Construction of functional neuronal circuitry in the olfactory bulb

•Glomerulus is a functional unit for odor information processing.•Lateral inhibition is mediated by short axon cells and granule cells.•Cortical projection is topographic in some area but non-topographic in other areas.•Odor information is both spatially and temporally represented in the olfactory bulb.•Interneurons may underlie plasticity of the olfactory bulb. Recent studies using molecular genetics, electrophysiology, in vivo imaging, and behavioral analyses have elucidated detailed connectivity and function of the mammalian olfactory circuits. The olfactory bulb is the first relay station of olfactory perception in the brain, but it is more than a simple relay: olfactory information is dynamically tuned by local olfactory bulb circuits and converted to spatiotemporal neural code for higher-order information processing. Because the olfactory bulb processes ∼1000 discrete input channels from different odorant receptors, it serves as a good model to study neuronal wiring specificity, from both functional and developmental aspects. This review summarizes our current understanding of the olfactory bulb circuitry from functional standpoint and discusses important future studies with particular focus on its development and plasticity.