Brain Cross-Training…how many hours to get real benefit?

Brain Cross-Training…how many hours to get real benefit?

Fortune magazine had a recent feature about cross-training your brain…but every example they gave involved the cross-training in childhood…particularly in music. So my question is…how much cross training would I need to do as an adult to get real benefit? Would 15 minutes a day help?…and how much help?…1%? 10%? What is the real-world cross benefit to mental cross training.