Intrinsic connections between representation zones in the cat motor cortex.

The functional organization of intrinsic connections in the cat motor cortex was examined by combining intracortical microstimulation with neuroanatomical tracers. After single injections of a dye into a cortical site from which wrist flexion was evoked, clusters of retrogradely labeled somata and of anterogradely labeled axon terminals were found throughout the forelimb representation zones. These intrinsic connections rarely involved representation zones of the hindlimb or the face musculature. These data indicate that extensive intracortical connections mediate reciprocal synaptic interactions among groups of cells involved in the execution of different movement segments. These clustered, horizontal connections may be used for coordinating the activity of different cortical representations for the execution of complex movements, and may also be involved in the pliability of motor representation maps.