Please note that I’m in no way a brain care specialist Here’s what I gather, and I would appreciate corrections and refinements from people who actually know what they’re talking about.
As far as the evidence goes, it’s more or less true that we don’t use all of our brain all the time. When we’re thinking about mathematics, we use different parts of our brain than when we’re looking at pictures of people’s faces. We also have some parts of our brain that are active all the time just keeping us alive -with the breathing and the heart beating and standing upright and all that. What that practically means is that some parts of our brains are specialized, and aren’t used all the time. What you cannot conclude from that, is that activating the whole brain would give us super smarts. It would probably lead to us seeing faces where there aren’t any, and thinking up mathmatical solutions to problems that don’t have any. If that sounds like an hallucinogenic trip, then you may very well be right.