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Santoshi Ramachandran, Vallabh E Das; Role of Superior Colliculus in fixation preference during a delayed saccade task in strabismic non-human primates. Invest. Ophthalmol. Vis. Sci. 2020;61(7):5082.
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Strabismic patients and non-human primates often develop the ability to saccade to and fixate on a target with either eye depending on the targets’ spatial location. Spatial fixation preference in strabismus could possibly be accounted for in a competitive decision framework wherein the brain chooses between two retinal errors (since eyes are pointing in different directions) to prepare a saccade. We tested this framework by recording from visuo-motor neurons in the superior colliculus (SC), a structure critical in target selection and saccade generation, during spatial fixation preference behavior.
Single cell neural recordings from the intermediate/deep SC were obtained while a head-fixed strabismic [M1, ~30° XT] monkey performed a delayed saccade task under binocular viewing conditions. Once the neuronal receptive field was localized, visual targets were presented at one of two locations corresponding to the receptive field location of either the viewing or deviated eye, and resulted in fixation-switch or no fixation-switch saccades. Amplitude and direction were matched (Exp 1 – two target condition). For certain target locations, fixation-switch and no fixation-switch saccades were in opposite directions (different colliculi) (Exp 2 – single target condition). Paired t-tests were performed to compare firing rates of visual, buildup and saccade related response in fixation-switch and no fixation-switch trials.
Exp 1 (n=10): Robust visual sensory responses were observed when targets were presented to either the viewing or deviated eye with evidence of only small interocular suppression. As expected, motor responses for fixation-switch and no-fixation switch trials were not significantly different since the saccade parameters are matched. Additionally, the mean build-up responses showed no difference in these trials since the cell corresponds to the ‘winning’ saccade. Exp 2 (n=11): For the single target condition, both visual and mean build-up responses were reduced for trials in which the cell did not correspond to the ‘winning’ eye, suggesting that the build-up activity may be used to facilitate eye choice. Analysis of more cells from M1 and data acquisition from a second animal is ongoing.
Analysis of neural data from SC visuo-motor cells suggests that this structure plays an important role in eye choice for visual stimuli in strabismus.
This is a 2020 ARVO Annual Meeting abstract.
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