We live in a world that is always on, where everyone is always connected. But we feel increasingly disconnected. Why? The answer lies in our brains. Carl D. Marci, MD, a leading expert on social and consumer neuroscience, reviews the mounting evidence that overuse of smart phones and social media is rewiring our brains, resulting in a losing deal: we are neglecting the relationships that sustain us and keep us healthy in favor of weaker and more ephemeral ties.