"Before you read this paper"

In mammals, most neurons are generated during embryonic stages. But even in adulthood, new neurons still continue to be generated and integrated into the neural circuits in a few parts of the brain. In particular, adult neurogenesis in the subgranular zone of the hippocampal dentate gyrus has been paid much attention and shown to play important roles in hippocampal functions including pattern separation. Although some earlier studies suggested the existence of adult neurogenesis, it had been commonly believed that neurogenesis does not occur in the mammalian brain in adulthood until late 1990s, when some influential papers were published. One of such papers, which was cited more than 6000 times, was chosen, but the discussion will not be restricted to the paper.