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Abstract
A series of recent anatomical and functional data has radically changed our view on
the organization of the motor cortex in primates. In the present article we present
this view and discuss its fundamental principles. The basic principles are the following:
(a) the motor cortex, defined as the agranular frontal cortex, is formed by a mosaic
of separate areas, each of which contains an independent body movement representation,
(b) each motor area plays a specific role in motor control, based on the specificity
of its cortical afferents and descending projections, (c) in analogy to the motor
cortex, the posterior parietal cortex is formed by a multiplicity of areas, each of
which is involved in the analysis of particular aspects of sensory information. There
are no such things as multipurpose areas for space or body schema and (d) the parieto-frontal
connections form a series of segregated anatomical circuits devoted to specific sensorimotor
transformations. These circuits transform sensory information into action. They represent
the basic functional units of the motor system. Although these conclusions mostly
derive from monkey experiments, anatomical and brain-imaging evidence suggest that
the organization of human motor cortex is based on the same principles. Possible homologies
between the motor cortices of humans and non-human primates are discussed.