Altered moral decision-making in patients with idiopathic Parkinson's disease

Moral decision-making essentially contributes to social conduct. Although patients with Parkinson's disease (PD) show deficits in (non-moral) decision making and related neuropsychological functions, i.e. executive functions, theory of mind (ToM), and empathy, moral decision-making has rarely been examined in PD patients. We examined possible alterations of moral decision-making and associated functions in PD.

Twenty non-demented PD patients and 23 age- and education-matched healthy control participants were examined with tests that assess reasoning, executive functions (set-shifting and planning), ToM and empathy, decision-making under risk, and moral intuitions. Moral decision-making was assessed with a close-to-everyday moral dilemma paradigm that opposes socially oriented "altruistic" choices to self-beneficial "egoistic" choices in 20 moral dilemma short stories (10 high and 10 low emotional). Concurrently, electrodermal activity was recorded.

PD patients made more egoistic moral decisions than healthy controls. Remarkably, while reasoning, planning and empathy correlated with moral decision-making in the control group, in the PD group neuropsychological functions and dopaminergic medication did not correlate with moral decisions. No evidence for reduced skin conductance responses in PD patients and no relationships between skin conductance responses and moral decisions were observed.

This study provides evidence for moral decision-making dysfunctions in PD patients who made more egoistic moral decisions. As a possible underlying mechanism, reduced exercise of attentional control due to a dysfunctional interplay between the prefrontal cortex and the basal ganglia is discussed. Future research will have to determine the impact of PD patients' moral decision-making dysfunctions on everyday life and further determine correlates of the deficits.