Cerebral dominance for action in the human brain: the selection of actions.

PET was used to study cerebral dominance for the selection of action. In one condition the subjects moved one of two fingers depending on the cue presented (choice reaction time), and in another they moved the same finger whatever the cue (simple reaction time). There was also a baseline condition in which cues were shown but no movements were made. A conjunction analysis was performed to reveal those areas which were more activated for the choice versus simple reaction time, irrespective of whether the right or left hand was used. The activations were in prefrontal, premotor and intraparietal areas, and they were all in the left hemisphere. Thus, while there were activations in the right hemisphere for the choice versus simple reaction time task when the subjects used their left (contralateral) hand, there were activations in left prefrontal, premotor and parietal areas whether the right (contralateral) or left (ipsilateral) hands were used. It is argued that the results suggest that the left hemisphere is dominant not only for speech but also for action in general.