Placebo Effect Improves Cognitive Function in Parkinson's

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Patients with Parkinson’s disease who were given a placebo in a trial involving a game saw improvements in learning-related brain activity that was similar to when they were given a drug that stimulates the release of dopamine.

Tor Wager, PhD, of the University of Colorado at Boulder, and colleagues had 18 patients with Parkinson’s play a computer game. Functional magnetic resonance imaging scans were taken as they played. The game was designed to measure reward learning by having participants determine which of two symbols was likely to lead to a better outcome.

The participants played the game three times; once while on neither placebo nor medication, the second after they had orange juice with the drug L-DOPA, which boosts dopamine levels, and the third with orange juice mixed with a placebo.

Parkinson’s patients often struggle with “reward learning,” making it difficult to make decisions and seek positive outcomes. The reason for this is the loss of cells that produce dopamine, which is common in Parkinson’s.

The striatum and the ventromedial prefrontal cortex—areas of the brain associated with reward learning that have high dopamine levels—were just as active when the participants played the game after taking the placebo as when they took the drug, the researchers reported in the journal Nature Neuroscience.

The study appears to indicate that the placebo effect—where people believe they have received the active drug—works by activating dopamine-rich areas in the brain of Parkinson’s patients.

“Recognizing that expectation and positive emotions matter has the potential to improve the quality of life for Parkinson's patients, and may also offer clues to how placebos may be effective in treating other types of diseases," Wager said in a statement.

Elderly woman
Placebo Effect Improves Cognitive Function in Parkinson's

Expectations have a powerful influence on how we experience the world. Neurobiological and computational models of learning suggest that dopamine is crucial for shaping expectations of reward and that expectations alone may influence dopamine levels.

However, because expectations and reinforcers are typically manipulated together, the role of expectations per se has remained unclear. We separated these two factors using a placebo dopaminergic manipulation in individuals with Parkinson's disease. We combined a reward learning task with functional magnetic resonance imaging to test how expectations of dopamine release modulate learning-related activity in the brain.

We found that the mere expectation of dopamine release enhanced reward learning and modulated learning-related signals in the striatum and the ventromedial prefrontal cortex.

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