Relative to the considerable work on fear conditioning in mature rodents and primates, far less work examines developmental aspects of fear conditioning using animal models . Research investigating the emergence of fear conditioning in infant rats has identified a sensitive period in which amygdala activation to aversive stimuli is inhibited. During early stages of postnatal development, newborns are equipped with innate abilities for appetitive learning . For instance, infant rats acquire the ability to orient toward their mother's odor to facilitate mother-infant attachment. In contrast, during the first 10 days, amygdala activation in response to threats is attenuated due to low neonatal cortisol levels, resulting in an approach response to the aversive stimuli. At postnatal day 10, stress-induced cortisol in young rats increases to adult-like levels, which in turn facilitates amygdala activation allowing fear conditioning to emerge. This plasticity in rats continues to develop into adolescence.