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The Relationship Between Stress, Depression, and Cognitive Functioning

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Stress is known to be one of the major causal factors of depression (Kendler, Karkowski, & Prescott, 1999). Large stressors in life, such as divorce or death in the family, are all known to be related to the development of depression in people (Kendler et al., 1999). Such traumatic, sudden events can place acute stress on a person that can lead to problems such as depression. However, equally as stressful to people is chronic stress - not as stressful as major stressors, but still pervasive enough day-to-day to contribute to an overall drop in positive affect. Although depression is often referred to as the “common cold” of psychology, it can still be a dangerous condition, particularly due to the increase of suicidal ideation that can occur in some people with depression. For this reason, research is constantly seeking to understand the condition better. Since much truly experimental research on humans with depression would constitute a breach of ethics, most research in this area focuses on animals. The study conducted by Henningson et al. that is the subject of this paper utilized rats to study the effects of depression due to chronic stress on cognitive performance.

As it is impossible for rats to indicate in the same way as humans that they are depressed, a model to mimic the development and progression was developed by researchers in the 1980s. Called the chronic mild stress model (CMS model), rats or mice are exposed to mild stressors for a number of weeks (anywhere from one to seven) and their intake of a particular sucrose solution is monitored. Decrease in sucrose consumption or preference is thought to reflect a decrease in sensitivity for rewards (Willner, 2005), a classic example of anhedonia, which is a common symp...

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...ion: Relation to anhedonic-like responses. Behavioural Brain Research, 198 (1), 136-141.

Kendler, K.S., Karkowski, L.M., & Prescott, C.A. (1999). Causal relationship between stressful life events and the onset of major depression. Journal of American Psychiatry, 156 (6), 837-841.

Nestler, E.J., Gould, E., Manj, H., Buncan, M., Dunman, R.S., Greshenfeld, H.K., et al. (2003) Preclinical models: Status of basic research in depression. Biological Psychiatry, 52 (6), 503-528.

Papp, M., Willner, P., & Muscat, R. (1991). An animal model of anhedonia: Attenuation of sucrose consumption and place preference conditioning by chronic unpredictable mild stress. Psychopharmacology, 104 (3), 255-259.

Willner, P. (2005). Chronic mild stress (CMS) revisited: Consistency and behavioural neuro-biological concordance in the effects of CMS. Neuropsychobiology, 52 (1), 90-110.
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