Neural and Behavioral Correlates of Saccadic Eye Movements to Moving Targets

The ability to catch moving objects with our line of sight is crucial for survival in our dynamic everyday environment, such as determining if the insect buzzing toward your head is a harmless fly or a “killer hornet.” Saccades, or rapid eye movements, are employed to shift our gaze to intercept moving targets. Due to an inherent neural transduction delay (~100ms), the sensory representation of a moving target’s position lags the target’s actual position. Fortunately, this discrepancy in target encoding does not hinder humans and non-human primates from intercepting moving targets, as both species can accurately catch a moving stimulus with their gaze. The oculomotor system could overcome this transmission delay by integrating the velocity of the target over the delay and adding it to the neural representation of the target’s position. How position and velocity information are combined to program saccades to moving targets (interceptive saccades) is currently unknown. In this study, we investigated the behavior and neural correlates of interceptive saccades. We found a consistent decrease in peak velocity for interceptive saccades compared to amplitude-matched saccades to static targets (control). The greatest reduction in peak velocity occurred between target speeds of 10-40 deg/s. We also investigated the superior colliculus (SC) as a possible location to combine position and velocity information, as it is the sensorimotor integration hub for the oculomotor system. We discovered that the SC population activity changes from a symmetrically-distributed activity to a streaked mound of activity for interceptive saccades, and the streak spreads along the target’s trajectory. The spread of the streak was also dependent on the speed of the moving stimulus. Our data are consistent with the interpretation that the SC reflects both the moving target’s position and velocity. Many neurological disorders, such as Parkinson’s and Alzheimer’s disease, cause a decrease in the ability to make predictive movements. We anticipate that once the interceptive saccade mechanism is determined, interceptive saccades can be used as non-invasive biomarkers to monitor patient health and track disease progression