Animal models of stress-related mechanisms in psychopathology have enormous potential. Compared to human studies, advantages include that the nature and timing of stressors can be systematically varied; the effects over substantial proportions of the subjects' short lives and over generations can be studied within the duration of a single research grant; and hypothesized neuroanatomical and neurochemical pathways can be examined directly. The research described in Dr. Huhman's chapter realizes this potential in many respects. The challenge is to determine what we can learn from these models. Enumerating the differences between Syrian hamsters and humans might lead to the immediate answer “not much.” Equally, the consistency of findings from studies of the key neuronal circuits in fear conditioning – involving not only Syrian hamsters, but many other animal species and humans – would suggest we can learn a great deal. This review considers some of the issues.

THE INTERPLAY BETWEEN SOCIAL EXPERIENCE AND BIOLOGY

Over a relatively short time, animal studies have informed a transformation from the separate study of the social and the biological to integrated study of the two levels of analysis. It is now well established across several mammalian species that social experiences often have long-term behavioral and biological effects, many mediated by variations in gene expression, and that these occur only over particular, sensitive periods in development (see Wiedenmayer; Szyf et al., this volume).