Spatial Interactions in the Superior Colliculus Predict Saccade Behavior in a Neural Field Model

摘要

During natural vision, eye movements are dynamically controllednby the combinations of goal-related top–down (TD) andnstimulus-related bottom–up (BU) neural signals that map ontonobjects or locations of interest in the visual world. In primates,nboth BU and TD signals converge in many areas of the brain,nincluding the intermediate layers of the superior colliculusn(SCi), a midbrain structure that contains a retinotopically codednmap for saccades. How TD and BU signals combine or interactnwithin the SCi map to influence saccades remains poorly understoodnand actively debated. It has been proposed that winnertake-nall competition between these signals occurs dynamicallynwithin this map to determine the next location for gaze. Here,nwe examine how TD and BU signals interact spatially within annartificial two-dimensional dynamic winner-take-all neural fieldnmodel of the SCi to influence saccadic RT (SRT). We measurednpoint images (spatially organized population activity on the SCnmap) physiologically to inform the TD and BU model parameters.nIn this model, TD and BU signals interacted nonlinearlynwithin the SCi map to influence SRT via changes to the (1) spatialnsize or extent of individual signals, (2) peak magnitude ofnindividual signals, (3) total number of competing signals, andn(4) the total spatial separation between signals in the visualnfield. This model reproduced previous behavioral studies ofnTD and BU influences on SRT and accounted for multiple inconsistenciesnbetween them. This is achieved by demonstratingnhow, under different experimental conditions, the spatial interactionsnof TD and BU signals can lead to either increases orndecreases in SRT. Our results suggest that dynamic winnertake-nall modeling with local excitation and distal inhibition inntwo dimensions accurately reflects both the physiological activitynwithin the SCi map and the behavioral changes in SRT thatnresult from BU and TD manipulations.