Article

0the initial organization of the sensory epithelium, in which recep-tor neurons are spatially organized based on their types and tun-ing (Luo and Flanagan, 2007; O’Leary et al., 1999). The olfactory system is unusual in this regard because olfactory sensory neu-rons (OSNs) expressing a given receptor gene out of a repertoire of 1000 are scattered in the olfactory epithelium (Buck and Axel, 1991; Mombaerts et al., 1996; Ressler et al., 1994; Vassar et al., 1994; Zhang and Firestein, 2002). This disarray is dramat-ically transformed to ordered organization at the level of glomer-ulus in the MOB. Here, OSNs expressing a common receptor gene converge precisely into one or two glomeruli with a stereo-set of OSNs that also express the endogenous M71 receptor. This receptor has a characterized ligand; thus, we were able to probe both anatomical and functional organization. By targeting tracers to genetically identified glomeruli, we uncovered an as yet unknown level of organization in the olfactory system, where bilateral isofunctional olfactory columns are precisely linked by neurons in the AONpE. We found that odorant-specific activation of the contralateral MOB required the AONpE. In addition, we developed a behavioral assay to establish the important role of the AONpE in crosslateral transfer of odorant-specific olfactory memory. These results thus demonstrate that the precision ofNeuro