Depression: seratonin deficiency/imbalance?

clipped from www.psychiatrictimes.com Is There Evidence That Antidepressants Correct a Serotonin Deficiency? Biological markers specific for depression have been elusive. Although a physician may tell a patient that a chemical imbalance causes their depression, Elliot S. Valenstein, Ph.D., has pointed out that the physician would be hard-pressed to provide any evidence to support this claim (1998). There is no test available that would demonstrate that any patient has a biological depression, as opposed to any other type, or even that such biological depressions exist. Although proponents claim that some of the antidepressants selectively affect only one system of the brain (such as the brain serotonin system), this does not reflect current understanding of how the brain works. We know that each brain neuron receives input from tens of thousands of other neurons and, in turn, sends output to tens of thousands of other neurons. It seems unlikely that the SSRIs only effect the serotonin systems in the brain, even initially.