Neurons Forming Optic Glomeruli Compute Figure–Ground Discriminations inDrosophila

Abstract

Many animals rely on visual figure-ground discrimination to aid in navigation, and to draw attention to salient features like conspecifics or predators. Even figures that are similar in pattern and luminance to the visual surroundings can be distinguished by the optical disparity generated by their relative motion against the ground, and yet the neural mechanisms underlying these visual discriminations are not well understood. We show in flies that a diverse array of figure-ground stimuli containing a motion-defined edge elicit statistically similar behavioral responses to one another, and statistically distinct behavioral responses from ground motion alone. From studies in larger flies and other insect species, we hypothesized that the circuitry of the lobula-one of the four, primary neuropiles of the fly optic lobe-performs this visual discrimination. Using calcium imaging of input dendrites, we then show that information encoded in cells projecting from the lobula to discrete optic glomeruli in the central brain group these sets of figure-ground stimuli in a homologous manner to the behavior; "figure-like" stimuli are coded similar to one another and "ground-like" stimuli are encoded differently. One cell class responds to the leading edge of a figure and is suppressed by ground motion. Two other classes cluster any figure-like stimuli, including a figure moving opposite the ground, distinctly from ground alone. This evidence demonstrates that lobula outputs provide a diverse basis set encoding visual features necessary for figure detection.

Drosophila Spatiotemporally Integrates Visual Signals to Control Saccades

“…from leading to trailing edge. Instead, we propose that the spatial field for bar motion integration is finite (Figure 2A), activated by the bar leading edge, consistent with prior findings showing that a revolving ‘curtain’ elicits steering responses similar to those generated by a discrete bar [32]. …”

Object-Detecting Neurons in Drosophila

“…Neurons downstream of LCs that interconnect multiple optic glomeruli in the central brain respond to small objects [17], raising the possibility that select LCs may themselves be tuned to small objects. Optophysiological and electrophysiological methods have demonstrated that several LCs are broadly sensitive to visual features such as edges or bars [18,19], yet no study to date has thoroughly explored LCs with small two-dimensional objects.…”

Sensorimotor Transformations Underlying Variability in Song Intensity during Drosophila Courtship

“…Further, their response profile has been shown to shift with changes in object size—a larger object will need to move at greater lateral speed to elicit the same response (Geurten et al, 2007). Although small target motion detectors have yet to be identified in Drosophila , recent work has identified a group of lobula plate neurons that encode the features required for a separate but similar behavior known as figure detection (Aptekar et al, 2015)—identifying a foreground stimulus moving against a distinct background. It is possible that these neurons have an important role in AMD, but as they were not probed with small visual targets, their potential role is still unclear.…”