The physiological approach to the definition and study of stress received its initialimpetus from the work of Selye (1950,1956). He defined stress as “a state manifested by a specific syndrome which consists of all the non-specific changes withinthe biologic system” that occur when challenged by aversive or noxious stimuli.Stress is treated as a generalised and nonspecific physiological response syndrome.For many years, the stress response waslargely conceived of in terms of the activation of two neuroendocrine systems, theanterior pituitary-adrenal cortical systemand the sympathetic-adrenal medullarysystem (Cox & Cox, 1985; Cox et al.,1983). The psychophysiology of stress isdiscussed in more detail in section 6.3.1.Selye (1950, 1956) argued that the physiological response was triphasic in natureinvolving an initial alarm stage (sympathetic-adrenal medullary activation) followedby a stage of resistance (adrenal corticalactivation) giving way, under some circumstances, to a final stage of exhaustion(terminal reactivation of the sympatheticadrenal medullary system). Repeated, intense or prolonged elicitation of thisphysiological response, it has been suggested, increases the wear and tear on the