TEMPORAL ORGANISATION OF VOLUNTARY ACTION PHASES WITHIN THE CARDIAC CYCLE IN ACTIVE TASK

Internal bodily states influence perceptual processing. Perceptual accuracy varies across the cardiac cycle, with reduced sensitivity during systole, both in passive paradigms (Al et al., 2021) and during active sensory sampling (Galvez-Pol et al., 2020). It remains unclear whether the execution of sensory-guided actions is temporally structured with respect to the cardiac cycle. We examined whether key kinematic events during a 2D reaching task align with the cardiac cycle. 12 (5 females) participants performed a motor task in which they slid their index finger across a fine-textured surface, while direct vision of the hand was occluded. Action execution therefore relied primarily on tactile and proprioceptive information. Electrocardiography (ECG) was continuously recorded throughout the task. Each trial comprised three task-relevant events indexing contact onset, motion onset and contact offset. ECG QRS complexes and T-wave end points were identified using established automated procedures, enabling beat-specific delineation of systolic and diastolic phases. To standardize the duration of the systolic and diastolic phases, cardiac cycle was expressed as a continuous circular variable (0-360°). Group-level analyses revealed significantly non-uniform phase distributions for all three kinematic events. Contact onset and motion onset showed preferential alignment with central diastole, whereas contact offset exhibited the strongest and most consistent phase clustering, with a mean phase located in later diastole. No preferential phase distribution was observed during a baseline interval, indicating that phase clustering was specific to task-relevant action events. These findings indicate that distinct phases of voluntary action are systematically organised with respect to the cardiac cycle.