Another reason to exercise: It’s good for your brain. That’s hardly a revelation. Anyone who exercises knows, for instance, that even a short 30-minute workout can boost your mood for the rest of the day. But just how extensive the relationship is between exercise and your brain may come as a surprise. That relationship is the subject of “Spark: The Revolutionary New Science of Exercise and the Brain,” by John J. Ratey and Eric Hagerman, $24.99, Little, Brown and Company. In addition to being a mood enhancer, the book explores how exercise can among other things, relieve stress, diffuse anxiety, help you focus, regulate hormones and grow brain cells. (The book isn’t new; it’s been out nearly two years. It’s just new to GGNC.) Haven’t gotten a copy yet; I will and will report periodically on what I learn. You can reviews in August 2008 issue of Psychiatric Services, a publication of the American Psychiatric Association, and at Blogcrtics.org.