Effects of stimulation area and temperature rates on offset analgesia.

Abstract

Offset analgesia describes the effect of a slightly reduced nociceptive stimulus, resulting in a disproportionate large reduction in the pain perception. This effect may be associated with descending pain inhibition, but parameters influencing this phenomenon are poorly understood. In this study, 2 separate experiments were conducted to investigate both, the spatial aspects of offset analgesia and the influence of different rates of temperature rise. In both experiments, 29 healthy participants received individualized and heat-based offset analgesia paradigms applied to the forearm, with continuous assessment of pain intensity. In experiment 1, offset analgesia paradigms with 3 different rates of temperature rise were applied, whereas in experiment 2, offset analgesia paradigms with 2 different heat application areas were used. The results of experiment 1 showed that different temperature rates had no effect on the offset analgesia response (P > 0.05). Experiment 2, however, showed the influence of the size of a stimulated area on offset analgesia (P = 0.009), which can be explained mainly by the influence of spatial summation of pain and habituation processes. The study showed a lack of influence of different temperature rates on offset analgesia; however, spatial aspects of offset analgesia could be identified. These are most likely based on spatial summation of pain and altered adaptation to pain.