Afferent Projections to the Cerebellum and the Spinal Pathways Involved

Abstract

The cerebellar projection and the spinal pathways involved in the conduction of impulses elicited by electrical stimulation of various peripheral nerves have been investigated in the cat, using oscillographic technics. Mixed nerves (tibial, deep flexor), nerves to muscles (branches to the lateral and medial heads of the gastrocnemius), knee joint nerve, sural in the hindlegs, superficial and deep branches of the radial nerve for the foreleg have been subjected to electrical stimulation. The parameters of the stimulus employed were those commonly used for activation of group A afferents. Nerves of all 4 legs were found to project to the same side of the anterior lobe. Nerves of all the contralateral side project slightly caudal to the nerves of the homolateral side. The findings of other investigators on the localization of the arm and leg areas were confirmed. Considerable overlapping was noted in some cases The latency of the cerebellar evoked potentials from stimulation of nerves from muscles and joints is consistently longer than that of potentials from mixed and cutaneous nerves. The possible significance and explanation of this finding is discussed. By means of acute incisions of the cord at the level of the 2d cervical segment, the following conclusions were reached: (1) section of the dorsal funiculi does not affect the conduction of these impulses to the cerebellum; (2) the dorsal (Flechsig) as well as the ventral (Gowers) spinocerebellar tracts contain both crossed and uncrossed components; (3) the crossed component appears to be the prominent in the ventral tract, the uncrossed in the dorsal tract; (4) both tracts project maximally to the same area of the anterior lobe of the cerebellum; (5) each tract conducts impulses originating from peripheral nerves of various functional significance; (6) impulses from cutaneous, muscular, and mixed nerves of both hindlegs may reach the cerebellum through a single spinal pathway; (7) the role of the spino-reticulocebellar and spino-olivocerebellar connections in transmitting impulses from peripheral receptors is discussed.