Just as placebos have been shown to bring relief from pain, researchers have now found that they can affect emotion, alleviating the impact of unpleasant experiences.
In an article in the June 16, 2005, issue of Neuron, researchers led by Predrag Petrovic of the Karolinska Institutet show that, in relieving anxiety, placebo treatment affects the same basic modulatory circuitry in the brain as it does for relieving pain.
In their experiments, the researchers tested the effect of placebo treatment on volunteer subjects' ratings of unpleasant pictures, such as images of mutilated bodies. Other researchers had shown that people's expectation of pain relief plays a major role in the effectiveness of placebos. So, in their experiments, the researchers first induced such an expectation in the subjects by administering an antianxiety drug to reduce the subjects' unpleasant perception of the pictures. They then administered an antidote to the drug, telling the subjects that it would restore the unpleasant perception.
In tests the following day, the subjects were told they would receive the same drugs. But instead, they received a saline solution as a placebo when they saw the pictures. The subjects' brains were also scanned during these experiments using functional magnetic resonance imaging (fMRI). This scanning technique uses harmless magnetic fields and radio waves to measure blood flow in brain regions, which reflects brain activity.
The researchers found that the placebo reduced the subjects' ratings of the unpleasant pictures by about 29%. Importantly, the fMRI scans showed that the placebo reduced activity in the brain's emotional centers, and this reduction correlated with a subject's amount of reduction in the rated unpleasantness of the pictures. That is, the subjects who reported the largest placebo response also showed the largest decrease in activity in the emotional centers.