I read this article today on the CBC and it just made me roar. It's a Danish study about the parts of the human brain that light up when a person is talking or praying to God. Apparently, it's the same regions that light up if you're talking to another human or even a dog for that matter, but that the more abstract the conception of God (even for believers), the more difficult it is to make the connection.
"the brain did not evolve to communicate with invisible supernatural beings."
Anyway, check out the article if you're interested.