The Biology of Depression: How Stress Affects the Brain and the Body

Biology of depression
Scientific studies have found that numerous brain areas show altered activity in patients suffering from depression, and this has encouraged advocates of various theories that seek to identify a biochemical origin of the disease, as opposed to theories that emphasize psychological or situational causes. Among the theories of a biologically based cause of depression are those involving genetics and circadian rhythms, but the most prominent and widely researched is the monoamine hypothesis. Source: http://en.wikipedia.org/wiki/Biology_of_depression