Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Hippocampal neurogenesis, which is linked to healthy cognition, declines with age across mammalian species (Kuhn et al., 1996; Eriksson et al., 1998; Cameron and McKay, 1999; Gould et al., 1999b; Bizon et al., 2004; Siwak-Tapp et al., 2007; Dupret et al., 2008; Hattiangady and Shetty, 2008; Aizawa…
Category: