Neuroimaging of pain: Possibilities of objective measurements of analgesic actions in human subjects

A major pursuit in neurobiology is to understand the mechanism by which the organism reacts to sensory information. Central nervous system (CNS) regions, from peripheral nerve to cortex, activated by painful stimuli can be defined using electrophysiological recordings or markers of activity, such as the immediate early gene fos (Hunt et al., 1987). Animal studies are limited because it is difficult to quantify affective responses to pain, and they may not completely model the human experience. Recent advances in neuroimaging techniques offer tools to understand integrative neuronal processing in acute and chronic pain. Plastic changes producing alterations in sensory processing in patients with neuropathic pain (Flor et aI., 1994; Borsook et aI., 1998), the potential objective measurement of the chronic pain state (Iadarola et aI., 1995), and the objective response to analgesic actions are potential areas of investigation.