We all know that exercise is a good thing—for body and for mind. Decades of data have established it as one of the best ways to lower the risk of heart disease and stave off other ailments of aging, including dementia. But even after many years of covering health as a reporter and editor, I was genuinely surprised to learn about the depth of the evidence showing how powerful exercise can be in battling major depression. In our cover story, “Head Strong,” contributing editor Ferris Jabr reveals how moderate to vigorous exercise can be as effective as medication and therapy for many people with mild to moderate depression—and it certainly has the most salutary side effects of any treatment.

“Scores of experiments now show that exercise is much more than a temporary distraction from mental woes,” Jabr writes. His story examines the research and explores the likely biological pathways through which working out works mental magic. These include strengthening our biochemical resistance to stress and promoting the growth of new brain cells.

Brain biochemistry looms large in another story in this issue. “The Currency of Desire,” written by journalist Maia Szalavitz, smashes some myths about everyone's favorite neurotransmitter. Dopamine, long reputed to be the brain chemical that signals pleasure, turns out to have more to do with wanting than with liking. “This little molecule,” Szalavitz writes, “may unlock the intricate mystery of what drives us,” which helps to explain its role in everything from initiating action to addiction.

How to help children achieve their potential is a challenge that all principled societies must face. Two stories take a look at this from very different angles. In “The Stamp of Poverty,” neuroscientist John D. E. Gabrieli of M.I.T. and psychologist Silvia A. Bunge of the University of California, Berkeley, describe recently discovered differences in brain anatomy and function between kids growing up in poverty and more affluent children—findings that add urgency to the issue of extreme income inequality. In “Nurturing Genius” journalist Tom Clynes reports on the lessons of a 45-year study of how best to educate our most intellectually gifted youth.

Finally, for a glimpse of a wildly different kind of intelligence, soak up “The Mind of an Octopus,” our excerpt from a new book by Peter Godfrey-Smith. You'll likely agree with the author that the octopus possesses the closest thing on earth to an alien intelligence.