[The sense of smell: analysis of odors and olfactory memory]

Olfactory transduction is mediated by neuroepithelial cells localized on turbinal crests in naris. Odorant molecules are uptaked by the mucosa which flows on epithelial surface and some of the molecules enter in contact with olfactory cells tentacles. Odorant molecules interact with molecular receptors bound to cell membrane and induced successive reactions leading to ion channels opening and then to receptor potential appearance. The receptor cells degenerate when molecular receptors are saturated and, further regenerate, according a genetic program and olfactory learning action potentials which appear at the basal pole of the receptor cell are propagated along the small olfactory nerves to the olfactory bulb glomerulus. Several hundred axons enter in one glomerulus among others and make synaptic contacts with one dendritic tree of a mitral cell. The selection of the numerous signals which converge in the glomerulus, the codage in intensity, duration and contrast are made at this level. One odorant molecule activates some glomeruli (rarely one); a complex odor activates a great number of glomeruli according a complex spatial distribution. Following odor stimulation, the electrical signals are analysed in the olfactory bulb which delivers to the olfactory cortex various informations about the odor components that are to be selected and compared to anterior olfactory learning. Animal experimentation and clinical data show that memory storage is made using short, medium and long term memorization. This memory is integrated in the limbic system at the interface of neural structures which regulate the main behaviors and physiological functions. This explains the modulatory role of smell in some behaviors but complicate our understanding of access to olfactory memory.