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Placebo analgesia involves the endogenous opioid system, as administration of the opioid antagonist naloxone decreases placebo analgesia. To investigate the opioidergic mechanisms that underlie placebo analgesia, we combined naloxone administration with functional magnetic resonance imaging. Naloxone reduced both behavioral and neural placebo effects as well as placebo-induced responses in pain-modulatory cortical structures, such as the rostral anterior cingulate cortex (rACC). In a brainstem-specific analysis, we observed a similar naloxone modulation of placebo-induced responses in key structures of the descending pain control system, including the hypothalamus, the periaqueductal gray (PAG), and the rostral ventromedial medulla (RVM). Most importantly, naloxone abolished placebo-induced coupling between rACC and PAG, which predicted both neural and behavioral placebo effects as well as activation of the RVM. These findings show that opioidergic signaling in pain-modulating areas and the projections to downstream effectors of the descending pain control system are crucially important for placebo analgesia.

Original publication

DOI

10.1016/j.neuron.2009.07.014

Type

Journal article

Journal

Neuron

Publication Date

27/08/2009

Volume

63

Pages

533 - 543

Keywords

Adult, Analgesia, Analgesics, Opioid, Double-Blind Method, Humans, Male, Naloxone, Pain, Pain Measurement, Placebo Effect, Pyramidal Tracts, Receptors, Opioid, Signal Transduction, Young Adult