Neurophysiology of stress: From historical to modern approach

Stress is present in our everyday lives and it is considered to be the driving force of evolution. Anxiety, chronic worries and panic attacks are the most common consequences of long-term and exhausting stress. The most significant fundamental contribution that is crucial for the development of the modern concept of stress was made by Claude Bernard who proposed the theory that the body was constantly maintaining a stable and well-balanced internal environment or "milieu interieur". Maintaining the internal environment constant was defined as homeostasis by Cannon who proposed two maintenance mechanisms - through negative feedback from the autonomic nervous system and through sensory organs. Hans Selye proposed stress as non-specific strain on the body, caused by an altered body function which is followed by the release of stress hormones. He named this process the general adaptation syndrome which had three stages: alarm reaction, initial phase exhibiting "fight or flight" response; resistance, when body is getting used to being stressed, and exhaustion, when resistance to stress is gradually decreased and collapses. Hans Selye was the first to coin the term "heterostasis" representing the procedure by which a new stable state was achieved by the activation of physiological adaptive mechanisms. Lazarus highlighted emotions as an important factor in behavior in response to stress and provided a description of various reactions to stressors. He emphasized the process of cognitive assessment as a mediator in dealing with stressors - how a person imagines or evaluates an event in order to understand stress reactions in people. Eustress, considered to be positive stress leads to toned emotions, motivation and focused energy, while distress, negative stress, occurs after prolonged stress that exceeds our ability to deal with it. Distress causes anxiety or withdrawal (depression and anxiety), and is accompanied by unpleasant feelings and reduced work ability leading to mental and physical illnesses.