Yeah, I see what you're getting at. Obviously it's not as simple as using one part of the brain or another, it's about comparing levels of activity in multiple areas. It was the case that when considering the "average American" the subjects showed different activity to when they considered self or God. The mPFC (an area already linked to self-reflection) was highly active for self/God. It was less active for the average American. From Epley's paper;
quote:
activity in the mPFC was lower when participants thought about the average American's attitudes than when they thought about their own attitude or God's attitudes (Ps < 0.05), whereas activity in the mPFC did not differ between the self and God conditions... These results expand considerably on the behavioral results observed in Studies 1—6 by demonstrating a relative similarity in the neural substrates involved in thinking about one's own beliefs and God's beliefs compared to when thinking about another person's beliefs.
Now if you're asking what the difference in brain activity might be when gauging the views of a specific known person, as opposed to the "average American", I can't say. Epley did not cover that.
I suspect that the more we know about a person and their beliefs and attitudes, the less the brain will be forced to fall back onto projecting our own views. If we know someone well, or know their views (as in a public figure), there is no need to project. We can simply fall back on our existing knowledge to gauge their opinion.
With God, we know a lot less, save that he is "good". Since we all like to think of ourselves as good and our own opinions as the most moral, it makes sense that we would project our own views onto God.
The way to go from here would be to see if the results are the same in those of other faiths and (perhaps even more interesting) in atheists and agnostics. It would also be interesting to see how the brain functions when considering the views of specific other people (as you suggest) and when considering fictional characters.
Mutate and Survive