Conservation of underlying stereotypy in olfaction.

The first stage of any sensory processing begins with the transformation from the external signal to the abstract space defined by receptor activity. For olfaction it is defined by the olfactory receptors (OR) located on the membrane of Olfactory Sensory Neurons (OSN) in the olfactory epithelium. Unlike other senses there is not yet a coherent definition of the abstract space defining the external signal (Ligands) within reach. While each OSN expresses a single OR gene, all OSN expressing the same gene send projections to the same place in the olfactory bulb. Therefore calcium imaging signal from the olfactory bulb is a good measure of the amount of receptors activated. Given data of mice glomeruli responses to a large number of chemicals we show conservation across animals of the underlying activity and therefore of the encoding transformation carried out by the receptors. The role of concentration effects is also discussed. Furthermore we assign corresponding pairs based on the similarity of the responses between glomeruli of different animals. We demonstrate that the geometrical locations of the glomeruli are therefore conserved.