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MDS: Placebo Effect Significant in Parkinson's Patients

High expectation of receiving active drug prompts maximal dopamine release in the striatum

FRIDAY, June 12 (HealthDay News) -- In Parkinson's disease patients, placebos can mimic the effect of active medication if there is a strong expectation of therapeutic benefit, according to research presented this week at the Movement Disorder Society's 13th International Congress of Parkinson's Disease and Movement Disorders, held from June 7 to 11 in Paris.

Before administering placebos, Sarah C. Lidstone, of the Pacific Parkinson's Research Centre in Vancouver, Canada, and colleagues told patients they had a certain probability of receiving active medication. After placebo administration, they used raclopride positron emission tomography to measure dopamine release in the striatum.

The researchers found that patients who believed they had a 75 percent probability of receiving active medication experienced maximal dopamine release, an effect not seen in patients who believed they had a lower probability. Although previous medication experience was the strongest predictor of dopamine release in the dorsal striatum, the researchers found that an expectation of therapeutic benefit also was required to drive dopamine release in the ventral striatum in response to placebo.

"Our findings demonstrate the importance of uncertainty and/or salience over and above a patient's prior treatment response in regulating the placebo effect, and have important implications for the interpretation and design of clinical trials," the authors conclude.

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