Motor Intention Drives Corticospinal Facilitation during Interception Planning
Intercepting a moving target requires integrating visual motion information with motor preparation, yet how active motor preparation and gaze strategy jointly shape corticospinal excitability during interception planning remains unclear. We applied single-pulse transcranial magnetic stimulation over primary motor cortex to probe corticospinal excitability while participants either prepared to intercept a moving target or passively viewed its motion. Targets moved at one of two speeds, and participants judged target speed relative to a reference after each trial. Across blocks, participants were instructed to either smoothly pursue the target or fixate their eyes on the interception zone. Motor-evoked potentials were elicited at baseline, after task instruction, early during target motion, or shortly before target arrival. Task and gaze strategy interacted to influence both perceptual judgments and corticospinal excitability. Preparing to intercept produced a robust facilitation of corticospinal excitability immediately before movement onset, regardless of gaze strategy. In contrast, corticospinal excitability during passive viewing did not differ from baseline. Smooth pursuit improved perceptual accuracy and reduced interception timing error compared with fixation but did not independently influence corticospinal facilitation. These findings demonstrate that active motor preparation is the primary determinant of the transition to a state of facilitated excitability during interception planning, whereas eye movements modulate perceptual estimates and support behavioral performance. New & NoteworthyThis study dissociates the contributions of visual tracking, eye movements, and active motor preparation to corticospinal excitability during interception. Here, we show that corticospinal facilitation emerges primarily when an action is planned, whereas passive viewing remains at baseline despite identical visual input. Smooth pursuit enhanced perceptual accuracy and interception timing but had a limited effect on corticospinal excitability, highlighting active motor preparation as the key driver of corticospinal output.