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Free keywords:
placebo analgesia; pain; functional magnetic resonance imaging; human; descending pain control; spinal cord; brainstem; opioid; naloxone; periaqueductal gray
Abstract:
Placebo analgesia is an illustrative example of the impact that psychological factors can have on the experience of pain. While this form of pain modulation is mediated by multiple neurobiological mechanisms, one influential explanation posits that a descending pain control system contributes to placebo effects in pain. Here, we first give an overview of descending pain control as established in animal studies, focusing on an opioid-dependent system that includes the periaqueductal gray (PAG) and rostral ventromedial medulla (RVM) as core regions and controls nociceptive processing already at the level of the spinal cord. We then review functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) studies that provide evidence for an involvement of this system in placebo analgesia. Finally, we have a look at the role of the spinal cord in placebo analgesia, focusing on spinal fMRI studies.
