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Samuel Adade, Vallabh E Das; Neural Innervation of Extraocular Muscles during Vertical Vergence. Invest. Ophthalmol. Vis. Sci. 2019;60(9):1770. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To compare the relationship between firing rate (FR) of extraocular muscle (EOM) motoneurons and vertical eye position during vertical vergence and conjugate vertical smooth-pursuit in non-human primates.
Scleral search coils were used to record movements of both eyes as two non-human primates performed a vertical vergence or vertical smooth-pursuit task. Vertical vergence was elicited using a frame-sequential presentation technique synced with LCD shutter goggles to elicit dichoptic viewing of a 50° x 50° stimulus which comprised a central fixation cross (4° x 4°) and sparse pattern of random dots. Vertical disparity was introduced by displacing the stimulus for one eye vertically (upward or downward) in small steps of 0.05°. For vertical smooth-pursuit, animals tracked a target moving vertically at 0.30Hz, +/- 15°. Single cell activity of neurons in the oculomotor nucleus supplying the cyclovertical muscles were recorded and cells were classified by their increase in activity with eye movements in a preferred direction and also by using microstimulation techniques.
We recorded 27 motoneurons from the left oculomotor nucleus out of which 24 showed modulation during vertical vergence. FR of 9 superior rectus cells decreased when the right eye moved downward with mean vertical position sensitivity (k) of 7.15 ± 0.80 sp/s/° but showed only slight modulation when the left eye moved up (k = 1.86 ± 0.46 sp/s/°). For 6 inferior rectus cells, FR decreased significantly when the left eye moved upward (k = 6.26 ± 0.70 sp/s/°) and slightly when the right eye moved down (k = 1.85 ± 0.31 sp/s/°). FR of 5 inferior oblique cells increased significantly during left eye moving up (k = 6.30 ± 0.91 sp/s/°) and slightly when the right eye moved downward (k = 1.68 ± 0.47 sp/s/°). FR of 4 cells (1 superior rectus, 2 inferior rectus and 1 inferior oblique) showed significant modulations when either eye moved. The mean sensitivity of motoneurons during vertical vergence (k = 6.67 ± 0.46 sp/s/°) was greater than during vertical smooth pursuit (k = 5.14 ± 0.45 sp/s/°; p< 0.05). Neural recording and analysis from the right oculomotor nucleus and both trochlear nuclei is ongoing.
Firing rate of all cyclovertical motoneuron subtypes correlate with vertical eye position of the innervated eye during vertical vergence indicating that all cyclovertical EOMs contribute to vertical vergence.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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