Physical activity is very important for a number of reasons—including that it helps to protect the structure and function of our brain as we age. This may be key in reducing the risk of developing certain neurodegenerative conditions, such as Alzheimer’s disease. Though researchers have known about the protective effect of exercise for many years, exactly why it has this effect on the brain has remained a mystery. But a recent study published in the Journal of Neuroscience might shed some light on this puzzle. According to its findings, physical activity alters the activity of the brain’s immune cells, which lowers inflammation in the brain. The brain contains a class of special immune cells known as microglia, which constantly survey the brain tissue for damage or infection and clear away debris or dying cells. Microglia also help direct the production of new neurons (nerve cells in the brain that communicate and send messages …