the history of how pain has been perceived across time and culture, but also how malleable an individual's perception of pain can be due to factors like situation, their visual perception of the pain, and previous history with pain.
Historical theories
Early theories
Because of the only relatively recent discovery of neurons and how they conduct and interpret signals, including sensations such as pain, within the body, various theories have been proposed as to the causes of pain and its role or function. Even within seemingly limited groups, such as the ancient Greeks, there were competing theories as to the root cause of pain. Aristotle did not include a sense of pain when he enumerated the five senses; he, like Plato before him, saw pain and pleasure not as sensations but as emotions ("passions of the soul"). Alternatively, Hippocrates believed that pain was caused by an imbalance in the vital fluids of a human. At this time, Aristotle did not believe that the brain had any role to play in pain processing, but rather implicated the heart as the central organ for the sensation of pain. He was the principal advocate of the cardio-centric theory of the soul, and differed in this from the encephalo-centric proposals of, among others, Hippocrate, who explicitly considered that the brain was the source of "our pains, grief, anxieties and tears" (Hippocrates, in: W.H.S. Jones (Ed.), The Sacred Disease, vol. 2, The Loeb Classical Library, Cambridge, 1923). The dichotomy between encephalocentrists and cardiocentrists extended well into Renaissance, the Aristotelic cardio-centric vision being the one that prevailed among philosophers, although disputed by eminent doctors such as Galen (Crivellato E, Ribatti D. Soul, mind, brain: Greek philosophy and the birth of neuroscience. Brain Research Bulletin 71 (2007) 327–336).
Middle ages and Early Modern Period
In the 11th century, Avicenna theorized that there were a number of feeling senses including touch, pain and titillation.
In a religious context, pain could be seen as a punishment or a trial from God. But this religious conception did not prevent Early Modern Physicians from being concerned by the problem of pain: they tried to cure it with pain-killers called "anodynes", they discussed the problem of the phantom-pain, described in the 16th century by the surgeon Ambroise Paré; and they proposed rich descriptions of the signs of pain.
In his Treatise of Man (published posth., 1664), René Descartes theorized that the body was more similar to a machine, and that pain was a disturbance that passed down along nerve fibers until the disturbance reached the brain. This theory transformed the perception of pain from a spiritual experience to a physical, mechanical sensation meaning that a cure for such pain could be found by researching and locating pain fibers within the bodies.
Specificity theory
The specificity theory, which states that pain is "a specific sensation, with its own sensory apparatus independent of touch and other senses," emerged in the nineteenth century, but had been prefigured by the work of Avicenna and Descartes.