“If something happens very slowly over quite some time, maybe over decades, the different parts of the brain take up functions that would normally be done by the part that is pushed to the side”

The way I see it, the Human Brain increases its efficiency (Assuming the 10% Brain Efficiency Myth is true) in such cases, to be able to do all the work that otherwise an entire Brian would have done. I'm curious what would happen if we were to somehow gradually disable parts of the brain, ensuring all functions of the Human Body are still intact, and then suddenly bring all of it back.