The effect of reward expectation and dopamine release on the mechanism of the placebo effect in Parkinson's disease

Parkinson’s disease (PD) is the second most common neurodegenerative disorder and affects about 100,000 Canadians. It occurs when cells that produce dopamine in the brain die. Without enough dopamine to send signals to the striatum, an area of the brain that controls movement, people with Parkinson’s develop tremors, stiffness and balance problems. Patients take medication to replace the missing dopamine, but this often produces troubling side effects. Interestingly, a significant placebo effect can occur in patients with Parkinson’s, with patents showing an improvement in symptoms due to their belief that a particular treatment will be beneficial. Sarah Lidstone is expanding on her earlier MSFHR-funded research to study how patients’ expectations for an improvement in symptoms actually produce measurable improvement. Using positron emission tomography (PET), a powerful brain scanning technique, Sarah has shown that patients with Parkinson’s disease release dopamine in the brain when given a placebo they thought was medication. Dopamine is also released in the same brain areas when people anticipate receiving a reward such as money or food, a response also generated in drug addiction. Sarah is examining whether the placebo mechanism in Parkinson’s taps into the same process as reward anticipation. If so, this research could lead to better treatments for the disorder. It could also inform treatment for drug addiction and other conditions influenced by a placebo effect or dopamine, including pain management, depression and obsessive-compulsive disorder.