Abstract
Purpose :
Strabismic humans and NHPs often develop the ability to saccade to a target with either eye depending on the targets’ spatial location. 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) of strabismic NHPs, a structure critical in target selection and saccade generation.
Methods :
Neural recordings from the intermediate/deep SC were obtained while two head-fixed strabismic (~30° XT) NHPs performed a delayed saccade task under binocular viewing conditions. In Exp. 1 (2-target condition), visual targets were presented at two locations corresponding to the neuronal receptive field of either the viewing or deviated eye, and resulted in fixation-switch or no fixation-switch saccades whose amplitude and direction were matched. In Exp 2. (1-target condition), a visual target was placed at a location (single neuronal receptive field) where the animal switched fixation on some trials and did not on other trials. Paired t-tests were performed to compare firing rates of visual, buildup and saccade related response in fixation-switch and no fixation-switch trials.
Results :
Exp. 1 (n=25): Robust visual sensory responses were observed when targets were presented at receptive field locations of either the viewing or deviated eye with evidence of only small interocular suppression in both NHPs. Motor responses for fixation-switch and no-fixation switch trials were not significantly different (saccade matched). Mean build-up responses showed no difference in these trials since the cell response corresponds to the ‘winning’ saccade. Exp. 2 (n=21): Both peak visual and mean build-up responses were reduced for trials in which the cell response did not correspond to the ‘winning’ eye, suggesting the presence of suppression and that the build-up activity may be used to facilitate eye choice. Data analysis from second NHP is ongoing.
Conclusions :
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 and provides important insight on how visual suppression influences eye choice behavior.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.