Journal of Neurophysiology, Vol 42, Issue 5 1282-1296, Copyright © 1979 by APS
Neural correlates of nystagmus in abducens nerve
V. Honrubia, D. B. Reingold, C. G. Lau and P. H. Ward
1. The firing rates of action potentials of abducens nerve single fibers
were recorded in the cat's orbit during a variety of vestibular and
optokinetic stimulations. 2. Comparison was made of the neural firing rates
associated with agonist and antagonist responses during slow and fast
components of vestibular and optokinetic nystagmus. It was found that the
relationship between the motoneuron firing rates and the eye motion was
independent of the reflex with which they were associated--vestibular or
optokinetic, or the type of response--agonist or antagonist. No neurons
were observed that responded only during the fast or only during the slow
nystagmus phase. Motoneuron firing rates were proportional to both velocity
and position of the eye in a ratio of 1 (spikes/s)/(deg/s) to 7.2
(spikes/s)/deg. The behavior of the motoneurons was compatible with the
hypothesis that thier firing rates are sufficient to overcome both elastic
and viscous forces by which the muscles and ligaments hold the eye in the
orbit. 3. For low-frequency head rotations, eye displacement and neural
responses showed a small phase angle difference. At higher frequencies,
however, while the eyes maintained a fixed relationship to the head
rotation, the neural responses showed an increasing phase lead. One
component of this phase lead compensated for the phase lag introduced by
the orbital mechanics. The other was modeled as a constant delay of
approximately 70 ms, which may be accounted for by neuromuscular
transmission and transduction.
