Ontogeny of Infant Fear Learning and the Amygdala

Abstract

To support attachment to the caregiver, altricial infants, including humans and rats, must identify, learn, and remember their caregiver. The early attachment process in the rat is distinguished by its behavior and underlying neural circuitry, which are both exquisitely suited to promoting the infant-caregiver relationship. Foremost, infants have the enhanced ability to acquire learned preferences, and this behavior is supported by the hyperfunctioning locus coeruleus and experience-induced changes in the olfactory bulb and anterior piriform cortex. But of equal importance, infants have a decreased ability to acquire learned aversions and fear, and this behavior is facilitated through attenuated amygdala activity. Presumably, this attachment circuitry constrains the infant to form only preferences for the caretaker regardless of the quality of the care received. With maturation and the end of the infant-caregiver attachment learning period, the developing rat's social behavior and underlying circuitry transition to accommodate life outside the nest. However, early-life environmental and physiological stressors can alter the dynamic nature of this circuitry, particularly in respect to the amygdala. Such changes likely provide a framework for the lasting effects of early stress on emotional and cognitive outcome.