I read that some people can even change the chemicals in their brains.
Like in a study by Raine (I think) he scanned murderers brains to see if there was any physiological difference in their brains and non-murderers....and there was in most cases but it also said it was possible to change the chemicals to make it look like you wern't a murderers....

I don't know how this is possible and I might have got the studys mixed up...haha