[Stress theories and the somatization process].

Stress theories aim at understanding pathophysiology of psychosomatic disorders. The first stress theories have been inspired by the principles of homeostasis. They view the response to stressors as a quasi reflex reaction which aims at normalizing disturbed homeostasis. More modern stress theories emphasize the intermediate role of cognitive and behavioural processes in the determinism of neuroendocrine and neurovegetative responses to stressors. Active attempts to control the situation are associated with activation of the sympathetic and adrenal medullary system whereas loss of control is associated with activation of the hypothalamic-pituitary-adrenal axis. Since the functional consequences of the activation of each of these physiological systems are not the same, the risk factors corresponding to each coping strategy are not the same. Whatever their details, physiological and psychobiological stress theories all emphasize the influence of psychic factors on bodily functions. However, mental states do not function independently of bodily functions. In the case of the influences of stress on immunity for instance, it has been shown that these influences represent the counterpart of feedback regulatory mechanisms in which the ability of the brain to regulate immune responses depends on the capacity of the immune system to influence brain functions. Activation of the immune system during infection or inflammation is accompanied by profound metabolic, neuroendocrine and behavioural changes which are mediated by the effects of immune products known as cytokines on brain cell targets. In view of the reciprocal relationships between peripheral organic systems and the brain, a purely psychosomatic view, from the psyche to the soma, is therefore no longer tenable. In addition, biological accounts of somatization processes run into the risk of minimizing the importance of perception and representation of somatic symptoms. Amplification of somatic symptoms is a common feature of neuroticism or negative affectivity and it bears no relationship with objective pathology. In order to understand somatization processes, there is therefore a need to study how the brain processes information it receives from the body and the way this information competes with information from the external environment.