actually depression does have symptoms and causes in the physical world although it is hard to distinguish between the two.
however, when the left and right hemispheres don't communicate well it is not called depression. most often it is epilepsy. the medications for epilepsy and depression are different. but you never know what an anticonvulsant is used for. when i was a teen i was misdiagnosed as a petit mal epileptic, so i know a little about both diseases.
the real question isn't cause in my opinion but instead trying to do something good with your life in spite of handicaps. treatment will be the same no matter what the cause is. you can't treat your life as a cautionary tale--a bad example to others based on this or that cause. good luck with that
-pi