What you do changes your brain
"The second half of a man's life is made up of nothing but the habits he has acquired during the first half." -- Fyodor Dostoevsky
This NY Times book review of Norman Doidge's book, The Brain that Changes Itself, reminds me of the reasons I'm so rabid about the negative statements that people make to themselves.
The reviewer, Abigail Zuger, cites numerous examples where changes in "wiring" in the brain occur because of changes in behavior. If you practice thinking nasty things about yourself, your brain will become accustomed to those neural pathways and allow those thoughts more easily in the future. If you sit down and write for 10 minutes every morning, your brain expects this and finds it easier to write.
I've just ordered this book.