Apathy is the most frequently observed non-motor symptom in Parkinson’s disease (PD) and has significant impact on quality of life. It is characterized as reduced goal-directed behaviour resulting in loss of motivation and interest. Prior work has examined its manifestation by dissecting the contributions of reward and effort in decision-making, both of which are associated with dopaminergic functioning. 

Yet, previous studies were limited to highly controlled laboratory experiments with artificial outcomes. To bridge the gap to everyday behaviour, this study used an Ecological Momentary Assessment design to examine how dopaminergic influences on decision-making manifest in everyday activities in people with PD. Via a smartphone-app, 30 PD participants and 21 healthy age- and education matched controls were monitored in their daily life for 14 consecutive days. 

Participants reported on their current activity by rating their apathy level, reward and effort valuations, and for PD-participants, their current dopaminergic state, via five short, daily questionnaires. The results showed a significant difference between PD and controls for effort valuation, but not for reward valuations. 

Moreover, dopamine improved experiences of reward, effort and apathy ratings when considering ON vs OFF states in participants with PD. Present findings suggested that dopamine may indirectly enhance reward and effort valuation through alleviating apathy levels. This direction of the relationship gives a better understanding of the pattern in real life, however more work is needed to investigate if such a mediating effect is robust and how to translate these findings into effective treatment approaches for apathy.