The sensation of pain is aversive at threshold and serves as an important teaching signal. Pain is defined as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage,” by the International Society for the Study of Pain (IASP). IntroductionĪny complete discussion of pain must include not only its somatosensory parameter that allows us to feel nociception, but must also include its motivational and affective qualities with which we experience pain. Increased understanding of pain modulatory systems will lead to development of more effective therapeutics for chronic pain. Disruptions in these systems may account for the existence idiopathic pan states such as fibromyalgia. The “pain matrix” can explain such varied phenomena as stress-induced analgesia, placebo effect and the role of expectation on pain perception. Projections from the periaqueductal grey (PAG) and the rostroventromedial medulla (RVM) to the trigeminal and spinal dorsal horns can inhibit or promote further nociceptive inputs. Brain imaging studies revealed a “pain matrix,” consisting of cortical and subcortical regions that respond to noxious inputs and can positively or negatively modulate pain through activation of descending pain modulatory systems.
Genomic studies of individuals with congenital insensitivity to pain or paroxysmal pain syndromes considerable increased our understanding of the function of peripheral nociceptors, and especially of the roles of voltage-gated sodium channels and of nerve growth factor (NGF)/TrkA receptors in nociceptive transduction and transmission. However, maladaptive pain, such as neuropathic or idiopathic pain, serves no survival function. Accordingly, pain serves as a powerful teaching signal enabling an organism to avoid injury, and is critical to survival. Pain is often perceived an unpleasant experience that includes sensory and emotional/motivational responses.
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