Small is realistic about the study -- despite his confidence in the early findings -- and the need for much more data to explain what that perfect storm looks like.

"I would say to (Clark), 'Yes, I know that you have a scan that looks different,' but we don't know what that means yet," Small said. "What I suspect is that it's not just the scan. There may be a lot of other variables that come into play that determine whether there's a close correlation between the tau deposits in the brain and any clinical symptoms."