Sometimes a sugar pill can work just as well as an aspirin, a bit of neurological chicanery known as the placebo effect. New research strengthens the connection between the placebo effect and the anticipation of other types of rewards. Scans of a particular brain area show that people who experience more intense placebo effects also respond more strongly to the promise of monetary gain.
MRI scans have shown that placebos can cause the levels of the neurotransmitter dopamine to shoot up in a small part of the forebrain called the nucleus accumbens. This region of the brain also fires up when people expect some type of reward, such as money or food. Scientists hypothesized that this release of dopamine in anticipation of feeling better may explain the placebo effect.
Jon-Kar Zubieta, a neurologist at the University of Michigan, Ann Arbor, and colleagues tested this connection by using PET scans to observe changes in the brains of 14 healthy people. First, the researchers told the volunteers that they were going to insert a needle into their jaws. Although the subjects expected pain, there was none, because a numbing agent was placed on the skin. The team compared brain images during the expectation of harm with those produced once the subjects were actually in pain, when another needle was inserted on the other side of the jaw. The subjects then received a placebo in the form of an intravenous saline solution. Scans of the brain at this point showed a surge of dopamine, and patients reported relief. Subjects with the strongest placebo effect also had the biggest dopamine release in the nucleus accumbens.
In the second part of the study, scientists measured neural activity using functional magnetic resonance imaging (fMRI). The subjects played a game where they could win various amounts of money. Anticipation of winning increased activity in the nucleus accumbens. Zubieta explains that the researchers found that subjects whose nucleus accumbens responded most strongly to the promise of money were also the ones who had experienced the largest placebo effect in the needle experiment.
"The study confirms there is a link between the placebo effect and expectation of reward," says Raul de la Fuente-Fernández, a neurologist at Hospital A. Marcide in Ferrol, Spain. He adds that the research might help scientists harness the placebo effect to aid patients. For example, scientists are looking at ways to determine when the placebo effect is more or less active, and what disrupts the release of dopamine. Zubieta's group is now focusing on the nuances of the neural activity, such as the way gender and genetics influence the release of dopamine and the placebo effect.