Nowadays, we hear a lot about how memories are the consequence of new neurons added in the brain or that every time you learn something, a new connection in your brain forms. Well, sorry to break it to you, but that's simply not the case ... Most of the time, when we learn something, it's because existing neurons, not new neurons, but existing neurons strengthen their connection through co-activation over and over and over through repetition or—and this is a very important or—or through very strong activation once and only once.