Principles of Glomerular Organization in the Human Olfactory Bulb - Implications for Odor Processing

Olfactory sensory neurons (OSN) in mice express only 1 of a possible 1,100 odor receptors ( OR) and axons from OSNs expressing the same odor receptor converge into similar to 2 of the 1,800 glomeruli in each olfactory bulb ( OB) in mice; this yields a convergence ratio that approximates 2:1, 2 glomeruli/OR. Because humans express only 350 intact ORs, we examined human OBs to determine if the glomerular convergence ratio of 2: 1 established in mice was applicable to humans. Unexpectedly, the average number of human OB glomeruli is >5,500 yielding a convergence ratio of similar to 16:1. The data suggest that the initial coding of odor information in the human OB may differ from the models developed for rodents and that recruitment of additional glomeruli for subpopulations of ORs may contribute to more robust odor representation.