One of my new favorite blogs on the internets, "'Et tu?' The Diary of a Former Athiest" writes about depression and self-identity.

For quite a few years in my late teens and early 20's, I struggled with depression. It was clear to me that there was some kind of chemical imbalance going on in my brain, and it permeated every aspect of my life and thoughts. I would sometimes lament the fact that I just wasn't "myself" anymore...yet I was never comfortable with that idea. In my worldview, the human person was nothing more than a collection of molecules; selfhood was nothing more than a unique set of chemical reactions firing in the brain. In that case, how could the current set of chemical reactions be less "me" than the chemical reactions that were going on a few years before?

Go read the whole thing. The author, Jennifer F. converted from certain athiest to believing Christian through an intellectual process first, then by emotional connection. I think most people, me included, do it the other way around. She's a good writer and it's worth a couple minutes to read.