Placebo effect

The placebo effect refers to the therapeutic efficacy of agents or procedures that are without any physiological or pharmacological action. In general, the more elaborate the placebo treatment the better its effectiveness. There is evidence which the placebo effect, at least whenever harnessed to decrease postoperative pain, can be blocked by naloxone and therefore depends upon endogenous opioid neurotransmission. Functional magnetic resonance imaging (MRI) shows that placebo analgesia is associated with decreased activity in the brain regions associated with pain but increased activity in the dorsal lateral prefrontal cortex, an area involved in cognition. The working hypothesis is that the expectation of pain relief activates a top-down recruitment of supraspinal opioid pathways.