Adult neurogenesis declines steadily with age in the hippocampus of every species in which this has been examined, including rats, mice, tree shrews, dogs and marmosets (Seki & Arai, 1995; Kuhn et al., 1996; Cameron & McKay, 1999; Simon et al., 2005; Leuner et al., 2007). Some evidence suggests that stress effects on adult neurogenesis may be greater in the aged animal than the young animal. There is a greater decrease in cell proliferation of aged tree shrews compared to young adult tree shrews following social stress (Simon et al., 2005).
