How do positive affirmations affect Biology?

Do you know how positive affirmations affect the body biologically? I haven't had much luck researching this topic. Will you please be so kind as to post links to any research that shows a body/mind connection through the practice of positive affirmations. I am only looking for credible research, case studies, etc. Thank you.

[edit on 24-4-2005 by checkers]

That was a big deal back in the 80s alone with subliminal tapes, I used to listen to them, I used to read them in the morning while I used to get ready to work.

I think they help if you really believe in it.