Neural Mechanisms of Offset Analgesia
One feels a disproportionately large decrease of pain sensation on a slight decrease of thermal pain stimulus. Such phenomenon is termed offset analgesia and considered mediated by endogenous analgesic mechanisms. Offset analgesia was found attenuated in patients with neuropathic pain. We further found that such attenuation occurred in a more heterogeneous population of patients with chronic pain. By functional magnetic resonance imaging, we also found negative blood oxygenation level-dependent signals at those areas concerned with descending pain modulatory and reward systems during offset analgesia in the same cohort of patients. We propose that dysfunction of those systems, as revealed by attenuation of offset analgesia, might well be part of neural mechanisms of pain chronification.
KeywordsOffset analgesia Chronic pain Functional magnetic resonance imaging Descending pain modulatory system Reward system
This work was supported by the Grants-in-Aid for Scientific Research (JP26460695). I thank Dr. Shigehito Sawamura for letting us use PATHWAY; and my co-workers, Drs. Koshi Makita, Hiroyuki Kobinata, Eri Ikeda, Shuo Zhang, Tianjiao Li, and Takashi Ota in accomplishing a series of studies presented here.