THE ORGANIZATION OF THE CORTICAL MOTOR SYSTEM - NEW CONCEPTS

A series of recent anatomical and functional data has radically change d our view on the organization of the motor cortex in primates. In the present article we present this view and discuss its fundamental prin ciples. The basic principles are the following: (a) the motor cortex, defined as the agranular frontal cortex, is formed by a mosaic of sepa rate areas, each of which contains an independent body movement repres entation, (b) each motor area plays a specific role in motor control, based on the specificity of its cortical afferents and descending proj ections, (c) in analogy to the motor cortex, the posterior parietal co rtex is formed by a multiplicity of areas, each of which is involved i n 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 anatomica l circuits devoted to specific sensorimotor transformations. These cir cuits transform sensory information into action. They represent the ba sic functional units of the motor system. Although these conclusions m ostly derive from monkey experiments, anatomical and brain-imaging evi dence 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. (C) 1998 Elsevier Scienc e Ireland Ltd.