Image-matching during ant navigation occurs through saccade-like body turns controlled by learned visual features

Abstract

Visual memories of landmarks play a major role in guiding the habitual foraging routes of ants and bees, but how these memories engage visuo-motor control systems during guidance is poorly understood. We approach this problem through a study of image matching, a navigational strategy in which insects reach a familiar place by moving so that their current retinal image transforms to match a memorized snapshot of the scene viewed from that place. Analysis of how navigating wood ants correct their course when close to a goal reveals a significant part of the mechanism underlying this transformation. Ants followed a short route to an inconspicuous feeder positioned at a fixed distance from a vertical luminance edge. They responded to an unexpected jump of the edge by turning to face the new feeder position specified by the edge. Importantly, the initial speed of the turn increased linearly with the turn's amplitude. This correlation implies that the ants' turns are driven initially by their prior calculation of the angular difference between the current retinal position of the edge and its desired position in their memorized view. Similar turns keep ants to their path during unperturbed routes. The neural circuitry mediating image-matching is thus concerned not only with the storage of views, but also with making exact comparisons between the retinal positions of a visual feature in a memorized view and of the same feature in the current retinal image.