Your Internet resource for information about the practice of psychology You may have heard people talk about chemical imbalances in the brain that occur in depression, suggesting that depression is a medical illness, without psychological causes. However, all psychological problems have some physical manifestations, and all physical illnesses have psychological components as well. In fact, the chemical imbalances that occur during depression usually disappear when you complete psychotherapy for depresson, without taking any medications to correct the imbalance. This suggests that the imbalance is the body's physical response to psychological depression, rather than the other way around.
Some types of depression do seem to run in families, suggesting a biological vulnerability.
This seems to be the case with bipolar depression and, to a lesser degree, severe major depression. Studies of families, in which members of each generation develop bipolar disorder, found that those with bipolar disorder have a somewhat different genetic makeup than those who are not diagnosed. However, the reverse is not true. Not everybody with the genetic makeup that causes this vulnerability to bipolar disorder develops the disorder. Additional factors, such as stress and other psychological factors, are involved in its onset as well.