Dopaminergic medication boosts action-effect binding in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder affecting voluntary motor control. However, little is known about the experience of voluntary action in PD patients. A key component of action experience is the feeling of controlling one's own actions, and through them, external events. In healthy individuals this sense of agency (SoA) is associated with a subjective compression of time, such that actions and their effects are perceived as bound together across time. This action-effect binding provides an indirect measure of SoA. Nine PD patients and age-matched controls judged the time of voluntary actions and of an auditory effect (a tone) of the action. The pattern of results resembled previous studies, with the perceived time of actions showing a shift towards the subsequent tone, relative to a baseline condition involving actions without tones. Similarly, the perceived times of tones showed a shift towards the preceding action that caused the tone, relative to a baseline condition involving tones only. The patients were tested both on and off dopaminergic medication. PD patients off medication showed no significant change in action-effect binding relative to controls. Conversely, PD patients on medication showed a significant increase in action-effect binding relative to their own performance off medication. Increased availability of dopamine strengthened the experience of association between actions and external events, enhancing the sense of agency. These results shed light on the contribution of dopamine to the experience of instrumental action, and also on impulse control disorders and psychosis in medicated PD patients.