Posttraumatic stress disorder is thepathological replay of emotional memory formed in response to painful, life-threatening, orhorrifying events. In contrast, depression is often precipitated by more social context-relatedstressors. New data suggest that different types of life experiences can differentially impactbiochemistry, physiology, anatomy, and behavior at the level of changes in gene expression.Repeated separation of neonatal rat pups from their mother results in many long-lastingalterations in biology and behavior paralleling that in depression, including hypercortisolism.The role of the amygdala in modulating emotional memory is highlighted, as well as some of itsunique properties such as metaplasticity (i.e., the differential direction of long-term adaptation,either potentiation or depression) in response to the same input as a function of the prior historyof stimulation. The implications of these emerging data on the physiological and molecularmechanisms underlying emotional memory emphasize the particular importance of preventionand early intervention.