Motor timing and the preparation for sequential actions.

Motor timing is essential for performing self-initiated movement sequences. Here, we investigated how sequence rhythm, or the timing for co-ordinating movements within a sequence, contributes to action preparation, compared with other processes occurring during sequence planning. First, we recorded the readiness potential (RP) in a condition of complex sequence rhythm and in condition of high demand on the timing for sequence initiation. We found that sequence rhythm and sequence initiation are independent processes, with sequence initiation contributing to early RP. Second, we compared the RP recorded in a condition of complex sequence rhythm and in a condition of complex sequence order, in which a complex combination of finger sub-movements had to be correctly ordered within a sequence. We found that sequence rhythm and sequence order share common processes occurring late RP. We suggest that the preparation for movement involves independent processes devoted to different aspects of motor timing and sequencing.