ABSTRACT
Views about what constitute the fundamental dimensions and functions of pain are remarkably different. Until the late 1960s pain was mainly seen as a specific neuronal system that functioned like other sensory systems: pain sensation intensity and duration were considered to be determined only by the intensity and duration of the peripheral stimulus, much like other exteroceptive systems directed toward the external environment. Sensory qualities of pain are unique and distinct from other body sensations. For example, unlike sensations of other modalities, pain often spreads in area as it becomes more intense, even when the stimulus itself is not spreading. Pain sometimes has an exteroceptive function, extracting information about events in the environment in order to execute behaviors that protect the organism from external threats. When the skin of mammals comes into contact with external objects that can cause tissue damage, specialized nociceptors are activated, ultimately leading to the initiation of escape and avoidance behaviors providing for self-protection.
