The cortico‐nigral projection in the cat an experimental study with silver impregnation methods

Following lesions of various parts of the cerebral cortex in cats the terminal distribution of cortico‐nigral fibers has been studied by means of silver impregnation methods. A modest number of cortico‐nigral fibers have been traced from the gyrus proreus, the “supplementary motor” area, the “primary sensory‐motor” area and the “secondary sensory” area. Lesions of the remaining regions of the cerebral cortex did not give rise to terminal degeneration in the substantia nigra. The number of cortico‐nigral fibers was considerably less than expected from the data available in the literature. The cortico‐nigral projection system is chiefly homolateral. A few crossed cortico‐nigral fibers were found following lesions of the gyrus proreus or the “supplementary motor” area. The majority of the corticofugal fibers from these two cortical region and the “secondary sensory” area terminate on the somata or the proximal dendrites of the cells in the nigra complex. Following lesions of the “primary sensory‐motor” area of the cerebral cortex, terminal degenerating fibers were only seen in the neuropil of the substantia nigra. The findings are discussed briefly.