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Mark M G Walton, Michael J. Mustari; Activity of near response cells during disjunctive saccades in normal monkeys. Invest. Ophthalmol. Vis. Sci. 2016;57(12):4586.
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© ARVO (1962-2015); The Authors (2016-present)
Vergence eye movements have low peak velocities when they occur in the absence of a saccade. When transferring fixation between targets that differ in both direction and distance, however, vergence velocity is substantially higher during the saccade. This phenomenon might be due to the saccadic system directly programming disjunctive saccades. Alternatively, a vergence velocity command might be facilitated by interactions with the saccadic system. To investigate this issue we sought to determine whether near response cells in the supraoculomotor area (SOA) encode this enhancement of vergence velocity.
A normal rhesus monkey was trained to fixate red, plus-shaped LEDs positioned at 12 different distances along the tops and bottoms of five triangle-shaped circuit boards. This system can elicit vergence angles ranging from 2° to 14°. We recorded single unit activity from 22 near response cells in SOA while the monkey made the necessary saccade and vergence movements to fixate each randomly selected target.
Three neurons (13.6%) showed robust bursts (>100 spikes/s above baseline) associated with large, on-direction intrasaccadic vergence changes. We were unable to evaluate the off-direction activity of four neurons because there was no tonic discharge associated with converged eye positions. Of the remaining 18, 13 (72%) consistently paused during the saccade when the intrasaccadic vergence change was in the off direction. Pauses were observed for 9 neurons that otherwise showed no evidence of a vergence velocity response.
These data suggest that most near response cells do not directly encode the enhancement of vergence velocity associated with saccades. However, most displayed pauses associated with off-direction intrasaccadic vergence. These pauses might contribute to fast intrasaccadic vergence by removing a strong drive to motoneurons serving the agonist muscle of one eye and the antagonist muscle of the other.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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