Is depression a brain disorder?

Depression whether there are brain lesions, then depression should be said, especially moderate to severe depression, the brain is a certain lesion, its main performance is: the first is the brain neurotransmitters, including serotonin, noradrenaline, dopamine and other neurotransmitter concentrations are reduced. The second change is to show some brain atrophy, especially the brain and hippocampus atrophy is more obvious, so depression patients, it can show memory decline is more obvious, learning difficulties.