Objective: Parkinson’s Disease (PD) is a degenerative motor disease that causes subtle deficits in decision-making as a result of striatal dysfunction due to dopamine depletion. Studies show that PD patients have learning and decision-making deficits. Yet, how various forms of learning directly affect decision-making in PD is not clear. Our goal in this study was to determine whether PD patients make value-based decisions differently than healthy controls and whether any such differences are modulated by dopaminergic medication.

Background: When faced with decisions based on value, we rely on past experiences to make choices by either basing our decisions on value averaged over previous encounters, or relying on memory for a single encounter. Average values are formed through incremental learning, which relies on the striatum. Memory for single encounters is thought to rely on hippocampus-dependent episodic memory mechanisms.

Method: Behavioral experiments were conducted in PD patients on and off dopaminergic medication, as well as age-matched controls. Participants performed a decision-making task in which they made a series of choices between two cards to win money. Each card was worth $0-$1. Cards were either from a red or a blue deck and one of the decks was luckier (i.e. it had a higher payoff) at any given time, allowing subjects to incrementally learn the average deck value of red vs. blue. In addition, each card showed an image of an object and some objects repeated one more time, allowing subjects to use episodic memory of a single past encounter.

Results: We found that healthy controls relied on both episodic (memory of repeated objects) and incrementally learned sources of value (average value of the deck). PD patients on and off medication also used episodic value information to make decisions to the same extent of controls. However, patients relied more on incrementally learned sources of value when on than off medication.

Conclusion: Results show that in the healthy brain, value-based decisions rely on both incremental learning and episodic memory. The loss of dopamine in PD and dopaminergic medication disproportionally affect the ability to use incremental learning to make value-based decisions, but did not affect decisions based on episodic memory. Dopaminergic medication had a compensatory effect and boosted the reliance on incremental learning in decision-making.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/how-parkinsons-disease-affects-value-based-decisions/