Figure 8.

iPN Inhibition Increases ePN Distances

(A and C) Euclidean (A) and cosine (C) distances between odors were calculated with the empirically derived transmission characteristics of the inhibitory high-pass filter (Figure 7C). The blocking strength of the filter was linearly adjusted according to the number of active glomeruli (Figure 5G). The scatter plot relates the 5,995 possible pairwise Euclidean distances between 110 odors after filtering to their unfiltered counterparts.

(B and D) Histograms of the effect sizes of inhibitory high-pass filtering on the Euclidean (B) and cosine (D) distances between 5,995 odor pairs. The filter causes mean increases in Euclidean distance of 5.5 spikes per s (B) or in cosine distance of 0.14 (D).

(E) Application of the empirically derived high-pass filter (Figure 7C) to the ePN activity vectors of two odors (point 1) stretches the cosine distance between the odors (point 2). According to the distance-discrimination model, this results in improved odor discrimination (point 3). Thus, the decision bias of WT flies with inhibition intact (point 4) is identical to the decision bias of flies in which iPN output is blocked but the distance-enhancing effect of inhibition is accounted for computationally (point 3).

(F) Sequential applications of the inhibitory high-pass filter and the distance-discrimination model predict the empirical distance-discrimination function of WT flies (red line, reproduced from Figure 2D) from the empirical distance-discrimination function of flies carrying Mz699-GAL4:UAS-shi^ts1 transgenes at the restrictive temperature of 32°C (black line, reproduced from Figure 6B).