Concurrent neural representations of the current and forthcoming movement plans in the frontal eye field during a saccade sequence

Abstract

We use sequences of saccadic eye movements to continually explore our visual environments. Previous studies have established that saccades in a sequence may be programmed in parallel by the oculomotor system. In this study, we tested the neural correlates of parallel programming of saccade sequences in the frontal eye field (FEF), using single-unit electrophysiological recordings from macaques performing a double-step saccade task. Neurons in the FEF range from visual neurons instantiating target selection, to movement neurons which prepare a saccadic response towards the selected target. The question of whether the FEF movement neurons undertake concurrent processing of multiple goals or saccade plans is yet unresolved. We show that when a peripheral target is foveated by a sequence of two saccades, FEF movement activity for the second saccade can be initiated whilst the first is still underway. Moreover, the onset of the movement activity varied parametrically with the behaviorally measured time available for parallel programming. Finally, the concurrent activity was specific for the final remapped motor vector connecting the first and the second targets and not the goal of the second saccade. In contrast, the upstream FEF visual-related neurons showed concurrent activity related to the goal of the second saccade, but not the remapped vector connecting the first and the second targets. Taken together, the results indicate that movement neurons, although located terminally in the FEF visual-motor spectrum, can accomplish concurrent processing of multiple saccade plans, leading to rapid execution of saccade sequences.