Topological Reorganization of Odor Representations in the Olfactory Bulb
Three-dimensional plots of factors representing distinct molecular features (long-chain, aromatic, and basic), averaged over individuals, during the early phase of the odor response. Factors were extracted from glomerular activity patterns (raw Ca2+ signals time-averaged between 0 and 2 s; dataset 1) and from MC and IN activity patterns (TDCa signals time-averaged between 0 and 768 ms; datasets 1 and 2) in individual OBs. Activity of factors was then binned in 40 × 40 × 40-μm3 voxels, centered on the centroid of the aromatic factor, and averaged over animals. Spheres represent voxels; color and size of spheres indicate average activity in each voxel. Voxels with activity smaller than an arbitrary threshold are not shown. Black cross indicates the centroid of the aromatic factor. Floor patterns are projections of three-dimensional activity distributions, binned in 20 × 20 × 20-μm3 voxels, onto the horizontal plane. Orientation is as indicated: posterior to anterior (P–A), lateral to medial (L–M), and dorsal to ventral (D–V). Blue cross indicates the centroid of the aromatic factor in the horizontal plane. Distinct volumes of dense activity in different factors are segregated along the anterior–ventral to posterior–dorsal axis. The topological organization of averaged factors is similar for glomeruli, MCs and INs, showing that chemotopic maps during the early phase of an odor response are topologically related across layers and stereotyped between animals.