Alex Honnold, the world’s greatest solo climber, doesn’t experience fear like the rest of us. He climbs to dizzying heights without a rope or protective equipment of any kind, shuffles across narrow sills of stone such as the “Thank God” ledge high atop the sheer granite face of Half Dome in Yosemite National Park. When J.B. MacKinnon, a Canadian freelance writer, approached Honnold about having scientists look at what goes on in his unusual brain, the climber said he once would have been afraid to submit himself to such scrutiny. But he agreed, and the result was a fascinating tour of the topography and activity of Honnold’s brain. When he and a control subject, another sensation-seeking rock climber, viewed gruesome, high-arousal photographs during functional magnetic resonance imaging brain scans, Honnold’s amygdala ─ the brain’s fear center ─ showed zero activation while the other climber’s lit up like a neon sign. The piece goes on to describe the known functions of the amygdala and the nucleus accumbens, another brain structure, and explores the concepts of consolidation and visualization. The study of Honnold’s brain was strictly observational, but the researcher involved said it raises intriguing questions about brain control and regulation that might be applicable to other conditions such as anxiety disorders. “Everyone seemed to be saying that Alex Honnold must be ‘wired differently’ in order to pull off his incredible feats of ropeless rock climbing, and I thought, ‘Well, these days we can find out if that’s true,’” MacKinnon said. “The answer proved to be more complicated and more fascinating. In the end, my own relationship with fear and climbing was so deeply changed that I was able to do some very humble ropeless rock climbing myself.” Robert Lee Hotz, a science writer for the The Wall Street Journal said MacKinnon’s story “lights up with the joy of great reporting and ambitious enterprise: Who else would put the world’s most adventurous free climber into a brain scanner to probe the neural circuits that make most of us shudder, squirm and squeal with panic?”