Psychiatrist Dr. Anna Lembke's new book, 'Dopamine Nation,' explores the brain's connection between pleasure and pain. It also helps explain addictions — not just to drugs and alcohol, but also to food, sex and smart phones. "Living in this modern age is very challenging," Lembke says. "We're now having to cope with: How do I live in a world in which everything is provided? And if I consume too much of it — which my reflexes compel me to do — I'm going to be even more unhappy."Maureen Corrigan reviews Yoon Choi's collection of stories 'Skinship.'