A placebo is a non-medicinal treatment or pill given in place of drugs to treat a particular condition. Many placebos are simply sugar or salt solutions. The placebo effect is when a person’s condition is improved after taking a placebo, simply because that person believes it will work.
Doctors know that about 35% of patients given a placebo will actually be cured. The conventional wisdom is that the placebo helps the patient cure themselves.
Now a new study has tracked down a brain region behind the placebo effect.
The study, published in the July issue of “Neuron,” was led by researchers at the University of Michigan, Ann Arbor. They studied a region of the brain called the “nucleus accumbens” (NAC), which is known to play a role in reward expectation.
Previous research had suggested that the NAC may be involved in the placebo effect, so the researchers decided to find out if this was, in fact, true.
The researchers recruited study participants and told them that they were testing a new painkilling drug. The participants were also told that they would receive either the drug or a placebo. But then the researchers gave all of the participants a placebo injection of salt solution.
The participants were then asked to rate their expectation of the painkilling effects of the “drug.” They were also asked to rate the level of pain relief they felt with and without the drug from a moderately painful injection of salt solution in their jaw muscle.
For the first experiment, the researchers used spectroscopy to measure the release of dopamine from the NAC. Dopamine is a chemical that triggers the brain’s reward response system.
The researchers discovered that the greater the participants’ expectation of the painkilling ability of the drug, the greater the dopamine release from the NAC. And the participants who reported more relief from the drug when they did experience pain, showed greater NAC activity when they received the placebo before the pain.
The researchers then used this discovery to conduct another experiment. They told the subjects to expect monetary rewards of different amounts, while scanning their brains with magnetic resonance imaging. The participants who showed greater activation of the NAC during this reward processing also showed a greater belief of the effectiveness of a placebo.
From the results of these two studies, the researchers have presented the theory that the NAC system may need to be activated to allow the placebo effect to occur. This knowledge may be used in the future to develop new therapies for a variety of conditions.