Jillean
You are correct, the rational centers of the brain would light up if you believe, or gave much thought to Psalm 23 as they tested. And it would not light up if it wasn't worth your time.
It would be interesting to see if you followed a group of people that did not have any strong religious or faith based ties, and at the beginning do the same Dr Azari study, and Pet scan their brains. They should all have very similar responses.
If it was feasible, folllow them for say 5 years, and hopefully/ perhaps some will be "saved," --- compare their pet scan before and after, with those who did not change.
If there was a significant change in the pet scan, in these rational centers of the brain and excluding any confounding factors, before and after saving faith, and between the control group and those that now believed then this would be evidence of this:
2 Corinthians 5: 17 " the old has gone and the new has come."