THE PREPARATION, EXECUTION AND SUPPRESSION OF COPIED MOVEMENTS IN THEHUMAN BRAIN

We used positron emission tomography (PET) to measure movement set-rel ated changes in regional cerebral blood flow (rCBF) when human subject s were asked to copy hand movements. Movement set-related activity in the brain is thought to reflect the processes of movement selection, p reparation and inhibition. Four conditions were used. In the first con dition, prepare and execute (PE), the hand stimulus to be copied was s hown to subjects 3 a before an auditory ''go''-cue instructed subjects to execute the movement, a large part of the scanning time was theref ore spent in preparing to move. In the immediate execution condition ( E), the hand stimulus and the go cue were presented simultaneously. Th e prepare-only condition (P) was similar to PE, except subjects only p repared to make the movement and did not actually execute any movement when they heard the auditory go-cue. The same stimuli were presented in a baseline condition (B), but the subjects were instructed to neith er prepare nor execute movements. There were 5 principle findings: (1) In contrast to a previous study of human set-related activity in whic h movements were instructed by an arbitrary pattern of LEDs, preparing to make a copied movement causes rCBF changes in area 44 in posterior Broca's area; (2) set-related activity can be recorded in the cerebel lar hemispheres and midline; (3) we confirmed that the supramarginal g yrus has a general role in preparing movements - there was more rCBF i n the P than the E condition; (4) the cerebellar nuclei and the basal ganglia may be particularly involved in the initiation and execution o f a planned movement; these regions were more active in the PE conditi on than the P condition; (5) the ventrolateral prefrontal cortex and a left anterior cingulate area are part of a distributed system involve d in the suppression of a motor response; these areas were significant ly more active in the P than the PE condition.