The human brain, guiding our every thought and action, is as complex as anything we know. Its almost unimaginable complexity arises from minute interconnections between tens of billions of nerve cells. If we could map every connection among the cells, we still would have only a rough foundation for understanding brain function, because those connections are changing every moment of our lives. They are recording our experiences, our emotions, our plans for the future, and they are constantly repairing disruption and injury. Evidence is mounting that intellectual challenge, social engagement, and regular physical activity can have a profound positive impact on our lives as we age. Why? Because they influence the ongoing alterations, or “plasticity,” in our ever-changing brains. This course examines the recent revolution in our views of brain function that gives us a new way to grasp how our brains work.