To determine whether: 1. Parkinson’s disease (PD) patients show behavioral differences during value-based decisions compared to healthy controls, and 2. these differences relate to the dopaminergic state.

Deciding between familiar options of similar value is time-consuming. These decisions may depend on accumulating evidence over time. Recent studies show that accumulation of evidence can be via memory rather than only striatal input. PD is a degenerative motor disease which causes subtle deficits in decision-making as a result of dopamine depletion of the basal ganglia. However, the mechanism by which dopamine might affect value-based decisions remains unknown. 

Behavioral experiments were conducted in individuals with PD on and off dopaminergic medication, as well as age-matched healthy controls. Participants performed a value-based decision task and made choices between pairs of familiar food items. The value of each item was determined in advance using

a separate food-rating task. The same participants also performed a control condition where they made perceptual decisions about the color of random dynamic dots with different coherence on each trial. The reaction times (RT) and choice performance in both tasks were measured and fitted.

In the value-based decision task, the healthy controls were slower when the food items were closer in value. Overall, PD patients were slower than control participants but showed a specific RT deficit on value-based trials. Also, PD patients made more variable choices in the food choice task when the value difference between the two food items was small. We also examined the effects of the dopaminergic state on RT and choice variability.

Results show that value-based decisions rely on the striatal input. The fact that dopaminergic

medications improve the performance and speed confirms that healthy interaction between memory structures and striatum is crucial for memory signals to benefit value-based decisions that are more difficult requiring further deliberation.