" By failing to engage it in intellectually challenging activities, your brain will fail to grow new connections, and it will indeed become disorganized and ultimately dysfunctional. The converse is also true for both body and brain. If someone who has not been physically active for a sustained period starts a program of physical therapy and regular exercise, she can regain her muscle mass and tone within a matter of months. The same thing is true of your brain. "

― Ray Kurzweil , Transcend: Nine Steps to Living Well Forever