I'm guessing the pieces were original works used just for the study, the article doesn't state what was used.
[0] http://news.stanford.edu/news/2006/may31/brainwave-053106.ht...
http://news.harvard.edu/gazette/story/2012/07/when-the-beat-...
http://www.psmag.com/blogs/news-blog/drummers-high-evidence-...
http://news.harvard.edu/gazette/story/2012/07/when-the-beat-...
http://www.psmag.com/blogs/news-blog/drummers-high-evidence-...