The vomeronasal system.

In addition to the main olfactory system, many vertebrates possess a vomeronasal system that conveys more specialized chemosensory information. Unlike the airborne, volatile stimuli detected by the main olfactory system, vomeronasal stimuli are typically proteins of the lipocalin family which bind small, volatile ligands. Despite the smaller number of vomeronasal receptor types, the projection patterns of the vomeronasal receptor neurons to multiple glomeruli in the accessory olfactory bulb appear to be more complicated than those of the main olfactory system. The vomeronasal system has a direct subneocortical projection to hypothalamic areas that mediates specific behavioural and hormonal responses to pheromonal stimuli. However, the integration and transmission of this information can be modulated by learning mechanisms. The aim of this article is to outline some of the functions of the vomeronasal system, and in particular to comment on recent advances in our understanding of how vomeronasal information is coded and processed.