Pain is a familiar experience for everyone, but its nature remains a troubling enigma for sufferers and scientists alike. Why do different patients who undergo the same surgical procedure experience markedly different post-operative pain? How is it that people with little or no medical explanation for a persistent pain become partially or totally disabled by it, even with extensive and resourceful treatment?
Many doctors would like to think of pain as a simple sensation that usefully calls disease or injury to our attention. But pain resists explanation as a simple sensation, just as music resists explanation as simple tones. A contemporary non-medical writer described the qualities of intense pain as including extreme unpleasantness, an ability to annihilate complex thoughts and other feelings, an ability to destroy language, and a strong resistance to objectification. She reminds physicians that, for the person suffering intense pain, what dominates awareness above all else is a powerful negative emotion.
Most of the time, pain occurs after simple nerve endings detect tissue injury in various ways and generate signals that travel to the spinal cord and from there to the brain. For many years, scientists thought that these signals traveled along a few well-defined routes to reach a relay station in the brain called the thalamus. From there, scientists believed, the signals went on to the part of the brain's cortex that managed body awareness, and somehow the cortex turned them into conscious experience. Unfortunately, the neural roadmap for sensory messages of tissue injury explains only a part of how we experience pain. It cannot explain why pain involves emotion and cognition.
Psychologists are quick to point out that whenever humans experience strong emotions, cognitions--thoughts, memories, expectations, beliefs, and interpretation of the situation--help form the experience. In other words, pain may begin with a neural message of tissue injury or disease, but it is the end product of complex events within the brain. The conscious experience of pain involves emotion and cognition as well as sensation. We always experience pain as a distressing thing happening in some part of the body, in some particular circumstance, and usually it has a particular meaning.