Both odor-preference and odor-aversion learning occur in perinatal pups before the maturation of brain structures that support this learning in adults. To characterize the development of odor learning, we compared three learning paradigms: (1) odor-LiCl (0.3M; 1% body weight, ip) and (2) odor-1.2-mA shock (hindlimb, 1sec)-both of which consistently produce odor-aversion learning throughout life and (3) odor-0.5-mA shock, which produces an odor preference in early life but an odor avoidance as pups mature. Pups were trained at postnatal day (PN) 7-8, 12-13, or 23-24, using odor-LiCl and two odor-shock conditioning paradigms of odor-0.5-mA shock and odor-1.2-mA shock. Here we show that in the youngest pups (PN7-8), odor-preference learning was associated with activity in the anterior piriform (olfactory) cortex, while odor-aversion learning was associated with activity in the posterior piriform cortex. At PN12-13, when all conditioning paradigms produced an odor aversion, the odor-0.5-mA shock, odor-1.2-mA shock, and odor-LiCl all continued producing learning-associated changes in the posterior piriform cortex. However, only odor-0.5-mA shock induced learning-associated changes within the basolateral amygdala. At weaning (PN23-24), all learning paradigms produced learning-associated changes in the posterior piriform cortex and basolateral amygdala complex. These results suggest at least two basic principles of the development of the neurobiology of learning: (1) Learning that appears similar throughout development can be supported by neural systems showing very robust developmental changes, and (2) the emergence of amygdala function depends on the learning protocol and reinforcement condition being assessed.Even in utero, infant rats rapidly learn to avoid odors paired with malaise (LiCl) as expressed by learning an odor aversion (Garcia et al. 1966(Garcia et al. , 1974Hennessey et al. 1976;Haroutunian and Campbell 1979;Smotherman 1982;Stickrod et al. 1982;Rudy and Cheatle 1983;Kucharski and Spear 1984;Smotherman and Robinson 1985, 1990;Alleva and Calamandrei 1986;Miller et al. 1990b; Best 1992, 1993;Richardson and McNally 2003;Gruest et al. 2004;Shionoya et al. 2006). In contrast to adult odor-LiCl learning, which relies on the amygdala (Touzani and Sclafani 2005), this early-life, odoraversion learning relies on the olfactory bulb until the pup approaches weaning age, when the amygdala is incorporated into the learning circuitry (Shionoya et al. 2006). In contrast, if infant rats receive an odor paired with a moderately painful stimulus (0.5-mA foot or tail shock, or tail pinch) the amygdala appears to be incorporated into this learning circuitry around postnatal day Here we expand assessment of the developing pups' odoraversion learning circuit by including the anterior and posterior piriform cortex, which have previously been demonstrated to be important for both pup and adult odor learning (Litaudon et al. 1997;Barkai and Saar 2001;Mouly et al. 2001;Mouly and Gervais 2002;Tronel and Sara 2002;Moriceau and Su...