I'm not sure what to make of this study, but it seems interesting.  This was a prospective trial that used people as their own controls for memory tests before and after blueberry juice consumption.  They also did a randomized controlled trial, where blueberry juice was compared to " berry placebo beverage."  There were only nine patients in the study.

Guess who sponsored the study?  "The juice used in the study was provided by the Wild Blueberry Association of North America."  according to the writeup on a nutritional website.

http://www.webmd.com/alzheimers/news/20100121/blueberry-juice-may-boost-memory

http://pubs.acs.org/doi/abs/10.1021/jf9029332?tokenDomain=presspac&tokenAccess=presspac&forwardService=showFullText&journalCode=jafcau

While this is interesting and important research, the pace of progress is so agonizing.  Have you priced blueberry juice recently?  It's so expensive.  So before I can commit to buying it regularly, I'm going to have to see some more data.