45Express saccades (ESs) are a manifestation of a visual grasp reflex triggered when 46 visual information arrives in the intermediate layers of the superior colliculus (SCi), 47 which in turn orchestrates the lower level brainstem saccade generator to evoke a 48 saccade with a very short latency (~100ms). A prominent theory regarding express 49 saccades generation is that they are facilitated by preparatory signals, presumably from 50 cortical areas, which prime the SCi prior to the arrival of visual information. Here, we 51 test this theory by reversibly inactivating a key cortical input to the SCi, the frontal eye 52 fields (FEF), while monkeys perform an oculomotor task that promotes ES generation.
53Across three tasks with a different combination of potential target locations and uni-or 54 bilateral FEF inactivation, we found a spared ability for monkeys to generate ESs, 55 despite decreases in ES frequency during FEF inactivation. This result is consistent with 56 the FEF having a facilitatory but not critical role in ES generation, likely because other 57 cortical areas compensate for the loss of preparatory input to the SCi. However, we did 58 find decreases in the accuracy and peak velocity of ESs generated during FEF 59 inactivation, which argues for an influence of the FEF on the saccadic burst generator 60 even during ESs. Overall, our results shed further light on the role of the FEF in the 61 shortest-latency visually-guided eye movements.62 63 64 65 3 New & Noteworthy 66 Express saccades (ESs) are the shortest-latency visually-guided saccade. The frontal 67 eye fields (FEF) is thought to promote ES by establishing the necessary preconditions 68 in the superior colliculus. Here, by reversibly inactivate the FEF either unilaterally or 69bilaterally, we support this view by showing that the FEF plays an assistive but not 70 critical role in ES generation. We also found that FEF inactivation lowered ES peak 71 velocity, emphasizing a contribution of the FEF to ES kinematics. 72 4 Introduction: 73 Express saccades (ESs) are the shortest-latency visually-guided saccades, with 74 reaction times (RTs) approaching the sensori-motor conduction delays between the 75 retina and extra-ocular muscles (Fischer and Boch 1983; Fischer and Ramsperger 76 1984). Express saccades are essentially a low-level visual grasp reflex that, somewhat 77 paradoxically, is potentiated by high-level preparation about the location, valence, or 78 timing of an upcoming visual target (Paré and Munoz 1996; Schiller et al. 2004). The 79 interaction between a low-level reflex and high-level preparation is seen in the activity 80 profiles within the intermediate superior colliculus (SCi), a structure whose integrity is 81 essential for ES generation (Schiller et al. 1987). Before regular (or non-express) 82 latency saccades, a subset of visuomotor neurons within the SCi emit a 'visual' burst of 83 action potentials shortly after visual target presentation, as well as a second 'motor' 84 burst of action potentials shortly before the...
