Selection and preparation of hand and foot movements: Cz activity as a marker of limb system preparation.

Event-related potentials were used to examine the preparation of hand and foot responses in tasks using both limb systems. As in tasks using only one system, opposite lateralized readiness potentials were observed for hand and foot responses (Experiment 1). Furthermore, movement-related activity at Cz was more positive prior to hand than foot responses, revealing that Cz activity can be used to index selective movement preparation by one limb system. In Experiment 2, two responses were cued prior to stimulus onset. Cue-related activity at Cz was more positive with hand than foot cuing, reinforcing the conclusion that Cz activity is sensitive to selective preparation for one of these limb systems. Overall, the results show that it is possible to carry out motor preparation of two responses within the same limb system and that differential Cz activity is a useful index of this preparation in tasks with hand versus foot movements.