Parallel processing within motor areas of cerebral cortex and basal ganglia in the monkey

The control of visually guided limb movements can be divided analytically into sequential levels of processing that successively determine target location, limb trajectory, joint kinematics, joint torques, and muscle activations. Whether the motor system uses such a serial approach was addressed. Monkeys were trained to perform motor tasks that dissociated behavioral variables related to three of the analytically defined motor processing levels. Task-related neuronal activity was recorded in three motor areas: the supplementary motor area (SMA), primary motor cortex (MC) and putaman. They found that multiple levels of processing were represented by neuronal activity within each of these areas. Target-level representations were more prevalent than trajectory/kinematics-level representations during the preparation for movement, while the pattern was reversed during movement execution. This suggests that higher levels of processing are emphasized during movement preparation, with a shift toward lower levels during execution. That multiple levels of processing were represented in all three structures indicates that motor processing is spatially distributed and not strictly localized or hierarchically segregated. The relative timing of onsets and offsets of task-related activity suggested a cascade of influences leading from SMA and MC to putamen