The functional and neural mechanisms underlying the processing of different action sequences in grasping.

Goal-directed grasping actions are often planned with respect to their intended final states, as reflected in the end-state comfort effect (ESC) where individuals adopt initially uncomfortable grasp postures to ensure a comfortable final posture. The present study investigates the neurophysiological mechanisms underlying the processing of action sequences in grasping using event-related potentials (ERPs) within a priming paradigm. Participants were presented with prime images showing initial grasp postures (overhand or underhand grip) followed by target images representing final grasp postures (thumb-up or thumb-down) that together depicted either possible or impossible action sequences. Participants responded to the color of the upper part of the bar in the target image, while grasp postures were task-irrelevant. The results reveal that responses to target images representing an uncomfortable final grasp (thumb-down) following an underhand grip in the prime were slower and elicited a stronger P300 amplitude compared to responses to comfortable final grasp targets (thumb-up). This effect was observed only when the prime-target sequence represented a physically possible action. These results suggest that perceiving an initial underhand grip leads to the anticipation of a functional final action state. Deviations from this expected outcome result in greater cognitive processing effort, as reflected by increased P300 amplitudes. This suggests that action representations in grasping are anticipatory in nature and incorporate information about likely future action outcomes. The findings are consistent with ideo-motor theories, highlighting the role of anticipated action effects in action processing, and provide novel insights into the cognitive and neural underpinnings of action representation.