Distribution of activity in the dominant (left) hemisphere was studied with a multidetector instrument during diagnostic measurements of regional cerebral blood flow in 6 patients, 4 of them neurologically normal. Computercalculated charts, in color, of the flow/activity distribution--"cerebral ideograms"-- were obtained in three situations: at rest, during motor ideation (attempts to conceive of rhythmic clenching movements of the right hand), and during actual movements of the right hand. Motor ideation changed the normal "hyperfrontal" resting flow distribution, and an increase of the hemisphere mean flow was recorded. The increase was especially marked in frontal and temporal structures. This pattern differed from the one during actual hand movements, when a rolandic flow increase was seen. The result suggests that centers for motor ideation have a different cerebral location than those which control the actual hand movement.