Figure 2. Orthonasal and retronasal glomerular response patterns elicited by the same odor overlap but differ in terms of response size. A–E, An example from a rat. A, Resting light intensity (RLI) image of the left bulb. B–D, Averaged (n = 3) odor maps for orthonasal 4% 2hex (B), orthonasal 4% MV (C), and retronasal 4% MV (D). Positions of two of the activated glomeruli (g1 and g12) are marked by the orange circle and blue square on each map. White lines indicate the boundaries of the bulb visible through the optical window. E, Bar diagram showing the glomerular response patterns for orthonasal 2hex versus orthonasal MV, and orthonasal versus retronasal MV. Between orthonasal 2hex and orthonasal MV, the responses of nine glomeruli (g1, g2, g4, g9, g10, and g12∼g15) were significantly different (*p < 0.05). Between orthonasal and retronasal MV, however, responses were significantly different only at g1 and g8 (*p < 0.05). F, G, Overall picture from nine rats. F, The average percentage of glomeruli in a rat responding only orthonasally (O; red), retronasally (R; green), or to both routes (O+R; blue) (based on noise-level set at < 0.05%ΔF/F). G, Scatter plot to show the correlation between all 894 orthonasal–retronasal glomerular response pairs (152 glomeruli, 5–9 rats, 3–7 odorants per rat).