The glomerular layer of the olfactory bulb constitutes the first stage where information from olfactory receptor neurons (ORNs

The glomerular layer of the olfactory bulb constitutes the first stage where information from olfactory receptor neurons (ORNs) is organized and processed. The projection from ORNs to glomeruli is extremely convergent with on average several thousands ORNs converging onto each glomerulus of the mammalian olfactory bulb. Each of the several thousand of ORNs expressing the same odor receptor converges onto one or a few glomeruli in the olfactory bulb. Thus, at the level of sensory input to the olfactory bulb, odor receptor identity is mapped across the surface of the olfactory bulb with the glomeruli serving as the anatomical units of this map. In addition, each glomerulus can be discretely activated in an odorant-specific manner which suggests that these discrete anatomical structures also serve as functional units in representing odor information. Recent studies have shed light on the complexity of the synaptic network in the glomerular layer which raises questions about the various roles this network plays in processing olfactory information.