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. Author manuscript; available in PMC: 2022 Oct 1.
Published in final edited form as: Neurosci Biobehav Rev. 2021 Aug 8;129:296–306. doi: 10.1016/j.neubiorev.2021.08.004

Figure 1. The circadian regulation of pain.

Figure 1.

Two hypotheses are proposed to explain the potential origins of circadian pain rhythms. On the left, the “Circadian Gatekeeper” hypothesis is shown. This hypothesis proposes that the descending pain modulatory system, dorsal horn, and DRG regulate ascending transmission of nociceptive input in a time-specific manner to produce diurnal alterations in pain responsiveness. On the right, the “Distributed Rhythms” hypothesis is depicted. Similar to the description of the pain system as a “Distributed System” (Coghill, 2020), this hypothesis suggests that circadian rhythms present throughout the entire pain system and interacting systems function together to produce an integrated circadian rhythm of pain responsiveness. The center graph was adapted from Hagenhauer et al. (Hagenauer et al., 2017). The white and black bar above the x-axis represent typical wake/sleep periods, respectively.