There is an interesting brief communication by Moriceau and Sullivan in Nature Neuroscience (vol. 9, pp. 1004 - 1006, 2006) describing how maternal presence can switch fear learning to attraction in preweanling (12–15 days old) rats. In the mother's absence, odor-shock conditioning produces amygdala activation and learned odor avoidance. With maternal presence, this same conditioning yields an odor preference without amygdala activation. Maternal presence acts through suppressing pup corticosterone and thus corticosterone's regulation of amygdala activity. Intra-amygdala corticosterone infusions that over-ride maternal suppression of corticosterone permit fear conditioning and amygdala activation to return.
The data suggest that preweanling pups have two odor-shock learning circuits, with maternal presence providing suppression of stress-induced corticosterone release and engaging the odor-shock circuit for odor preference learning supporting infant-mother attachment. The data suggest a way in which the functional maturation of brain development may be disrupted by stress.. The mother's ability to modify fear learning circuitry may provide clues to abusive attachment and predisposition for mental illness and altered emotional expression later in life. The validity of an animal model of abusive attachment is strengthened by the wide phylogenetic representation of abusive attachment, which has been documented in chicks, infant dogs, rodents and nonhuman primates.