Figure 3. Cortical feedback inputs representing different odors are diffusely distributed at the spatial scale of individual glomeruli.

A) Boutons responding to particular odors are not spatially segregated. A₁) Results from one granule cell layer imaging field showing all bouton ROIs (left) and map of the preferred odor for each responsive bouton (right). Color scale indicates each of the seven tested odors (Cin; cineole, Cit; citral, Hept; heptanal, BA; butyric acid, 4H; heptan-4-on, IA; isoamyl acetate, ET; ethyl tiglate. ROIs are shown enlarged for clarity. A₂) Cumulative frequency distribution of the pairwise distance between all boutons in A₁ with the same (Matched, n=296) or different (Mismatched, n=1702) odor preference. The two distributions are not significantly different (p=0.29, KS test). B) Summary data (grey, n=22 fields) reveals no significant difference in the mean distance between matched and mismatched responsive boutons (red, average±SEM). C) Rank-ordering orders by their probability of eliciting excitatory responses in individual imaging fields indicates that the fraction of responses elicited by any odor is random. Red circles, responses to rank ordered odors for both granule cell layer and glomerular imaging fields (mean ± SEM, n = 22 fields). The observed values fall within the curves expected by chance for the largest (n=406) and smallest (n=23) number of responsive boutons per imaging field (dotted lines). Inset, response probability distribution for the most represented odor (Odor #1) derived from random subsampling using the sample sizes from 22 imaging fields. Experimentally measured probability (red line) falls within central 90% of the distribution (dotted lines).