Previous studies have shown that Parkinson's disease--which is the result of the death of certain dopamine-generating cells in the brain--is receptive to placebos. A standard treatment is levodopa, a synthetic substance that is converted in the brain to dopamine. When patients are informed that they are receiving a dose of the drug--or, better yet, a more expensive alternative--their brains often respond to feelings of "heightened expectation and positive anticipation" by (you guessed it) releasing dopamine.

In the journal Neurology, a research team led by Dr. Alberto Espay of the University of Cincinnati describes a small-scale study of 12 people with moderate to severe Parkinson's disease. On their first visit, all were given their standard medication; after it took effect, their motor skills were assessed to determine the degree to which the medicine had helped them.

Their second visit, which occurred within a week of the first, was more complicated. Participants were told they would be trying two new drugs: one "cheap" ($100 per dose) and the other "expensive" ($1,500 per dose). In fact, they were simply injected with saline solution.

Half received the faux expensive drug first, followed by the faux cheap drug four hours later. Before and after each injection, their motor skills were tested, and their brain activity was measured using fMRI technology.

The key result: "A larger motor benefit was achieved by a 'costlier' intervention, particularly when given first," the researchers write. Specifically, they found a nine percent greater overall improvement with the "expensive" placebo compared to the cheap one--a difference that rose to 14 percent when the "expensive" one was given first.