Organization of motor control by the normal human brain

The research on the cerebral motor system in man was reviewed and supplemented by new results. Electrical stimulation and recordings of electrical activity, or measurements of the regional cerebral blood flow (rCBF) or metabolism in awake humans suggested that man has three cortical motor areas: The premotor area, the supplementary motor area, and the primary motor area. Subcortically the caudate nucleus, putamen, globus pallidus, and ventral thalamus participated in the planning and execution of voluntary movements. With the exception of the primary motor area, all these structures were bilaterally activated in unilateral movements. The supplementary motor area participated in the planning of motor subroutines, speech included. The premotor area participated in non-routine voluntary movements or movements carried out contingent or dependent on sensory information. The primary motor area was the executive locus for voluntary movements. In addition to these motor areas other cortical areas were recruited dependent on whether internal volitions, perceptions, or language had to be translated into motor codes. The superior prefrontal cortex participated in this recruitment. In the parietal lobe different areas were recruited depending on whether the movements were carried out in intrapersonal or extrapersonal space. The bilateral activation of motor structures was assumed to reflect bilateral elaboration of motor programs and also bilateral encoding of motor memory.