The hippocampal region is crucial for encoding complex associations such as unrelated word pairs, associating items with spatiotemporal context, and representing spatial layouts. Neurogenesis has been shown to be important for hippocampal-dependent learning (Shors et al, Nature, 2001). The question addressed here is: what is the role of hippocampal neurogenesis in hippocampal-dependent memory formation? We have developed a computational model of the hippocampal memory circuit that incorporates neurogenesis in the dentate gyrus (Becker, submitted); our model predicts that neurogenesis is important for minimizing interference between highly similar events. Here, we consider another role for neurogenesis in long-term memory, namely, in the retention of long-term memories after delays of several weeks. Snyder et al (SFN abstracts 2003) studied long-term retention with and without neurogenesis using irradiation to prevent survival of newly generated neurons. Rats irradiated prior to learning in the Morris water...