Functional organization of the ventral spino-cerebellar tract in the cat. I. Electrophysiological identification of the tract.

Abstract

Summary. The experiments were performed on cats under Nembutal anesthesia. The mass discharge in the ventral spino‐cerebellar tract (VSCT) was recorded from the cerebella surface, the superior cerebella peduncle (SCP) and from different levels of the spinal cord on stimulation of various hind leg nerves. The characteristics of the VSCT mass discharge was determined by recording from the surface of the SCP, where the tract is found in isolation from other ascending spinal tracts. A mass discharge in the VSCT appears on stimulation of contra lateral muscle nerves but not on stimulation of skin nerves or unilateral muscle nerves. The mass discharge recorded at the SCP on stimulation of thigh muscle nerves has duration of about 2 msec and appears after a latency of about 5 msec. The discharge remains after contralateral hemisection of the spinal cord and after c section of Flechsig's fasciculus but disappears after a superficial lesion of the ipsilateral ventral quadrant. As judged from the ingoing volley recorded at the dorsal root entry zone, the discharge is due to activation of the second component of the group I volley thus suggesting excitatory action from Golgi tendon organ afferents. The transmission from the group I muscle afferents to the VSCT neurons is monosynaptic as judged from the duration of the synaptic delay. The conduction velocity of the fastest fibres in the VSCT is higher than that in the DSCT and amounts to about 120 m/sec. The VSCT is completely or almost completely crossed whereas the DSCT is completely or almost completely uncrossed. Both spino‐cerebellar tracts cause potentials at the surface of the anterior vermis after a latency of about 5 msec on stimulation of thigh muscle nerves. The potentials due to VSCT activity are largest on the side contralateral to the tract indicating crossing of most VSCT fibres in the cerebellar commisure.