Coordination of eye and head components of movements evoked by stimulation of the paramedian pontine reticular formation

Abstract

Constant frequency microstimulation of the paramedian pontine reticular formation (PPRF) in head-restrained monkeys evokes a constant velocity eye movement. Since the PPRF receives significant projections from structures that control coordinated eye-head movements, we asked whether stimulation of the pontine reticular formation in the head-unrestrained animal generates a combined eye-head movement or only an eye movement. Microstimulation of most sites yielded a constant-velocity gaze shift executed as a coordinated eye-head movement, although eye-only movements were evoked from some sites. The eye and head contributions to the stimulationevoked movements varied across stimulation sites and were drastically different from the lawful relationship observed for visually-guided gaze shifts. These results indicate that the microstimulation activated elements that issued movement commands to the extraocular and, for most sites, neck motoneurons. In addition, the stimulation-evoked changes in gaze were similar in the head-restrained and head-unrestrained conditions despite the assortment of eye and head contributions, suggesting that the vestibuloocular reflex (VOR) gain must be near unity during the coordinated eye-head movements evoked by stimulation of the PPRF. These findings contrast the attenuation of VOR gain associated with visually-guided gaze shifts and suggest that the vestibulo-ocular pathway processes volitional and PPRF stimulation-evoked gaze shifts differently.

Cerebellar control of saccade dynamics: contribution of the fastigial oculomotor region

“…In our study, it ranged from 15 to 35 ms with suprathreshold microstimulations. This range is compatible with the 17-ms latency reported by Noda et al (1991) (see also Cogdell et al 1977) and exceeds the latency range of movements evoked by stimulation in the pontine reticular formation (7-18 ms; Gandhi et al 2008). The second set combines observations made after muscimol injection in the cFN.…”

The relative impact of microstimulation parameters on movement generation

“…In contrast, stimulation in the pontine and reticular formations produces movements that continue for the duration of the stimulation (until biomechanical limits). In addition, the kinematics of these movements has been shown to linearly scale with frequency (Cohen and Komatsuzaki 1972;Gandhi et al 2008;Quessy and Freedman 2004). This discrepancy in stimulation effects suggests a general neural network property, in which direct or indirect recruitment of neurons within a topographically organized structure activates a network level response that can dominate the stimulation-induced activation, whereas the network level response is weaker or nonexistent in regions that operate primarily with a rate code (see NOTE ADDED…”

Stimulation of Pontine Reticular Formation in Monkeys With Strabismus

“…Previous studies in normal monkeys have reported that PPRF stimulation evokes ipsiversive movements with latencies of approximately 14 ms. 24 For the present study, the issue of latency is complicated by the fact that, for some sites, robust horizontal movements were evoked in only one eye. Since movement onset was based on a velocity threshold, and there often were large differences in the velocities of the two eyes, we were not confident that a robust quantitative comparison could be made.…”

“…Stimulation of PPRF in normal monkeys evokes constant velocity, ramp-like, ipsiversive eye movements that persist as long as the train continues. 23,24 There are several potential explanations for saccade disconjugacy in strabismus. First, it could be that saccades are unequal due to inappropriate activity in near response cells, which would exert opposite effects on the movement amplitudes of the two eyes.…”