Neurogenic correlates of an olfactory discrimination task in the adult olfactory bulb.

In the main olfactory bulb, stimuli are coded within the spatio-temporal pattern of mitral cells' activity. Granule cells are interneurons that shape the mitral cells' activity, and are continuously generated in the adult main olfactory bulb. However, the role of granule cell renewal remains elusive. We show here that an associative olfactory discrimination task reduces the survival of newborn neurons. However, when the olfactory task involves perceptually related odorants, the learning process is slower and does not induce such a reduction in the number of new neurons. Mapping newborn cells within the granule cell layer of the main olfactory bulb reveals a clustered distribution that evolves with learning as a function of odorant similarity and partly overlaps with the immediate-early gene Zif268 expression pattern. These data provide insight into the functional mechanisms underlying olfactory discrimination learning, and promote the importance of neurogenesis as a cellular basis for the restructuring of odor images in the main olfactory bulb.