Every single time you move your body, you are releasing a whole bunch of neurochemicals. And some of them we've talked about—the good mood comes from dopamine and serotonin, noradrenaline. But the thing that gets released, also, particularly with aerobic exercise, is a growth factor called brain-derived neurotrophic factor, or BDNF. And that is so important because what it does is it goes directly to your hippocampus, and it helps brand new brain cells grow in your hippocampus.