New research has come to light to show the “placebo effect” involves evolutionarily old pain control pathways in the human brainstem.
Placebo analgesia refers to a person’s relief from pain following being given a chemically inert substance. It is thought to be due to a person’s belief that a potent pain medication was administered. Endogenous opioids are naturally produced by the brain in small amounts and play a key role in the relief of pain and anxiety. Brain imaging studies have shown placebo analgesia stimulates release of endogenous opioids from higher brain regions.
“It has been hypothesized that placebo analgesia also recruits the opioidergic descending pain control system, which inhibits pain processing in the spinal cord and, therefore, subsequently reduces pain-related responses in the brain, leading to a decreased pain experience,” says Falk Eippert.
Eippert and his colleagues used advanced brain imaging techniques to examine higher cortical and lower brainstem responses in two groups of subjects. The first one received a drug called naloxone which blocks opioid signaling. The second had a natural opioid state. Expectations of pain relief were induced in both groups using an established placebo analgesia paradigm.
I was found that naloxone reduced behavioral placebo effects as well as placebo-induced decreases in pain-related brain responses. In addition and most important to the results is that under placebo, cortical areas interacted with brainstem structures implicated in pain control and that these interactions were dependent on endogenous opioids. Further they were related to the strength of experienced placebo effects.
“Taken together, our findings show that opioid signaling in pain-modulating areas and the projections to downstream effectors of the descending pain control system are crucially important for placebo analgesia,” states Falk Eppert.
Adapted from materials provided by Cell Press.