Saccade-Related Activity in Superior Colliculus Predicts Eye Choice for Goal-Directed Saccades in Monkeys With Strabismus.

Purpose: Infantile strabismus syndrome is a common disorder characterized by a chronic misalignment of the eyes that is present in infancy. The disorder is associated with a wide range of abnormalities including severe impairments of binocular vision, impaired depth perception, impaired motion perception, amblyopia, nystagmus, a loss of disparity vergence, asymmetrical smooth pursuit gain, and saccade disconjugacy. The chronic inability to direct both eyes to the same visual target forces the brain to decide which eye to bring to any given object of interest in the visual field. We wondered if different populations of saccade-related neurons in superior colliculus might be activated, depending on which eye is to be brought to the target. We hypothesized, therefore, that the height of the movement field peak might differ for right-eye-to-target versus left-eye-to-target saccades. Methods: This study used single-unit, extracellular recording to investigate the bursts of saccade-related neurons in the superior colliculus in a nonhuman primate model of this disorder. Movement fields were plotted separately for saccades that brought the left eye or right eye to the target. Several statistical methods were used to compare the height of the peak between conditions. Results: A majority of the isolated neurons showed significantly stronger bursts when a particular eye was directed to a visual target, compared to when the fellow eye was brought to the target. Conclusions: These results imply that, in monkeys with strabismus, different (but overlapping) populations of burst neurons are active depending on which eye is directed to a visual target.