Cortical motor representation in view of recent experiments on cortico-spinal relations.

The results of recent experiments using either intracortical stimulation or stimulation of the surface of the motor cortex were reviewed from the point of view of "muscle" and "movement" cortical representation. It has been concluded that there is no satisfactory evidence for location of the pyramidal tract (PT) cells which project directly (monosynaptically) to motoneurones of one muscle in primates within small and separate cortical areas; such evidence is even weaker for PT cells which exert their effects via polysynaptic pathways in other species. The available evidence shows in contrast a very pronounced overlap of cortical areas of projection to different motor nuclei.