I wrote about wanting to research popular culture in the Midwest, and I've grown more and more interested in American environmental history, although I am still interested in popular culture and its relation to environmentalism. My time period would remain the same, although the location within the United States might change.
Some further history: I recently finished a distance master's program in library science at my school, which is located in the Midwest, and I conducted research on a certain digital collection as part of that program. One of the history professors mentioned that he was looking for a student to study that collection, and I mentioned in my SOP that I'd be interested in continuing to research it. While finishing my research last year, I grew to hate the collection and really don't want to study it any further. I'd much rather focus on environmental history, and there is at least one professor who is doing this sort of research.