Michael Pollan is best-known for his best-selling books about food and our relationship to food and the natural world. His new book explores the little-known history about the promising medical and scientific studies of psychedelics in the 1950s and 60s. He’s been writing about this subject in The New Yorker and elsewhere for a few years now. In “How to Change Your Mind,” Pollan also details the modern revival of this research and describes his own experience with a variety of these drugs, mostly with a professional — albeit underground — guide.