Flexible, adaptive behavior is critically dependent on inhibitory control. For example, if you suddenly notice you are about to step on a tack and would prefer not to, the ability to halt your ongoing movement is critical. To address limitations in existing approaches for studying your ability to rapidly terminate your movement ('stopping'), we developed a novel stop task. This task requires termination of ongoing motor programs, provides a direct measure of SSRT, and allows for comparison of the same behavior (stopping) in conditions that elicit either prepared or reactive inhibitory control. Here, we present and evaluate our novel Continuous Movement Stop Task (CMST). We examined several versions of the task in a total of 49 participants. Our data reveal that the CMST is effectively able to dissociate stopping behavior between the planned and unplanned conditions. Additionally, within the subset of participants for which we measured speed, we found that participants initiated stopping (with respect to the stop signal) significantly earlier on planned stop compared to unplanned stop trials. Finally, participants took longer to arrive at full motor arrest (i.e. SSRT) following stop initiation on planned than on unplanned stop trials. This novel task design will enable a more precise quantification of stopping behavior and, in conjunction with neuroscientific methods, could provide more rigorous characterization of brain networks underlying stopping.

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Flexible, adaptive behavior is critically dependent on inhibitory control. For example, if you suddenly notice you are about to step on a tack and would prefer not to, the ability to halt your ongoing movement is critical. However, this behavior is usually not probed by current inhibitory control tasks, which often focus instead on inhibiting a movement before its initiation. To address limitations in existing approaches for studying termination of an ongoing movement, we developed a novel stop task with which we can directly observe and compare prepared and reactive termination of a continuous movement. Here, we present and evaluate our novel continuous movement stop task (CMST) and compare task performance to performance on the traditional stop signal task. Our data reveal that the CMST effectively dissociates planned and unplanned stopping behaviors. We found that participants initiated and completed stopping significantly earlier on planned compared with unplanned stop trials and that the variability for each measure was greater for planned compared with unplanned stop trials. In addition, we found that the time at which participants initiated the stopping process was more variable than the time it took participants to complete the stopping process. We also found that participants slowed before stopping significantly more on planned than unplanned stop trials. Finally, our data suggest that preparatory mechanisms may be similar between the two tasks, but the tasks were not related by any other measure. The unambiguous quantification of prepared and reactive stopping behavior provided by the CMST will help support future investigation of different kinds of stopping behavior.

Beta oscillations (~13-30 Hz) recorded from the sensorimotor cortex have canonical amplitude changes during movement. Specifically, a movement-related beta decrease (MRBD) occurs before movement, and a post-movement beta rebound (PMBR) follows. We investigated how the MRBD and PMBR vary with movement speed. Individuals performed a task with blocks that generated longer reaction times (RTs) and shorter RTs (Slow and Fast blocks, respectively) while scalp-electroencephalography (EEG) was recorded. The timing of task events before movement was also modulated to generate blocks with certain and uncertain timing (Fixed and Varied blocks, respectively). Beta modulation was reduced in Slow blocks compared to Fast blocks (i.e., a less negative MRBD and less positive PMBR). For the movement certainty manipulation, we saw mixed behavioral and EEG results. Our primary findings align with previous work which has shown reduced movement-related beta modulation in patients with Parkinson's disease. We propose that a "slowed movement state", whether it is experimentally induced or a manifestation of Parkinson's disease bradykinesia, is represented through reduced beta dynamics. Altogether, the MRBD and PMBR may represent motor speed on a continuum with Parkinson's disease as an extreme example of slowed movement.