Most studies investigating the functional impact of new neurons in the hippocampus have tended to focus on their potential role in learning and memory. Antiproliferative agents (Shors et al., 2001; Garthe et al., 2009), irradiation (Madsen et al., 2003), and transgenic models (Garcia et al., 2004b), all ways to reduce cell proliferation in the hippocampus, have been shown to produce changes in cognitive tasks associated with the hippocampus. Decreased hippocampal neurogenesis has no effect on hippocampal-independent cued fear conditioning, but impairs hippocampal-dependent context fear conditioning (Winocur et al., 2006; Saxe et al., 2006; Warner-Schmidt et al., 2008; Imayoshi et al., 2008; Farioli-Vecchioli et al., 2008). In rats, context fear deficits do not appear until at least 4 weeks following neurogenesis ablation (Snyder et al., 2009a), suggesting that a certain degree of new neuron maturation is critical for context fear conditioning in rats. In the Morris water maze paradigm, rats show deficits in lasting retention of spatial information at least 4 weeks following ablation of hippocampal neurogenesis, but not before (Shors et al., 2002; Madsen et al., 2003; Snyder et al.,
