Fig. 3. A set of FB tangential inputs promote wind navigation behavior.

A Trans-synaptic tracing reveals connections between upwind-promoting MB/LH neurons and FB tangential neurons. Trans-tango signal driven by LH1396-GAL4 (top) and MB052B-GAL4 (bottom). Trans-synaptic signal (magenta) was observed in horizontal layers of the dorsal FB in both cases. Neuropil is shown in blue. The FB is outlined in gray. Scale bar 50 µm. B Optogenetic activation results for FB inputs, including dorsal tangential inputs, ventral tangential inputs, columnar PFNs, and empty-GAL4 and empty-split-GAL4 controls. Two dorsal inputs and two ventral inputs drove significant increases in upwind velocity. Control lines drove no significant change in any measured behavioral parameter (see Methods). C Optogenetic activation results for split GAL4 lines labeling dorsal and ventral tangential FB inputs, and for a line labeling FB5AB (21D07-GAL4||CLIN). One split-GAL4 line labeling ventral FB tangential inputs drove a significant increase in upwind velocity. Legend applies to B and C. D Schematic showing feedforward connectivity onto FB5AB from three upwind-promoting MBONs (MBON 19, MBON 12, MBON 13), one upwind-promoting LHON (AD1b2), and one downwind-promoting MBON (MBON05). Pathways converge onto FB5AB directly or indirectly through LHCENT3 and LHPV5e1. Numbers represent the average synaptic weight between each cell type and the right-sided LHCENT3 (id: 487144598), LHPV5e1 (id: 328611004), or right-sided FB5AB (id: 5813047763). E Number of parallel lateral horn pathways from vinegar-responsive projection neurons (estimated from ORN responses in⁴¹) to each FB tangential input neuron. Pathways consist of two synapses: projection neuron to lateral horn neuron, and lateral horn neuron to FB tangential input neuron. Blue bar represents the number of pathways converging onto FB5AB. F Upwind displacement responses to optogenetic activation of FB tangential input lines outlast the stimulus while responses to activation of MB/LH lines do not. Timecourses of average relative y-displacement (arena position) across flies, following stimulus OFF for each line. Individual fly’s average positions across trials were set to 0 and relative change in position for 10 s following stimulus OFF was averaged across flies for each genotype. All statistics in B, C used two-sided Wilcoxon signed rank test and corrected using the Bonferroni method. Legend displays equivalent uncorrected alpha level.