Stress and Anxiety
Stress is a complex multisystem response to conditions or environmental changes that are disruptive to the organism's homeostasis (Anisman and Merali 1999, McEwen and Stellar, 1993). The anatomy and physiology of mammals and other organisms have evolved responses to stressful stimuli, and many of these evolutionary changes have had an impact on brain structure and function, as well as changes in endocrine systems. Stressors can be either environmental stimuli with direct impact on homeostasis (systemic stressors) or they can be conditioned outcomes as a result of associative processes (e.g., conditioned fears or expectancies that arise in part from cognitive processes, also called processive stressors) (Anisman and Merali 1999).
Systemic stressors tend to have pronounced effects on the peripheral nervous system and brain regions - primarily hypothalamic - that interact directly with the autonomic nervous system. Processive stressors can also activate these systems, but in addition they often activate emotional/arousal centers within the brain, including regions of the limbic system. Stressful stimuli can bring about a number of states in the CNS that have traditionally been viewed in terms of psychological constructs such as fear, anxiety and mood alterations (e.g. depression). It is now clear that these psychologically defined states are linked to physiological changes in particular brain regions such as the limbic system and other cortical and subcortical regions.
Anxiety is one of several manifestations of exposure to stressful events. Anxiety is a change in cognitive processes or a behavior bias that is brought about by repeated stressors of a threatening nature or by the anticipation that such stressors will be encountered (Volpicelli et al., 1999). Changes in behavior associated with increased anxiety often include avoidance of particular stimuli and environmental situations. Experimentally, and in human etiological studies, stressful events that are perceived as uncontrollable are most likely to result in states of heightened anxiety.
The neuroanatomical and neurochemical bases of anxiety have become increasingly well understood over the past two decades. However many of the most crucial systems overlap and interact with circuitry involved in other responses to stress. One remarkable common denominator to almost all responses to stress is the involvement of the hypothalamic corticotrophin releasing factor CRF and modulation of pituitary and adrenal hormone secretion.
References
- Anisman, H. and Merali, Z. (1999) Understanding stress: characteristics and caveats. Alc. Health Res. World 23: 241-249.
- McEwen BS and Stellar E. Stress and the individual. Arch Intern Med. 153:2093-2101, 1993.
- Volpicelli J, Balaraman G, Hahn J, Wallace H, Bux D. The role of uncontrollable trauma in the development of PTSD and alcohol addiction. Alcohol Research and Health 23:256-262, 1999.