Differential involvement of parietal and precentral regions in movement preparation and motor intention.

Flexible goal-oriented behavior relies on spatial coordinate transformations and motor control mechanisms, but also on the capability to take advantage of contextual information for steering the sensorimotor machinery. Although accurate performance of a sensorimotor task requires parietal and frontal regions, their differential contribution and functional relationship with other associative regions remains obscure. We have used event-related functional magnetic resonance imaging to measure human cerebral activity associated with motor cognitive processes in the context of delayed performance of an associative visuomotor task. Movement instruction (specified by visual cues) and motor performance (specified by an auditory cue) were separated by a variable delay period. By manipulating the predictive value of the instruction cue, we distinguished delay-related activity influenced by response probabilities (motor preparation and motor inhibition) from delay-related activity unaffected by the likelihood of providing a motor response (motor intention). We found delay-related activity distributed across a cerebral network involving not only frontal circuitry, but also extrastriate and mediotemporal regions. Areas showing motor intentions and preparatory responses were spatially intermingled. Posterior parietal cortex deviated from this pattern, showing delay-related activity regardless of movement probability, but no specific preparatory responses. These results suggest that posterior parietal cortex and dorsal precentral cortex play different strategic roles in handling associative visuomotor problems. While parietal regions cover a range of potential responses defined by the task setting, precentral regions focus on a likely movement. Temporo-prefrontal regions might incorporate contextual information in the visuomotor process by defining potential and probable responses on the basis of the task contingencies.