Influence of the early (first 4 days) and late (last 4 days) phases of learning on neurogenesis. Latency to find the escape platform in a water-maze task (a,c,e,g). Number of BrdU-IR cells in rats injected with BrdU during the early (b), late (d,f) and early+late phase of learning (h). The late phase of learning induced an increase in the number of BrdU-IR cells (d) that survived for 4 weeks (f). The black bar represents the period of BrdU injections. Arrows indicate the day of killing.