Well, the flippant thing to say would be that human beings only use 10% of their brain capacity anyway (and some less than that), but I've seen what I perceive to be alcohol/drug-induced brain damage in people I know, and it can be extremely sobering in the literal and figurative sense to witness. One friend of mine...and he's consumed massive quantities of drugs and alcohol since he was in his teens...is a big, big Ramones fan-- I've always liked them, but I'm nowhere near the fan he is. When Joey Ramone died, they buried him in the Jewish section of a non-denominational NJ cemetery where I have relatives buried. I offered to show my friend where Joey's grave was, and he looked forward to it with great alacrity. One Sunday afternoon, I drove him over there, and he took some pictures, left a small stone on Joey's tombstone in the Jewish tradition, and we left. Some weeks later, I asked him if he ever got the photos developed, and he replied, "What photos?" "The photos you took at Joey Ramone's grave." "I've been to Joey Ramone's grave? When was this?" Initially, I thought he was joking, but he wasn't. I'm not an expert on the science of alcoholic brain damage (I've heard of "wet brain" and so on, but I don't pretend to be any kind of expert), but I remember reading a biography of Truman Capote by Gerald Clarke, in which a doctor examined Capote near the end of his life and told him that his brain was atrophying...literally shrinking...due to his massive, long-term consumption of alcohol and drugs. Capote essentially told the doctor that "I don't care." Needless to say, he was dead not long after that. My understanding is that we do have billions of brain cells, but they don't regenerate once they've been destroyed, and one drunken spree can destroy thousands.