I'll add that my first known episode of major depression occurred when I was sober for about eleven years, fourteen years prior to my relapse. For many people, SSRIs produce cognitive benefits: clarity of thought, heightened awareness (not to be confused with hypervigilance), and increased decisiveness, among others. Again, I don't believe that they cause these conditions, but stimulate something that is already there.
As for people who report that antidepressants "changed who they are" or made them "feel like zombies," I at first learned -- with the help of both a very well trained psychiatrist and therapist -- and then came to believe that my feeling as well as I did once I started on the meds was something I had never before experienced, and was therefore alien to me. But my core personality was in no way changed.