Raul de la Fuente-Fernandez and colleagues used positron emission tomography (PET) to study the brains of 12 patients suffering from Parkinson¿s disease while they received treatment. Half of the patients received two courses of injections. During the first round, they didn¿t know whether they were receiving a placebo or an active drug. In the second, however, the patients were told which injection they were receiving. The remaining patients, who had similarly severe symptoms, were tested only in an open manner. The team measured the amount of dopamine released by the brain¿s damaged neurons¿the signature effect of drug treatment on the disease. Intriguingly, patients who received placebo injections exhibited significant dopamine releases. The authors conclude that dopamine release "is linked to expectation of a reward¿ in this case, the anticipation of therapeutic benefit."
The researchers also investigated whether the placebo effect might actually enhance the results of active drug therapy in a synergistic manner. They found, however, that the placebo response does not strengthen the effect of an active drug. In fact, they write, their results "suggest that in some patients, most of the benefit obtained from an active drug might derive from a placebo effect."