Historical approach and evolution of the stress concept: a personal account.

As a matter of research or as a process, stress remains one of the most cited construct in biomedical literature; a medline survey accounts for more than 210,000 citations since 1970. It is difficult to define. It is frequently used in a vague manner, including undifferently the agent, the process, and the response. The concept is multidimensional and composite, including emotion and arousal. Stress has an implicit: it implies alteration of a theoretical balance or equilibrium within physiological systems, and it seems to characterize a process leading to disease. Large individual differences exist in the way to react to a stressor. Psychological and cognitive determinants are central for the course of the process. The homeostasis concept is not useful anymore and has been replaced by the more accurate and flexible concept of allostasis. The physiological hormonal and neural bases of this process are now identified. New perspectives identify stressors, chronic or not, to be a source of vulnerabilities through epigenetic mechanisms and a series of biobehavioral disorders characteristic of our modern civilizations. The evolution of the concept is not linear. It has been enriched by recent neurobiological-neuroendocrinological discoveries and also by behavioral-cognitive sciences.