Scientists have always known that a majority of the brain’s neurons, specialized cells responsible for transmitting information throughout the body, are formed at the fetal stage. However, after studies on mammals, like rats, showed that neurogenesis continues in the dentate gyrus, a part of the hippocampus area of the brain vital to memory formation, through adulthood, it was assumed the same was true for humans as well. However, scientists from the University of California, San Francisco are challenging this long-held belief with a new study which asserts the human brain stops adding new neurons by age 13.