Anhedonia is a multifaceted construct characterized by a diminished ability to express motivational behavior and is a significant non-motor deficit in patients with Parkinson's disease (PD). This condition encompasses several interconnected mechanisms: cue recognition, motor response execution, pleasure experience, and learning. Our research specifically examines two components of anhedonia: motor response execution and the experience of pleasure. Dopamine is primarily implicated in executing motor responses, whereas the opioid and endocannabinoid systems are involved in the pleasurable experience upon reward attainment.
In our study, we examine the impact of Parkinson's disease on the expression of anhedonia. The PD population was selected due to the characteristic reduction in central dopamine levels. The effect of the disease was assessed using the translated Temporal Experience of Pleasure Scale (TEPS). This scale measures two different components: anticipatory and consummatory. The anticipatory component relates to the motor aspects of anhedonia, while the consummatory component pertains to the mechanisms of pleasure experience upon reward access. The scale uses 18 statements to assign nominal values from one to six for each component and an overall anhedonia score.
The study involved 25 PD patients and 66 age-matched healthy participants. The PD group included newly diagnosed individuals and those undergoing regular treatment. The participating patients were in the on phase and did not show signs of cognitive decline, depression, and apathy.
Consistent with the models of anhedonia used, we measure statistically significantly lower expression of the anticipatory component of anhedonia in PD (p=0.007). Although the consummatory component was lower, on average, the difference was not statistically significant (p=0.08).
The results concur with the theoretical concepts and confirm the temporal distinction between motivation and pleasure expression components. They further specify the activity of the dopaminergic system primarily in the execution of motor behavior required to reach the reward, but not in modulating the experience of pleasure upon reaching the reward itself. Lastly, an additional outcome of the study is the translated but not validated Slovene version of the Temporal Experience of Pleasure Scale.
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