Researchers conducting the study found that sustained aerobic exercise had positive effects on brain structure and function, including on a process called adult hippocampal neurogenesis (AHN), which basically means nerve growth in the hippocampus. If you're forgetting your biology, the hippocampus plays a role in memory and spatial navigation, so you want to take care of it.
The same study concluded that anaerobic exercise, like HIIT and weightlifting, didn't necessarily have the same AHN-boosting effects.
How reliable is this study?
As with most studies, you should take the results with a grain of salt, since they were obtained from rats. On the other hand, rats have ruled the New York City subway system for decades, so they must be doing something right.
For anyone who's ever experienced the legendary "runner's high," though, it makes sense that aerobic work would be good for the brain. Jordan Metzl, a nationally recognized sports medicine physician, best-selling author, and fitness instructor, agrees. After all, "The mammalian brain is the mammalian brain," he says, which means you're more like the rats of NIMH than you'd like to admit.