A key figure in our understanding of the mind-body interaction and the concept of stress is American physiologist, professor and chairman of the Department of Physiology at Harvard Medical School, Walter B. Cannon (1871-1945). He is credited with the discovery of the process of homeostasis and the fight or flight stress reaction. In investigating the process of homeostasis, Cannon hypothesized that if a living organism is threatened by change, the change is automatically interpreted as threatening and corrective mechanisms are initiated to avert the threat or restore the status quo.
The research that made possible the discovery of the mechanism of homeostasis began with the study of the emergency function of the adrenal medulla. Cannon and his colleagues at Harvard University linked emotional excitement to the physiological changes that occurred in response to the secretions by the adrenal glands. Cannon hypothesized that the sympathetic nervous system is responsible for mobilizing the body’s defenses during intense fear or rage. He correctly identified these emotions as the prime movers of the body’s mobilization toward meeting a physical or psychological danger. The pathway of mobilization (the hypothalamic-pituitary-adrenal axis, HPA) initiates in the hypothalamus, which stimulates the anterior pituitary gland to secrete the activating hormone ACTH, which in turn stimulates the adrenal glands to produce excitatory hormones that activate the body’s defenses.
Got idea that adrenals in excitement serve to affect muscular power and mobilize sugar for muscular use—thus in wild state readiness for fight or run! — Entry in Cannon’s journal dated January 20, 1911
In 1929, Cannon first used the term fight or flight response to describe this emergency mobilization. He attributed the system-wide arousal of the body to a neurochemical produced by sympathetic nerve endings which he called sympathin, now known as norepinephrine. Cannon began using the term homeostasis in 1932 to describe the body’s physiological processes, controlled by the sympathetic nervous system, aimed at maintaining or restoring a stable internal environment.
In time, Cannon came to conceptualize physical and psychological stress as disturbances of homeostasis under conditions of cold, lack of oxygen, low blood sugar, and powerful emotions such as fear and rage. It was the first connection ever made, and verified by laboratory research, between the disruption of equilibrium caused by stressors and the body’s attempts to meet the threat and restore balance.