Neural correlates for preparatory set associated with pro-saccades and anti-saccades in primate prefrontal cortex

Abstract

Difficulties to suppress prepotent responses is one of the hallmarks of the prefrontal syndrome. This deficit becomes clear in the anti-saccade task in which subjects have to suppress a reflexive saccade towards a peripheral visual stimulus and instead generate a voluntary saccade towards the mirror location. To investigate the role of the prefrontal cortex (PFC) in anti-saccade generation, we trained two monkeys on a task with randomly interleaved pro- and anti-saccade trials in which the color of the central fixation point instructed the monkeys either to generate a pro- or an anti-saccade upon stimulus presentation. Single neuron activity was recorded from the lateral PFC while monkeys performed the task. The location of the recording chamber was visualized in situ by magnetic resonance imaging and registered with the anatomy. Across all our neurons, we analyzed the neural activity during the pro-saccade and the anti-saccade instruction periods before the presentation of the peripheral stimulus for the saccade and found higher activity levels when the monkeys were instructed to make a pro-saccade as compared to an anti-saccade (P<0.01). A proportion of the sample of PFC neurons also showed excitatory and inhibitory stimulus-related responses for the peripheral cue. These neurons exhibited a significantly larger stimulus-related response on pro-saccade trials compared to anti-saccade trials (P<0.01). Surprisingly these findings show similar response to what has previously been reported for saccade and visual neurons in the frontal eye fields and superior colliculus. This suggests that the PFC does not provide saccade suppression signals to these two oculomotor areas. Instead, we hypothesize that the PFC participates in the suppression of reflexive saccades by reducing the excitatory input to saccade-related brain areas on anti-saccade trials.