According to these researchers, one's fitness level can affect the size of one's hippocampus. What is the hippocampus, you ask? Just like most other brain area, the hippocampus has numerous functions, but one of the most interesting is that it is what transfers memories stored in short-term memory to long-term memory. Think about it: if your brain didn’t make any distinction between long and short term memory, you’d be stuck with all of those embarrassing moments from growing up or it would be too hard to forget that scary story your Uncle Joe told you about cemeteries at night. So while we don’t want to remember everything, we do want to remember a lot more than we presently do, and having a larger hippocampus can help that. No wonder why these researchers found that fitter kids did better on memory tests!