About a decade ago, some early scientific research suggested that playing memory games could increase “fluid intelligence,” which is–the capacity to solve problems in novel situations, independent of acquired knowledge. A spate of apps, books and classes resulted, all claiming to make people smarter. Unfortunately, later studies proved that “braintraining” (as it’s sometimes call) has no effect on your general intelligence. The most recent research in psychology and neuroscience, however, has found five effective strategies…