I am not a scientist or psychically able to look inside my own brain or others to see exactly what goes on and compare it with others and I can't prove or no one can that depression is because of only due to chemical imbalance or genetics. The brain Is a physical organ part of our body, it is different from our mind, which has stored memories, images and is directed by thoughts and feelings and conscious or sub conscious responses to things. we do have choice and control over our mental and physical wellbeing. Our state of mind affects our physical body too.