Post Traumatic Stress Disorder
Basic Stress Physiological Responses: Stress Relief and Anxiety
When trying to understand stress response syndromes it is useful to consider comparative physiology and behaviour and trace the roots of human adaptation in its phylogenic development. The ontogeny of the human individual reflects this also to a great extent. The literature on behavioural and psychological physiology describes two important responses to adaptational challenges. Both can be seen as efforts to survive confrontations with members of their own species, predators, or physical dangers.
The first is the defence reaction, described in 1915 by Walter B. Cannon as a preparation for fight or flight. It consists of both behavioural and physiological components. The behavioural components are species-specific; the physiological are more general, such as: pupillodilation; pilo-erection; increase of muscle tone, ventilation, cardiac output, oxygen consumption and muscle blood flow; decrease of
blood flow in the skin, intestine and kidneys; bladder and bowel emptying; and many others like eurohumoral, hormonal, immunological and haemostatic changes. The functional anatomy of the defence system has its organisational centre in the amygdala, particularly its central nucleus, but the central or peri-aquaductal grey matter is also involved .
Outflow is mainly through the sympathetic system and the adrenal medulla. Understanding of the ethology and comparative physiology of the defence reaction permits excellent understanding of the psychophysiology of alarm and anxiety in humans. From a biological point of view, there are good reasons why, so often, physical symptoms are the first signals of post-traumatic syndromes. The core of the response to any form of existential menace is the inborn repertoire for survival behaviour present in all mammals. The other important survival response is the general adaptation syndrome described by Hans Selye later in the century. It is characterised by behavioural inhibition when all possible active ways of surviving a challenge are being blocked off.
It can be compared to the psychodynamic concept of unsolvable conflict or to Martin P. Seligman’s behavioural model of learned helplessness, while James P. Henry described it from a comparative physiological and ethological point of view as conservation-withdrawal . The corresponding euroanatomical organisation is centralised in the septo-hippocampal system. It produces its physiological outflow through the anterior pituitary and the vagal motor system, and activates glucocorticoid hormone release. The physiology of inhibition in the human has much resemblance to what is known in ethology as subordinate behaviour.