McCurdy, J. R.; Zlatopolsky, D.; Doshi, R.; Xu, J.; Barany, D. A.

Successfully intercepting a moving object requires precisely timing the optimal moment to act by integrating information about the target\'s visual motion properties. Neurophysiological evidence indicates that activity in the primary motor cortex (M1) during interception preparation is sensitive to both the target\'s kinematic features and motor planning. However, how visual motion signals are integrated within M1 to guide interception timing is unclear. In the present study, we applied single-pulse transcranial magnetic stimulation (TMS) over M1 to examine how a target\'s kinematics influence corticospinal excitability during interception preparation. Participants were instructed to abduct their right index finger to intercept a target moving horizontally at a constant speed toward a fixed interception zone. Target speed (Fast or Slow) and travel distance (Far or Close) were manipulated while controlling motion duration across conditions. Motor-evoked potentials (MEPs) were elicited at five latencies before target arrival at the interception zone. Consistent with previous behavioral findings, movement initiation occurred earlier for faster targets and was delayed when TMS was applied closer to the target\'s arrival. Though MEPs were generally suppressed relative to baseline at earlier timepoints and facilitated closer to movement initiation, we observed that target speed - but not distance - influenced the time course of MEP modulation. When adjusting for movement initiation times, there was an overall reduced suppression and increased facilitation for faster-moving targets, possibly reflecting a heightened urgency to move. These results suggest M1 activity during interception preparation integrates internal estimates of target motion, which may serve to optimize interception timing and performance.