Quantitative analysis of the distribution of the motor cortex representations of the fore-and hindlimbs in the red nucleus of the cat.

A quantitative analysis of the distribution of corticorubral fibers was performed after precise electrolytic lesioning of the lateral and medial margins of the posterior sigmoid gyrus--the motor representations of the fore-and hindlimbs respectively--in cats. The cortical representations of the forelimbs were found to project to the whole of the rostrocaudal extent of the red nucleus (RN). The number of efferent fibers terminating at the rostral margin of the RN was almost twice that terminating in the caudal third of the RN. Efferent fibers of the cortical representation of the hindlimbs did not project to the rostral two thirds of the RN but ended in its caudal third; the number of projecting corticorubral fibers was the same as the number running from the cortical representation of the forepaws to the caudal third of the RN. The significantly (almost double) greater number of fibers running from the cortical representation of the forelimbs in comparison with the number directed from the representation of the hindlimbs found in the present study is probably evidence of the greater functional importance of corticorubral connections in movement reactions performed by the forelimbs.