Fig. 6. Expansion microscopy (ExM) confirms heterogeneity of presynaptic inputs across flies.

a Schematic of the experiment. b Confocal image of a medulla in which Tm9 dendrites are marked with rCD2::GFP (green) and Tm16 presynapses with Brp[short]::mCherry (magenta). c Confocal images showing the boxed area in (b). All presynapses are identified (blue, middle), and the ones in close proximity to Tm9 dendrites are sorted into columns (different colors, bottom). All scale bars are 20 μm. d Barplots showing the percent columns in which a specific presynaptic neuron (Tm16, Dm12, and C3) makes a certain number of connections with Tm9. Bar graphs of ExM data show mean, 95% confidence interval and all individual data points. Tm16 n = 5, Dm12 n = 5, and C3 n = 4 flies. e A visual scene as sampled by a columnar visual neuron with uniform spatial receptive fields (top) or by a columnar visual neuron with spatial receptive fields of various sizes (bottom). Small receptive fields are spatially more precise (green), whereas bigger receptive fields can contribute to more robust contrast computation (green).