Electrophysiological evidence for lateralization of preparatory motor processes.

Event-related potentials were recorded during a warned choice reaction time task in which the warning signal was informative (it signaled the specific response to be required) or uninformative (it gave no response-specific information). The response signal specified a key press with either the middle or the ring finger of the left or the right hand. The informative warning signal facilitated reaction time in two separate protocols. The contingent negative variation elicited following the informative warning signal was larger than that following the uninformative warning signal, and this effect was larger over the left hemisphere than over the right hemisphere. This finding gives converging evidence that preparatory motor processes are predominantly lateralized to the dominant hemisphere.