Biological responses to disasters.

The pathogenic effect of extreme events has been equated with their immediate stressfulness, and thereby with the biology of stress. This article extends this classical view to include, among other pathogenic factors the biological dimensions of learning, social interaction, territorial behavior, and a top-down brain process that links personal and cultural meanings with emotional and bodily responses. The paper depicts the way in which mechanisms related to stress and aversive learning trigger an initial response and those related to separation, loss and sensitization shape its long-term consequences. Traumatic events are followed by a critical period of increased brain plasticity, during which irreversible neuronal changes may occur in those who develop traumatic stress disorders.