Conduction velocities in the abducens nerve correlated with vestibular nystagmus in cats

Abstract

In encéphale isolé cat preparations the conduction velocities of nerve fibers teased from the central stump of the abducens nerve emerging from the pons were measured by determining the time necessary for the nerve spike to travel from the first to the second pair of electrodes over which the nerve bundle had been placed. Lateral rectus muscle contraction was recorded simultaneously with nerve activity. Conduction velocities were distributed in two groups: slow, 6–40 m/sec, and fast, 41–83 m/sec. Slow fibers were active in the absence of movement, in both phases of nystagmus and during slow spontaneous eye deviations. Fast fibers were active during the fast phase and towards the latter portion of the slow phase of nystagmus. Fast fibers were never seen to discharge in the absence of movement. Thus it appears that the slow fibers are active principally during tonic movements and the fast fibers principally during phasic movements, although each type of fiber contributes to some portion of each type of movement.