Pup attachment learning changes over development. During the earliest days of life, pups have a sensitive period when odor-shock conditioning produces an odor preference. At 10-days of age, pups begin the Transitional Sensitive Period, when pups endogenous corticosterone levels have increased sufficiently to enable amygdala dependent fear/avoidance learning. However, with the mother present at this age pups will revert back to the approach learning of the sensitive period. That is, the mother’s presence will socially buffer pups (i.e. attenuate pups shock-induced corticosterone release) and pups learn a preference. As pups mature, maternal social buffering continues to lower corticosterone but pups only have access to the amygdala dependent fear learning (Moriceau and Sullivan 2006; Raineki et al. 2009; Shionoya et al. 2007; Sullivan et al., 2000a).