Interesting because this is a rarely reported consequence. It seems no one would object to have denser grey matter, but if it is thinner somewhere, it feels like you lost something.
As a side note, I was raised Roman Catholic. Although I have not gone to church since college I hear interesting sciency things now and then. One, which I don't have a citation for, is that nuns who are experienced at prayer exhibit similar fMRI results when they pray.
I think lose is an ok word but not quite right for what's really going on.
Do you mean ROI?