Michael Merzenich — American Scientist

Michael M. Merzenich is a professor emeritus neuroscientist at the University of California, San Francisco. His contributions to the field are numerous. He took the sensory cortex maps developed by his predecessors like Archie Tunturi, Clinton Woolsey, Vernon Mountcastle, Wade Marshall, and Philip Bard, and refined them using dense micro-electrode mapping techniques. Using this, he definitively showed there to be multiple somatotopic maps of the body in the postcentral sulcus, and multiple tonotopic maps of the acoustic inputs in the superior temporal plane... (wikipedia)

My brain power depends on my retained mastery of analyzing in detail what's happening in my world and in my mind and body. I must continue to practice to retain my constructive and analytic powers. The goal is to be a master of my environment.
If a brain is exercised properly, anyone can grow intelligence, at any age, and potentially by a lot. Or you can just let your brain idle - and watch it slowly, inexorably, go to seed like a sedentary body.
Your brain - every brain - is a work in progress. It is 'plastic.' From the day we're born to the day we die, it continuously revises and remodels, improving or slowly declining, as a function of how we use it.
My mantra: Brainless exercise is a lost opportunity for improvement.