Substantial evidence from neuroscience, genetics, and clinical investigation shows that depressive illnesses are disorders of the brain. However, the precise causes of these illnesses continue to be a matter of intense research.
Modern brain imaging technologies reveal that, in depression, neural circuits responsible for the regulation of moods, thinking, sleep, appetite, and behavior fail to function properly, and critical neurotransmitterschemicals that brain cells use to communicate are out of balance. Studies of brain chemistry, including the effects of antidepressant medications, continue to inform our understanding of the biochemical processes involved in depression.
In some families, depressive disorders seem to occur generation after generation; however, they can also occur in people with no family history of these illnesses. Genetics research indicates that risk for depression results from the influence of multiple genes acting together with environmental or other nongenetic factors.
Very often, a combination of genetic, cognitive, and environmental factors is involved in the onset of a depressive disorder. Trauma, loss of a loved one, a difficult relationship, a financial problem, or any stressful change in life patterns, whether the change is unwelcome or desired, can trigger a depressive episode in vulnerable individuals. Later episodes of depression may occur without an obvious cause.