Synchronizing effect of clock rhythm on the 'when to move' decision in repeated voluntary movements

In 13 volunteers, surface EEGs from F-z, C-z, C-3, C-4, and P-z electrodes and EMG from the flexor digitorum communis were recorded during an experime ntal task in which the performance of wrist flexion was linked with the sel ection of a clock sound. In the epoch from 4 to 1 s before movement, more t han 95% of the records exhibited a small negative shift from the baseline. The position of these shifts on the time axis made it possible to create gr oups of time trials. The average EEG curves from these groups showed one pr ominent negative shift from the baseline, which could be related to the pos ition of particular clock sounds. The slope values of these shifts were hig hest under the F-z and C-z electrodes. We suggested that these negative shi fts coincided with 'when to move' decisions, which preceded the execution o f the movement at varying intervals. (C) 2000 Elsevier Science B.V. All rig hts reserved.