Pontine Omnipause Activity During Conjugate and Disconjugate Eye Movements in Macaques

Abstract

. Previous reports have shown that saccades executed during vergence eye movements are often slower and longer than conjugate saccades. Lesions in the nucleus raphe interpositus, where pontine omnipause neurons (OPNs) are located, were also shown to result in slower and longer saccades. If vergence transiently suppresses the activity of the OPNs just before a saccade, then reduced presaccadic activity might mimic the behavioral effects of a lesion. To test this hypothesis, 64 OPNs were recorded from 7 alert rhesus monkeys during smooth vergence and saccades with and without vergence. The firing rate of many OPNs was modulated by static vergence angle but not by version and showed transient changes during slow vergence without saccades. This modulation was smooth, and not the abrupt pause seen for saccades, indicating that OPNs do not act as gates for vergence commands. We confirmed that saccades made during both convergence and divergence are significantly slower and longer than conjugate saccades. OPNs paused for all saccades, and the pause lead (interval between pause onset and saccadic onset) was significantly longer for saccades with convergence, in agreement with our hypothesis. Contrary to our hypothesis, pause lead was not longer for saccades with divergence, even though these saccades were slowed as much as those occurring during convergence. Furthermore, there was no significant correlation, on a trial-by-trial basis, between pause lead and saccadic slowing. These results suggest that it is unlikely that presaccadic slowing of OPNs is responsible for the slower saccades seen during vergence movements.

The Brain Stem Saccadic Burst Generator Encodes Gaze in Three-Dimensional Space

“…Since the onset of saccade-facilitated vergence is coincident with saccade onset (Busettini and Mays 2005a), our results show that the premotor drive from the saccadic burst generator is appropriately timed to facilitate vergence velocity during disconjugate saccades. Moreover, these results complement those of Busettini and Mays (2003) showing that the OPN pause is similarly linked to the saccadic component of disconjugate saccades. Taken together these findings provide strong evidence that the vergence facilitation observed during disconjugate saccades occurs only when the saccadic burst generator (i.e., SBNs) is active.…”

A Review of Convergence Insufficiency: What are we Really Accomplishing with Exercises?

“…More recently, the role of specific areas in the pons has been clarified with respect to vergence. Omnipause neurons located in the nucleus raphe interpositus in the pons slow firing activity just before a fast vergence movement (vergence pulse), [52][53] while cells in the nucleus reticularis tegmenti pontis are active during slow vergence (vergence step). 54 These two groups of pontine nuclei project to different areas of the cerebellum.…”

Tests of Models for Saccade–Vergence Interaction using Novel Stimulus Conditions

“…Premotor burst neurons for horizontal saccades lie in the paramedian pontine reticular formation (PPRF) (Horn et al 1997), whereas those for vertical saccades lie in the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) in the midbrain (Horn and Büttner-Ennever 1998). The activity of both sets of premotor, saccadic burst neurons is controlled by omnipause neurons, which lie in the pontine nucleus raphe interpositus (Horn et al 1994), and are tonically active except during saccades (Yoshida et al 1999;Busettini and Mays 2003;Mays 2003).…”