Did you know that the brain is the most complex object in the universe? Or that it's made up of more than 100 billion nerve cells? Learn more about your gray matter and how to keep it resilient in The Healthy Brain Kit (Sounds True, 2007). Designed by Andrew Weil, MD, and Gary Small, MD, this box of mind-bending riddles, factoids, and lifestyle tips will train your brain with pointers such as these: Switch computer-operating systems; try out a new language; and brush your hair with your weaker hand.