Does using your brain more often have permanent benefits? does it make you smarter?

Unknown: Studies show that patients who are active mentally and physically are less likely to have dementia as they get older. That does not mean that these activites prevent dementia. This is called selection bias. People who are active mentally and physically don't have dementia. As dementia develops patients become less active physically and mentally. An association does not mean causality.

Yes it does: The more you use it the more 'engaged' it is.This is why the elderly population is encouraged to do puzzles etc.