Constitutive neurogenesis clearly occurs within the adult central nervous system of almost all mammals. This process generates new neurons in at least two areas of the brain: the olfactory bulb (OB) and the dentate gyrus (DG) of the hippocampus. However, it remains unknown why new neurons specifically populate those two neural structures rather than other areas. In empirical experiments, adult neurogenesis was impaired and the consequences of this impairment for the neural circuitry and behavior of animals were investigated with a view to determining the role of new neurons in the adult brain. In the December issue of the Journal of Neuroscience, Breton-Provencher et al. addressed this issue, by using drugs to establish a transient blockade of adult neurogenesis and combining several techniques to evaluate the consequences of this blockade for OB circuits and particular types of behavior. Here, we summarize and discuss some of their findings in light of other recently published data.