Metabolic mapping of sensorimotor integration in the human brain

Studies of regional cerebral flow and regional cerebral oxidative metabolism have revealed that humans have three major cortical motor areas: the premotor, supplementary motor and primary motor areas. The premotor area participates in organizing non-routine voluntary movements, especially those carried out contingent to or dependent on sensory information. The supplementary motor area participates in the planning of all motor subroutines. The primary motor area is the executive locus for voluntary movements. Subcortically the caudate nucleus, putamen, globus pallidus, parasagittal cerebellum and ventral thalamus are the main structures which increase their metabolism during voluntary movements of the upper limbs. All these cortical and subcortical structures except the primary motor area are bilaterally activated even during strictly unilateral movements of the upper limbs. However, recent studies of oxidative metabolism show that the caudate nucleus, putamen and lateral cerebellum also participate in cognitive functions and non-motor learning. Before any specific brain work is executed, voluntary movements included, the brain tunes and prepares cortical fields measuring a few square centimetres in the areas that are supposed to participate in information transmission. The superior prefrontal cortex has a special role in this recruitment of cortical fields. Depending on the information needed to execute the voluntary movements, cortical fields are activated in the anterior parietal lobe and the dysgranular frontal cortex.