Electrophysiological Signatures of Planned and Unplanned Continuous Movement Termination in Parkinson’s Disease

The ability to inhibit and adapt our behavior in response to changing stimuli is a critical component of everyday life. Individuals with Parkinson’s disease (PD) may struggle to inhibit behavior, particularly in the presence of dopaminergic therapy, which can result in impulsive behavior. Impulse control disorders are often operationalized in the laboratory using motor inhibition tasks. However, deficits of motor inhibition tasks are not always observed in PD, perhaps because of the nature of the motor inhibition that is engaged in typical tasks (e.g., suppression of incipient movement such as a button press). We employed a novel continuous movement stop task to investigate planned and unplanned motor inhibition during ongoing movement. EEG was recorded during task performance from individuals with PD (OFF and ON dopaminergic medication) and age-matched healthy controls (HC). Participants were of any sex. We found that the time it took for participants to stop a continuous movement was impaired (i.e., longer) in PD patients ON medication compared to both patients OFF medication and HC. This finding was accompanied by diminished midfrontal theta power following the stop signal in PD (ON and OFF) compared to HC. Additionally, an increase in midfrontal beta power was observed, which was higher in unplanned stopping compared to planned for all groups. However, this increase in beta occurred late - after the time of outright stopping. Together, these findings demonstrate that stopping ongoing movements was impaired in PD patients ON medication and that theta and beta power play distinct roles in inhibition of movement in PD. Significance statement Parkinson’s disease (PD) is associated with impairments in cognition and movement, both of which are engaged during motor inhibition. Using a continuous movement stop task that directly probes both functions, we tested individuals with PD (ON and OFF medications) and healthy controls using EEG. We found that levodopa medication worsened behavioral stop completion times and suppressed event-related theta (4-7 Hz) power, supporting the paradoxical nature of dopamine in cognitive control. Also, there was an increase in beta power following the stop signal, however this increase was too late to be triggering the motor inhibition itself. Our findings demonstrate that levodopa can impair motor inhibition and support distinct roles for theta and beta activity in the termination of an ongoing movement.