DORSAL PREMOTOR CORTEX AND CONDITIONAL MOVEMENT SELECTION - A PET FUNCTIONAL MAPPING STUDY

Positron emission tomography (PET) brain mapping was used to investiga te whether or not human dorsal premotor cortex is involved in selectin g motor acts based on arbitrary visual stimuli. Normal subjects perfor med four movement selection tasks. A manipulandum with three graspable stations was used. An imperative visual cue (LEDs illuminated in rand om order) indicated which station to grasp next with no instructional delay period. In a power task, a large aperture power grip was used fo r all trials, irrespective of the LED color. In a precision task, a pi ncer grasp of thumb and index finger was used. In a conditional task, the type of grasp (power or precision) was randomly determined by LED color. Comparison of the conditional selection task versus the average of the power and precision tasks revealed increased blood flow in lef t dorsal premotor cortex and superior parietal lobule. The average rat e of producing the different grasp types and transport to the manipula ndum stations was equivalent across this comparison, minimizing the co ntribution of movement attributes such as planning the individual move ments (as distinct from planning associated with use of instructional stimuli), kinematics, or direction of target or limb movement. A compa rison of all three movement tasks versus a rest task identified moveme nt related activity involving a large area of central, precentral and postcentral cortex. In the region of the precentral sulcus movement re lated activity was located immediately caudal to the area activated du ring selection. The results establish a role for human dorsal premotor cortex and superior parietal cortex in selecting stimulus guided move ments and suggest functional segregation within dorsal premotor cortex .