The goal, then, is to train your brain to anticipate, and not overreact, to unexpected stress. For a whitewater kayaker, that means staying calm and making the right strokes after getting caught in a hole; for a runner, it means pushing through the pain to stay on pace late in a race. Paulus believes that neurofeedback training, in which subjects try to alter their resiliency-related brain patterns based on real-time data from an fMRI scanner, is not far off.

For now, the most promising technique is one that's already familiar to many professional athletes: meditation. Paulus's latest study put 30 Marine recruits through a program in mindfulness, an approach to self-awareness with roots in Buddhist teachings. "You learn to monitor how your body actually feels while suspending judgment about it," Paulus explains.

This is part of deliberate practice for athletes: muscle memory kicks in and you don't think.

That's the key to keeping calm.