I experienced a brain I jury back in 1996 from a fall so I might have some insight. The depression is due to the injury itself (lack of brain activity while the brain is healing) and the circumstances in your life (study, employment, relationships, etc.) that have been disrupted as a result of the injury. So for me, I could no longer work as an engineer and became unemployed. I became isolated, another cause of depression. I also lost hope for the future. I had to put various things in place to address these (woodworking hobby, volunteering, stopped drinking alcohol.) Social contact is important because it's natural to isolate yourself.
