The activation in the brain of chemical receptors, called mu-opioid receptors, appears to be involved in producing what is known as the "placebo effect," according to a report in The Journal of Neuroscience.
The placebo effect occurs when people are given an inactive drug or therapy, but experience an improvement in their symptoms anyway. Researchers often compare new drugs to placebo to gauge the true benefit of a therapy.
Dr. Jon-Kar Zubieta (from The University of Michigan, Ann Arbor, Michigan) and colleagues examined the effect of deep sustained pain — produced by a prolonged infusion of 5 percent hypertonic saline into the masseter muscle –with or without a placebo in young male volunteers.
The researchers used positron emission tomography (PET) and molecular imaging to examine whether introducing a placebo with the expectation of pain relief activates the brain to produce opiate-like substances.
Introducing the placebo was effective in reducing the sensation of pain, the team reports, as evidenced by higher ratings of pain relief and by an increase in the rate of painful stimulus required to maintain the same level of pain.
The changes in the sensation of pain intensity correlated with mu-opioid system activation in the several different regions of the brain, the researchers note.