Dopamine deficiency is associated with risk aversion but not loss aversion in Parkinson's disease

Background: Clinical evidence suggests that Parkinson9s Disease (PD) patients are risk-averse, but clear experimental evidence of this is surprisingly lacking. Anti-parkinsonian therapy has been reported to increase tolerance for risk, though findings have been mixed, and it has remained unclear whether this results from altered attitudes towards potential rewards, potential punishments or both. In some cases, alterations in reinforcement learning may have also been responsible for the findings. Objective: To disambiguate the effects of PD and its therapy on attitudes towards rewards vs. losses in the context of risky decision making unconfounded by reinforcement learning. Method: 36 patients with idiopathic PD receiving levodopa monotherapy and 36 healthy age-matched controls performed two behavioural economic tasks aimed at quantifying 1) risk tolerance/ aversion in the gain frame and 2) valuation of gains relative to losses. PD patients performed the tasks on and off their usual dose of levodopa in randomized order; the healthy controls performed the same tasks twice. Results: Relative to the healthy controls, unmedicated PD patients showed significant risk aversion in the gain frame, which was normalized by levodopa. There was no difference between PD patients and controls in valuation of gains relative to losses. In addition, across both tasks and regardless of medication state, choices of the PD patients were more driven by expected values of the prospects than were the choices made by controls. Conclusion: Dopamine deficiency in PD was associated with risk aversion but not with an altered valuation of gains relative to losses.