" The beauty of exercise is that it attacks the problem from both directions at the same time. It gets us moving, naturally, which stimulates the brain stem and gives us more energy, passion, interest, and motivation. We feel more vigorous. From above, in the prefrontal cortex, exercise shifts our self-concept by adjusting all the chemicals I’ve mentioned, including serotonin, dopamine, norepinephrine, BDNF, VEGF, and so on. And unlike many antidepressants, exercise doesn’t selectively influence anything—it adjusts the chemistry of the entire brain to restore normal signaling. "

― John J. Ratey , Spark: The Revolutionary New Science of Exercise and the Brain