Jigsaws are supposedly good for the mind. However the best thing for the or brain that is, is keeping it challenged. Try something new everyday. Trying brushing your teeth with the opposite hand from what you normally use. Try learning something new everyday.
By the way, there are free courses on the internet. You can learn just about anything now for free. Even MIT, Michigan Institute of Technology, offers courses for free. Some colleges will accept these courses for college credit.