Fig. 2.

Bilateral symmetry of functional representations.A–C, Dorsal views of both olfactory bulbs in an adult mouse, imaged through thinned bone. Bilateral olfactory maps were evoked by 1% propanal (A), 1% butanal (B), and 1% hexanal (C). Responses to all three odorants activate roughly corresponding regions in the two hemispheres; in the case of hexanal (C), an apparently corresponding glomerulus was activated in each hemisphere. In all panels, caudal is at thetop of the panel. D–F, Duplicate maps of images (A–C), respectively, in which one copy has been flipped horizontally, pseudocolored (original is red and inverted copy is green), and superimposed on the original. Overlapping regions of activity are yellow. Activity patterns show only partial overlap, indicating that in general they are not precise mirror images. G, Color-coded activity maps comparing active regions for propanal (green) superimposed on butanal map (red) reveal that odorants which differ by only one carbon show some overlapping regions (yellow).H, I, Superimposed activity maps for odors differing by two carbons (H, butanal, green; hexanal,red) or three carbons (I, propanal,green; hexanal, red) show no overlap. Scale bar (shown in A for A–I): 500 μm.