Abstract
Natural vision involves the constant coordination of multiple different types of eye movements. Prior research has tended to focus on behavioral and neuronal correlates of a single type of eye movement (e.g., only saccades or only smooth pursuit). These investigations have set the stage for our current work on the selection and control of different types of eye movements. We recorded neuronal activity in the macaque frontal eye fields, a region of prefrontal cortex with an established role in saccadic control and smooth pursuit, while monkeys made saccades and pursuit in one of eight directions. Although the interaction of saccade and pursuit signals is traditionally thought to be minimal in FEF, we set out to test this idea by recording from populations of neurons using multi-contact linear electrode arrays. Taking inspiration from the classic characterization of visual-saccadic activity in FEF ("VMI"; visual-motor index), we created a contrast ratio called the Saccade Pursuit Index (SPI) to measure the relative firing rates of individual neurons to saccadic and smooth pursuit eye movements. We found that a large proportion of neurons elicited roughly equal firing rates during saccades and pursuit, forming a relatively continuous and unimodal distribution of SPI values. We extended our analyses to pairs of simultaneously recorded neurons, where the independence of saccadic and pursuit signals was evaluated using spike count correlations ("noise" correlations). Our results suggest that FEF neurons interact across different types of eye movements more than previously assumed, implicating FEF in the online control of real-time oculomotor decisions.