what depression does to the brain
Regions of the brain that may be affected by depression include the hypothalamus, hippocampus, anterior cingulate gyrus, amygdala, and all parts of the limbic system (which is involved with emotion formation as well as processing, learning, and memory). Certain parts of the brain associated with emotion, memory, and learning, particularly the prefrontal cortex and the hippocampus, can shrink in size. 2  This might explain some of the emotional changes observed in people with depression.
This study reveals the answer: Depression comes first; the brain damage follows... According to co-author Professor Ian Hickie: [The] more episodes of depression a person had, the greater the reduction in hippocampus size.