Discharge Characteristics of Vestibular Saccade Neurons in Alert Monkeys. Chris R. S. Kaneko and Kikuro Fukushima. Department of Physiology & Biophysics and Regional Primate Research Center, University of Washington, Seattle, Washington 98195 and Department of Physiology Hokkaido University School of Medicine, West 7, North 15, Sapporo 060, Japan.
APStracts 4:283N, 1997.
ABSTRACT
We previously described a class of neurons, located in and around the interstitial nucleus of Cajal of the cat that discharged during vestibular stimulation and before saccades which we labeled vestibular saccade neurons (VSNs). In the present study, we characterized similar neurons in the monkey. These neurons discharged before vertical saccades and during vertical vestibular stimulation, as well as vertical smooth pursuit. Like cat VSNs, the discharge metrics of these VSNs were poorly related to saccade metrics and showed only occasional, weak sensitivity to eye position. They discharged most intensely (on-direction) for movements that were either upward or downward and their on-directions were consistent during pitch and pursuit but not for eye position. For saccades, the correlation coefficient of number of spikes and vertical saccade size varied from 0.08 to 0.90 with a mean of about 0.6. The average sensitivity (i.e., slope) of the number of spikes and vertical saccade size linear regression was 0.3EñE0.2 spike/­. Average correlations between peak discharge rate and peak saccade velocity and between burst duration and saccade duration were 0.5 and 0.4; sensitivities were 0.2EñE0.2 spike/s per ­/s and 0.6EñE0.5 ms/ms respectively. Average vestibular sensitivities during 0.5 Hz, ñE10­ sinusoidal pitch while the animals suppressed their vestibular ocular reflex were 0.97 spike/s per ­/s for up VSNs and 0.66 spike/s per ­/s for down VSNs. The average static position sensitivity for the population of 39 VSNs tested was 0.55 spike/s/­. The average gain for VSNs tested during 0.5 Hz, ñ10E­ sinusoidal smooth pursuit tracking was 1.4 spike/s per ­/s. As we were unable to identify analogous neurons in the region of the monkey ponto-medullary junction, we conclude that horizontal on-direction VSNs do not exist in the monkey. We discuss a possible functional role for VSNs and similar neurons described in previous studies and conclude that these neurons are most likely involved with the process of neural integration (in a mathematical sense) of velocity-coded inputs from a variety of oculomotor subsystems and are not a pivotal element in saccade generation. ®MDNM¯ 

Received 8 July 1997; accepted in final form 3 October 1997.
APS Manuscript Number J565-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 29 October 1997