Read this short provocative article in the New York Times.
http://well.blogs.nytimes.com/2016/02/17/which-type-of-exercise-is-best-for-the-brain/?action=click&pgtype=Homepage&version=Moth-Visible&moduleDetail=inside-nyt-region-2&module=inside-nyt-region®ion=inside-nyt-region&WT.nav=inside-nyt-region