You’re struggling up a hill halfway through a ten-mile race. Your breathing is ragged, and your footfalls seem heavy. You lurch toward the water station, grab a cup, and gulp it down. Back in the middle of the pack, you feel strengthened and pick up the pace.

Your decision to lope over to the water station relied on your interoceptive sense—the ability to sense your internal state. When you talk to your physician about a nagging pain or discomfort, you are also acting on information passing through your brain’s interoceptive system. Facing a major mental and physical challenge, however, requires you to do more. You need to match your internal sensations with an assessment of what the environment will demand of you. Do you need to slow down to summit the hill, or can you power through to the next water station?

A group from the University of California at San Diego and the Naval Health Research Center theorizes that the extra edge that allows certain people to perform particularly well in stressful situations may come not from a physiological advantage but from differences in the brain. To explore this question, they tested a group of Navy SEALs, adventure racers, and Marines, all of whom have learned to triumph over physical challenges without succumbing to stress. “Navy SEALs don’t all share a prototypical body type—they’re all different,” Nate Thom, a stress physiologist at the Naval Health Research Center, says. Nonetheless, they share a certain amount of resilience.

Specifically, they surmised that individuals who shine in tough circumstances may benefit from highly attuned interoception, which then informs the decision-making areas of the brain. Interoception is thought to rely heavily on the insula, a small brain area that plays an important role in self-awareness and emotional experiences.

To test their theory, the researchers first compared 11 Navy SEALs and 10 age- and education-matched healthy controls. Both groups were assessed on their ability to read happy and fearful faces. As the scientists had expected, the SEALs showed increased right insula activity across all emotional categories as compared with the healthy control subjects. They also were slightly slower to detect emotions, which may either be a fluke or may reflect the importance of accurately identifying an individual’s facial expression on the battlefield: it could be vital to detecting whether a setting is dangerous or safe.

In a second study, adventure racers—the type who sprint, paddle, and climb their way through wilderness endurance challenges—were subjected to the same emotion recognition task. They also underwent a breathing restriction task, which feels vaguely like suffocation and is intended to induce mild stress. The adventure racers also showed increased activity in the right insula in the emotion recognition task and less engagement of the region during the restriction test than controls, suggesting a lower stress response.

The results, presented in a poster session at the Society for Neuroscience, are the first two stages in a study that will compare SEALS with Marines and also assess the effectiveness of mindfulness training, which has been shown to improve interoceptive awareness. Staying in touch with both your insides and your outsides, it seems, may give you an added boost when you need it most.

Image courtesy of emmett.hume and flickr.