Objective: To evaluate decision making under risk in Parkinson’s disease patients, both medicated and un-medicated states probing constituent cognitive operations driving choice. 

Background: Prior literature suggests that decision making is altered in Parkinson’s disease.  However, the findings have been mixed and have differed depending on the task used prohibiting the ability isolate specific cognitive constituents of the decision making process in Parkinson’s disease.  Furthermore, the majority of studies have examined decision making in Parkinson’s disease in the medicated state, and it remains unclear to what degree the reported decision making alterations are a result of medication.

Methods: 24 non-depressed patients with idiopathic Parkinson’s disease (17 males, 7 females) on levodopa monotherapy and 19 controls (11 males, 8 females), matched to the patients on age and cognitive functioning performed a battery of 3 decision making tasks, which measure component processes involved in decision making under risk and ambiguity. Parkinson’s disease patients performed the battery both on and off their usual dose of levodopa in counterbalanced order; healthy controls also performed the battery twice.

Results: While controls showed the typical over-estimation of small and under-estimation of large probabilities, the patients showed a trend towards a less distorted  perception of probability, with some patients even showing the reverse tendency to over-estimate large and under-estimate small probabilities.  This tendency to under-estimate smaller probabilities, which may have resulted in more risk-averse decisions by the Parkinson’s disease group, was partially normalized by levodopa. On the second task, patients with Parkinson’s disease both on and off medication were more likely than controls to increase their stakes for the gambles with higher expected value.

Conclusions: Patients with Parkinson’s disease show alterations in decision-making under risk. In the un-medicated state, they appear to have a levodopa-sensitive altered perception of probability , which contributes to risk aversion in gain-only gambles.  They are also more prone raising stakes for prospects with higher expected value , a levodopa-insensitive tendency that could be considered a form of impulsivity. 

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MDS Abstracts - https://www.mdsabstracts.org/abstract/decision-making-under-uncertainty-in-medicated-and-un-medicated-parkinsons-disesase/