7 Myths About the Brain -- Separating Fact From Fiction Myth 1: You only use 10 percent of your brain. 2: Brain damage is permanent. 3: People are either "right-brained" or "left-brained." 4: Humans have the biggest brains. 5: We are born with all the brain cells we ever have, and once they die, these cells are gone forever. 6: Drinking alcohol kills brain cells. 7: There are 100 billion neurons in the human brain.