Extended Data Figure 4. Cortical odor representations are stable from trial to trial and not chemotopically organized.

a, (Left), Pairwise odor chemical correlation matrices for the global, clustered and tiled odor sets. Rows and columns are sorted according to the chemical similarity between odors as assessed by hierarchical clustering (see Methods). (Middle and Right), Pairwise correlation distances of single-trial, population representations for odors in the global, clustered, and tiled odor experiments in PCx L2 and L3 (and boutons for the tiled odor set). Rows and columns are sorted according to the chemical similarity between odors as on (Left). Chemical color code (x and y axis labels of matrices, indicating functional group associated with each group of molecules) is shown in the legend. R values indicate Pearson’s correlation to odor chemistry.

b, (Top), Structured odor relationships persist from trial to trial over the course of the experiment. Blue line represents the similarity of two correlation distance matrices built from population responses obtained on consecutive trials. Grey dashed line indicates mean across all trial-pair comparisons (10 trials, 9 trial pairs; clustered odor set, L3). (Bottom), chemistry-based odor relationships correspond to matched cortical relationships obtained on a trial-by-trial basis. Dashed grey line represents the similarity of chemical and neural activity distances on a trial-by-trial basis.

c, Correspondence between odor structure in PCx L3 (clustered odor set) and odor chemistry using 3 different distance metrics (correlation distances, Euclidean distances and cosine distances). Distance matrices calculated from population activity are obtained using instantaneous ΔF/F₀ over 130 ms increments (F₀: baseline fluorescence averaged over a 1 second sliding window). Vertical lines delimit the 2 second odor presentation.

d, Odor chemical relationships emerge within a few hundred milliseconds after odor onset and persist for several seconds after odor offset (see Extended Data Fig. 1e for associated PID traces.

e, Example PCx L2 and L3 FOVs from a single animal with each responsive neuron colored according to its preferred odor in the clustered odor set. Neurons preferring odors belonging to different classes (legend) appear spatially intermingled in both L2 and L3.

f, Contour plots of pairwise signal correlations, plotted with respect to distance in L2 and L3 for the clustered and tiled experiments. Darker colors indicate increased density (see margin distributions). Pearson’s r is overlaid and indicates no spatial organization of odor representations in PCx.