The causes of depression are a mystery as yet unsolved. Ask people what causes depression, and you'll get a variety of answers, but one I've often heard and used myself was: "Chemical imbalance in the brain." In theory, antidepressant medication can help bring the balance back. But, depression is a bit more complicated than simply restoring some kind of balance. Researchers still don't have all the answers, but they are learning more about the complexity of emotions.
Two articles helped me understand some of these biological complexities; they are listed at the end of this post. What caught my attention was how little we know about the science behind depression. Though we have learned much and have some good ideas to explore concerning depression's mechanisms, we are still very much in the dark. Some things these articles pointed to as biological explanations of depression:
-a smaller hippocampus: stress may slow the growth of neurons in the hippocampus, antidepressants might help that growth
-activity in the amygdala is higher when a person is sad or depressed
-corticotropin-releasing hormone (CRH): this hormone is found to be higher in people experiencing depression
-trauma: some disturbing events may cause changes at the cellular level, affecting the functioning of nerve cells in the brain, leading to an unbalanced concentration of neurotransmitters
That we don't have many clear answers about what causes depression might explain why the medications we use to treat it aren't always effective. (Antidepressants work around 50% of the time to relieve symptoms of depression.) Most antidepressants are selective-serotonin-reuptake-inhibitors (SSRI). For some, the action of SSRIs might be exactly what is needed. For others, though, SSRIs may not be addressing the biological roots of their unique depression.