(A) Experimental setup depicting a fly expressing the transgenic calcium indicator GCaMP6 in projection neurons. Briefly, the fly is fixed to an aluminum chamber with wax and the cuticle above the antennal lobes is removed, which allows imaging of the antennal lobes from the dorsal side. A tube is placed in front of its antennae for odors to be delivered (carrier stream flow rate = 2,000 ml/min).

(B) Temporal course of the average fluorescence signal in response to different odors in the entire antennal lobe. Shadowed traces represent SEM for the change in fluorescence. The blue rectangle depicts the 2 s time window after response onset, used for quantitative analyses. Inset bar plot shows that pure atf1− yeast odor and atf1− odor supplemented with PA elicit significantly weaker responses than WT yeast odor and atf1− yeast odor supplemented with EA and IA, respectively (n = 14 flies; ∗p < 0.02; paired t test).

(C) Representative antennal lobe activity maps corresponding to different yeast and ester odors as well as paraffin oil as control, respectively. Calcium responses were averaged during the 2 s window shown in (B).

(D) Regions of interest manually assigned to each responsive glomerulus based on activity maps for the fly shown in (C). On the right, the corresponding glomerulus-based response profiles for the different odors and control are shown. Profiles were constructed for the 2 s window shown in (B).

(E) Correlation matrix representing the pairwise similarities for the different odor response profiles (n = 14 flies). Note that atf1− yeast odors supplemented with esters are more correlated to WT yeast odor than atf1− yeast odor alone.

(F) Principal component analysis of the odor response profiles. The first three components are shown (total variances explained by first three principle components [PCs] = 79.6%; PC1 = 59.4%; PC2 = 12.8%; PC3 = 7.4%). Upon addition of more esters, the atf1− yeast odor representations are progressively pushed in the direction of the representations of the WT yeast odor, indicating a more-similar response.