<qa>  What is the paradigm based on?DNIC evaluates an individuals capacity to engage endogenous pain inhibition. The paradigm is a spatial inhibition model based on the principle that pain-inhibits-pain in which pain in a local area is inhibited by a second pain that can be anywhere else in the body. DNIC is traditionally studied by observing a reduction of pain produced by a focal pain stimulus contact heat as a result of a second painful stimulus. Research from our lab and others suggests that pain inhibition is reduced in a number of chronic pain conditions. The investigators preliminary data suggests that pain inhibition during DNIC is modulated in part by endogenous opioids; however, results from other DNIC studies have been mixed. In addition, it is possible that reductions in the ability to engage endogenous inhibitory systems in chronic pain patients are due to a weakening of the endogenous opioid system. While pharmacological studies have been conducted with healthy cohorts, only one study has examined the opioid involvement in chronic pain patients. 