Posttraumatic stress disorder is the
pathological replay of emotional memory formed in response to painful, life-threatening, or
horrifying events. In contrast, depression is often precipitated by more social context-related
stressors. New data suggest that different types of life experiences can differentially impact
biochemistry, 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-lasting
alterations 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 its
unique 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 history
of stimulation. The implications of these emerging data on the physiological and molecular
mechanisms underlying emotional memory emphasize the particular importance of prevention
and early intervention.