Neural correlates of curved saccades in the primate frontal eye field

Abstract

Previous behavioral and microstimulation studies have shown that saccade curvature indexes unresolved distractor competition just before initiation of a saccade to a target in the superior colliculus (SC) and frontal eye field (FEF). This unresolved competition can produce curvature towards or away from a distractor depending on temporal factors. In order to better understand the neural mechanisms underlying curved saccades, we recorded from single neurons in the FEF of a rhesus monkey shifting gaze to a target while a distractor appeared either left or right of the target at various moments after target presentation (distractor target onset asynchrony). We found that saccades curved toward or away from competing distractors as function of distractor target onset asynchrony relative to saccade reaction times (RT)—the longer the RT, the more saccades curved away from the distractor, and the shorter the RT, the more saccades curved toward the distractor. These results are similar to a human psychophysical study, which suggested that saccade curvature toward vs. away from distractors is due to the transition from excitatory to inhibitory oculomotor distractor-related processing over time (Kehoe and Fallah 2017). Investigating FEF neuronal activity, we found the activity of a subset of neurons in a brief pre-saccadic interval correlated with the amount of saccade curvature toward the distractor in the motor field or away from the distractor outside of the motor field. These preliminary data suggest that FEF target selection is not a complete winner-takes-all process. A distractor can transiently coactivate a competing saccade which is vector averaged with the primary target saccades, ultimately leading to curved saccade trajectories.