A review of mechanisms of response to pain therapy: Why voodoo works

A person's response to pain treatment may be due to factors other than the direct effect of analgesics. Amelioration of pain is often associated with modalities that appear to make no scientific sense. This review outlines the mechanisms of pain amelioration other than that by medication. These mechanisms help to explain why pain relief may follow the administration of allopathic modalities. Pain is modulated, enhanced, or diminished by both cerebral and peripheral mechanisms. Cerebral factors include the placebo response, psychological phenomena, and conscious cognitive activation. In addition to evoking endogenous opioids, these central mechanisms activate antinociceptive pathways beginning in the limbic forebrain and relayed in the periaqueductal gray matter to primary afferent nociceptive sites in the spinal cord dorsal horn (and medullary nucleus caudalis). Obvious peripheral factors that may diminish pain perception are those that decrease afferent stimuli. Paradoxically, stimulation of afferent neurons may also ameliorate pain by activating spinal or supraspinal inhibitory mechanisms. Finally, improvement in pain or other symptoms is often falsely attributed to a therapy when remission occurs because the underlying illness has run its normal course.