 Exercise is interesting in terms of the effects on the brain because it works in about four or five different ways. One of the most obvious ways is blood flow. And so if you get your heart working, your brain's going to be filled with oxygen-rich blood and nutrients. So that's the main way that we thought it helps. The other way that's sort of interesting is it's been thought that exercise produces new neurons. So exercise induces the production of growth factors, one's called BDNF, and it actually stimulates the production of new brain cells. Now, when I was in school 20 years ago, we were told you can't get any new brain cells. So when you're born, that's your lot, you know, you're not going to make any more. But more recently, we found that exercise is a really good way of stimulating brain cell production. And some of these are functional. And so just this notion that something that you can do can generate new brain cells is a really great thing to think about. So we were wondering why exercise helps the brain. And what one theory is, it just reduces stress. So maybe it's not that your blood is coming to the brain, maybe you're less stressed and then, you know, that was something that imaging allowed us to test. And so we scanned a whole lot of people with high cortisol levels. So if you're stressed, if you're angry about something, or even if you're stuck in traffic, your cortisol levels can be very high. One of the things we found is that the people with high cortisol levels lost brain tissue faster. Well, that's a serious problem. So as soon as you know that's true, you can look at ways of reducing your cortisol. And so that's a very easy thing to do. I mean, we can get less stressed by exercising, walking, taking breaks. So imaging established a physical connection between something in your blood, cortisol, that's a sign of stress, and actual physical changes in the brain that's very useful to know. Take care of your brain. And there's a lot of ways we know that you can take care of your brain. You can eat a good diet. You can exercise. You can reduce stress. You can make sure you're well educated. And these things just build up a sort of mental bank account for the future. And so even though it seems like work is hard, I mean, you're building a store of brain connections that you'll need for the rest of your life. So these are practical messages that we've learned from imaging a lot of people.