There have always been two theories of the sensation of pain, a quantitative, or intensity, theory and a stimulus-specific theory. According to the former, pain results from excessive stimulation (e.g., excessive heat or cold or excessive damage to the tissues). This theory in its simplest form entails the belief that the same afferent nerve fibers are activated by all of these various stimuli; pain is felt merely when they are conducting far more impulses than usual. But knowledge acquired in the 20th century has shown that the quantitative theory—at least in its classic form—is wrong. Peripheral nerve fibers are stimulus-specific; ...(100 of 37287 words)