Fig. 1: Cortical populations encode identity of conspecifics.

a Odors from emitter mice or a natural floral odor (0.1% ylang ylang), and peanut butter were presented to head-fixed receiver mice in pseudorandomized trials. Each emitter mouse, namely male, unfamiliar C57BL/6#1 and C57BL/6#2 as well as a male CD1, was placed into a sealed isobaric container with continuous air flow regulated by the olfactometer. The combination of individual emitter mice was permuted to avoid repetition of unique combinations of emitter mice. Each session contained 20 trials per odor with a 1 s stimulus presentation and jittered trial durations of 10–12 s. b Stability of the firing rate response to social odors is shown for the AON in sequential blocks of 5 trials (grayscale, mean ± SEM, number of trials is indicated in the figure). All odors show initial adaptation in the first block. After the first five trials, responses were stable in amplitude and shape throughout the session (see Supplementary Fig. 2b for non-social odors). c The population vectors encode two components. Firstly, they encode the individual identity of an odor in their orientation, which stems from differential cortical activation patterns. Secondly, we hypothesize that they encode features like familiarity in their overall response amplitude, which can be quantified using the Euclidean distance from baseline. d Population responses in a representative experiment with 75 simultaneously recorded neurons from AON responding to the 5 different odorants. Single emitter individuals can be discriminated based on diverging responses in single-units. e The confusion matrices of linear decoders, which were trained to predict the odor identity of a single trial from the neuronal population activity, shows high accuracy in AON, pPC and LEC. Prediction accuracy was determined on trials, that were not included in the training dataset. f The temporal evolution of the Euclidean distance from baseline of the population vector in the AON (mean ± SEM, n = 20 trials per odor). Gray bar represents odor duration. g The mean Euclidean distance from baseline was compared for the different odors (0 to +1 s relative to odor onset; repeated-measures one-way ANOVA with a post-hoc two-sided Tukey’s test for multiple comparisons). None of the recorded cortices showed significant differences between the two unfamiliar mice from the same genetic background (see Supplementary Fig. 2d, g, h for all pairwise comparison results). h The sniff frequency response also did not differ between the two C57BL/6 mice (repeated-measures one-way ANOVA with post-hoc two-sided Tukey’s test for multiple comparisons; n = 13 animals with 1 session each; see Supplementary Fig. 5c for all pairwise comparison results). In the figure, test results are indicated as exact p-values or as a heatmap (see also Supplementary Table 4 for details on test statistics). Boxplots with a horizontal line as median, the box edges indicating the 25th to 75th percentiles, a vertical line extending to the most extreme data points excluding outliers, and outliers plotted individually as circles. Source data are provided as a Source Data file.