The mode of termination and temporal course of degeneration of cortical association pathways in the cerebellum of the cat

The Nauta‐Laidlaw silver degeneration technique was used to study the mode of termination and temporal course of degeneration of cerebellar cortical association pathways in the cat. All associational pathways examined appeared to terminate identically in their respective folia of termination. Two specific cerebellar cortical areas were chosen for detailed discussion and illustration. In the vermis lobules (V and VI), fibers pass from one folium to the adjacent caudal two or three folia, and these pathways can be studied conveniently in the sagittal plane. Long connections extend from anterior lobe paravermal cortex (lobule V) to caudal hemispheral folia of the same side, and these terminations could be examined at a site some distance from the lesion. Projections of associational pathways displayed a rather strict localization, with terminal areas corresponding in size and location to the area of damaged cortex giving rise to the pathway. Terminal degeneration was found distributed at Purkinje cell levels and in basal portions of the molecular layer. Some of the degenerated fibers in the molecular layer showed relationships with Purkinje cell dendrites, suggesting that they might be climbing fibers. Early degenerative changes occurred at two days postoperatively. Maximal fine fiber degeneration occurred at eight days. Fragments of large degenerated fibers were stainable in terminal areas and in folial white matter for as long as 41 days postoperatively.